LM61460-Q1
ZHCSKA7F – MAY 2019 – REVISED JUNE 2021
LM61460-Q1 汽车类 3V 至 36V、6A 低 EMI 同步降压转换器
1 特性
•
•
•
•
•
•
3 说明
符合面向汽车应用的 AEC-Q100 标准
– 温度等级 1：–40°C 至 +150°C，TJ
提供功能安全
– 可帮助进行功能安全系统设计的文档
针对超低 EMI 要求进行了优化
– HotRod™ 封装和并行输入路径可以尽可能减少
开关节点振铃
– 展频可降低峰值发射
– 可调节 SW 节点上升时间
专为汽车应用而设计
– 支持 42V 的汽车负载突降
– ±1% 的总输出稳压精度
– VOUT 可在 1V 至 95% 的 VIN 范围内调节
– 在 4A 负载下具有 0.4V 压降（典型值）
可在所有负载下进行高效电源转换
– 在 13.5VIN、3.3VOUT 下具有 7µA 的无负载电流
– 在 1mA、13.5VIN、5VOUT 下 PFM 效率为 83%
– 具有用于提升效率的外部偏置选项
适用于可扩展电源
– 与以下器件引脚兼容：
• LM61440-Q1（36V、4A、可调节 fSW）
• LM62440-Q1（36V、4A、固定 fSW）
• LMQ61460-Q1（36V、6A、内部电容）
2 应用
•
LM61460-Q1 专门设计用于降低 EMI。该器件具有假
随机展频、可调节 SW 节点上升时间和低 EMI，并采
用具有低开关节点振铃和易于使用、优化型引脚排列的
VQFN-HR 封装。开关频率可在 200kHz 至 2.2MHz 范
围内
设置或同步，从而避开噪声敏感频段。另外，可以选择
频率，从而在低工作频率下提高效率，或在高工作频率
下缩小解决方案尺寸。
自动模式可在轻负载运行时进行频率折返，实现仅
7µA （ 典 型 值 ） 的 空 载 电 流 消 耗 和 高 轻 负 载 效 率 。
PWM 和 PFM 模 式 之 间 无 缝 转 换 ， 以 及 极 低 的
MOSFET 导通电阻和外部偏置输入，均确保在整个负
载范围内实现卓越的效率。
器件信息
器件型号
LM61460-Q1
(1)
汽车信息娱乐系统与仪表组：音响主机、媒体集线
器、USB 充电器、显示屏
汽车 ADAS 和车身电子装置
封装(1)
VQFN-HR (14)
封装尺寸（标称值）
4.00mm × 3.50mm
如需了解所有可用封装，请参阅数据表末尾的可订购产品附
录。
100%
95%
90%
Efficiency (%)
•
LM61460-Q1 是 一 款 汽 车 专 用 的 高 性 能 直 流 / 直 流
同步降压转换器。该器件具有集成式高侧和低侧
MOSFET，能够在 3.0V 至 36V 的宽输入电压范围内
提供高达 6A 的输出电流；可耐受 42V 电压，简化了
输入涌流保护设计。LM61460-Q1 可对压降进行软恢
复，因此无需对输出进行过冲。
85%
80%
75%
70%
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
YELLOW: PEAK
BLUE: AVERAGE
65%
60%
0.0001
传导 EMI：VOUT = 5V，IOUT = 5A
0.001
0.01
0.1 0.2 0.5 1
Load Current (A)
2 3 5 710
LM61
效率：，VOUT = 5V，FSW = 400kHz
本文档旨在为方便起见，提供有关 TI 产品中文版本的信息，以确认产品的概要。有关适用的官方英文版本的最新信息，请访问
www.ti.com，其内容始终优先。TI 不保证翻译的准确性和有效性。在实际设计之前，请务必参考最新版本的英文版本。
English Data Sheet: SNVSB70
LM61460-Q1
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ZHCSKA7F – MAY 2019 – REVISED JUNE 2021
Table of Contents
1 特性................................................................................... 1
2 应用................................................................................... 1
3 说明................................................................................... 1
4 Revision History.............................................................. 2
5 Description (continued).................................................. 2
6 Device Comparison Table...............................................3
7 Pin Configuration and Functions...................................4
8 Specifications.................................................................. 5
8.1 Absolute Maximum Ratings ....................................... 5
8.2 ESD Ratings .............................................................. 5
8.3 Recommended Operating Conditions ........................5
8.4 Thermal Information ...................................................6
8.5 Electrical Characteristics ............................................6
8.6 计时特性......................................................................9
8.7 Systems Characteristics .......................................... 10
8.8 Typical Characteristics.............................................. 11
9 Detailed Description......................................................13
9.1 Overview................................................................... 13
9.2 Functional Block Diagram......................................... 14
9.3 Feature Description...................................................15
9.4 Device Functional Modes..........................................24
10 Application and Implementation................................ 30
10.1 Application Information........................................... 30
10.2 Typical Application.................................................. 30
11 Power Supply Recommendations..............................45
12 Layout...........................................................................46
12.1 Layout Guidelines................................................... 46
12.2 Layout Example...................................................... 48
13 Device and Documentation Support..........................49
13.1 Documentation Support.......................................... 49
13.2 接收文档更新通知................................................... 49
13.3 支持资源..................................................................49
13.4 Trademarks............................................................. 49
13.5 静电放电警告.......................................................... 49
13.6 术语表..................................................................... 49
14 Mechanical, Packaging, and Orderable
Information.................................................................... 49
4 Revision History
注：以前版本的页码可能与当前版本的页码不同
Changes from Revision E (April 2021) to Revision F (June 2021)
Page
• Added Added EVM thermal resistance..............................................................................................................6
Changes from Revision D (April 2020) to Revision E (April 2021)
Page
• 更新了整个文档中的表格、图和交叉参考的编号格式。..................................................................................... 1
• 添加了 LMQ61460-Q1 链接................................................................................................................................ 1
• Changed RθJA from 59 to 58.7............................................................................................................................6
• Changed θJC(top) from 19 to 26.1.........................................................................................................................6
• Added IQ_VIN ...................................................................................................................................................... 6
• Removed TJ = 25°C from VFB_acc test condition.................................................................................................6
• Changed VEN-ACC from ±8.1% to ±5%................................................................................................................ 6
5 Description (continued)
The LM61460-Q1 is qualified to automotive AEC-Q100 grade 1 and is available in a 14-pin VQFN-HR package
with wettable flanks. Electrical characteristics are specified over a junction temperature range of –40°C to
+150°C. Find additional resources in the Related Documentation.
2
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6 Device Comparison Table
DEVICE
LM61460-Q1
ORDERABLE PART
NUMBER
REFERENCE PART
NUMBER
LIGHT LOAD
MODE
SPREAD
SPECTRUM
OUTPUT
VOLTAGE
SWITCHING
FREQUENCY
LM61460AANQRJRRQ1
LM61460AAN-Q1
LM61460AASQRJRRQ1
LM61460AAS-Q1
Auto Mode
No
Adjustable
Adjustable
Auto Mode
Yes
Adjustable
Adjustable
LM61460AFSQRJRRQ1
LM61460AFS-Q1
FPWM
Yes
Adjustable
Adjjustable
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CBOOT
RBOOT
VIN2
13
12
1
5
11
PGND2
10
SW
9
8
PGOOD
VIN1
4
7
FB
EN/
SYNC
2
3
6
VCC
AGND
RT
BIAS
14
7 Pin Configuration and Functions
PGND1
图 7-1. 14-Pin VQFN-HR RJR Package Top View
表 7-1. Pin Functions
PIN
NAME
4
NO.
I/O
DESCRIPTION
BIAS
1
P
Input to internal LDO. Connect to output voltage point to improve efficiency. Connect an optional
high quality 0.1-µF to 1-µF capacitor from this pin to ground for improved noise immunity. If output
voltage is above 12 V, connect this pin to ground.
VCC
2
O
Internal LDO output. Used as supply to internal control circuits. Do not connect to any external
loads. Connect a high-quality 1-µF capacitor from this pin to AGND.
AGND
3
G
Analog ground for internal circuitry. Feedback and VCC are measured with respect to this pin.
Must connect AGND to both PGND1 and PGND2 on PCB.
FB
4
I
Output voltage feedback input to the internal control loop. Connect to feedback divider tap point
for adjustable output voltage. Do not float or connect to ground.
PGOOD
5
O
Open-drain power-good status output. Pull this pin up to a suitable voltage supply through a
current limiting resistor. High = power OK, low = fault. PGOOD output goes low when EN = low,
VIN > 1 V.
RT
6
I/O
Connect this pin to ground through a resistor with value between 5.76 kΩ and 66.5 kΩ to set
switching frequency between 200 kHz and 2200 kHz. Do not float or connect to ground.
EN/SYNC
7
I
Precision enable input. High = on, Low = off. Can be connected to VIN. Precision enable allows
the pin to be used as an adjustable UVLO. See 节 10. Do not float. EN/SYNC also functions as a
synchronization input pin. Triggers on rising edge of external clock. A capacitor must be used to
AC couple the synchronization signal to this pin. When synchronized to external clock, the device
functions in forced PWM and disables the PFM light load efficiency mode. See 节 9.
VIN1
8
P
Input supply to the converter. Connect a high-quality bypass capacitor or capacitors from this pin
to PGND1. Low impedance connection must be provided to VIN2.
PGND1
9
G
Power ground to internal low-side MOSFET. Connect to system ground. Low impedance
connection must be provided to PGND2. Connect a high-quality bypass capacitor or capacitors
from this pin to VIN1.
SW
10
O
Switch node of the converter. Connect to output inductor.
PGND2
11
G
Power ground to internal low-side MOSFET. Connect to system ground. Low impedance
connection must be provided to PGND1. Connect a high-quality bypass capacitor or capacitors
from this pin to VIN2.
VIN2
12
P
Input supply to the converter. Connect a high-quality bypass capacitor or capacitors from this pin
to PGND2. Low impedance connection must be provided to VIN1.
RBOOT
13
I/O
Connect to CBOOT through a resistor. This resistance must be between 0 Ω and open and
determines SW node rise time.
CBOOT
14
I/O
High-side driver upper supply rail. Connect a 100-nF capacitor between SW pin and CBOOT. An
internal diode connects to VCC and allows CBOOT to charge while SW node is low.
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8 Specifications
8.1 Absolute Maximum Ratings
Over the recommended operating junction temperature range of -40℃ to +150℃ (unless otherwise noted)(1)
Input Voltage
PARAMETER
MIN
VIN1, VIN2 to AGND, PGND
-0.3
42
V
RBOOT to SW
-0.3
5.5
V
CBOOT to SW
-0.3
5.5
V
BIAS to AGND, PGND
-0.3
16
V
EN/SYNC to AGND, PGND
-0.3
42
V
RT to AGND, PGND
-0.3
5.5
V
FB to AGND, PGND
-0.3
16
V
0
20
V
PGOOD to AGND, PGND
PGND to
Output Voltage
AGND(3)
MAX
UNIT
-1
2
V
SW to AGND, PGND(2)
-0.3
VIN+0.3
V
VCC to AGND, PGND
-0.3
5.5
V
10
mA
Current
PGOOD sink current(4)
TJ
Junction temperature
-40
150
°C
Tstg
Storage temperature
-40
150
°C
(1)
(2)
(3)
(4)
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress
ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under
Recommended Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device
reliability.
A voltage of 2 V below GND and 2 V above VIN can appear on this pin for ≤ 200 ns with a duty cycle of ≤ 0.01%.
This specification applies to voltage durations of 100 ns or less. The maximum D.C. voltage should not exceed ± 0.3 V.
Do not exceed pin’s voltage rating.
8.2 ESD Ratings
VALUE
V(ESD)
(1)
Electrostatic discharge
Human body model (HBM), per AEC
Device HBM Classification Level 2
Q100-002(1)
UNIT
±2000
V
Charged device model (CDM), per AEC Q100-011
Device CDM Classification Level C5
±750
AEC Q100-002 indicates that HBM stressing shall be in accordance with the ANSI/ESDA/JEDEC JS-001 specification.
8.3 Recommended Operating Conditions
Over the recommended operating junction temperature range of -40°C to 150°C (unless otherwise noted) (1)
MIN
Input voltage
Input voltage range after start-up
(2)
NOM
MAX
3
36
UNIT
V
Output voltage
Output voltage range for adjustable version
1
0.95 * VIN
Frequency
Frequency adjustment range
200
2200
kHz
Sync frequency
Synchronization frequency range
200
2200
kHz
Load current
Output DC current range (3)
0
6
A
Temperature
Operating junction temperature TJ range
–40
150
°C
(1)
(2)
(3)
V
Recommended operating conditions indicate conditions for which the device is intended to be functional, but do not ensure specific
performance limits. For ensured specifications, see Electrical Characteristics table.
Under no conditions should the output voltage be allowed to fall below zero volts.
Maximum continuous DC current may be derated when operating with high switching frequency and/or high ambient temperature. See
Application section for details.
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8.4 Thermal Information
The value of RθJA given in this table is only valid for comparison with other packages and cannot be used for design
purposes. These values were calculated in accordance with JESD 51-7, and simulated on a 4-layer JEDEC board. They do
not represent the performance obtained in an actual application. For example, with a 4-layer PCB, a RΘJA = 25℃/W can be
achieved. For design information see Maximum Ambient Temperature versus Output Current.
LM61460-Q1
THERMAL METRIC (1) (2)
RJR (QFN)
UNIT
14 PINS
RθJA
Junction-to-ambient thermal resistance (LM61460-Q1 EVM)
25
°C/W
RθJA
RθJC(top)
Junction-to-ambient thermal resistance (JESD 51-7)
58.7
°C/W
Junction-to-case (top) thermal resistance
26.1
°C/W
RθJB
Junction-to-board thermal resistance
19.2
°C/W
ΨJT
Junction-to-top characterization parameter
1.4
°C/W
ΨJB
Junction-to-board characterization parameter
19
°C/W
RθJC(bot)
Junction-to-case (bottom) thermal resistance
-
°C/W
(1)
(2)
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report.
The value of RθJA given in this table is only valid for comparison with other packages and cannot be used for design purposes.
These values were calculated in accordance with JESD 51-7, and simulated on a 4-layer JEDEC board. They do not represent the
performance obtained in an actual application.
8.5 Electrical Characteristics
Limits apply over the recommended operating junction temperature range of -40°C to +150°C, unless otherwise stated.
Minimum and Maximum limits are specified through test, design or statistical correlation. Typical values represent the most
likely parametric norm at TJ = 25°C, and are provided for reference purposes only. Unless otherwise stated the following
conditions apply: VIN = 13.5 V. VIN1 shorted to VIN2 = VIN. VOUT is converter output voltage.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNI
T
SUPPLY VOLTAGE AND CURRENT
Needed to start up
3.95
VIN_OPERATE
Input operating voltage(3)
VIN_OPERATE_H
Hysteresis(3)
IQ_VIN
Operating quiescent current (not
switching)(4)
VFB = +5%, VBIAS = 5 V
9
18
µA
IQ
Operating quiescent current (not
switching); measured at VIN pin(1)
VFB = +5%, VBIAS = 5 V
0.6
6
µA
IBIAS
Current into BIAS pin (not switching,
VFB = +5%, VBIAS = 5 V, Auto Mode
maximum at TJ = 125°C)(1)
24
31.2
µA
ISD
Shutdown quiescent current;
measured at VIN pin
0.6
6
µA
Once operating
V
3.0
1
EN = 0 V, TJ = 25℃
V
ENABLE
VEN
Enable input threshold voltage rising
VEN-ACC
Enable input threshold voltage rising deviation from typical
-5
VEN-HYST
Enable threshold hysteresis as
percentage of VEN (TYP)
24
VEN-WAKE
Enable wake-up threshold
IEN
Enable pin input current
VEN_SYNC
Edge height necessary to sync using
Rise/fall time 3.4 V, CCM Operation(3)
3.3
VBIAS = 3.1 V, Non-switching
3.1
Internal VCC input under voltage
lock-out
VCC rising under voltage threshold
3.6
V
Internal VCC input under voltage
lock-out
Hysteresis below VCC_UVLO
1.1
V
VFB_acc
Initial reference voltage accuracy
VIN = 3.3 V to 36 V, FPWM Mode
IFB
Input current from FB to AGND
Adjustable versions only, FB = 1 V
VCC
Internal VCC voltage
VCC_UVLO
VCC_UVLO_HYST
V
FEEDBACK
-1
1
10
%
nA
OSCILLATOR
fADJ
Minimum adjustable frequency by RT
RT = 66.5 kΩ
or SYNC
0.18
0.2
0.22 MHz
Adjustable frequency by RT or SYNC
RT = 33.2 kΩ
with 400 kHz setting
0.36
0.4
0.44 MHz
Maximum adjustable frequency
by RT or SYNC
1.98
2.2
2.42 MHz
RT = 5.76 kΩ
fS SS
Frequency span of spread spectrum
operation - largest deviation from
Spread spectrum active
center frequency
fPSS
Spread spectrum pattern
frequency(3)
Spread spectrum active, fSW = 2.1
MHz
RDS(ON)_HS
Power switch on-resistance
High side MOSFET RDS(ON)
41
82 mΩ
RDS(ON)_LS
Power switch on-resistance
Low side MOSFET RDS(ON)
21
45 mΩ
VBOOT_UVLO
Voltage on CBOOT pin compared
to SW which will turn off high-side
switch
2
%
1.5
Hz
MOSFETS
2.1
V
CURRENT LIMITS
IL-HS
High side switch current limit(2)
IL-LS
Low side switch current limit
IL-ZC
Zero-cross current
limit. Positive current direction is
out of SW pin
Auto Mode, static measurement
IL-NEG
Negative current limit FPWM and
SYNC Modes. Positive current
direction is out of SW pin.
IPK_MIN_0
Duty Cycle approaches 0%
8.9
10.3
11.5
A
6.1
7.1
8.1
A
0.25
A
FPWM operation
-3
A
Minimum peak command in Auto
Mode / device current rating
Pulse duration < 100 ns
25
%
IPK_MIN_100
Minimum peak command in Auto
Mode / device current rating
Pulse duration > 1 µs
12.5
%
VHICCUP
Ratio of FB voltage to in-regulation
FB voltage
Not during soft start
40
%
PGDOV
PGOOD upper threshold - rising
% of VOUT setting
105
107
110
%
PGDU V
PGOOD lower threshold - falling
% of VOUT setting
92
94
96.5
%
PGDHYST
PGOOD upper threshold (rising &
falling)
% of VOUT setting
POWER GOOD
1.3
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Limits apply over the recommended operating junction temperature range of -40°C to +150°C, unless otherwise stated.
Minimum and Maximum limits are specified through test, design or statistical correlation. Typical values represent the most
likely parametric norm at TJ = 25°C, and are provided for reference purposes only. Unless otherwise stated the following
conditions apply: VIN = 13.5 V. VIN1 shorted to VIN2 = VIN. VOUT is converter output voltage.
PARAMETER
VIN(PGD_VALID)
VPGD(LOW)
RPGD
TEST CONDITIONS
Input voltage for proper
PGOOD function
MIN
MAX
1.0
Low level PGOOD function output
voltage
RDS(ON) of PGOOD output
UNI
T
V
46 µA pullup to PGOOD pin, VIN =
1.0 V, EN = 0 V
0.4
1 mA pullup to PGOOD pin, VIN =
13.5 V, EN = 0 V
0.4
2 mA pullup to PGOOD pin, VIN =
13.5 V, EN = 3.3 V
0.4
V
1 mA pullup to PGOOD pin, EN = 0
V
17
40
Ω
1 mA pullup to PGOOD pin, EN =
3.3 V
40
90
Ω
Pull down current at the SW node
under over voltage condition
IOV
TYP
0.5
mA
THERMAL SHUTDOWN
TSD_R
TSD_HYST
(1)
(2)
(3)
(4)
8
Thermal shutdown rising threshold(3)
Thermal shutdown
hysteresis(3)
158
168
10
180
℃
℃
This is the current used by the device while not switching, open loop, with FB pulled to +5% of nominal. It does not represent the
total input current to the system while regulating. For additional information, reference the Systems Chracaterisitics Table and the Input
Supply Current Section.
High side current limit is function of duty factor. High side current limit is highest at small duty factor and less at higher duty factors.
Parameter specified by design, statistical analysis and production testing of correlated parameters.
IQ_VIN = IQ + IBIAS × (VOUT / VIN)
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8.6 计时特性
限制值适用于推荐的 -40°C 至 +150°C 工作结温范围，除非另有说明。最小和最大限制经过测试、设计和统计相关性分析确
定。典型值表示 TJ = 25°C 条件下最有可能达到的参数标准，仅供参考。除非另有说明，以下条件适用：VIN = 13.5V。
参数
测试条件
最小值
典型值
最大值 单位
开关节点
VIN = 20V，IOUT = 2A，RBOOT 短接
至 CBOOT
tON_MIN
最小高侧开关导通时间
tON_MAX
最大高侧开关导通时间
tOFF_MIN
最小低侧开关导通时间
tSS
从第一个 SW 脉冲到 90% VREF 的时
VIN ≥ 4.2V
间
tSS2
从第一个 SW 脉冲到 FPWM 锁定
释放的时间（如果输出未处于稳压状 VIN ≥ 4.2V
态）
tW
短路等待时间（“断续”时间）
55
70
ns
9
VIN = 4.0V，IOUT = 1A，RBOOT 短
接至 CBOOT
μs
65
85
ns
3.5
5
7
ms
9.5
13
17
ms
80
ms
0.7
ms
使能
CVCC= 1µF 时从 EN 高电平到第一个
SW 脉冲的时间（如果输出从 0V 开
始）
tEN
导通延迟(1)
tB
上升沿或下降沿后 EN 消隐(1)
tSYNC_EDGE
启用边沿后同步信号保持时间以进行
边沿识别
100
tPGDFLT(rise)
PGOOD 高电平信号的延迟时间
1.5
tPGDFLT(fall)
PGOOD 功能的干扰滤波器时间常数
4
28
µs
ns
电源正常
(1)
2
2.5
ms
120
µs
使用相关参数的设计、统计分析和生产测试指定参数；未经量产测试。
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8.7 Systems Characteristics
The following values are specified by design provided that the component values in the typical application circuit are
used. Limits apply over the junction temperature range of -40°C to +150°C, unless otherwise noted. Minimum and Maximum
limits are derived using test, design or statistical correlation. Typical values represent the most likely parametric norm at TJ
= 25°C, and are provided for reference purposes only. Unless otherwise stated the following conditions apply: VIN = 13.5
V. VIN1 shorted to VIN2 = VIN. VOUT is output setting. These parameters are not tested in production.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNI
T
EFFICIENCY
ƞ5V_2p1MHz
ƞ3p3V_2p1MHz
ƞ5V_400kHz
Typical 2.1 MHz efficiency
Typical 2.1 MHz efficiency
Typical 400 kHz efficiency
VOUT = 5 V, IOUT = 4 A, RBOOT = 0 Ω
93
VOUT = 5 V, IOUT = 100
µA,
RBOOT = 0 Ω, RFBT = 1
MΩ
73
VOUT = 3.3 V, IOUT = 4 A,
0Ω
91
RBOOT =
%
%
VOUT = 3.3 V, IOUT = 100
µA,
RBOOT = 0 Ω, RFBT = 1
MΩ
71
VOUT = 5 V, IOUT = 4 A, RBOOT = 0 Ω
95
VOUT = 5 V, IOUT = 100
µA,
RBOOT = 0 Ω, RFBT = 1
MΩ
76
%
RANGE OF OPERATION
VVIN_MIN1
VIN for full functionality at reduced
load, after start-up.
VOUT set to 3.3 V
3.0
V
VVIN_MIN2
VIN for full functionality at 100% of
maximum rated load, after start-up.
VOUT set to 3.3 V
3.95
V
VOUT = 3.3 V, IOUT = 0 A, Auto mode,
RFBT=1 MΩ
Operating quiescent current(1)
IQ-VIN
VDROP1
VDROP2
DMAX
7
µA
VOUT = 5 V, IOUT = 0 A, Auto mode,
RFBT=1 MΩ
10
VOUT = 3.3 V, IOUT = 4 A, -3% output
Input to output voltage differential to accuracy at 25℃
maintain regulation accuracy without
VOUT = 3.3 V, IOUT = 4 A, -3% output
inductor DCR drop
accuracy at 125℃
Input to output voltage differential
to maintain fSW ≥ 1.85MHz, without
DCR drop
Maximum switch duty cycle
0.4
V
0.55
VOUT = 3.3 V, IOUT = 4 A, -3%
regulation accuracy at 25℃
0.8
VOUT = 3.3 V, IOUT = 4 A, -3%
regulation accuracy at 125℃
1.2
fSW =1.85 MHz
87
While in frequency fold back
V
98
%
%
RBOOT
tRISE
(1)
10
SW node rise time
RBOOT = 0 Ω, IOUT = 2 A (10% to
80%)
RBOOT = 100 Ω, IOUT = 2 A (10% to
80%)
2.15
ns
2.7
ns
See detailed description for the meaning of this specification and how it can be calculated.
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8.8 Typical Characteristics
Unless otherwise specified, VIN = 13.5 V and fSW = 400 kHz.
1.5
4000
1.25
Shutdown Current (nA)
Quiescent Current (µA)
3500
1
0.75
3000
2500
2000
1500
1000
-40C
25C
150C
500
0.5
-50
0
-25
0
25
50
75
Temperature (°C)
100
125
0
150
5
10
SNVS
30
35
40
SNVS
VEN = 0 V
VFB = 1 V
图 8-2. Shutdown Supply Current
图 8-1. Non-Switching Input Supply Current
1.01
11
1.006
10
9
1.002
Current (A)
Voltage (V)
15
20
25
Input Voltage (V)
0.998
8
7
0.994
6
0.99
-50
-25
0
25
50
75
Temperature (°C)
100
125
5
-50
150
snvs
0
25
50
75
Temperature (°C)
100
125
150
SNVS
70
FREQ = 200 kHz
FREQ = 400 kHz
FREQ = 2.2 MHz
60
RDS-ON (m-Ohm)
Frequency (kHz)
-25
图 8-4. LM61460-Q1 High-side and Low-side
Current Limits
图 8-3. Feedback Voltage
3500
3250
3000
2750
2500
2250
2000
1750
1500
1250
1000
750
500
250
0
-50
HS
LS
50
40
30
20
-25
0
25
50
75
Temperature (°C)
100
125
150
10
-50
HS Switch
LS Switch
-25
SNVS
图 8-5. Switching Frequency Set by RT Resistor
0
25
50
75
Temperature (°C)
100
125
150
SNVS
图 8-6. High-side and Low-side Switches RDS_ON
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1.4
1.3
1.2
1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
-50
115
110
VEN Rising
VEN Falling
VEN_WAKE Rising
VEN_WAKE Falling
-25
0
25
50
75
Temperature (°C)
100
图 8-7. Enable Thresholds
12
PGOOD Threshold (%)
Enable Threshold (V)
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125
105
100
95
90
OV Tripping
OV Recovery
UV Recovery
UV Tripping
85
150
snvs
80
-50
-25
0
25
50
75
Temperature (°C)
100
125
150
SNVS
图 8-8. PGOOD Thresholds
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9 Detailed Description
9.1 Overview
The LM61460-Q1 is a wide input, synchronous peak-current mode buck regulator designed for a wide variety of
automotive applications. The regulator can operate over a wide range of switching frequencies including sub-AM
band at 400 kHz and above the AM band at 2.1 MHz. This device operates over a wide range of conversion
ratios. If minimum on-time or minimum off-time does not support the desired conversion ratio, the frequency is
reduced automatically, allowing output voltage regulation to be maintained during input voltage transients with a
high operating-frequency setting.
The LM61460-Q1 has been designed for low EMI and is optimized for both above and below AM band operation:
•
•
•
•
•
Meets CISPR25 class 5 standard
Hotrod™ package minimizes switch node ringing
Parallel input path minimizes parasitic inductance
Spread spectrum reduces peak emissions
Adjustable SW node rise time
These features together can eliminate shielding and other expensive EMI mitigation measures.
This device is designed to minimize end-product cost and size while operating in demanding automotive
environments. Operation at 2.1 MHz allows for the use of small passive components. State-of-the-art current
limit function allows the use of inductors optimized for 4-A and 6-A regulators. In addition, this device has low
unloaded current consumption, which is desirable for off-battery, always on applications. The low shutdown
current and high maximum operating voltage also allow for the elimination of an external load switch and input
transient protection. To further reduce system cost, an advanced PGOOD output is provided, which can often
eliminate the use of an external reset or supervisory device.
The LM61460-Q1 devices are AEC-Q100-qualified and have electrical characteristics ensured up to a maximum
junction temperature of 150°C.
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9.2 Functional Block Diagram
VCC
Clock
VCC
Oscillator
RT
BIAS
VCC UVLO
Slope
compensation
SYNC
Detect
LDO
Over
Temperature
detect
Sync
Frequency Foldback
FPWM/Auto
RBOOT
System enable
Enable
EN/SYNC
VIN
OTP
CBOOT
HS Current
sense
Error
amplifier
±
VIN
System enable
OTP
Hiccup active
Soft start
circuit and
bandgap
VCC UVLO
AGND
VIN2
Clock
High and
low limiting
circuit
Output
low
FB
+
+
±
Comp Node
+
VIN1
+
HS
Current
Limit
±
SW
Drivers and
logic
LS
Current
Limit
±
+
Voltage Reference
±
LS
Current
Min
FPWM/Auto
PGOOD
PGOOD
Logic with
filter and
release delay
PGND1
+
PGND2
Vout UV/OV
LS Current
sense
System enable
14
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9.3 Feature Description
9.3.1 EN/SYNC Uses for Enable and VIN UVLO
Start-up and shutdown are controlled by the EN/SYNC input and VIN UVLO. For the device to remain in
shutdown mode, apply a voltage below VEN_WAKE (0.4 V) to the EN pin. In shutdown mode, the quiescent current
drops to 0.6 µA (typical). At a voltage above VEN_WAKE and below VEN, VCC is active and the SW node is
inactive. Once the EN voltage is above VEN, the chip begins to switch normally, provided the input voltage is
above 3 V.
The EN/SYNC pin cannot be left floating. The simplest way to enable the operation is to connect the EN/SYNC
pin to VIN, allowing self-start-up of the LM61460-Q1 when VIN drives the internal VCC above its UVLO level.
However, many applications benefit from the employment of an enable divider network as shown in 图 9-1,
which establishes a precision input undervoltage lockout (UVLO). This can be used for sequencing, preventing
re-triggering of the device when used with long input cables, or reducing the occurrence of deep discharge of a
battery power source. Note that the precision enable threshold, VEN, has a 8.1% tolerance. Hysteresis must be
enough to prevent re-triggering. External logic output of another IC can also be used to drive the EN/SYNC pin,
allowing system power sequencing.
VIN
RENT
EN/SYNC
RENB
AGND
图 9-1. VIN UVLO Using the EN pin
Resistor values can be calculated using 方程式 1. See 节 10.2.2.11 for additional information.
RENB = RENT Â
VEN
VON Å 9EN
(1)
where
•
VON is the desired typical start-up input voltage for the circuit being designed
Note that since the EN/SYNC pin can also be used as an external synchronization clock input. A blanking time,
tB, is applied to the enable logic after a clock edge is detected. Any logic change within the blanking time is
ignored. Blanking time is not applied when the device is in shutdown mode. The blanking time ranges from 4 µs
to 28 µs. To effectively disable the output, the EN/SYNC input must stay low for longer than 28 µs.
9.3.2 EN/SYNC Pin Uses for Synchronization
The LM61460-Q1 EN/SYNC pin can be used to synchronize the internal oscillator to an external clock. The
internal oscillator can be synchronized by AC coupling a positive clock edge into the EN pin, as shown in 图
9-2. It is recommended to keep the parallel combination value of RENT and RENB in the 100-kΩ range. RENT
is required for synchronization, but RENB can be left unmounted. Switching action can be synchronized to an
external clock ranging from 200 kHz to 2.2 MHz. The external clock must be off before start-up to allow proper
start-up sequencing.
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VIN
RENT
CSYNC
EN/SYNC
Clock
Source
RENB
AGND
AGND
图 9-2. Typical Implementation Allowing Synchronization Using the EN Pin
Referring to 图 9-3, the AC-coupled voltage edge at the EN pin must exceed the SYNC amplitude threshold,
VEN_SYNC_MIN, to trip the internal synchronization pulse detector. In addition, the minimum EN/SYNC rising pulse
and falling pulse durations must be longer than tSYNC_EDGE(MIN) and shorter than the blanking time, tB. A 3.3-V or
higher amplitude pulse signal coupled through a 1-nF capacitor, CSYNC, is suggested.
EN Voltage
VEN
tSYNC_EDGE
VEN_SYNC
0
VEN_SYNC
t
tSYNC_EDGE
Time
图 9-3. Typical SYNC/EN Waveform
After a valid synchronization signal is applied for 2048 cycles, the clock frequency abruptly changes to that of
the applied signal. Also, if the device in use has the spread-spectrum feature, the valid synchronization signal
overrides spread spectrum, turning it off, and the clock switches to the applied clock frequency.
9.3.3 Clock Locking
Once a valid synchronization signal is detected, a clock locking procedure is initiated. LMQ62440-Q1 devices
receive this signal over the MODE/SYNC pin. After approximately 2048 pulses, the clock frequency completes
a smooth transition to the frequency of the synchronization signal without output variation. Note that while the
frequency is adjusted suddenly, phase is maintained so the clock cycle that lies between operation at the default
frequency and at the synchronization frequency is of intermediate length. This eliminates very long or very short
pulses. Once frequency is adjusted, phase is adjusted over a few tens of cycles so that rising synchronization
edges correspond to rising SW node pulses. See 图 9-4.
Pulse 1
Pulse 2
Pulse 3
Pulse
~2048
Pulse 4
Pulse
~2049
Pulse
~2050
Pulse
~2051
VSYNCDH
VSYNCDL
Synchronization
signal
SW Node
Spread Spectrum is on between pulse 1 and pulse 2048,
there is no change to operating frequency. At pulse 4,
the device transitions from Auto Mode to FPWM.
On approximately pulse 2048, spread
spectrum turns off
Also clock frequency matches the
synchronization signal and phase
locking begins
Phase lock achieved, Rising edges
align to within approximately 45 ns,
no spread spectrum
VIN
GND
图 9-4. Synchronization Process
16
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9.3.4 Adjustable Switching Frequency
A resistor tied from the device RT pin to AGND is used to set operating frequency. Use Equation 2 or refer to
图 9-5 for resistor values. Note that a resistor value outside of the recommended range can cause the device to
shut down. This prevents unintended operation if RT pin is shorted to ground or left open. Do not apply a pulsed
signal to this pin to force synchronization. If synchronization is needed, refer to 节 9.3.2.
RRT(kΩ) = (1 / fSW(kHz) - 3.3 x 10-5) × 1.346 x 104
(2)
70
60
Rt (kOhm)
50
40
30
20
10
0
200
400
600
800 1000 1200 1400 1600 1800 2000 2200
Frequency (kHz)
RTvs
图 9-5. Setting Clock Frequency
9.3.5 PGOOD Output Operation
The PGOOD function is implemented to replace a discrete reset device, reducing BOM count and cost. The
PGOOD pin voltage goes low when the feedback voltage is outside of the specified PGOOD thresholds (see 图
8-8). This can occur in current limit and thermal shutdown, as well as while disabled and during normal start-up.
A glitch filter prevents false flag operation for short excursions of the output voltage, such as during line and
load transients. Output voltage excursions that are shorter than tPGDFLT_FALL do not trip the power-good flag.
Power-good operation can be best understood by referring to 图 9-6.
The power-good output consists of an open-drain NMOS, requiring an external pullup resistor to a suitable logic
supply or VOUT. When EN is pulled low, the flag output is also forced low. With EN low, power good remains valid
as long as the input voltage is ≥ 1 V (typical).
Input
Voltage
Output
Voltage
Input Voltage
tPGDFLT(fall)
tPGDFLT(rise)
tPGDFLT(rise)
VPGD_HYST
tPGDFLT(fall)
tPGDFLT(fall)
tPGDFLT(fall)
VPGD_UV (falling)
VIN_OPERATE (rising)
VIN_OPERATE (falling)
VIN(PGD_VALID)
GND
< 18 V
PGOOD
PGOOD may
not be valid if
input is below
VIN(PGD_VALID)
Startup
delay
Small glitches do not
reset tPGDFLT(rise) timer
Small glitches
do not cause
PGOOD to
signal a fault
PGOOD may not
be valid if input is
below VIN(PGD_VALID)
图 9-6. PGOOD Timing Diagram (Excludes OV Events)
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表 9-1. Conditions That Cause PGOOD to Signal a Fault (Pull Low)
(1)
FAULT CONDITION INITIATED
FAULT CONDITION ENDS (AFTER WHICH tPGDFLT(rise) MUST PASS
BEFORE PGOOD OUTPUT IS RELEASED)(1)
VOUT < VOUT-target × PGDUV AND t > tPGDFLT(fall)
Output voltage in regulation:
VOUT-target × (PGDUV + PGDHYST) < VOUT < VOUT-target × (PGDOV PGDHYST) (See 图 8-8)
VOUT > VOUT-target × PGDOV AND t > tPGDFLT(fall)
Output voltage in regulation
TJ > TSD_R
TJ < TSD_F AND output voltage in regulation
EN < VEN Falling
EN > VEN Rising AND output voltage in regulation
VCC < VCC_UVLO - VCC_UVLO_HYST
VCC > VCC_UVLO AND output voltage in regulation
As an additional operational check, PGOOD remains low during soft start, defined as until the lesser of either full output voltage
reached or tSS2 has passed since initiation.
9.3.6 Internal LDO, VCC UVLO, and BIAS Input
The VCC pin is the output of the internal LDO used to supply the control circuits of the LM61460-Q1. The
nominal output is 3 V to 3.3 V. The BIAS pin is the input to the internal LDO. This input can be connected to
VOUT to provide the lowest possible input supply current. If the BIAS voltage is less than 3.1 V, VIN1 and VIN2
directly powers the internal LDO.
To prevent unsafe operation, VCC has a UVLO that prevents switching if the internal voltage is too low. See
VCC_UVLO and VCC_UVLO_HYST in 节 8.5. Note that these UVLO values and the dropout of the LDO are used to
derive minimum VIN_OPERATE and VIN_OPERATE_H values.
9.3.7 Bootstrap Voltage and VCBOOT-UVLO (CBOOT Pin)
The driver of the High-Side (HS) switch requires bias higher than VIN. The capacitor, CBOOT, connected
between CBOOT and SW, works as a charge pump to boost voltage on the CBOOT pin to SW + VCC. A boot
diode is integrated on the LM61460-Q1 die to minimize external component count. It is recommended that a
100-nF capacitor rated for 10 V or higher is used. The VBOOT_UVLO threshold (2.1 V typ.) is designed to maintain
proper HS switch operation. If the CBOOT capacitor voltage drops below VBOOT_UVLO, then the device initiates a
charging sequence, turning on the low-side switch before attempting to turn on the HS switch.
9.3.8 Adjustable SW Node Slew Rate
To allow optimization of EMI with respect to efficiency, the LM61460-Q1 is designed to allow a resistor to select
the strength of the driver of the high-side FET during turn on. See 图 9-7. The current drawn through the RBOOT
pin (the dotted loop) is magnified and drawn through from CBOOT (the dashed line). This current is used to turn
on the high-side power MOSEFT.
18
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VIN
VCC
CBOOT
HS FET
HS
Driver
RBOOT
SW
LS FET
图 9-7. Simplified Circuit Showing How RBOOT Functions
With RBOOT short circuited to CBOOT, rise time is very fast. As a result, SW node harmonics do not "roll off"
until above 150 MHz. A boot resistor of 100 Ω corresponds to approximately 2.7-ns SW node rise, and this
100-Ω boot resistor virtually eliminates SW node overshoot. The slower rise time allows energy in SW node
harmonics to roll off near 100 MHz under most conditions. Rolling off harmonics eliminates the need for shielding
and common mode chokes in many applications. Note that rise time increases with increasing input voltage.
Noise due to stored charge is also greatly reduced with higher RBOOT resistance. Switching with slower slew
rate also decreases the efficiency.
9.3.9 Spread Spectrum
Spread spectrum is a factory option. To find which devices have spread spectrum enabled, see 节 6. The
purpose of spread spectrum is to eliminate peak emissions at specific frequencies by spreading these emissions
across a wider range of frequencies rather than apart with fixed frequency operation. In most systems containing
the LM61460-Q1, low frequency-conducted emissions from the first few harmonics of the switching frequency
can be easily filtered. A more difficult design criterion is reduction of emissions at higher harmonics that fall in the
FM band. These harmonics often couple to the environment through electric fields around the switch node and
inductor. The LM61460-Q1 uses a ±2% spread of frequencies which can spread energy smoothly across the FM
and TV bands but is small enough to limit subharmonic emissions below the device switching frequency. Peak
emissions at the switching frequency of the part are only reduced slightly, by less than 1 dB, while peaks in the
FM band are typically reduced by more than 6 dB.
The LM61460-Q1 uses a cycle-to-cycle frequency hopping method based on a linear feedback shift register
(LFSR). This intelligent pseudo-random generator limits cycle-to-cycle frequency changes to limit output ripple.
The pseudo-random pattern repeats at less than 1.5 Hz, which is below the audio band.
The spread spectrum is only available while the clock of the LM61460-Q1 devices are free running at their
natural frequency. Any of the following conditions overrides spread spectrum, turning it off:
•
•
•
•
The clock is slowed during dropout.
The clock is slowed at light load in auto mode. In FPWM mode, spread spectrum is active even if there is no
load.
At a high input voltage/low output voltage ratio when the device operates at minimum on-time, the internal
clock is slowed, disabling spread spectrum. See 节 8.6.
The clock is synchronized with an external clock.
9.3.10 Soft Start and Recovery From Dropout
The LM61460-Q1 uses a reference-based soft start that prevents output voltage overshoots and large inrush
currents during start-up. Soft start is triggered by any of the following conditions:
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•
•
•
•
Power is applied to the VIN pin of the IC, releasing UVLO.
EN is used to turn on the device.
Recovery from a hiccup waiting period
Recovery from shutdown due to overtemperature protection
Once soft start is triggered, the IC takes the following actions:
•
•
The reference used by the IC to regulate output voltage is slowly ramped. The net result is that output voltage
takes tSS to reach 90% of its desired value.
Operating mode is set to auto, activating diode emulation. This allows start-up without pulling output low if
there is a voltage already present on output.
These actions together provide start-up with limited inrush currents and also allow the use of larger output
capacitors and higher loading conditions that cause current to border on current limit during start-up without
triggering hiccup. See 图 9-8.
EN and Output Voltages
tEN
V
tSS
If selected, FPWM
is enabled after
regulation but no
later than tSS2
VEN
VOUT Set
Point
VOUT
90% of
VOUT Set
Point
0V
tSS2
Time
t
Triggering event
tEN
EN and Output Voltages
Triggering event
V
tSS
If selected, FPWM
is enabled after
regulation but no
later than tSS2
VEN
VOUT Set
Point
VOUT
90% of
VOUT Set
Point
0V
tSS2
Time
t
Soft start works with both output voltages starting from 0 V on the left curves, or if there is already voltage on the output, as shown on
right. In either case, output voltage must reach within 10% of the desired value tSS after soft start is initiated. During soft start, FPWM
and hiccup are disabled. Both hiccup and FPWM are enabled once output reaches regulation or tSS2, whichever happens first.
图 9-8. Soft-Start Operation
Any time the output voltage falls more than a few percent, the output voltage ramps up slowly. This condition is
called recovery from dropout and differs from soft start in three important ways:
•
•
•
The reference voltage is set to approximately 1% above what is needed to achieve the existing output
voltage.
Hiccup is allowed if output voltage is less than 0.4 times its set point. Note that during dropout regulation
itself, hiccup is inhibited.
FPWM mode is allowed during recovery from dropout. If the output voltage were to suddenly be pulled up by
an external supply, the LM61460-Q1 can pull down on the output.
Despite being called recovery from dropout, this feature is active whenever output voltage drops to a few percent
lower than the set point. This primarily occurs under the following conditions:
•
•
20
Dropout: When there is insufficient input voltage for the desired output voltage to be generated
Overcurrent: When there is an overcurrent event that is not severe enough to trigger hiccup
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V
Input and Output
Voltage
VIN
Slope
the same
as during
soft start
VOUT
VOUT Set
Point
t
Time
Whether output voltage falls due to high load or low input voltage, once the condition that causes output to fall below its set point
is removed, the output climbs at the same speed as during start-up. Even though hiccup does not trigger due to dropout, it can, in
principle, be triggered during recovery if output voltage is below 0.4 times the output set point for more than 128 clock cycles.
图 9-9. Recovery From Dropout
VOUT
(2 V/DIV)
IINDUCTOR
(1 A/DIV)
VIN
(5 V/DIV)
Time (2 ms/DIV)
图 9-10. Recovery From Dropout (VOUT = 5 V, IOUT = 4 A, VIN = 13.5 V to 4 V to 13.5 V)
9.3.11 Output Voltage Setting
A feedback resistor divider network between the output voltage and the FB pin is used to set output voltage
level. See 图 9-11.
VOUT
RFBT
FB
RFBB
AGND
图 9-11. Setting Output Voltage of Adjustable Versions
The LM61460-Q1 uses a 1-V reference voltage for the feedback (FB) pin. The FB pin voltage is regulated by
the internal controller to be the same as the reference voltage. The output voltage level is then set by the ratio
of the resistor divider. Equation 3 can be used to determine RFBB for a desired output voltage and a given
RFBT. Usually RFBT is between 10 kΩ and 1 MΩ. 100 kΩ is recommended for RFBT for improved noise immunity
compared to 1 MΩ and reduced current consumption compared to lower resistance values.
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RFBB =
RFBT
VOUT Å 1
(3)
In addition, a feedforward capacitor, CFF, connected in parallel with RFBT can be required to optimize the
transient response.
9.3.12 Overcurrent and Short Circuit Protection
The LM61460-Q1 is protected from overcurrent conditions with cycle-by-cycle current limiting on both the highside and the low-side MOSFETs.
High-side MOSFET overcurrent protection is implemented by the nature of the peak-current mode control. The
HS switch current is sensed when the HS is turned on after a short blanking time. Every switching cycle,
the HS switch current is compared to either the minimum of a fixed current set point or the output of the
voltage regulation loop minus slope compensation. Because the voltage loop has a maximum value and slope
compensation increases with duty cycle, HS current limit decreases with increased duty cycle when duty cycle is
above 35%. See 图 9-12.
12
Command Current (A)
10
8
6
4
2
HS Maximum Current
Rated Maximum Output
0
0
0.2
0.4
0.6
Duty Cycle
0.8
1
FEAT
图 9-12. Maximum Current Allowed Through the HS FET - Function of Duty Cycle for LM61460-Q1
When the LS switch is turned on, the switch current is also sensed and monitored. Like the high-side device, the
low-side device turns off as commanded by the voltage control loop and low-side current limit. If the LS switch
current is higher than ILS_Limit at the end of a switching cycle, the switching cycle is extended until the LS current
reduces below the limit. The LS switch is turned off once the LS current falls below its limit, and the HS switch is
turned on again as long as at least one clock period has passed since the last time the HS device has turned on.
22
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SW Voltage
VSW
VIN
tON < tON_MAX
0
t
Inductor Current
Typically, tSW > Clock setting
iL
IL-HS
IOUT
IL-LS
t
0
图 9-13. Current Limit Waveforms
Since the current waveform assumes values between IL-HS and IL-LS, the maximum output current is very close
to the average of these two values. Hysteretic control is used and current does not increase as output voltage
approaches zero.
The LM61460-Q1 employs hiccup overcurrent protection if there is an extreme overload, and the following
conditions are met for 128 consecutive switching cycles:
•
•
•
Output voltage is below approximately 0.4 times the output voltage set point.
Greater than tSS2 has passed since soft start has started; see 节 9.3.10.
The part is not operating in dropout, which is defined as having minimum off-time controlled duty cycle.
In hiccup mode, the device shuts itself down and attempts to soft start after tW. Hiccup mode helps reduce the
device power dissipation under severe overcurrent conditions and short circuits. See 图 9-14.
Once the overload is removed, the device recovers as though in soft start; see 图 9-15.
VOUT
(500 mV/DIV)
VOUT
(2 V/DIV)
IINDUCTOR
(2 A/DIV)
IINDUCTOR
(2 A/DIV)
Time (20 ms/DIV)
Time (20 ms/DIV)
图 9-14. Inductor Current Bursts During Hiccup
图 9-15. Short-Circuit Recovery
9.3.13 Thermal Shutdown
Thermal shutdown prevents the device from extreme junction temperatures by turning off the internal switches
when the IC junction temperature exceeds 165°C (typical). Thermal shutdown does not trigger below 158°C.
After thermal shutdown occurs, hysteresis prevents the device from switching until the junction temperature
drops to approximately 155°C. When the junction temperature falls below 155°C (typical), the LM61460-Q1
attempts to soft start.
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While the LM61460-Q1 is shut down due to high junction temperature, power continues to be provided to VCC.
To prevent overheating due to a short circuit applied to VCC, the LDO that provides power for VCC has reduced
current limit while the part is disabled due to high junction temperature. The VCC current limit is reduced to a few
milliamperes during thermal shutdown.
9.3.14 Input Supply Current
The LM61460-Q1 is designed to have very low input supply current when regulating light loads. This is achieved
by powering much of the internal circuitry from the output. The BIAS pin is the input to the LDO that powers the
majority of the control circuits. By connecting the BIAS input pin to the output of the regulator, a small amount of
current is drawn from the output. This current is reduced at the input by the ratio of VOUT / VIN.
IQ _ VIN
SW
§ 1 ·
§ Output Voltage ·
IEN IQ _ VIN u ¨
¸ Idiv u ¨
¸
© Keff ¹
© Input Voltage u Keff ¹
(4)
where
•
•
•
•
•
IQ_VIN is the current consumed by the operating (switching) buck converter while unloaded.
IQ is the current drawn from the VIN terminal. See IQ in 节 8.5.
IEN is current drawn by the EN terminal. Include this current if EN is connected to VIN. See IEN in 节 8.5. Note
that this current drops to a very low value if connected to a voltage less than 5 V.
Idiv is the current drawn by the feedback voltage divider used to set output voltage.
ηeff is the light-load efficiency of the buck converter with IQ_VIN removed from the input current of the buck
converter. ηeff = 0.8 is a conservative value that can be used under normal operating conditions.
9.4 Device Functional Modes
9.4.1 Shutdown Mode
The EN pin provides electrical ON and OFF control of the device. When the EN pin voltage is below 0.4 V, both
the converter and the internal LDO have no output voltage and the part is in shutdown mode. In shutdown mode,
the quiescent current drops to typically 0.6 µA.
9.4.2 Standby Mode
The internal LDO has a lower EN threshold than the output of the converter. When the EN pin voltage is above
1.1 V (maximum) and below the precision enable threshold for the output voltage, the internal LDO regulates the
VCC voltage at 3.3 V typical. The precision enable circuitry is ON once VCC is above its UVLO. The internal
power MOSFETs of the SW node remain off unless the voltage on EN pin goes above its precision enable
threshold. The LM61460-Q1 also employs UVLO protection. If the VCC voltage is below its UVLO level, the
output of the converter is turned off.
9.4.3 Active Mode
The LM61460-Q1 is in active mode whenever the EN pin is above VEN, VIN is high enough to satisfy
VIN_OPERATE, and no other fault conditions are present. The simplest way to enable the operation is to connect
the EN pin to VIN, which allows self start-up when the applied input voltage exceeds the minimum VIN_OPERATE.
In active mode, depending on the load current, input voltage, and output voltage, the LM61460-Q1 is in one of
five modes:
•
•
•
•
•
24
Continuous conduction mode (CCM) with fixed switching frequency when load current is above half of the
inductor current ripple.
Auto Mode - Light Load Operation: PFM when switching frequency is decreased at very light load.
FPWM Mode - Light Load Operation: Discontinuous conduction mode (DCM) when the load current is lower
than half of the inductor current ripple.
Minimum on-time: At high input voltage and low output voltages, the switching frequency is reduced to
maintain regulation.
Dropout mode: When switching frequency is reduced to minimize voltage dropout.
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9.4.3.1 CCM Mode
The following operating description of the LM61460-Q1 refers to 节 9.2 and to the waveforms in 图 9-16.
In CCM, the LM61460-Q1 supplies a regulated output voltage by turning on the internal high-side (HS) and
low-side (LS) NMOS switches with varying duty cycle (D). During the HS switch on-time, the SW pin voltage,
VSW, swings up to approximately VIN, and the inductor current, iL, increases with a linear slope. The HS switch
is turned off by the control logic. During the HS switch off-time, tOFF, the LS switch is turned on. Inductor current
discharges through the LS switch, which forces the VSW to swing below ground by the voltage drop across the
LS switch. The converter loop adjusts the duty cycle to maintain a constant output voltage. D is defined by the
on-time of the HS switch over the switching period:
D = TON / TSW
(5)
In an ideal buck converter where losses are ignored, D is proportional to the output voltage and inversely
proportional to the input voltage:
D = VOUT / VIN
(6)
SW Voltage
VSW
D=
VIN
tON
VOUT
§
tSW
VIN
tOFF
tON
0
- IOUTÂ5DSLS
t
tSW
Inductor Current
iL
ILPK
IOUT
Iripple
0
t
图 9-16. SW Voltage and Inductor Current Waveforms in Continuous Conduction Mode (CCM)
9.4.3.2 Auto Mode - Light Load Operation
The LM61460-Q1 can have two behaviors while lightly loaded. One behavior, called auto mode operation, allows
for seamless transition between normal current mode operation while heavily loaded and highly efficient light
load operation. The other behavior, called FPWM Mode, maintains full frequency even when unloaded. Which
mode the LM61460-Q1 operates in depends on which factory option is employed. See 节 6 for options. Note that
all parts operate in FPWM mode when synchronizing frequency to an external signal.
In auto mode, light load operation is employed in the LM61460-Q1. Light load operation employs two techniques
to improve efficiency:
•
•
Diode emulation, which allows DCM operation
Frequency reduction
Note that while these two features operate together to create excellent light load behavior, they operate
independently of each other.
9.4.3.2.1 Diode Emulation
Diode emulation prevents reverse current through the inductor which requires a lower frequency needed to
regulate given a fixed peak inductor current. Diode emulation also limits ripple current as frequency is reduced.
With a fixed peak current, as output current is reduced to zero, frequency must be reduced to near zero to
maintain regulation.
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VOUT
tON
<
VIN
tSW
D=
VSW
SW Voltage
VIN
tON
tOFF
tHIGHZ
0
t
tSW
Inductor Current
iL
ILPK
IOUT
0
t
In auto mode, the low-side device is turned off once SW node current is near zero. As a result, once output current is less than half of
what inductor ripple would be in CCM, the part operates in DCM which is equivalent to the statement that diode emulation is active.
图 9-17. PFM Operation
The device has a minimum peak inductor current setting while in auto mode.Once current is reduced to a low
value with fixed input voltage, on-time is constant. Regulation is then achieved by adjusting frequency. This
mode of operation is called PFM mode regulation.
9.4.3.2.2 Frequency Reduction
The LM61460-Q1 reduces frequency whenever output voltage is high. This function is enabled whenever Comp,
an internal signal, is low and there is an offset between the regulation set point of FB and the voltage applied
to FB. The net effect is that there is larger output impedance while lightly loaded in auto mode than in normal
operation. Output voltage must be approximately 1% high when the part is completely unloaded.
Output Voltage
VOUT
Current
Limit
1% Above
Set point
VOUT Set
Point
0
Output Current
IOUT
In auto mode, once output current drops below approximately 1/10th the rated current of the part, output resistance increases so that
output voltage is 1% high while the buck is completely unloaded.
图 9-18. Steady State Output Voltage versus Output Current in Auto Mode
In PFM operation, a small DC positive offset is required on the output voltage to activate the PFM detector. The
lower the frequency in PFM, the more DC offset is needed on VOUT. If the DC offset on VOUT is not acceptable, a
dummy load at VOUT or FPWM Mode can be used to reduce or eliminate this offset.
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9.4.3.3 FPWM Mode - Light Load Operation
Like auto mode operation, FPWM mode operation during light load operation is selected as a factory option.
In FPWM Mode, frequency is maintained while lightly loaded. To maintain frequency, a limited reverse current is
allowed to flow through the inductor. Reverse current is limited by reverse current limit circuitry, see 节 8.5 for
reverse current limit values.
VSW
D=
SW Voltage
VIN
tON
VOUT
§
tSW
VIN
tOFF
tON
0
t
Inductor Current
tSW
iL
ILPK
IOUT
0
Iripple
t
In FPWM mode, Continuous Conduction (CCM) is possible even if IOUT is less than half of Iripple.
图 9-19. FPWM Mode Operation
For all devices, in FPWM mode, frequency reduction is still available if output voltage is high enough to
command minimum on-time even while lightly loaded, allowing good behavior during faults which involve output
being pulled up.
9.4.3.4 Minimum On-time (High Input Voltage) Operation
The LM61460-Q1 continues to regulate output voltage even if the input-to-output voltage ratio requires an
on-time less than the minimum on-time of the chip with a given clock setting. This is accomplished using valley
current control. At all times, the compensation circuit dictates both a maximum peak inductor current and a
maximum valley inductor current. If for any reason, valley current is exceeded, the clock cycle is extended until
valley current falls below that determined by the compensation circuit. If the converter is not operating in current
limit, the maximum valley current is set above the peak inductor current, preventing valley control from being
used unless there is a failure to regulate using peak current only. If the input-to-output voltage ratio is too high,
even though current exceeds the peak value dictated by compensation, the high-side device cannot be turned
off quickly enough to regulate output voltage. As a result, the compensation circuit reduces both peak and valley
current. Once a low enough current is selected by the compensation circuit, valley current matches that being
commanded by the compensation circuit. Under these conditions, the low-side device is kept on and the next
clock cycle is prevented from starting until inductor current drops below the desired valley current. Since on-time
is fixed at its minimum value, this type of operation resembles that of a device using a Constant On-Time (COT)
control scheme; see 图 9-20.
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SW Voltage
VSW
D=
VIN
tON
VOUT
§
tSW
VIN
tON = tON_MIN
tOFF
0
- IOUTÂ5DSLS
t
Inductor Current
tSW > Clock setting
iL
IOUT
Iripple
ILVLY
t
0
In valley control mode, minimum inductor current is regulated, not peak inductor current.
图 9-20. Valley Current Mode Operation
9.4.3.5 Dropout
Dropout operation is defined as any input-to-output voltage ratio that requires frequency to drop to achieve the
required duty cycle. At a given clock frequency, duty cycle is limited by minimum off-time. Once this limit is
reached, if clock frequency were maintained, output voltage would fall. Instead of allowing the output voltage
to drop, the LM61460-Q1 extends on-time past the end of the clock cycle until needed peak inductor current
is achieved. The clock is allowed to start a new cycle once peak inductor current is achieved or once a
pre-determined maximum on-time, tON_MAX, of approximately 9 µs passes. As a result, once the needed duty
cycle cannot be achieved at the selected clock frequency due to the existence of a minimum off-time, frequency
drops to maintain regulation. If input voltage is low enough so that output voltage cannot be regulated even with
an on-time of tON_MAX, output voltage drops to slightly below the input voltage, VDROP1. For additional information
on recovery from dropout, reference 图 9-9.
Output Voltage
iL
VDROP1
Output
Setting
0
Switching Frequency
VDROP2 if
frequency =
1.85 MHz
Input
Voltage
Output
Voltage
Input Voltage
VIN
iL
Frequency
Setting
~100kHz
0
IOUT
Input Voltage
VIN
Output voltage and frequency versus input voltage: If there is little difference between input voltage and output voltage setting, the IC
reduces frequency to maintain regulation. If input voltage is too low to provide the desired output voltage at approximately 110 kHz,
input voltage tracks output voltage.
图 9-21. Frequency and Output Voltage in Dropout
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SW Voltage
VSW
VIN
D=
tON
VOUT
§
tSW
VIN
tOFF = tOFF_MIN
tON < tON_MAX
0
- IOUTÂ5DSLS
t
Inductor Current
tSW > Clock setting
iL
ILPK
IOUT
0
Iripple
t
Switching waveforms while in dropout. Inductor current takes longer than a normal clock to reach the desired peak value. As a result,
frequency drops. This frequency drop is limited by tON_MAX.
图 9-22. Dropout Waveforms
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10 Application and Implementation
备注
以下应用部分中的信息不属于 TI 器件规格的范围，TI 不担保其准确性和完整性。TI 的客 户应负责确定
器件是否适用于其应用。客户应验证并测试其设计，以确保系统功能。
10.1 Application Information
The LM61460-Q1 step-down DC-to-DC converter is typically used to convert a higher DC voltage to a lower
DC voltage with a maximum output current of 6 A. Using a 4-layer LM61460EVM at 400kHz, the LM61460-Q1
can sustain a continuous 6 A load up to an ambient temperature of approximately 95⁰C; see 图 10-2. If ambient
temperature is 105°C and the frequency is set to 2.1 MHz, the current must be limited to 4 A; see 图 10-3. The
following design procedure can be used to select components for the LM61460-Q1.
10.2 Typical Application
图 10-1 shows a typical application circuit for the LM61460-Q1. This device is designed to function with a wide
range of external components and system parameters. However, the internal compensation is optimized for a
certain range of external inductance and output capacitance. As a quick start guide, 表 10-2 provides typical
component values for some of the common configurations.
5 V to 36 V input
RENT
CIN_HF1
VIN1
VIN2
PGND1
CIN_HF2
CIN-BLK
PGND2
EN/SYNC
PGOOD
RPG
BIAS
Output
L1
SW
CBT
RT
COUT
RFF
CBOOT
RFBT
VCC
RRT
CFF
RBOOT
CVCC
AGND
FB
RFBB
图 10-1. Example Application Circuit
10.2.1 Design Requirements
表 10-1 provides the parameters for the detailed design procedure example:
表 10-1. Detailed Design Parameters
30
DESIGN PARAMETER
EXAMPLE VALUE
Input voltage
13.5 V (5 V to 36 V)
Input voltage for constant fSW
8 V to 18 V
Output voltage
5V
Maximum output current
0 A to 6 A
Switching frequency
400 kHz
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表 10-2. Typical External Component Values
fSW
(kHz)
VOUT (V)
L1 (µH)
COUT (RATED)
RFBT
(kΩ)
RFBB
(kΩ)
CBOOT
(µF)
RBOOT
(Ω)
CVCC
(µF)
2100
400
3.3
1
3 × 22 µF ceramic
100
43.2
0.1
0
3.3
4.7
3 × 47 µF ceramic
100
43.2
0.1
0
2100
5
1.5
2 × 22 µF ceramic
100
24.9
0.1
400
5
4.7
2 × 47 µF ceramic
100
24.9
0.1
CFF (pF)
RFF (kΩ)
1
10
1
1
4.7
1
0
1
22
1
0
1
22
1
10.2.2 Detailed Design Procedure
The following design procedure applies to 图 10-1 and 表 10-1.
10.2.2.1 Choosing the Switching Frequency
The choice of switching frequency is a compromise between conversion efficiency and overall solution size.
Lower switching frequency implies reduced switching losses and usually results in higher system efficiency.
However, higher switching frequency allows for the use of smaller inductors and output capacitors, hence, a
more compact design.
When choosing operating frequency, the most important consideration is thermal limitations. This constraint
typically dominates frequency selection. See 图 10-2 for circuits running at 400 kHz and 图 10-3 for circuits
running at 2.1 MHz. These curves show how much output current can be supported at a given ambient
temperature given these switching frequencies. Note that power dissipation is layout dependent so while these
curves are a good starting point, thermal resistance in any design will be different from the estimates used to
generate 图 10-2 and 图 10-3. The maximum temperature ratings are based on a 100-mm x 80-mm, 4-layer
EVM PCB design, LM61460EVM. Unless a larger copper area or cooling is provided to reduce the effective
RθJA, if ambient temperature is 105°C and the switching frequency is set to 2.1 MHz, the load current must
typically be limited to 4 A.
135
130
VIN = 13.5 V
VIN = 16 V
VIN = 24 V
120
VIN = 13.5 V
VIN = 16 V
VIN = 24 V
125
Ambient Temperature (°C)
Ambient Temperature (°C)
125
115
110
105
100
95
115
105
95
85
75
90
85
65
3
3.5
fSW = 400 kHz
4
4.5
5
Output Current (A)
PCB RθJA = 25°C/W
5.5
6
2
2.5
3
snvs
VOUT = 5 V
图 10-2. Maximum Ambient Temperature versus
Output Current
fSW = 2100 kHz
3.5
4
4.5
Output Current (A)
PCB RθJA = 25°C/W
5
5.5
6
snvs
VOUT = 5 V
图 10-3. Maximum Ambient Temperature versus
Output Current
Two other considerations are what maximum and minimum input voltage the part must maintain its frequency
setting. Since the LM61460-Q1 adjusts its frequency under conditions in which regulation would normally be
prevented by minimum on-time or minimum off time, these constraints are only important for input voltages
requiring constant frequency operation.
If foldback is undesirable at high input voltage, then use 方程式 7:
fSW G
VOUT
VIN(MAX2) Â WON_MIN(MAX)
(7)
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If foldback at low input voltage is a concern, use 方程式 8:
fSW ”
VINeff(MIN2) ± VOUT
VINeff(MIN2) Â WOFF_MIN(MAX)
(8)
where:
•
VINeff(MIN2) = VIN(MIN2) ± IOUT(MAX) Â (RDS(ON)_HS(MAX) + DCR(MAX))
•
•
•
DCR(MAX) = maximum DCR of the inductor
tOFF_MIN(MAX) = see 节 8.5
RDS(ON)_HS(MAX) = see 节 8.5
The fourth constraint is the rated frequency range of the IC. See fADJ in 节 8.5. All previously stated constraints
(thermal, VIN(MAX2), VIN(MIN2), and device-specified frequency range) must be considered when selecting
frequency.
Many applications require that the AM band can be avoided. These applications tend to operate at either 400
kHz below the AM band or 2.1 MHz above the AM band. In this example, 400 kHz is chosen.
10.2.2.2 Setting the Output Voltage
The output voltage of LM61460-Q1 is externally adjustable using a resistor divider network. The range of
recommended output voltage is found in 节 8.3. The divider network is comprised of RFBT and RFBB, and closes
the loop between the output voltage and the converter. The converter regulates the output voltage by holding
the voltage on the FB pin equal to the internal reference voltage, VREF. The resistance of the divider is a
compromise between excessive noise pickup and excessive loading of the output. Smaller values of resistance
reduce noise sensitivity but also reduce the light load efficiency. The recommended value for RFBT is 100 kΩ with
a maximum value of 1 MΩ. If 1 MΩ is selected for RFBT, then a feedforward capacitor must be used across this
resistor to provide adequate loop phase margin (see 节 10.2.2.10). Once RFBT is selected, 方程式 3 is used to
select RFBB. VREF is nominally 1 V. For this 5-V example, RFBT = 100 kΩ and RFBB = 24.9 kΩ are chosen.
10.2.2.3 Inductor Selection
The parameters for selecting the inductor are the inductance and saturation current. The inductance is based
on the desired peak-to-peak ripple current and is normally chosen to be in the range of 20% to 40% of
the maximum output current. Experience shows that the best value for inductor ripple current is 30% of the
maximum load current for systems with a fixed input voltage and 25% for systems with a variable input voltage
such as the 12 volt battery in a car. Note that when selecting the ripple current for applications with much smaller
maximum load than the maximum available from the device, the maximum device current must still be used. 方
程式 9 can be used to determine the value of inductance. The constant K is the percentage of inductor current
ripple. For this example, K = 0.25 was chosen and an inductance of approximately 5.2 µH was found. The next
standard value of 4.7 μH was selected.
L=
VIN Å 9OUT
VOUT
Â
fSW Â . Â ,OUT(MAX)
VIN
(9)
The saturation current rating of the inductor must be at least as large as the high-side switch current limit,
IL-HS (see 节 8.5). This ensures that the inductor does not saturate even during a short circuit on the output.
When the inductor core material saturates, the inductance falls to a very low value, causing the inductor current
to rise very rapidly. Although the valley current limit, IL-LS, is designed to reduce the risk of current run-away,
a saturated inductor can cause the current to rise to high values very rapidly. This can lead to component
damage; do not allow the inductor to saturate. Inductors with a ferrite core material have very hard saturation
characteristics, but usually have lower core losses than powdered iron cores. Powdered iron cores exhibit a soft
saturation, allowing some relaxation in the current rating of the inductor. However, they have more core losses at
frequencies typically above 1 MHz. In any case, the inductor saturation current must not be less than the device
32
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high-side current limit, IL-HS (see 节 8.5). To avoid subharmonic oscillation, the inductance value must not be less
than that given in 方程式 10. The maximum inductance is limited by the minimum current ripple required for the
current mode control to perform correctly. As a rule-of-thumb, the minimum inductor ripple current must be no
less than about 10% of the device maximum rated current under nominal conditions.
/ • 0.32 Â
VOUT
fSW
(10)
方程式 10 assumes that this design must operate with input voltage near or in dropout. If minimum operating
voltage for this design is high enough to limit duty factor to below 50%, 方程式 11 can be used in place of 方程式
10.
/ • 0.2 Â
VOUT
fSW
(11)
Note that choosing an inductor that is larger than the minimum inductance calculated using 方程式 9 through 方
程式 11 results in less output capacitance being needed to limit output ripple but more output capacitance being
needed to manage large load transients. See 节 10.2.2.4.
10.2.2.4 Output Capacitor Selection
The value of the output capacitor and its ESR determine the output voltage ripple and load transient
performance. The output capacitor is usually determined by the load transient requirements rather than the
output voltage ripple. 表 10-3 can be used to find the output capacitor and CFF selection for a few common
applications. Note that a 1-kΩ RFF can be used in series with CFF to further improve noise performance. In this
example, improved transient performance is desired giving 2 x 47-µF ceramic as the output capacitor and 22 pF
as CFF.
表 10-3. Recommended Output Ceramic Capacitors and CFF Values
3.3-V OUTPUT
5-V OUTPUT
FREQUENCY
TRANSIENT
PERFORMANCE
CERAMIC OUTPUT CAPACITANCE
CFF
CERAMIC OUTPUT CAPACITANCE
CFF
2.1 MHz
Minimum
3 x 22 µF
10 pF
2 x 22 µF
22 pF
2.1 MHz
Better Transient
2 x 47 µF
33 pF
3 x 22 µF
33 pF
400 kHz
Minimum
3 x 47 µF
4.7 pF
2 x 47 µF
10 pF
400 kHz
Better Transient
3 x 47 µF
33 pF
3 x 47 µF
33 pF
To minimize ceramic capacitance, a low-ESR electrolytic capacitor can be used in parallel with minimal
ceramic capacitance. As a starting point for designing with an output electrolytic capacitor, 表 10-4 shows the
recommended output ceramic capacitance CFF values when using an electrolytic capacitor.
表 10-4. Recommended Electrolytic and Ceramic Capacitor and CFF Values
FREQUENCY
TRANSIENT
PERFORMANCE
400 kHz
400 kHz
3.3-V OUTPUT
5-V OUTPUT
COUT
CFF
COUT
CFF
Minimum
2 x 47 µF ceramic + 1 x 470 µF, 100-mΩ electrolytic
10 pF
3 x 22 µF ceramic + 1 x 470 µF, 100-mΩ
electrolytic
10 pF
Better Transient
3 x 47 µF ceramic + 2 x 280 µF,100-mΩ electrolytic
33 pF
4 x 22 µF ceramic + 1 x 560 µF, 100-mΩ
electrolytic
22 pF
Most ceramic capacitors deliver far less capacitance than the rating of the capacitor indicates. Be sure to check
any capacitor selected for initial accuracy, temperature derating, and voltage derating. 表 10-3 and 表 10-4
have been generated assuming typical derating for 16-V, X7R, automotive grade capacitors. If lower voltage,
non-automotive grade, or lower temperature rated capacitors are used, more capacitors than listed are likely to
be needed.
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10.2.2.5 Input Capacitor Selection
The ceramic input capacitors provide a low impedance source to the converter in addition to supplying the
ripple current and isolating switching noise from other circuits. A minimum of 10 μF of ceramic capacitance
is required on the input of the device. This must be rated for at least the maximum input voltage that the
application requires; preferably twice the maximum input voltage. This capacitance can be increased to help
reduce input voltage ripple and maintain the input voltage during load transients. In addition, a small case
size 100-nF ceramic capacitor must be used at each input/ground pin pair, VIN1/PGND1 and VIN2/PGND2,
immediately adjacent to the converter. This provides a high-frequency bypass for the control circuits internal
to the device. These capacitors also suppress SW node ringing, which reduces the maximum voltage present
on the SW node and EMI. The two 100 nF must also be rated at 50 V with an X7R or better dielectric. The
VQFN-HR (RJR) package provides two input voltage pins and two power ground pins on opposite sides of the
package. This allows the input capacitors to be split, and placed optimally with respect to the internal power
MOSFETs, thus improving the effectiveness of the input bypassing. In this example, two 4.7-μF and two 100-nF
ceramic capacitors are used, one at each VIN/PGND location. A single 10-μF can also be used on one side of
the package.
Many times, it is desirable and necessary to use an electrolytic capacitor on the input in parallel with the
ceramics. This is especially true if long leads or traces are used to connect the input supply to the converter.
The moderate ESR of this capacitor can help damp any ringing on the input supply caused by the long power
leads. The use of this additional capacitor also helps with momentary voltage dips caused by input supplies with
unusually high impedance.
Most of the input switching current passes through the ceramic input capacitors. The approximate worst case
RMS value of this current can be calculated from 方程式 12 and must be checked against the manufacturers'
maximum ratings.
IRMS §
IOUT
2
(12)
10.2.2.6 BOOT Capacitor
The LM61460-Q1 requires a bootstrap capacitor connected between the CBOOT pin and the SW pin. This
capacitor stores energy that is used to supply the gate drivers for the high-side power MOSFET. A high-quality
(X7R) ceramic capacitor of 100 nF and at least 10 V is required.
10.2.2.7 BOOT Resistor
A BOOT resistor can be connected between the CBOOT and RBOOT pins. Unless EMI for the application
being designed is critical, these two pins can be shorted. A 100-Ω resistor between these pins eliminates
overshoot. Even with 0 Ω, overshoot and ringing are minimal, less than 2 V if input capacitors are placed
correctly. A boot resistor of 100 Ω, which corresponds to approximately 2.7-ns SW node rise time and decreases
efficiency by approximately 0.5% at 2 MHz. To maximize efficiency, 0 Ω is chosen for this example. Under
most circumstances, selecting an RBOOT resistor value above 100 Ω is undesirable since the resulting small
improvement in EMI is not enough to justify further decreased efficiency.
10.2.2.8 VCC
The VCC pin is the output of the internal LDO used to supply the control circuits of the converter. This output
requires a 1-μF, 16-V ceramic capacitor connected from VCC to AGND for proper operation. In general, avoid
loading this output with any external circuitry. However, this output can be used to supply the pullup for the
power-good function (see 节 9.3.5). A pullup resistor with a value of 100 kΩ is a good choice in this case. Note,
VCC remains high when VEN_WAKE< EN < VEN. The nominal output voltage on VCC is 3.3 V. Do not short this
output to ground or any other external voltage.
34
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10.2.2.9 BIAS
Because VOUT = 5 V in this design, the BIAS pin is tied to VOUT to reduce LDO power loss. The output voltage
is supplying the LDO current instead of the input voltage. The power saving is ILDO × (VIN – VOUT). The power
saving is more significant when VIN >> VOUT and with higher frequency operation. To prevent VOUT noise and
transients from coupling to BIAS, a series resistor, 1 Ω to 10 Ω, can be added between VOUT and BIAS. A
bypass capacitor with a value of 1 μF or higher can be added close to the BIAS pin to filter noise. Note the
maximum allowed voltage on the BIAS pin is 16 V.
10.2.2.10 CFF and RFF Selection
A feedforward capacitor, Cff, is used to improve phase margin and transient response of circuits which have
output capacitors with low ESR. Since this capacitor can conduct noise from the output of the circuit directly
to the FB node of the IC, a 1-kΩ resistor, Rff, can be placed in series with Cff. If the ESR zero of the output
capacitor is below 200 kHz, no Cff must be used.
If output voltage is less than 2.5 V, Cff has little effect, so it can be omitted. If output voltage is greater than 14 V,
Cff must not be used since it introduces too much gain at higher frequencies.
10.2.2.11 External UVLO
In some cases, an input UVLO level different than that provided internal to the device is needed. This can be
accomplished by using the circuit shown in 图 10-4. The input voltage at which the device turns on is designated
VON while the turnoff voltage is VOFF. First, a value for RENB is chosen in the range of 10 kΩ to 100 kΩ, then 方
程式 14 is used to calculate RENT and VOFF. RENB is typically set based on how much current this voltage divider
must consume. RENB can be calculated using 方程式 13.
RENB =
VEN Â 9IN
IDIVIDER Â 9ON
(13)
VIN
RENT
EN/SYNC
RENB
AGND
图 10-4. UVLO Using EN
RENT =
VON
Å 1 Â 5ENB
VEN
VOFF = VON Â (1 Å 9EN-HYST)
(14)
where
•
•
•
VON = VIN turnon voltage
VOFF = VIN turnoff voltage
IDIVIDER = voltage divider current
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10.2.3 Application Curves
100%
100%
95%
95%
90%
85%
Efficiency (%)
Efficiency (%)
90%
85%
80%
75%
80%
75%
70%
65%
70%
60%
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
65%
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
55%
50%
60%
0.001
0.010.02 0.05 0.1 0.2 0.5
Output Current (A)
VOUT = 3.3 V
1
0
2 3 4 5 7 10
1
2
LM61
FSW = 400 kHz
Auto Mode
VOUT = 3.3 V
图 10-5. LM61460-Q1 Efficiency
3
4
Output Current (A)
5
6
7
LM61
FSW = 400 kHz
FPWM Mode
图 10-6. LM61460-Q1 Efficiency
100%
100%
95%
95%
90%
85%
Efficiency (%)
Efficiency (%)
90%
85%
80%
75%
80%
75%
70%
65%
70%
60%
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
65%
60%
0.001
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
55%
50%
0.010.02 0.05 0.1 0.2 0.5
Output Current (A)
VOUT = 3.3 V
1
FSW = 2100 kHz
2 3 4 5 7 10
0
1
2
LM61
AUTO Mode
VOUT = 3.3 V
图 10-7. LM61460-Q1 Efficiency
3
4
Output Current (A)
5
6
7
LM61
FSW = 2100 kHz
FPWM Mode
图 10-8. LM61460-Q1 Efficiency
100%
100%
95%
95%
90%
85%
Efficiency (%)
Efficiency (%)
90%
85%
80%
75%
80%
75%
70%
65%
70%
60%
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
65%
60%
0.0001
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
55%
50%
0.001
VOUT = 5 V
0.01
0.1 0.2 0.5 1
Load Current (A)
FSW = 400 kHz
2 3 5 710
AUTO Mode
0
VOUT = 5 V
图 10-9. LM61460-Q1 Efficiency
36
1
LM61
2
3
4
Load Current (A)
5
FSW = 400 kHz
6
7
LM61
FPWM Mode
图 10-10. LM61460-Q1 Efficiency
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10.2.3 Application Curves (continued)
100%
100%
95%
95%
90%
85%
Efficiency (%)
Efficiency (%)
90%
85%
80%
75%
80%
75%
70%
65%
70%
60%
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
65%
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
55%
50%
60%
0.001
0.010.02 0.05 0.1 0.2 0.5
Load Current (A)
VOUT = 5 V
1
FSW = 2100 kHz
0
2 3 4 5 7 10
1
2
LM61
AUTO Mode
VOUT = 5 V
图 10-11. LM61460-Q1 Efficiency
3
4
Load Current (A)
5
FSW = 2100 kHz
FPWM Mode
3.37
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
3.35
3.35
Output Voltage (V)
Output Voltage (V)
7
LM61
图 10-12. LM61460-Q1 Efficiency
3.37
3.33
3.31
3.33
3.31
3.29
3.29
0
1
2
VOUT = 3.3 V
3
4
Output Current (A)
5
6
7
0
1
2
SNVS
FSW = 400 kHz
Auto Mode
VOUT = 3.3 V
图 10-13. LM61460-Q1 Load and Line Regulation
3
4
Output Current (A)
5
6
7
SNVS
FSW = 400 kHz
FPWM Mode
图 10-14. LM61460-Q1 Load and Line Regulation
3.37
3.37
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
3.35
3.35
Output Voltage (V)
Output Voltage (V)
6
3.33
3.31
3.33
3.31
3.29
3.29
0
1
VOUT = 3.3 V
2
3
4
Output Current (A)
FSW = 2100 kHz
5
6
7
0
1
SNVS
AUTO Mode
图 10-15. LM61460-Q1 Load and Line Regulation
VOUT = 3.3 V
2
3
4
Output Current (A)
FSW = 2100 kHz
5
6
7
SNVS
FPWM Mode
图 10-16. LM61460-Q1 Load and Line Regulation
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5.11
5.11
5.09
5.09
5.07
5.07
Output Voltage (V)
Output Voltage (V)
10.2.3 Application Curves (continued)
5.05
5.03
5.01
4.99
5.01
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
4.97
4.95
4.95
0
1
2
VOUT = 5 V
3
4
Output Current (A)
5
6
7
0
1
2
SNVS
FSW = 400 kHz
AUTO Mode
VOUT = 5 V
图 10-17. LM61460-Q1 Load and Line Regulation
3
4
Output Current (A)
5.11
5.09
5.09
5.07
5.07
5.05
5.03
5.01
4.99
6
7
SNVS
FSW = 400 kHz
FPWM Mode
5.05
5.03
5.01
4.99
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
4.97
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
4.97
4.95
4.95
0
1
2
VOUT = 5 V
3
4
Output Current (A)
5
6
7
0
1
2
SNVS
FSW = 2100 kHz
AUTO Mode
VOUT = 5 V
图 10-19. LM61460-Q1 Load and Line Regulation
3
4
Output Current (A)
5
6
7
SNVS
FSW = 2100 kHz
FPWM Mode
图 10-20. LM61460-Q1 Load and Line Regulation
3.5
3.25
3.25
Output Voltage (V)
3.5
3
2.75
3
2.75
IOUT = 0.01 A
IOUT = 3 A
IOUT = 6 A
IOUT = 0.01 A
IOUT = 3 A
IOUT = 6 A
2.5
2.5
3
3.25
VOUT = 3.3 V
3.5
3.75
4
4.25
Input Voltage (V)
FSW = 400 kHz
4.5
4.75
5
3
3.25
SNVS
AUTO Mode
图 10-21. LM61460-Q1 Dropout Curve
38
5
图 10-18. LM61460-Q1 Load and Line Regulation
5.11
Output Voltage (V)
Output Voltage (V)
5.03
4.99
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
4.97
Output Voltage (V)
5.05
VOUT = 3.3 V
3.5
3.75
4
4.25
Input Voltage (V)
FSW = 2100 kHz
4.5
4.75
5
SNVS
AUTO Mode
图 10-22. LM61460-Q1 Dropout Curve
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6
6
5.5
5.5
Ouput Voltage (V)
Output Voltage (V)
10.2.3 Application Curves (continued)
5
4.5
4
IOUT = 0.01 A
IOUT = 3 A
IOUT = 6 A
3.5
5
4.5
4
IOUT = 0.01 A
IOUT = 3 A
IOUT = 6 A
3.5
3
3
4
4.2
4.4
4.6
4.8
5
5.2 5.4
Input Voltage (V)
VOUT = 5 V
5.6
5.8
6
4
4.2
FSW = 400 kHz
AUTO Mode
2.5E+6
2.25E+6
4E+5
Switching Frequency (Hz)
Switching Frequency (Hz)
5E+5
3.5E+5
3E+5
2.5E+5
2E+5
1.5E+5
1E+5
IOUT = 3 A
IOUT = 6 A
5E+4
VOUT = 3.3 V
3.75
4
Input Voltage (V)
FSW = 400 kHz
4.25
1E+6
7.5E+5
5E+5
IOUT = 3 A
IOUT = 6 A
3
4.5
3.5
4
Input Voltage (V)
4.5
5
snvs
snvs
VOUT = 3.3 V
AUTO Mode
4E+5
3.5E+5
3E+5
2.5E+5
2E+5
1.5E+5
1E+5
IOUT = 3 A
IOUT = 6 A
5E+4
AUTO Mode
2E+6
1.75E+6
1.5E+6
1.25E+6
1E+6
7.5E+5
5E+5
IOUT = 3 A
IOUT = 6 A
2.5E+5
0
0
5.75
FSW = 2100 kHz
图 10-26. LM61460-Q1 Frequency Dropout Curve
Switching Frequency (Hz)
Switching Frequency (Hz)
1.5E+6
2.5E+6
FSW = 400 kHz
AUTO Mode
1.25E+6
2.25E+6
VOUT = 5 V
FSW = 2100 kHz
2E+6
5E+5
5.5
Input Voltage (V)
6
SNVS
1.75E+6
4.5E+5
5.25
5.8
0
图 10-25. LM61460-Q1 Frequency Dropout
5
5.6
2.5E+5
0
3.5
4.8
5
5.2 5.4
Input Voltage (V)
图 10-24. LM61460-Q1 Dropout Curve
4.5E+5
3.25
4.6
VOUT = 5 V
图 10-23. Dropout Curve
3
4.4
SNVS
6
5
5.5
6
Input Voltage (V)
6.5
7
snvs
snvs
AUTO Mode
图 10-27. LM61460-Q1 Frequency Dropout Curve
VOUT = 5 V
FSW = 2100 kHz
AUTO Mode
图 10-28. LM61460-Q1 Frequency Dropout Curve
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10.2.3 Application Curves (continued)
VOUT Ripple
(10 mV/DIV)
VOUT Ripple
(10 mV/DIV)
VSW
(5 V/DIV)
VSW
(5 V/DIV)
IINDUCTOR
(2 A/DIV)
IINDUCTOR
(2 A/DIV)
Time (2 µs/DIV)
Time (20 µs/DIV)
VOUT = 5 V
FSW = 2100 kHz
IOUT = 50 mA
VIN = 13.5 V
AUTO Mode
图 10-29. LM61460-Q1 Switching Waveform and VOUT Ripple
VOUT = 5 V
FSW = 2100 kHz
IOUT = 50 mA
VIN = 13.5 V
图 10-30. LM61460-Q1 Switching Waveform and VOUT Ripple
VOUT
(2 V/DIV)
VOUT
(2 V/DIV)
IINDUCTOR
(1 A/DIV)
IINDUCTOR
(1 A/DIV)
VPG
(5 V/DIV)
VPG
(5 V/DIV)
VEN
(5 V/DIV)
VEN
(5 V/DIV)
Time (1 ms/DIV)
Time (1 ms/DIV)
VOUT = 5 V
FSW = 2100 kHz
IOUT = 50 mA
VIN = 13.5 V
FPWM Mode
AUTO Mode
图 10-31. LM61460-Q1 Start-up with 50-mA Load
VOUT
(2 V/DIV)
VOUT = 5 V
FSW = 2100 kHz
IOUT = 50 mA
VIN = 13.5 V
FPWM Mode
图 10-32. LM61460-Q1 Start-up with 50-mA
VOUT
(2 V/DIV)
IINDUCTOR
(1 A/DIV)
VPG
(5 V/DIV)
IINDUCTOR
(2 A/DIV)
VEN
(5 V/DIV)
Time (200 µs/DIV)
Time (1 ms/DIV)
VOUT = 3.3 V
FSW = 2100 kHz
IOUT = 3.25 A
VIN = 13.5 V
FPWM Mode
FSW = 2100 kHz
IOUT = 5 A to Short Circuit
图 10-33. LM61460-Q1 Start-up with 3.25-A
40
VOUT = 5 V
FPWM Mode
VIN = 13.5 V
图 10-34. LM61460-Q1 Short Circuit Protection
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10.2.3 Application Curves (continued)
VOUT
(2 V/DIV)
VOUT
(500 mV/DIV)
IINDUCTOR
(2 A/DIV)
IINDUCTOR
(2 A/DIV)
Time (20 ms/DIV)
Time (20 ms/DIV)
VOUT = 5 V
FSW = 2100 kHz
IOUT = Short Circuit to 5 A
VOUT = 5 V
FPWM Mode
图 10-35. LM61460-Q1 Short Circuit Recovery
VOUT
(200 mV/DIV)
IINDUCTOR
(1 A/DIV)
VIN
(5 V/DIV)
IOUT
(2 A/DIV)
FSW = 2100 kHz
VIN = 13.5 V
Time (50 µs/DIV)
Time (2 ms/DIV)
IOUT = 4 A
FPWM Mode
图 10-36. LM61460-Q1 Short Circuit Performance
VOUT
(2 V/DIV)
VOUT = 5 V
FSW = 2100 kHz
IOUT = Short Circuit
VIN = 13.5 V
VOUT = 5 V
FSW = 400 kHz
AUTO Mode
IOUT = 0 A to 6 A to 0 A
VIN = 13.5 V
TR = TF = 6 µs
FPWM Mode
VIN = 13.5 V to 4 V to 13.5 V
图 10-38. LM61460-Q1 Load Transient
图 10-37. Graceful Recovery from Dropout
VOUT
(200 mV/DIV)
VOUT
(200 mV/DIV)
IOUT
(2 A/DIV)
IOUT
(2 A/DIV)
Time (50 µs/DIV)
Time (50 µs/DIV)
VOUT = 5 V
FSW = 400 kHz
FPWM Mode
VOUT = 5 V
FSW = 400 kHz
AUTO Mode
IOUT = 0 A to 6 A to 0 A
VIN = 13.5 V
TR = TF = 6 µs
IOUT = 2 A to 5 A to 2 A
VIN = 13.5 V
TR = TF = 3 µs
图 10-39. LM61460-Q1 Load Transient
图 10-40. LM61460-Q1 Load Transient
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10.2.3 Application Curves (continued)
VOUT
(200 mV/DIV)
VOUT
(200 mV/DIV)
IOUT
(2 A/DIV)
IOUT
(2 A/DIV)
Time (50 µs/DIV)
Time (50 µs/DIV)
VOUT = 5 V
FSW = 400 kHz
AUTO Mode
IOUT = 50 mA to 6 A to 50
VIN = 13.5 V
TR = TF = 6 µs
VOUT = 3.3 V
FSW = 400 kHz
AUTO Mode
IOUT = 0 A to 6 A to 0 A
VIN = 13.5 V
TR = TF = 6 µs
图 10-42. LM61460-Q1 Load Transient
mA
图 10-41. LM61460-Q1 Load Transient
VOUT
(200 mV/DIV)
VOUT
(200 mV/DIV)
IOUT
(2 A/DIV)
IOUT
(2 A/DIV)
Time (50 µs/DIV)
Time (50 µs/DIV)
VOUT = 3.3 V
FSW = 400 kHz
AUTO Mode
VOUT = 5 V
FSW = 2100 kHz
AUTO Mode
IOUT = 2 A to 4 A to 2 A
VIN = 13.5 V
TR = TF = 2 µs
IOUT = 0 A to 6 A to 0 A
VIN = 13.5 V
TR = TF = 6 µs
图 10-43. LM61460-Q1 Load Transient
图 10-44. LM61460-Q1 Load Transient
VOUT
(200 mV/DIV)
IOUT
(2 A/DIV)
Time (50 µs/DIV)
VOUT = 5 V
FSW = 2100 kHz
FPWM Mode
IOUT = 0 A to 6 A to 0 A
VIN = 13.5 V
TR = TF = 6 µs
FSW = 400 kHz
图 10-45. LM61460-Q1 Load Transient
VOUT = 5 V
IOUT = 5 A
Frequency Tested: 150 kHz to 30 MHz
图 10-46. Conducted EMI versus CISPR25 Limits (Yellow: Peak
Signal, Blue: Average Signal)
42
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10.2.3 Application Curves (continued)
VOUT = 5 V
VOUT = 5 V
FSW = 400 kHz
FSW = 400 kHz
IOUT = 5 A
Frequency Tested: 150 kHz to 30 MHz
IOUT = 5 A
图 10-48. Radiated EMI Rod versus CISPR25 Limits
Frequency Tested: 30 MHz to 108 MHz
图 10-47. Conducted EMI versus CISPR25 Limits (Yellow: Peak
Signal, Blue: Average Signal)
VOUT = 5 V
FSW = 400 kHz
IOUT = 5 A
VOUT = 5 V
Frequency Tested: 30 MHz to 300 MHz
图 10-49. Radiated EMI Bicon Vertical versus CISPR25 Limits
VOUT = 5 V
FSW = 400 kHz
FSW = 400 kHz
IOUT = 5 A
Frequency Tested: 30 MHz to 300 MHz
IOUT = 5 A
图 10-50. Radiated EMI Bicon Horizontal versus CISPR25 Limits
VOUT = 5 V
Frequency Tested: 300 MHz to 1 GHz
FSW = 400 kHz
IOUT = 5 A
Frequency Tested: 300 MHz to 1 GHz
图 10-51. Radiated EMI Log Vertical versus CISPR25 Limits
图 10-52. Radiated EMI Log Horizontal versus CISPR25 Limits
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10.2.3 Application Curves (continued)
744316220
L=2.2µH
VIN
IN+
IN-
GND
CF5=2.2uF
CF6=2.2uF
CF3=2.2uF
CF4= 2.2uF
CF1=470nF
CF2=470nF
FSW = 2100 kHz
FSW = 400 kHz
Note: Measurements taken with
VOUT = 5 V
IOUT = 5 A
Frequency Tested: 150 kHz to 30 MHz
LM61460EVM
图 10-54. Conducted EMI versus CISPR25 Limits (Yellow: Peak
Signal, Blue: Average Signal)
图 10-53. Recommended Input EMI Filter
74438356010
L=1µH
VIN
IN+
IN-
GND
CF5=2.2uF
CF6=2.2uF
FSW = 2100 kHz
VOUT = 5 V
CF3=2.2uF
CF4= 2.2uF
CF1=470nF
CF2=470nF
IOUT = 5 A
Frequency Tested: 30 MHz to 108 MHz
图 10-55. Conducted EMI versus CISPR25 Limits (Yellow: Peak
Signal, Blue: Average Signal)
FSW = 2100 kHz
图 10-56. Recommended Input EMI Filter
表 10-5. BOM for Typical Application Curves
44
VOUT
FREQUENCY
RFBB
RT
COUT
CIN + CHF
L
CFF
3.3 V
400 kHz
43.2 kΩ
33.2 kΩ
6 x 22 µF
2 x 4.7 µF + 2 x 100 nF
4.7 µH (XHMI6060)
22 pF
3.3 V
2100 kHz
43.2 kΩ
6.04 kΩ
3 x 22 µF
2 x 4.7 µF + 2 x 100 nF
1 µH (XEL5030)
22 pF
5V
400 kHz
24.9 kΩ
33.2 kΩ
4 x 22 µF
2 x 4.7 µF + 2 x 100 nF
4.7 µH (XHMI6060)
22 pF
5V
2100 kHz
24.9 kΩ
6.04 kΩ
3 x 22 µF
2 x 4.7 µF + 2 x 100 nF
1 µH (XEL5030)
22 pF
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11 Power Supply Recommendations
The characteristics of the input supply must be compatible with Absolute Maximum Ratings and Recommended
Operating Conditions in this data sheet. In addition, the input supply must be capable of delivering the required
input current to the loaded converter. The average input current can be estimated with 方程式 15.
IIN =
VOUT Â ,OUT
VIN Â
(15)
where
•
η is the efficiency
If the converter is connected to the input supply through long wires or PCB traces, special care is required to
achieve good performance. The parasitic inductance and resistance of the input cables can have an adverse
effect on the operation of the converter. The parasitic inductance, in combination with the low-ESR, ceramic
input capacitors, can form an under-damped resonant circuit, resulting in overvoltage transients at the input to
the converter or tripping UVLO. The parasitic resistance can cause the voltage at the VIN pin to dip whenever
a load transient is applied to the output. If the application is operating close to the minimum input voltage, this
dip can cause the converter to momentarily shutdown and reset. The best way to solve these kind of issues is to
reduce the distance from the input supply to the converter and use an aluminum input capacitor in parallel with
the ceramics. The moderate ESR of this type of capacitor helps damp the input resonant circuit and reduce any
overshoot or undershoot at the input. A value in the range of 20 µF to 100 µF is usually sufficient to provide input
damping and help hold the input voltage steady during large load transients.
In some cases, a transient voltage suppressor (TVS) is used on the input of converters. One class of this
device has a snap-back characteristic (thyristor type). The use of a device with this type of characteristic is not
recommended. When the TVS fires, the clamping voltage falls to a very low value. If this voltage is less than
the output voltage of the converter, the output capacitors discharge through the device back to the input. This
uncontrolled current flow can damage the TVS and cause large input transients.
The input voltage must not be allowed to fall below the output voltage. In this scenario, such as a shorted input
test, the output capacitors discharge through the internal parasitic diode found between the VIN and SW pins of
the device. During this condition, the current can become uncontrolled, possibly causing damage to the device. If
this scenario is considered likely, then a Schottky diode between the input supply and the output must be used.
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12 Layout
12.1 Layout Guidelines
The PCB layout of any DC-DC converter is critical to the optimal performance of the design. Bad PCB layout can
disrupt the operation of an otherwise good schematic design. Even if the converter regulates correctly, bad PCB
layout can mean the difference between a robust design and one that cannot be mass produced. Furthermore,
the EMI performance of the converter is dependent on the PCB layout, to a great extent. In a buck converter, the
most critical PCB feature is the loop formed by the input capacitor or capacitors and power ground, as shown in
图 12-1. This loop carries large transient currents that can cause large transient voltages when reacting with the
trace inductance. These unwanted transient voltages disrupt the proper operation of the converter. Because of
this, the traces in this loop must be wide and short, and the loop area as small as possible to reduce the parasitic
inductance. 图 12-2 shows a recommended layout for the critical components for the circuit of the device.
•
•
•
•
•
•
•
•
46
Place the input capacitor or capacitors as close as possible input pin pairs: VIN1 to PGND1 and VIN2
to PGND2. Each pair of pins are adjacent, simplifying the input capacitor placement. With the VQFN-HR
package, there are two VIN/PGND pairs on either side of the package. This provides for a symmetrical layout
and helps minimize switching noise and EMI generation. Use a wide VIN plane on a lower layer to connect
both of the VIN pairs together to the input supply.
Place bypass capacitor for VCC close to the VCC pin and AGND pins: This capacitor must routed with short,
wide traces to the VCC and AGND pins.
Use wide traces for the CBOOT capacitor: Place the CBOOT capacitor as close to the device with short, wide
traces to the CBOOT and SW pins. It is important to route the SW connection under the device through the
gap between VIN2 and RBOOT pins, reducing exposed SW node area. If an RBOOT resistor is used, place
as close as possible to CBOOT and RBOOT pins. If high efficiency is desired, RBOOT and CBOOT pins can
be shorted. This short must be placed as close as possible to RBOOT and CBOOT pins as possible.
Place the feedback divider as close as possible to the FB pin of the device: Place RFBB, RFBT, and CFF, if
used, physically close to the device. The connections to FB and AGND through RFBB must be short and close
to those pins on the device. The connection to VOUT can be somewhat longer. However, this latter trace must
not be routed near any noise source (such as the SW node) that can capacitively couple into the feedback
path of the converter. For fixed output variants, the FB pin must be directly routed to the output of the device.
Layer of the PCB beneath the top layer with the IC must be a ground plane: This plane acts as a noise shield
and a heat dissipation path. Using the layer directly next to the IC reduces the inclosed area in the input
circulating current in the input loop, reducing inductance.
Provide wide paths for VIN, VOUT, and GND: These paths must be wide and direct as possible to reduce any
voltage drops on the input or output paths of the converter and maximizes efficiency.
Provide enough PCB area for proper heat sinking: Enough copper area must be used to ensure a low RθJA,
commensurate with the maximum load current and ambient temperature. Make the top and bottom PCB
layers with two-ounce copper and no less than one ounce. If the PCB design uses multiple copper layers
(recommended), thermal vias can also be connected to the inner layer heat-spreading ground planes. Note
that the package of this device dissipates heat through all pins. Wide traces must be used for all pins except
where noise considerations dictate minimization of area.
Keep switch area small: Keep the copper area connecting the SW pin to the inductor as short and wide as
possible. At the same time, the total area of this node must be minimized to help reduce radiated EMI.
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VIN1
VIN2
HS
FET
CIN_HF1
CIN_HF2
SW
LS
FET
PGND1
PGND2
图 12-1. Input Current Loop
12.1.1 Ground and Thermal Considerations
As mentioned above, TI recommends using one of the middle layers as a solid ground plane. A ground plane
provides shielding for sensitive circuits and traces. It also provides a quiet reference potential for the control
circuitry. The AGND and PGND pins must be connected to the ground planes using vias next to the bypass
capacitors. PGND pins are connected directly to the source of the low-side MOSFET switch, and also connected
directly to the grounds of the input and output capacitors. The PGND net contains noise at the switching
frequency and can bounce due to load variations. The PGND trace, as well as the VIN and SW traces, must be
constrained to one side of the ground planes. The other side of the ground plane contains much less noise and
must be used for sensitive routes.
TI recommends providing adequate device heat sinking by using vias near ground and VIN to connect to the
system ground plane or VIN strap, both of which dissipate heat. Use as much copper as possible, for system
ground plane, on the top and bottom layers for the best heat dissipation. Use a four-layer board with the copper
thickness for the four layers, starting from the top as: 2 oz / 1 oz / 1 oz / 2 oz. A four-layer board with enough
copper thickness and proper layout, provides low current conduction impedance, proper shielding, and lower
thermal resistance.
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12.2 Layout Example
GND POUR
VIAS to BIAS
VIA to Feedback
divider
VOUT
COUT2
COUT1
GND POUR
GND POUR
INDUCTOR
Inductor
CIN_HF2
CIN2
CIN_HF1
11
10
12
CIN1
9
8
VIN
7
6
13
14
CBOOT
1
2 3 4
VIN
5
RBOOT
VOUT
IC
REN
CVCC
RMODE
RFBB
CFF
GND POUR
RFBT
GND POUR
RFF
VOUT
INNER GND PLANE ± LAYER 2
Top Trace/Pour
VIA to Signal Layer
Inner GDN Plane
VIA to GND
图 12-2. Layout Example
48
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13 Device and Documentation Support
13.1 Documentation Support
13.1.1 Related Documentation
For related documentation see the following:
• Texas Instruments, Designing High Performance, Low-EMI, Automotive Power Supplies Application Report
• Texas Instruments, LM61460-Q1 EVM User's Guide
• Texas Instruments, 30 W Power for Automotive Dual USB Type-C Charge Port Reference Design
• Texas Instruments, EMI Filter Components and Their Nonidealities for Automotive DC/DC Regulators
Technical Brief
• Texas Instruments, AN-2020 Thermal Design by Insight, Not Hindsight Application Report
• Texas InstrumentsOptimizing the Layout for the TPS54424/TPS54824 HotRod QFN Package for Thermal
Performance Application Report
• Texas Instruments, AN-2162 Simple Success With Conducted EMI From DC-DC Converters Application
Report
• Texas Instruments, Practical Thermal Design With DC/DC Power Modules Application Report
13.2 接收文档更新通知
要接收文档更新通知，请导航至 ti.com 上的器件产品文件夹。点击订阅更新 进行注册，即可每周接收产品信息更
改摘要。有关更改的详细信息，请查看任何已修订文档中包含的修订历史记录。
13.3 支持资源
TI E2E™ 支持论坛是工程师的重要参考资料，可直接从专家获得快速、经过验证的解答和设计帮助。搜索现有解
答或提出自己的问题可获得所需的快速设计帮助。
链接的内容由各个贡献者“按原样”提供。这些内容并不构成 TI 技术规范，并且不一定反映 TI 的观点；请参阅 TI
的《使用条款》。
13.4 Trademarks
HotRod™, Hotrod™, and TI E2E™ are trademarks of Texas Instruments.
所有商标均为其各自所有者的财产。
13.5 静电放电警告
静电放电 (ESD) 会损坏这个集成电路。德州仪器 (TI) 建议通过适当的预防措施处理所有集成电路。如果不遵守正确的处理
和安装程序，可能会损坏集成电路。
ESD 的损坏小至导致微小的性能降级，大至整个器件故障。精密的集成电路可能更容易受到损坏，这是因为非常细微的参
数更改都可能会导致器件与其发布的规格不相符。
13.6 术语表
TI 术语表
本术语表列出并解释了术语、首字母缩略词和定义。
14 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OUTLINE
RJR0014A
VQFN-HR - 1 mm max height
SCALE 3.200
PLASTIC QUAD FLATPACK - NO LEAD
4.1
3.9
B
A
PIN 1 INDEX AREA
3.6
3.4
0.1 MIN
(0.05)
SECTION A-A
SECTION
A-A
SCALE
30.000
TYPICAL
1.0
0.8
C
SEATING PLANE
0.05
0.00
0.08 C
2X 0.625
2X 1.6
2X 0.5
2X 0.45
2X 0.55
0.1
0.05
0.4
0.3
C A B
C
0.35
0.25
0.7
0.5
2X
6
(0.2) TYP
9
5
A
2X 0.525
0.45
0.35
A
SYMM
10
2X 1.15
2.2 0.05
PIN 1
ID
2X
11
1
0.45
0.35
C A B
C
0.9
0.7
4X
0.1
0.05
2X
14
0.6
0.4
2X
0.3
0.2
C A B
C
PKG
6X
0.1
0.05
7X
0.6
0.4
0.45
2X
0.35
0.1
0.05
0.45
0.35
0.1
0.05
C A B
C
C A B
C
4223976/D 11/2019
NOTES:
1. All linear dimensions are in millimeters. Any dimensions in parenthesis are for reference only. Dimensioning and tolerancing
per ASME Y14.5M.
2. This drawing is subject to change without notice.
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EXAMPLE BOARD LAYOUT
RJR0014A
VQFN-HR - 1 mm max height
PLASTIC QUAD FLATPACK - NO LEAD
2X (0.7)
PKG
(0.5)
2X
(0.35)
(0.625)
4X (1)
14
2X (0.8)
2X
(0.4)
2X
(0.4)
2X (1)
1
11
4X (0.4)
SEE SOLDER MASK
DETAIL
(2.4)
(0.3)
SYMM
10
(0.4)
(0.525)
(3.2)
(1)
(R0.05)
TYP
(2.9)
7X (0.7)
9
5
6
6X (0.25)
(0.45)
(1.85)
LAND PATTERN EXAMPLE
EXPOSED METAL SHOWN
SCALE: 25X
0.07 MIN
ALL AROUND
0.07 MAX
ALL AROUND
METAL UNDER
SOLDER MASK
METAL EDGE
EXPOSED
METAL
SOLDER MASK
OPENING
NON SOLDER MASK
DEFINED
(PREFERRED)
EXPOSED
METAL
SOLDER MASK
OPENING
SOLDER MASK DEFINED
SOLDER MASK DETAIL
4223976/D 11/2019
NOTES: (continued)
3. This package is designed to be soldered to thermal pads on the board. For more information, see Texas Instruments literature
number SLUA271 (www.ti.com/lit/slua271).
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EXAMPLE STENCIL DESIGN
RJR0014A
VQFN-HR - 1 mm max height
PLASTIC QUAD FLATPACK - NO LEAD
2X (0.8)
(0.625)
2X
(0.3)
4X (1)
PKG
(0.5)
2X (0.7)
2X
(0.35)
2X
(0.4)
14
EXPOSED METAL
TYP
2X (1)
1
11
4X (0.35)
2X (1.1)
(2.9)
(0.3)
SYMM
10
2X (0.4)
(0.525)
(3.2)
(0.35)
EXPOSED
METAL
(1.65)
(R0.05)
TYP
7X (0.7)
9
5
6
6X (0.25)
(0.45)
(1.85)
SOLDER PASTE EXAMPLE
BASED ON 0.1 mm THICK STENCIL
PADS 1, 5, 9 & 11:
90% PRINTED SOLDER COVERAGE BY AREA
SCALE: 25X
4223976/D 11/2019
NOTES: (continued)
4. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate
design recommendations.
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PACKAGE OPTION ADDENDUM
www.ti.com
9-Nov-2025
PACKAGING INFORMATION
Orderable part number
(1)
Status
Material type
(1)
(2)
Package | Pins
Package qty | Carrier
RoHS
(3)
Lead finish/
Ball material
MSL rating/
Peak reflow
(4)
(5)
Op temp (°C)
Part marking
(6)
LM61460AANQRJRRQ1
Active
Production
VQFN-HR (RJR) | 14
3000 | LARGE T&R
Yes
SN
Level-2-260C-1 YEAR
-40 to 150
6146Q1
AAN
LM61460AANQRJRRQ1.A
Active
Production
VQFN-HR (RJR) | 14
3000 | LARGE T&R
Yes
SN
Level-2-260C-1 YEAR
-40 to 150
6146Q1
AAN
LM61460AASQRJRRQ1
Active
Production
VQFN-HR (RJR) | 14
3000 | LARGE T&R
Yes
SN
Level-2-260C-1 YEAR
-40 to 150
6146Q1
AAS
LM61460AASQRJRRQ1.A
Active
Production
VQFN-HR (RJR) | 14
3000 | LARGE T&R
Yes
SN
Level-2-260C-1 YEAR
-40 to 150
6146Q1
AAS
LM61460AFSQRJRRQ1
Active
Production
VQFN-HR (RJR) | 14
3000 | LARGE T&R
Yes
SN
Level-2-260C-1 YEAR
-40 to 150
6146Q1
AFS
LM61460AFSQRJRRQ1.A
Active
Production
VQFN-HR (RJR) | 14
3000 | LARGE T&R
Yes
SN
Level-2-260C-1 YEAR
-40 to 150
6146Q1
AFS
PLM61460AASQRJRTQ1
Obsolete
Preproduction
VQFN-HR (RJR) | 14
-
-
Call TI
Call TI
-40 to 150
Status: For more details on status, see our product life cycle.
(2)
Material type: When designated, preproduction parts are prototypes/experimental devices, and are not yet approved or released for full production. Testing and final process, including without limitation quality assurance,
reliability performance testing, and/or process qualification, may not yet be complete, and this item is subject to further changes or possible discontinuation. If available for ordering, purchases will be subject to an additional
waiver at checkout, and are intended for early internal evaluation purposes only. These items are sold without warranties of any kind.
(3)
RoHS values: Yes, No, RoHS Exempt. See the TI RoHS Statement for additional information and value definition.
(4)
Lead finish/Ball material: Parts may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead finish/Ball material values may wrap to two lines if the finish value exceeds the maximum
column width.
(5)
MSL rating/Peak reflow: The moisture sensitivity level ratings and peak solder (reflow) temperatures. In the event that a part has multiple moisture sensitivity ratings, only the lowest level per JEDEC standards is shown.
Refer to the shipping label for the actual reflow temperature that will be used to mount the part to the printed circuit board.
(6)
Part marking: There may be an additional marking, which relates to the logo, the lot trace code information, or the environmental category of the part.
Multiple part markings will be inside parentheses. Only one part marking contained in parentheses and separated by a "~" will appear on a part. If a line is indented then it is a continuation of the previous line and the two
combined represent the entire part marking for that device.
Addendum-Page 1
PACKAGE OPTION ADDENDUM
www.ti.com
9-Nov-2025
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OTHER QUALIFIED VERSIONS OF LM61460-Q1 :
• Catalog : LM61460
NOTE: Qualified Version Definitions:
• Catalog - TI's standard catalog product
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
1-Oct-2025
TAPE AND REEL INFORMATION
REEL DIMENSIONS
TAPE DIMENSIONS
K0
P1
B0 W
Reel
Diameter
Cavity
A0
B0
K0
W
P1
A0
Dimension designed to accommodate the component width
Dimension designed to accommodate the component length
Dimension designed to accommodate the component thickness
Overall width of the carrier tape
Pitch between successive cavity centers
Reel Width (W1)
QUADRANT ASSIGNMENTS FOR PIN 1 ORIENTATION IN TAPE
Sprocket Holes
Q1
Q2
Q1
Q2
Q3
Q4
Q3
Q4
User Direction of Feed
Pocket Quadrants
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
LM61460AANQRJRRQ1
VQFNHR
RJR
14
3000
330.0
12.4
3.8
4.3
1.15
8.0
12.0
Q2
LM61460AANQRJRRQ1
VQFNHR
RJR
14
3000
330.0
12.4
3.8
4.3
1.5
8.0
12.0
Q2
LM61460AASQRJRRQ1
VQFNHR
RJR
14
3000
330.0
12.4
3.8
4.3
1.5
8.0
12.0
Q2
LM61460AASQRJRRQ1
VQFNHR
RJR
14
3000
330.0
12.4
3.8
4.3
1.15
8.0
12.0
Q2
LM61460AFSQRJRRQ1
VQFNHR
RJR
14
3000
330.0
12.4
3.8
4.3
1.5
8.0
12.0
Q2
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
1-Oct-2025
TAPE AND REEL BOX DIMENSIONS
Width (mm)
W
L
H
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
LM61460AANQRJRRQ1
VQFN-HR
RJR
14
3000
367.0
367.0
38.0
LM61460AANQRJRRQ1
VQFN-HR
RJR
14
3000
367.0
367.0
35.0
LM61460AASQRJRRQ1
VQFN-HR
RJR
14
3000
367.0
367.0
35.0
LM61460AASQRJRRQ1
VQFN-HR
RJR
14
3000
367.0
367.0
38.0
LM61460AFSQRJRRQ1
VQFN-HR
RJR
14
3000
367.0
367.0
35.0
Pack Materials-Page 2
PACKAGE OUTLINE
RJR0014A
VQFN-HR - 1 mm max height
SCALE 3.200
PLASTIC QUAD FLATPACK - NO LEAD
4.1
3.9
B
A
PIN 1 INDEX AREA
3.6
3.4
0.1 MIN
0.08 MAX
SECTION A-A
SECTION A-A
SCALE 30.000
TYPICAL
1.0
0.8
C
SEATING PLANE
0.05
0.00
0.08 C
2X 0.625
2X 1.6
2X 0.5
2X 0.45
2X 0.55
0.1
0.05
0.4
0.3
C A B
C
0.35
0.25
2X
6
0.7
0.5
(0.2) TYP
9
5
A
2X 0.525
0.45
0.35
A
SYMM
10
2X 1.15
2.2 0.1
PIN 1
ID
2X
11
1
0.45
0.35
C A B
C
0.9
0.7
4X
0.1
0.05
2X
14
0.6
0.4
2X
0.3
0.2
C A B
C
PKG
6X
0.1
0.05
7X
0.6
0.4
2X
0.45
0.35
0.1
0.05
0.45
0.35
0.1
0.05
C A B
C
C A B
C
4223976/G 05/2025
NOTES:
1. All linear dimensions are in millimeters. Any dimensions in parenthesis are for reference only. Dimensioning and tolerancing
per ASME Y14.5M.
2. This drawing is subject to change without notice.
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EXAMPLE BOARD LAYOUT
RJR0014A
VQFN-HR - 1 mm max height
PLASTIC QUAD FLATPACK - NO LEAD
2X (0.7)
PKG
(0.5)
2X
(0.35)
(0.625)
4X (1)
14
2X (0.8)
2X
(0.4)
2X
(0.4)
2X (1)
1
11
4X (0.4)
SEE SOLDER MASK
DETAIL
(2.4)
(0.3)
SYMM
10
(0.4)
(0.525)
(3.2)
(1)
(R0.05)
TYP
(2.9)
7X (0.7)
9
5
4X (R0.12)
6
6X (0.25)
(0.45)
(1.85)
LAND PATTERN EXAMPLE
EXPOSED METAL SHOWN
SCALE: 25X
0.07 MIN
ALL AROUND
0.07 MAX
ALL AROUND
METAL UNDER
SOLDER MASK
METAL EDGE
EXPOSED
METAL
NON SOLDER MASK
DEFINED
(PREFERRED)
SOLDER MASK
OPENING
EXPOSED
METAL
SOLDER MASK
OPENING
SOLDER MASK DEFINED
SOLDER MASK DETAIL
4223976/G 05/2025
NOTES: (continued)
3. This package is designed to be soldered to thermal pads on the board. For more information, see Texas Instruments literature
number SLUA271 (www.ti.com/lit/slua271).
www.ti.com
EXAMPLE STENCIL DESIGN
RJR0014A
VQFN-HR - 1 mm max height
PLASTIC QUAD FLATPACK - NO LEAD
2X (0.8)
(0.625)
2X
(0.3)
4X (1)
PKG
(0.5)
2X (0.7)
2X
(0.35)
2X
(0.4)
14
EXPOSED METAL
TYP
2X (1)
1
11
4X (0.35)
2X (1.1)
(2.9)
(0.3)
SYMM
10
2X (0.4)
(0.525)
(3.2)
(0.35)
EXPOSED
METAL
(1.65)
(R0.05)
TYP
7X (0.7)
9
5
4X (R0.17)
6
6X (0.25)
(0.45)
(1.85)
SOLDER PASTE EXAMPLE
BASED ON 0.1 mm THICK STENCIL
PADS 1, 5, 9 & 11:
90% PRINTED SOLDER COVERAGE BY AREA
SCALE: 25X
4223976/G 05/2025
NOTES: (continued)
4. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate
design recommendations.
www.ti.com
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