LM63615-Q1, LM63625-Q1
SNVSB55F – FEBRUARY 2019 – REVISED MARCH 2021
LM636x5-Q1 3.5-V to 36-V, 1.5-A, and 2.5-A Automotive Step-down Voltage Converter
1 Features
2 Applications
•
•
•
•
•
•
•
•
AEC-Q100-Qualified for automotive applications
– Device temperature grade 1: –40°C to +125°C
ambient operating temperature
Functional Safety-Capable
– Documentation available to aid functional safety
system design
Supports automotive system requirements
– Input voltage range: 3.5 V to 36 V
– Short minimum on-time of 50 ns
– Good EMI performance
Pseudo-random spread spectrum
Compatible with CISPR 25
– Low operating quiescent current of 23 µA
– Junction temperature range –40°C to +150°C
High design flexibility
– Pin selectable VOUT: 3.3 V, 5 V, adjustable
1 V to 20 V
– Pin compatible with LM63610/LM63635 (1A,
3.25 A)
– Pin selectable frequency: 400 kHz, 2.1 MHz,
adjustable 250 kHz to 2200 kHz
– Pin selectable FPWM, AUTO, sync modes
– TSSOP: Thermally-enhanced package
– WSON: For space-constrained applications
Small solution size
– As small as: 10 mm x 10 mm for 2.5 A, 2.2 MHz
with WSON package
– Highly integrated solution
– Low component count
Automotive infotainment and cluster
Automotive body electronics and lighting
Automotive ADAS
3 Description
The LM636x5D-Q1 regulator is an easy-to-use,
synchronous, step-down DC/DC converter designed
for rugged automotive applications. The LM636x5DQ1 can drive up to 1.5-A or 2.5-A of load current
from an input of up to 36 V. The converter has high
light load efficiency and output accuracy in a small
solution size. Features such as a RESET flag and
precision enable provide both flexible and easy-to-use
solutions for a wide range of applications. Automatic
frequency foldback at light load improves efficiency
while maintaining tight load regulation. Integration
eliminates many external components and provides
a pinout designed for simple PCB layout. Protection
features include thermal shutdown, input undervoltage
lockout, cycle-by-cycle current limit, and hiccup shortcircuit protection. LM636x5D-Q1 is available in the
HTSSOP 16-pin power package, with PowerPAD™ ,
and the WSON 12-pin power package.
Device Information(1)
PART NUMBER
PACKAGE
BODY SIZE (NOM)
LM636x5-Q1
HTSSOP (16)
5.00 mm × 4.00 mm
LM636x5-Q1
WSON (12)
3.00 mm x 3.00 mm
(1)
For all available packages, see the orderable addendum at
the end of the data sheet.
space
CBOOT
VIN
CIN
VIN
CBOOT
EN
VOUT
SW
L1
COUT
PGND
FB
SYNC/
MODE
RESET
VSEL
VCC
RT
CVCC
AGND
Simplified Schematic
Typical Solution Example IOUT = 2.5 A, ƒSW = 2200
kHz
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LM63615-Q1, LM63625-Q1
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SNVSB55F – FEBRUARY 2019 – REVISED MARCH 2021
Table of Contents
1 Features............................................................................1
2 Applications..................................................................... 1
3 Description.......................................................................1
4 Revision History.............................................................. 2
5 Device Comparison Table...............................................3
6 Pin Configuration and Functions...................................4
7 Specifications.................................................................. 6
7.1 Absolute Maximum Ratings ....................................... 6
7.2 ESD Ratings .............................................................. 6
7.3 Recommended Operating Conditions ........................6
7.4 Thermal Information ...................................................7
7.5 Electrical Characteristics ............................................8
7.6 Timing Characteristics ..............................................10
7.7 Switching Characteristics ......................................... 11
7.8 System Characteristics ............................................ 12
7.9 Typical Characteristics.............................................. 13
8 Detailed Description......................................................14
8.1 Overview................................................................... 14
8.2 Functional Block Diagram......................................... 14
8.3 Feature Description...................................................14
8.4 Device Functional Modes..........................................19
9 Application and Implementation.................................. 24
9.1 Application Information............................................. 24
9.2 Typical Application.................................................... 24
9.3 What to Do and What Not to Do............................... 39
10 Power Supply Recommendations..............................40
11 Layout........................................................................... 41
11.1 Layout Guidelines................................................... 41
11.2 Layout Example...................................................... 43
12 Device and Documentation Support..........................46
12.1 Documentation Support.......................................... 46
12.2 Receiving Notification of Documentation Updates..46
12.3 Support Resources................................................. 46
12.5 Glossary..................................................................46
12.6 Electrostatic Discharge Caution..............................46
13 Mechanical, Packaging, and Orderable
Information.................................................................... 46
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision E (June 2020) to Revision F (March 2021)
Page
• Updated the numbering format for tables, figures and cross-references throughout the document. .................1
• Added WSON option for the LM636x5C.............................................................................................................4
• Removed redundant wording..............................................................................................................................7
• Added IPEAK-MIN minimum values....................................................................................................................... 8
• Added second WSON package layout............................................................................................................. 43
Changes from Revision D (April 2020) to Revision E (June 2020)
Page
• Added WSON (DRR) package .......................................................................................................................... 1
Changes from Revision C (January 2020) to Revision D (April 2020)
Page
• Changed Figure 9-1 to correct error................................................................................................................. 24
Changes from Revision B (October 2019) to Revision C (January 2020)
Page
• Added the functional safety bullet to the Section 1 ............................................................................................1
• Added thermal curve for DRR package............................................................................................................ 29
Changes from Revision A (July 2019) to Revision B (October 2019)
Page
• Changed device status from Advance Information to Production data ..............................................................1
2
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5 Device Comparison Table
ORDER NUMBER
LM63615DQ
LM63625DQ
PACKAGE
RATED CURRENT
PWP0016D
(HTSSOP)
1.5 A
LM63615DQ
LM63625Q
LM63615C
2.5 A
1.5 A
DRR0012
(WSON)
LM63625C
Fsw
5.00 mm x 4.00 mm
Adjustable with RT
resistor
2.5 A
1.5 A
BODY SIZE (NOM)
Fixed 2.1 MHz
3.00 mm x 3.00 mm
2.5 A
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SNVSB55F – FEBRUARY 2019 – REVISED MARCH 2021
6 Pin Configuration and Functions
SW
1
16
PGND
SW
2
15
PGND
CBOOT
3
VCC
4
RT
5
VSEL
SYNC/MODE
RESET
14
N/C
DAP
13
VIN
(17)
12
VIN
6
11
EN
7
10
AGND
8
9
SW
1
12
VIN
BOOT
2
11
N/C
VCC
3
10
EN
PGND/DAP
13
RT
4
9
AGND
VSEL
5
8
FB
SYNC/MODE
6
7
RESET
FB
Figure 6-2. 12-Pin WSON With PowerPad DRR
Package_LM636x5D (Top View)
Figure 6-1. 16-Pin HTSSOP With PowerPAD PWP
Package (Top View)
SW
1
12
VIN
BOOT
2
11
N/C
N/C
3
10
EN
PGND/DAP
13
VCC
4
9
AGND
SYNC/MODE
5
8
N/C
RESET
6
7
FB
Figure 6-3. 12-Pin WSON With PowerPad DRR Package_LM636x5C (Top View)
Table 6-1. Pin Functions
PIN
4
TSSOP
WSON
LM636x5D
1, 2
1
3
WSON
LM636x5C
DESCRIPTION
NAME
TYPE
1
SW
P
Regulator switch node. Connect to power inductor.
2
2
CBOOT
P
Bootstrap supply voltage for internal high-side driver. Connect a highquality, 220-nF capacitor from this pin to the SW pin.
4
3
4
VCC
A
Internal 5-V LDO output. Used as supply to internal control circuits.
Do not connect to external loads. Can be used as logic supply for
regulator functions. Connect a high-quality, 1-µF capacitor from this pin
to PGND.
5
4
-
RT
A
Frequency programming input. Tie to VCC for 400 kHz or to AGND
for 2.1 MHz or connect to an RT timing resistor. See Section 8.3.3 for
details. Do not float.
6
5
-
VSEL
A
Output voltage select input. Tie to VCC for 5-V output or to AGND for
3.3-V output; connect to a 10-kΩ for an adjustable output. See Section
8.3.2 for details. Do not float.
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Table 6-1. Pin Functions (continued)
PIN
TSSOP
WSON
LM636x5D
7
6
8
WSON
LM636x5C
DESCRIPTION
NAME
TYPE
5
SYNC/
MODE
A
Mode selection and synchronization input. Tie to VCC for FPWM mode,
AGND for AUTO mode, or supply an external synchronizing clock to
this input.
7
6
RESET
A
Open-drain power-good flag output. Connect to suitable voltage supply
through a current limiting resistor. High = power OK, low = power bad.
Flag pulls low when EN = Low. Can be open when not used.
9
8
7
FB
A
Feedback input to regulator. Connect to output capacitor for 5-V or
3.3-V fixed option or tap point of the feedback voltage divider for ADJ
option. Do not float; do not ground.
10
9
9
AGND
G
Analog ground for regulator and system. Ground reference for internal
references and logic. All electrical parameters are measured with
respect to this pin. Connect to system ground on PCB.
11
10
10
EN
A
Enable input to regulator. High = ON, Low = OFF. Can be connected
directly to VIN. Do not float.
12, 13
12
12
VIN
P
Input supply to regulator. Connect a high-quality bypass capacitors
directly to this pin and PGND.
14
11
3, 8, 11
NC
-
No internal connection to device
15, 16
13
13
PGND
G
Power ground terminal. Connect to system ground and AGND.
Connect to bypass capacitor with short wide traces.
17
13
13
DAP
G
Electrical ground and heat sink connection. Solder directly to system
ground plane.
A = Analog, P = Power, G = Ground
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7 Specifications
7.1 Absolute Maximum Ratings
Over the recommended junction temperature range(1)
PARAMETER
MIN
MAX
UNIT
VIN to PGND (HTSSOP package)
–0.3
40
V
VIN to PGND (WSON package)
–0.3
42
V
EN to AGND (HTSSOP package)
–0.3
40
V
EN to AGND (WSON package)
–0.3
42
V
SYNC/MODE to AGND
–0.3
6
V
VOUT_SEL and RT to AGND
–0.3
5.5
V
RESET to AGND
–0.3
16
V
FB to AGND (Fixed VOUT mode)
–0.3
16
V
FB to AGND (Adjustable VOUT mode)
–0.3
5.5
V
AGND to PGND
–0.3
0.3
V
SW to PGND for transients of less than 10ns (HTSSOP package)
-6
40
V
SW to PGND for transients of less than 10ns (WSON package)
-6
42
V
BOOT to SW
–0.3
5.5
V
VCC to AGND
–0.3
5.5
V
TJ
Junction temperature
–40
150
°C
Tstg
Storage temperature
–65
150
°C
(1)
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.
7.2 ESD Ratings
V(ESD)
(1)
Electrostatic discharge
VALUE
UNIT
Human-body model (HBM), per AEC Q100-002(1) HBM ESD
Clasification Level 2
±2000
V
Charged-device model (CDM), per AEC Q100-011 CDM ESD
clasiffication Level C5
±750
V
AEC Q100-002 indicates that HBM stressing shall be in accordance with the ANSI/ESDA/JEDEC JS-001 specification.
7.3 Recommended Operating Conditions
Over the recommended junction temperature range of –40°C to 150°C (unless otherwise noted)(1)
MIN
MAX
3.5
36
V
EN
0
36
V
SYNC/MODE, VOUT_SEL and RT to AGND
0
5
V
RESET
0
5
V
VIN to PGND
VOUT
(2)
1
20
V
2.7
5.25
V
IOUT, LM63625
0
2.5
A
IOUT, LM63615
0
1.5
A
VCC
(1)
6
UNIT
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 the Electrical Characteristics Table.
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(2)
SNVSB55F – FEBRUARY 2019 – REVISED MARCH 2021
Under no conditions should the output voltage be allowed to fall below zero volts.
7.4 Thermal Information
THERMAL
METRIC(1)
LM636x5
LM636X5
DRR0012 (WSON)
HTSSOP (PWP)
12 PINS
16 PINS
UNIT
RθJA
Junction-to-ambient thermal resistance(2)
47.4
43.1
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
44.6
35.4
°C/W
RθJB
Junction-to-board thermal resistance
20.7
18.5
°C/W
ΨJT
Junction-to-top characterization parameter
0.7
0.9
°C/W
ΨJB
Junction-to-board characterization parameter
20.7
18.5
°C/W
RθJC(bot)
Junction-to-case (bottom) thermal resistance
6.3
4.5
°C/W
(1)
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
(2)
The value of RΘJA given in this table is only valid for comparison with other packages and can not 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 design information please see the Maximum Ambient Temperature section.
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7.5 Electrical Characteristics
Limits apply over the junction temperature (TJ) 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.(1)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
SUPPLY VOLTAGE (VIN PIN)
VIN
Minimum operating input voltage
IQ
Non-switching input current; measured at
VEN = 3.3 VFB = 1.2x regulation point
VIN pin(2)
ISD
Shutdown quiescent current; measured at
VEN = 0
VIN pin
VUVLO_R
Minimum operating voltage threshold
Rising VIN, IVCC = 0
VUVLO_F
Minimum operating voltage threshold
Falling VIN, IVCC = 0
2.6
IPOR
Pull down current on SW when OVP is
triggered
VEN = 0 VSW = 5 V
0.5
3.5
V
23
40
µA
5.3
10
µA
3.5
V
3
V
1.5
2.5
mA
ENABLE (EN PIN)
VEN-VCC
VCC enable voltage
VEN rising
VEN-H
Precision enable high level for VOUT
VEN rising
0.85
VEN-L
Precision enable low level for VOUT
VEN falling
ILKG-EN
Enable input leakage current
VEN = 13.5 V, WSON package
ILKG-EN
Enable input leakage current
VEN = 13.5 V, HTSSOP package
–100
1.425
1.5
0.9
0.94
–100
V
1.575
V
0.2
300
nA
0.2
150
nA
50
kΩ
V
OUTPUT VOLTAGE SELECTION (VSEL PIN)
RSEL-ADJ
Resistor range for valid adjustable output
voltage selection at startup
8
INTERNAL LDO
VCC
Internal VCC voltage
6 V ≤ VIN ≤ Max Operating VIN
4.75
5
5.25
V
VCCM
VCC Clamp Voltage
1mA sourced into VCC
5.25
5.55
5.8
V
1
1.015
V
VOLTAGE REFERENCE (FB PIN)
VFB_ADJ
Feedback voltage
VIN = 3.5-Max Operating VIN
0.985
VFB_5V
Feedback voltage
VIN = 5.5-Max Operating VIN
4.925
5
5.075
V
VFB_3p3V
Feedback voltage
VIN = 3.8-Max Operating VIN
3.25
3.3
3.35
V
IFB_ADJ
Input leakage current at FB PIN
FB = 1.0 V
0.2
100
nA
IFB_5V
Input leakage current at FB PIN
FB = 5.0 V
2.89
3.4
µA
IFB_3p3V
Input leakage current at FB PIN
FB = 3.3V
1.67
2
µA
CURRENT LIMITS
ISC
Short circuit high side current Limit
3.18
3.75
4.41
A
ILS-LIMIT
Low side current limit
2.55
3
3.53
A
0.373
0.65
1.0
A
–2.35
–1.8
–1.25
A
2.5-A Version
IPEAK-MIN Minimum Peak Inductor Current
IL-NEG
Negative current limit
ISC
Short circuit high side current Limit
1.9
2.25
2.7
A
ILS-LIMIT
Low side current limit
1.5
1.8
2.12
A
0.122
0.375
0.7
A
–1.49
–1.2
–0.75
A
37%
42%
47%
IPEAK-MIN Minimum Peak Inductor Current
IL-NEG
Negative current limit
VHICCUP
Hiccup threshold on FB pin
1.5-A Version
POWER GOOD (RESET PIN)
VRESETHIGH
VRESETLOW
8
RESET upper threshold - Rising
% of FB voltage
110%
112%
115%
RESET lower threshold - Falling
% of FB voltage
91%
93%
95%
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Limits apply over the junction temperature (TJ) 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.(1)
PARAMETER
VRESETHYS
TEST CONDITIONS
RESET hysteresis
% of FB voltage,
MIN
TYP
MAX
UNIT
1.1%
1.8%
2.5%
0.7
1.04
1.25
V
VRESET_V Minimum input voltage for proper PG
function
ALID
Measured when VRESET < 0.4 V with
10kOhm pullup to external 5-V
RRESET
RESET ON resistance,
VEN = 5.0 V, 1mA pull-up current
60
150
Ω
RRESET
RESET ON resistance,
VEN = 0 V, 1mA pull-up current
40
125
Ω
1.5
1.8
V
OSCILLATOR (SYNC/MODE PIN)
VSYNCHIGH
VSYNCHYS
VSYNCLOW
RSYNC
Sync input and mode high level threshold
Sync input hysteresis
Sync input and mode low level threshold
0.8
Pulldown on MODE pin
0.355
V
1.15
V
100
kΩ
MOSFETS(2)
RDS-ONHS
RDS-ONLS
VCBOOTUVLO
High-side MOSFET on-resistance
Load = 1 A
93
mΩ
Low-side MOSFET on-resistance
Load = 1 A
61
mΩ
Cboot - SW UVLO threshold(3)
2.13
V
(1)
MIN and MAX limits are 100% production tested at 25ºC. Limits over the operating temperature range verified through correlation using
Statistical Quality Control (SQC) methods. Limits are used to calculate Average Outgoing Quality Level (AOQL).
(2)
This is the current used by the device open loop. It does not represent the total input current of the system when in regulation.
(3)
When the voltage across the CBOOT capacitor falls below this voltage, the low side MOSFET is turn to recharge the boot capacitor
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7.6 Timing Characteristics
Limits apply over the junction temperature (TJ) 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.(1)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
CURRENT LIMITS AND HICCUP
NOC
Number of switching current limit
continuous events before hiccup is
tripped
tOC
Overcurrent hiccup retry delay time
70
104
140
ms
tOC_active
Time after soft start done timer before
hiccup current protection is enabled
11
16
22
ms
1
1.6
2.2
ms
5
8
11
ms
10
17
30
µs
2
3
5
ms
128
Cycles
SOFT START
tSS
Internal soft-start time
tSS_DONE Soft-start done timer
POWER GOOD (/RESET PIN) and OVERVOLTAGE PROTECTION
tdg
RESET edge deglitch delay
tRISE-
RESET active time
DELAY
Time FB must be valid before RESET is
released.
OSCILLATOR (SYNC/MODE PIN)
tON_OFFSYNC
(1)
10
Sync input ON and OFF-time
100
ns
MIN and MAX limits are 100% production tested at 25°C. Limits over the operating temperature range are verified through correlation
usingStatistical Quality Control (SQC) methods. Limits are used to calculate Average Outgoing Quality Level (AOQL).
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7.7 Switching Characteristics
Limits apply over the junction temperature (TJ) 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.(1)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
PWM LIMITS (SW PINS)
tON-MIN
Minimum switch on-time
VIN =12 V, ISW = 1 A
50
75
ns
tOFF-MIN
Minimum switch off-time
VIN = 5 V
50
100
ns
tON-MAX
Maximum switch on-time
HS timeout in dropout
7
10
µs
5.4
OSCILLATOR (RT and SYNC PINS)
fOSC
Internal oscillator frequency
RT = GND
1.85
2.1
2.35
MHz
fOSC
Internal oscillator frequency
RT = VCC
360
400
440
kHz
fADJ1
RT = 66.5 kΩ, 1%
240
kHz
fADJ2
RT = 7.15 kΩ, 1%
2200
kHz
fSYNC
Synchronization Frequency Range
250
2200
kHz
SPREAD SPECTRUM
fPSS (2)
Spread spectrum pseudo random pattern
FOSC= 2.1MHz
frequency
fSPREAD
Spread of internal oscillator with Spread
Spectrum Enabled
LM636x5DQ Option (HTSSOP package)
fSPREAD
Spread of internal oscillator with Spread
Spectrum Enabled
LM636x5DQ Option (WSON package)
(1)
0.98
Hz
–3.6%
3.6%
–5%
5%
MIN and MAX limits are 100% production tested at 25°C. Limits over the operating temperature range are verified through correlation
usingStatistical Quality Control (SQC) methods. Limits are used to calculate Average Outgoing Quality Level (AOQL).
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7.8 System Characteristics
The following specifications apply only to the typical applications circuit with nominal component values. Specifications in the
typical (TYP) column apply to TJ = 25°C only. Specifications in the minimum (MIN) and maximum (MAX) columns apply to
the case of typical components over the temperature range of TJ = –40°C to 150°C. These specifications are not ensured by
production testing.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
SUPPLY VOLTAGE (VIN PIN)
ISUPPLY
Input supply current when in regulation
VIN = 12 V, VOUT = 3.3 V, IOUT = 0 A, RFBT
= 1 MΩ
VDROP
Dropout voltage; (VIN – VOUT)
VDROP
DMAX
23
µA
VOUT = 5 V, IOUT = 1 A, fSW = 1850 kHz
0.95
V
Dropout voltage; (VIN – VOUT)
VOUT = 5 V, IOUT = 1 A, VOUT -1% of
regulation, fSW = 140 kHz
150
mV
Maximum switch duty cycle(2)
VIN = VOUT = 12 VOUT = 1 A
98%
VOLTAGE REFERENCE (FB PIN)
VOUT (1)
VOUT (1)
VOUT = 5 V
VIN = 7 V to 30 V , IOUT = 1 A to full load,
CCM
–1.5%
1.5%
VOUT = 5 V
VIN = 7 V to 30 V, IOUT = 0 A to full load,
AUTO mode
–1.5%
2.5%
VOUT = 3.3 V
VIN = 3.8 V to 30 V , IOUT = 1 A to full
load, CCM
–1.5%
1.5%
VOUT = 3.3 V
VIN = 3.8 V to 30 V , IOUT = 0 A to full
load, AUTO mode
–1.5%
2.5%
tSYNC-L
Delay from sync clock staying low to PFM
entry
100
ns
tSYNC-H
Delay from sync clock staying high to
default frequency
100
ns
THERMAL SHUTDOWN
TSD
Thermal shutdown temperature
Shutdown temperature
TSDR
Thermal shutdown temperature
Recovery temperature
155
163
150
175
°C
°C
(1)
Deviation is with respect to VIN =13.5 V, IOUT = 1 A.
(2)
In dropout the switching frequency drops to increase the effective duty cycle. The lowest frequency is clamped at approximately: fMIN =
1 / (tON-MAX + TOFF-MIN). DMAX = tON-MAX /(tON-MAX + tOFF-MIN).
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7.9 Typical Characteristics
Unless otherwise specified the following conditions apply: TA = 25°C, VIN = 13.5 V
OUTPUT VOLTAGE (0.9V/DIV)
12
Input Current (PA)
10
8
6
4
-40C
25C
125C
DN
2
5
10
15
20
25
Input Voltage (V)
30
35
0
OFF_
INPUT VOLTAGE (1V/DIV)
EN = 0 V
IOUT = 1 mA
1000
600
950
575
900
850
800
750
700
-40C
25C
125C
650
IOUT = 0 A
15
20
25
Input Voltage (V)
VOUT = 5 V
30
35
550
525
500
475
450
-40C
25C
125C
425
600
10
400
40
5
10
Ipea
ƒSW = 2100 kHz
See Figure 9-44
See Figure 9-44
Figure 7-2. UVLO Thresholds
Peak Inductor Current (mA)
Peak Inductor Current (mA)
Figure 7-1. Input Supply Current in Shutdown
Mode
5
UP
40
A.
IOUT = 0 A
15
20
25
Input Voltage (V)
VOUT = 5 V
30
35
40
Ipea
See Figure 9-44
ƒSW = 2100 kHz
Figure 7-3. IPEAK-MIN for LM63625
Figure 7-4. IPEAK-MIN for LM63615
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8 Detailed Description
8.1 Overview
The LM636x5D-Q1 device is a synchronous peak-current-mode buck regulator designed for a wide variety of
automotive applications. The regulator automatically switches modes between PFM and PWM, depending on
load. At heavy loads, the device operates in PWM at a constant switching frequency. At light loads, the mode
changes to PFM with diode emulation, allowing DCM. This reduces the input supply current and keeps efficiency
high. The device features the following:
•
•
•
•
Adjustable switching frequency
Forced PWM mode (FPWM)
Frequency synchronization
Selectable output voltage
The RESET output allows easy system sequencing. In addition, internal compensation reduces design time and
requires fewer external components than externally compensated regulators.
8.2 Functional Block Diagram
SYNC/MODE
RT
EN
VSEL
1.0 V
Reference
VIN
INT. REG.
BIAS
OSCILLATOR
ENABLE
LOGIC
VCC
CBOOT
HS CURRENT
SENSE
PWM
COMP.
SW
CONTROL LOGIC
DRIVER
+
+
FB
Feedback
Divider
±
±
LS CURRENT
SENSE
PFM MODE
CONTROL
RESET
RESET
CONTROL
AGND
PGND
8.3 Feature Description
8.3.1 Sync/Mode Selection
The LM636x5D-Q1 features selectable operating modes through the SYNC/MODE input. Table 8-1 shows the
selection programming. Mode changes can be made on the fly anytime after the device is powered up. It is not
recommended that this input be allowed to float, however, an internal 100 kΩ pulls the input to ground if left
floating. The value of this internal resistor and the logic thresholds for this input can be found in Section 7.5. See
Section 8.4 for details of the operating modes.
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Table 8-1. Mode Selection Settings
SYNC/MODE INPUT
MODE
VCC
FPWM
AGND
AUTO
Synchronizing clock
FPWM; synchronized to external clock
Float (not recommended)
AUTO
8.3.2 Output Voltage Selection
The output voltage of the LM636x5D-Q1 is set by the condition of the VSEL input. The condition of this input is
tested when the device is first enabled. Once the converter is running, the voltage selection is fixed and cannot
be changed until the next power-on cycle. Table 8-2 shows the selection programming. The LM636x5D-Q1
contains an integrated voltage divider connected to the FB input. The converter regulates the voltage on the FB
input to 5 V, 3.3 V, or 1 V, as selected. In ADJ mode, the voltage on the FB input is regulated to 1 V and the
internal divider is disabled. In this case, an external voltage divider is used to set the desired output voltage
anywhere within the recommended operating range. ADJ mode is programmed by connecting 10 kΩ from the
VSEL input to ground. Although not recommenced, if this input is left floating, the device enters ADJ mode. See
Section 9.2.2.2 for details of selecting the FB divider resistors.
See Section 7 for ensured specifications regarding the accuracy of the FB voltage and input current to the FB
pin.
Providing internal voltage dividers for the 5-V and 3.3-V modes saves external components, reducing both board
space and component cost. The relatively large values of the internal dividers reduce the load on the output,
helping to improve the light load efficiency of the converter. In addition, since the divider is inside the device, it is
less likely to pick up externally generated noise.
Table 8-2. Output Voltage Settings
VSEL INPUT
OUTPUT VOLTAGE
VCC
5V
AGND
3.3 V
10 kΩ to AGND
ADJ
Float (not recommended)
ADJ
8.3.3 Switching Frequency Selection
The switching frequency is set by the condition of the RT input. The condition of this input is tested when the
device is first enabled. Once the converter is running, the switching frequency selection is fixed and cannot be
changed until the next power-on cycle. Table 8-3 shows the selection programming. In the adjustable frequency
mode, the switching frequency can be set between 250 kHz and 2200 kHz by proper selection of the value of
RT. The curve in Figure 8-1 indicates the required resistor value for RT to set a desired switching frequency. It
is not recommended that this input be allowed to float; the switching action ceases with no generated output
voltage under this condition.
RT
15770
fSW
(1)
where
•
•
RT = value of RT timing resistor in kΩ
ƒSW = switching frequency in kHz
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Table 8-3. Switching Frequency Settings
RT INPUT
SWITCHING FREQUENCY
VCC
400 kHz
AGND
2100 kHz
RT to AGND
Adjustable according to RT value
Float (not recommended)
No switching
80
70
RT (kŸ)
60
50
40
30
20
10
0
200
600
1000
1400
1800
2200
Switching Frequency (kHz)
C002
Figure 8-1. Switching Frequency versus RT
8.3.3.1 Spread Spectrum Option
The LM636x5D-Q1 is available with a spread spectrum clock dithering feature. This feature uses a pseudorandom pattern to dither the internal clock frequency. The pattern repeats at a 0.98-Hz rate while the depth of
modulation is ±3%.
The purpose of the spread spectrum is to eliminate peak emissions at specific frequencies by spreading
emissions across a wider range of frequencies than a part with fixed frequency operation. In most systems
containing the LM636x5D-Q1 device, 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 which fall in the FM band. These harmonics often couple to the environment through electric fields
around the switch node. The LM636x5D-Q1 device use a ±3% spread of frequencies which spreads energy
smoothly across the FM band but is small enough to limit subharmonic emissions below its switching frequency.
8.3.4 Enable and Start-up
Start-up and shutdown are controlled by the EN input. This input features precision thresholds, allowing the use
of an external voltage divider to provide an adjustable input UVLO (see Section 9.2.2.8). Applying a voltage
greater than VEN-VCC causes the device to enter standby mode, powering the internal VCC, but not producing an
output voltage. Increasing the EN voltage to VEN-H fully enables the device, allowing it to enter start-up mode and
begin the soft-start period. When the EN input is brought below VEN-L, the regulator stops running and enters
standby mode. Further decrease in the EN voltage to below VEN-VCC completely shuts down the device. Figure
8-2 shows this behavior. The EN input can be connected directly to VIN if this feature is not needed. This input
must not be allowed to float. The values for the various EN thresholds can be found in Section 7.
The LM636x5D-Q1 uses a reference-based soft start that prevents output voltage overshoots and large inrush
currents as the regulator is starting up. Figure 8-3 shows a typical start-up waveform along with typical timings.
Once EN goes high, there is a delay of about 1 ms before the soft-start period begins. The output voltage begins
to rise and reaches the final value in about 1.5 ms (tss). After a delay of about 3 ms (trise-delay), the RESET flag
goes high. During start-up, the device is not allowed to enter FPWM mode until the tss-done time has elapsed.
This time is measured from the rising edge of EN.
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EN
VEN-H
VEN-L
VEN-VCC
VCC
5V
0
VOUT
VOUT
0
Figure 8-2. Precision Enable Behavior
EN, 4V/DIV
VOUT, 2V/DIV
RESET, 5V/DIV
Inductor Current,
2A/DIV
1ms/DIV
Figure 8-3. Typical Start-up Behavior VIN = 12 V, VOUT = 5 V, IOUT = 2.5 A
8.3.5 RESET Flag Output
The RESET flag function (RESET output pin) of the LM636x5D-Q1 device can be used to reset a system
microprocessor whenever the output voltage is out of regulation. This open-drain output goes low under fault
conditions, such as current limit and thermal shutdown, as well as 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 lasting less than tdg do not trip the RESET flag. Once the FB voltage has returned to
the regulation value and after a delay of trise-delay, the RESET flag goes high. RESET operation can best be
understood by reference to Figure 8-4 and Figure 8-5.
The RESET output consists of an open-drain NMOS, requiring an external pullup resistor to a suitable logic
supply. It can also be pulled up to either VCC or VOUT through an appropriate resistor, as desired. Pullup resistor
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values in the range of 10 kΩ to 100 kΩ are reasonable. If this function is not needed, the RESET pin can be left
floating. When EN is pulled low, the flag output is also forced low. With EN low, RESET remains valid as long as
the input voltage is ≥ 1.2 V (typical). Limit the current into the RESET flag pin to approximately 5 mA D.C. The
maximum current is internally limited to approximately 50 mA when the device is enabled and approximately 65
mA when the device is disabled. The internal current limit protects the device from any transient currents that
can occur when discharging a filter capacitor connected to this output.
VOUT
VRESET-HIGH
VRESET-HYS
VRESET-HYS
VRESET-LOW
RESET
High = Power Good
Low = Fault
Figure 8-4. Static RESET Operation
Glitches do not cause false operation nor reset timer
VOUT
VRESET-LOW
< tdg
t
RESET
t
Trise-delay
tdg
Trise-delay
Figure 8-5. RESET Timing Behavior
8.3.6 Undervoltage Lockout and Thermal Shutdown and Output Discharge
The LM636x5D-Q1 incorporates an undervoltage-lockout feature on the output of the internal LDO (at the VCC
pin). When VIN reaches approximately VPOR-R, the device is ready to receive an EN signal and start up. When
VIN falls below VPOR-F, the device shuts down, regardless of EN status. Since the LDO is in dropout during these
transitions, the above values roughly represent the VCC voltage levels during the transitions. An extended input
voltage UVLO can also be accomplished as shown in Section 9.2.2.8.
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Thermal shutdown is provided to protect the regulator from excessive junction temperature. When the junction
temperature reaches about 163°C, the device shuts down; re-start occurs when the temperature falls to about
150°C.
The LM636x5D-Q1 features an output voltage discharge FET connected from the SW pin to ground. This FET
is activated when the EN input is below VEN-L, or when the output voltage exceeds VRESET-HIGH. This way, the
output capacitors are discharged through the power inductor. At output voltages above about 5 V, the discharge
current is approximately constant at IPOR or about 1.4 mA. Below this voltage, the FET characteristic looks
approximately resistive at a value of 2.5 kΩ.
8.4 Device Functional Modes
8.4.1 Overview
In typical usage, the device is put in AUTO mode (SYNC/MODE pin = ground). In AUTO mode, the device
moves between PWM and PFM as the load changes. At light loads, the regulator operates in PFM where the
switching frequency is varied to regulate the output voltage. At higher loads, the mode changes to PWM with the
switching frequency set by the condition of the RT pin (see Section 8.3.3).
In PWM mode, the regulator operates as a current mode, constant frequency converter using PWM to regulate
the output voltage. While operating in this mode, the output voltage is regulated by switching at a constant
frequency and modulating the duty cycle to control the power to the load. This provides excellent line and load
regulation and low output voltage ripple.
In PFM mode, the high-side MOSFET is turned on in a burst of one or more pulses to provide energy to the load.
The duration of the burst depends on how long it takes the inductor current to reach IPEAK-MIN. The periodicity
of these bursts is adjusted to regulate the output, while diode emulation (DEM) is used to maximize efficiency
(see the Glossary). This mode provides high light-load efficiency by reducing the amount of input supply current
required to regulate the output voltage at small loads. This trades off very good light-load efficiency for larger
output voltage ripple and variable switching frequency. Also, a small increase in output voltage occurs at light
loads. See Section 9.2.4 for output voltage variation with load in PFM mode. Figure 8-6 and Figure 8-7 show the
typical switching waveforms in PFM and PWM.
There are four cases where the switching frequency does not conform to the condition set by the RT pin:
•
•
•
•
Light load operation (AUTO mode)
Dropout
Minimum on-time operation
Current limit
Under all of these cases, the switching frequency folds back, meaning it is less than that programmed by the
RT control pin. During these conditions, by definition, the output voltage remains in regulation, except for current
limit operation.
When the device is placed in forced PWM mode (FPWM), the switching frequency remains constant as
programmed by the RT pin for all load conditions. This mode essentially turns off the light-load PFM frequency
foldback mode detailed in Section 8.4.2. See Section 8.3.1 and Section 8.4.2.1 for details.
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Switch Voltage
5 V/DIV
Switch Voltage
5 V/DIV
0
Inductor Current
200 mA/DIV
Inductor Current
1 A/DIV
5 µs/DIV
0
100 ns/DIV
Figure 8-6. Typical PFM Switching Waveforms VIN =
12 V, VOUT = 5 V, IOUT = 10 mA
Figure 8-7. Typical PWM Switching Waveforms
Without Spread Spectrum VIN = 12 V, VOUT = 5 V,
IOUT = 2.5 A, ƒSW = 2100 kHz
Switch Voltage
5 V/DIV
Switch Voltage
5 V/DIV
0
Inductor Current
200 mA/DIV
0
100 ns/DIV
100 ns/DIV
Figure 8-8. Typical PWM Switching Waveforms
With Spread Spectrum VIN = 12 V, VOUT = 5 V, IOUT =
2.5 A, ƒSW = 2100 kHz
Figure 8-9. Typical PWM Switching Waveforms
FPWM VIN = 12 V, VOUT = 5 V, IOUT = 0 A, ƒSW =
2100 kHz
8.4.2 Light Load Operation
During light load operation, the device is in PFM mode with DEM. This provides high efficiency at the lower load
currents. The actual switching frequency and output voltage ripple depend on the input voltage, output voltage,
and load. The output current at which the device moves in and out of PFM can be found in Section 9.2.4. The
output current for mode change depends on the input voltage, inductor value, and the programmed switching
frequency. The curves apply for the BOM shown in Table 9-4. At higher programmed switching frequencies,
the load at which the mode change occurs is greater. For applications where the switching frequency must be
known for a given condition, the transition between PFM and PWM must be carefully tested before the design is
finalized. Alternatively, the mode can be set to FPWM.
8.4.2.1 Sync/FPWM Operation
The forced PWM mode (FPWM) can be used to turn off AUTO mode and force the device to switch at the
frequency programmed by the RT pin, even for small loads. This has the disadvantage of lower efficiency at light
loads.
When a valid clock signal is present on the SYNC/MODE input, the switching frequency is locked to the external
clock. The device mode is also FPWM. The mode can be changed dynamically by the system. See Figure 8-10
and Figure 8-11 for typical examples of SYNC/MODE function changes.
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Sync Burst
SYNC/MODE
Input
0
Output Voltage
50 mV/DIV
Output Voltage
50 mV/DIV
5V
5V
Inductor Current
500 mA/DIV
0
0
Inductor Current
500 mA/DIV
2 ms/DIV
Figure 8-10. Typical Transition from FPWM to
AUTO Mode VIN = 12 V, VOUT = 5 V, IOUT = 1 mA
200 µs/DIV
Figure 8-11. Typical Transition from Sync Mode to
FPWM Mode VIN = 12 V, VOUT = 5 V, IOUT = 1 mA
8.4.3 Dropout Operation
The dropout performance of any buck regulator is affected by the RDSON of the power MOSFETs, the DC
resistance of the inductor, and the maximum duty cycle that the controller can achieve. As the input voltage level
approaches the output voltage, the off-time of the high-side MOSFET starts to approach the minimum value (see
Section 7). Beyond this point, the switching can become erratic and the output voltage can fall out of regulation.
To avoid this problem, the LM636x5D-Q1 automatically reduces the switching frequency to increase the effective
duty cycle and maintain regulation. There are two definitions of dropout voltage used in this data sheet. For both
definitions, the dropout voltage is the difference between the input and output voltage under a specific condition.
For the first definition, the difference is taken when the switching frequency has dropped to 1850 kHz (obviously
this applies to cases where the nominal switching frequency is >1850 kHz). For this condition, the output voltage
is within regulation. For the second definition, the difference is taken when the output voltage has fallen by 1% of
the nominal regulation value. In this condition, the switching frequency has reached the lower limit of about 130
kHz. See Section 9.2.4 for details on these characteristics. Typical overall dropout characteristics can be found
in Figure 8-12.
5
1.5 A
2.5 A
4.8
Output Voltage (V)
4.6
4.4
4.2
4
3.8
3.6
3.4
3.5
4
4.5
5
5.5
6
Input Voltage (V)
6.5
7
7.5
8
drop
Figure 8-12. Overall Dropout Characteristic VOUT = 5 V
8.4.4 Minimum On-time Operation
Every switching regulator has a minimum controllable on-time dictated by the inherent delays and blanking
times associated with the control circuits. This imposes a minimum switch duty cycle and, therefore, a minimum
conversion ratio. The constraint is encountered at high input voltages and low output voltages. To help extend
the minimum controllable duty cycle, the LM636x5D-Q1 automatically reduces the switching frequency when
the minimum on-time limit is reached. This way, the converter can regulate the lowest programmable output
voltage at the maximum input voltage. Use Equation 2 to find an estimate for the approximate input voltage for
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a given output voltage before frequency foldback occurs. The values of tON and ƒSW can be found in Section 7.
As the input voltage is increased, the switch on-time (duty-cycle) reduces to regulate the output voltage. When
the on-time reaches the limit, the switching frequency drops while the on-time remains fixed. This relationship is
highlighted in ƒSW versus VIN curves in Section 9.2.4.
VIN d
VOUT
t ON ˜ fSW
(2)
8.4.5 Current Limit and Short-Circuit Operation
The LM636x5D-Q1 incorporates both peak and valley inductor current limits to provide protection to the device
from overloads and short circuits and limit the maximum output current. Valley current limit prevents inductor
current run-away during short circuits on the output, while both peak and valley limits work together to limit the
maximum output current of the converter. A "hiccup" type mode is also incorporated for sustained short circuits.
Finally, a zero current detector is used on the low-side power MOSFET to implement DEM at light loads (see the
Glossary). The nominal value of this limit is about 0 A.
As the device is overloaded, a point is reached where the valley of the inductor current cannot reach below
ILS-LIMIT before the next clock cycle. When this occurs, the valley current limit control skips that cycle, causing
the switching frequency to drop. Further overload causes the switching frequency to continue to drop, but the
output voltage remains in regulation. As the overload is increased, both the inductor current ripple and peak
current increase until the high-side current limit, ISC, is reached. When this limit is activated, the switch duty cycle
is reduced and the output voltage falls out of regulation. This represents the maximum output current from the
converter and is given approximately by Equation 3. The output voltage and switching frequency continue to
drop as the device moves deeper into overload while the output current remains at approximately IOMAX. If the
inductor ripple current is large, the high-side current limit can be tripped before the low-side limit is reached. In
this case, Equation 4 gives the approximate maximum output current.
IOMAX |
ISC
IOMAX | ISC
ILS
2
LIMIT
VIN
(3)
VOUT
2 ˜ L ˜ fSW
˜
VOUT
VIN
(4)
If a severe overload or short circuit causes the FB voltage to fall below VHICCUP, the convert enters "hiccup"
mode. VHICCUP represents about 40% of the nominal programmed output voltage. In this mode, the device stops
switching for tOC, or about 100 ms, and then goes through a normal restart with soft start. If the short-circuit
condition remains, the device runs in current limit for a little longer than tOC_active, or about 23 ms, and then
shuts down again. This cycle repeats (as shown in Figure 8-13) as long as the short-circuit condition persists.
This mode of operation reduces the temperature rise of the device during a sustained short on the output. The
output current in this mode is approximately 20% of IOMAX. Once the output short is removed and the tOC delay is
passed, the output voltage recovers normally as shown in Figure 8-14.
See Figure 8-15 for the overall output voltage versus output current characteristic.
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Short Applied Short Removed
Output Voltage
2 V/DIV
0
Inductor Current
2 A/DIV
Inductor Current
500 mA/DIV
50 ms/DIV
20 ms/DIV
0
0
Figure 8-13. Inductor Current Burst in Short-Circuit Figure 8-14. Short-Circuit Transient and Recovery;
LM63625
Mode; LM63625
Output
Voltage
VOUT
0.4· VOUT
0.2· IOMAX
IOMAX
Output
Current
Figure 8-15. Output Voltage versus Output Current in Current Limit
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9 Application and Implementation
Note
Information in the following applications sections is not part of the TI component specification,
and TI does not warrant its accuracy or completeness. TI’s customers are responsible for
determining suitability of components for their purposes, as well as validating and testing their design
implementation to confirm system functionality.
9.1 Application Information
The LM636x5D-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 1.5 A or 2.5 A. The following design procedure can be used to
select components for the LM636x5D-Q1.
Note
In this data sheet, the effective value of capacitance is defined as the actual capacitance under
D.C. bias and temperature, not the rated or nameplate values. Use high-quality, low-ESR, ceramic
capacitors with an X5R or better dielectric throughout. All high value ceramic capacitors have a
large voltage coefficient in addition to normal tolerances and temperature effects. Under D.C. bias,
the capacitance drops considerably. Large case sizes and higher voltage ratings are better in this
regard. To help mitigate these effects, multiple capacitors can be used in parallel to bring the minimum
effective capacitance up to the required value. This can also ease the RMS current requirements on
a single capacitor. A careful study of bias and temperature variation of any capacitor bank must be
made to ensure that the minimum value of effective capacitance is provided.
9.2 Typical Application
Figure 9-1 shows a typical application circuit for the LM636x5D-Q1. This device is designed to function over 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, see Table 9-1 and Table
9-2 for typical component values.
L
VIN
VOUT 5 V
SW
VIN
2.2 µH
6 V to 36 V
CIN
10 µF
CHF
220 nF
CBOOT
EN
2.5 A
COUT
BOOT
2x 22 µF
0.22 µF
VSEL
RT
SYNC/
MODE
VCC
FB
RESET
PGND
AGND
100 NŸ
CVCC
1 µF
RESET
Figure 9-1. Example Application Circuit VIN = 12 V, VOUT = 5 V, IOUT = 2.5 A, ƒSW = 2.1 MHz
24
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Table 9-1. Typical External Component Values for 1.5-A Output Current
ƒSW
(kHz)
VOUT
L (µH)(1)
TYPICAL(2)
COUT
MINIMUM(2)
COUT
VSEL
RT
CIN
CBOOT
CVCC
400
3.3
10
4 × 10 µF
2 × 10 µF
AGND
VCC
4.7 µF + 220 nF
220 nF
1 µF
2100
3.3
4.7
2 × 10 µF
1 × 10 µF
AGND
AGND
4.7 µF + 220 nF
220 nF
1 µF
400
5
10
4 × 10 µF
2 × 10 µF
VCC
VCC
4.7 µF + 220 nF
220 nF
1 µF
2100
5
4.7
2 × 10 µF
1 × 10 µF
VCC
AGND
4.7 µF + 220 nF
220 nF
1 µF
(1)
See Section 9.2.2.3.
(2)
See Section 9.2.2.4.
Table 9-2. Typical External Component Values for 2.5-A Output Current
ƒSW
(kHz)
VOUT
L (µH)(1)
TYPICAL(2)
COUT
MINIMUM(2)
COUT
VSEL
RT
CIN
CBOOT
CVCC
400
3.3
6.8
3 × 22 µF
2 × 22 µF
AGND
VCC
4.7 µF + 220 nF
220 nF
1 µF
2100
3.3
2.2
2 × 22 µF
1 × 22 µF
AGND
AGND
4.7 µF + 220 nF
220 nF
1 µF
400
5
6.8
3 × 22 µF
2 × 22 µF
VCC
VCC
4.7 µF + 220 nF
220 nF
1 µF
2100
5
2.2
2 × 22 µF
1 × 22 µF
VCC
AGND
4.7 µF + 220 nF
220 nF
1 µF
(1)
See the Section 9.2.2.3.
(2)
See the Section 9.2.2.4.
9.2.1 Design Requirements
Table 9-3 provides the parameters for the detailed design procedure:
Table 9-3. Detailed Design Parameters
DESIGN PARAMETER
EXAMPLE VALUE
Input voltage
12 V (6 V to 36 V)
Output voltage
5V
Maximum output current
0 A to 2.5 A
Switching frequency
2.1 MHz
9.2.2 Detailed Design Procedure
The following design procedure applies to Figure 9-1 and Table 9-3.
9.2.2.1 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 the use of smaller inductors and output capacitors, and hence, a
more compact design. 2100 kHz was chosen for this example.
9.2.2.2 Setting the Output Voltage
The output voltage of the LM636x5D-Q1 is set by the condition of the VSEL input. This example requires a 5-V
output, so the VSEL input is connected to VCC and the FB input is connected directly to the output capacitor.
For cases where the desired output voltage is other than 5 V or 3.3 V, an external feedback divider is required.
As shown in Figure 9-2, the divider network is comprised of RFBT and RFBB, and closes the loop between the
output voltage and the converter. In this case, a 10-kΩ resistor is connected from the VSEL input to ground.
The converter regulates the output voltage by holding the voltage on the FB pin equal to the internal reference
voltage, 1 V. 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 Section 9.2.2.2.1). Once RFBT is selected, Equation 5 is used to select RFBB. VREF is nominally 1 V.
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RFBB
RFBT
ª VOUT
«
¬ VREF
º
1»
¼
(5)
VOUT
RFBT
FB
VSEL
RFBB
10 kŸ
Figure 9-2. Feedback Divider for Adjustable Output Voltage Setting
9.2.2.2.1 CFF Selection
In some cases, a feedforward capacitor can be used across RFBT to improve the load transient response or
improve the loop-phase margin. This is especially true when values of RFBT > 100 kΩ are used. Large values
of RFBT in combination with the parasitic capacitance at the FB pin can create a small signal pole that interferes
with the loop stability. A CFF helps mitigate this effect. Equation 6 can be used to estimate the value of CFF. The
value found with Equation 6 is a starting point; use lower values to determine if any advantage is gained by the
use of a CFF capacitor. The Optimizing Transient Response of Internally Compensated DC-DC Converters with
Feedforward Capacitor Application Report is helpful when experimenting with a feedforward capacitor.
CFF
VOUT ˜ COUT
120 ˜ RFBT ˜
VREF
VOUT
(6)
9.2.2.3 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. Larger values of ripple current can restrict the maximum output current, before current
limit is reached. This trade-off can be examined with the help of Equation 3 and the ensured current limits found
in Section 7. Smaller values of ripple current reduce the SNR of the current mode controller and can lead to
increased jitter in the duty cycle. Both the inductor and switching frequency tolerance have an impact on the
selection of ripple current, and, therefore, inductor value. Use the maximum device current when calculating the
ripple current for applications with much smaller maximum load than the maximum available from the device.
The ratio of inductor ripple current over maximum output current is designated as K in the following equations.
Equation 7 can be used to determine the value of inductance. K = 0.2 was chosen for this example and L = 2.8
µH inductance was found. A standard value of 2.2 µH was selected. This gives a new K = 0.25.
L
VIN VOUT
V
˜ OUT
fSW ˜ K ˜ IOUT max VIN
(7)
Ideally, the saturation current rating of the inductor is at least as large as the high-side switch current limit,
ISC (see Section 7). 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, ILIMIT, 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. Powered iron cores exhibit a soft
saturation, allowing some relaxation in the current rating of the inductor. However, they have more core losses at
26
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frequencies above about 1 MHz. In any case, the inductor saturation current must not be less than the maximum
peak inductor current at full load.
To avoid subharmonic oscillation, the inductance value must not be less than that given in Equation 8. 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.
LMIN t M ˜
VOUT
fSW
(8)
where
•
•
M = 0.42 for 2.5 A device
M = 0.69 for 1.5 A device
9.2.2.4 Output Capacitor Selection
The value of the output capacitor and its ESR determine the output voltage ripple and load transient
performance. The output capacitor bank is usually limited by the load transient requirements rather than the
output voltage ripple. Use Equation 9 to estimate a lower bound on the total output capacitance, and an upper
bound on the ESR, which are required to meet a specified load transient.
COUT t
ESR d
D
fSW
'IOUT
˜ 'VOUT ˜ K
ª
˜«1 D ˜ 1 K
«¬
º
K2
˜ 2 D»
12
»¼
2 K ˜ 'VOUT
ª
2 ˜ 'IOUT «1 K
«¬
K2
12
§
1 ·º
¸¸»
˜ ¨¨1
© (1 D) ¹»¼
VOUT
VIN
(9)
where
•
•
•
ΔVOUT = output voltage transient
ΔIOUT = output current transient
K = ripple factor from Section 9.2.2.3
Once the output capacitor and ESR have been calculated, use Equation 10 to check the peak-to-peak output
voltage ripple, Vr.
Vr # 'IL ˜ ESR 2
1
8 ˜ fSW ˜ COUT
2
(10)
The output capacitor and ESR can then be adjusted to meet both the load transient and output ripple
requirements.
This example requires a ΔVOUT of ≤ 150 mV for an output current step of ΔIOUT = 2.5 A. Equation 9 gives a
minimum value of 23 µF and a maximum ESR of 0.053 Ω. Assuming a 20% tolerance and a 10% bias de-rating,
the user arrives at a minimum capacitance of 32 µF. This can be achieved with a bank of 2 × 22-µF, 16-V,
ceramic capacitors in the 1210 case size. More output capacitance can be used to improve the load transient
response. Ceramic capacitors can easily meet the minimum ESR requirements. In some cases, an aluminum
electrolytic capacitor can be placed in parallel with the ceramics to build up the required value of capacitance.
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When using a mixture of aluminum and ceramic capacitors, use the minimum recommended value of ceramics
and add aluminum electrolytic capacitors as needed.
In general, use a capacitor rating of at least 10 V for output voltages of 3.3 V or less, and use a capacitor of 16 V
or more for output voltages of 5 V and above.
The recommendations given in Table 9-1 and Table 9-2 provide typical and minimum values of output
capacitance for the given conditions. These values are the rated or nameplate figures. If the minimum values
are to be used, the design must be tested over all of the expected application conditions, including input
voltage, output current, and ambient temperature. This testing must include both bode plot and load transient
assessments. The maximum value of total output capacitance must be limited to about 10 times the design
value, or 1000 µF, whichever is smaller. Large values of output capacitance can adversely affect the start-up
behavior of the regulator as well as the loop stability. If values larger than noted here must be used, then a
careful study of start-up at full load and loop stability must be performed.
In practice, the output capacitor has the most influence on the transient response and loop phase margin. Load
transient testing and bode plots are the best way to validate any given design and must always be completed
before the application goes into production. In addition to the required output capacitance, a small ceramic
placed on the output can reduce high frequency noise. Small case size ceramic capacitors in the range of 1 nF
to 100 nF can help reduce spikes on the output caused by inductor and board parasitics.
9.2.2.5 Input Capacitor Selection
The ceramic input capacitors provide a low impedance source to the regulator in addition to supplying the
ripple current and isolating switching noise from other circuits. A minimum of 4.7 µF of ceramic capacitance is
required on the input of the LM636x5D-Q1, connected directly between VIN and PGND. 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. More input capacitance is required for larger output currents. In addition, a small case size, 220-nF
ceramic capacitor must be used at the input as close a possible to the regulator, typically within 1 mm of the
VIN and PGND pins. This provides a high frequency bypass for the control circuits internal to the device. For this
example, a 10-µF, 50-V, X7R (or better) ceramic capacitor is chosen. Two 4.7-µF capacitors can also be used.
The 220 nF must also be rated at 50 V with an X7R dielectric and preferably a small case size, such as an 0603.
Many times, it is desirable 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 regulator. 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 voltage dips caused by input supplies with unusually high impedance.
Most of the input switching current passes through the ceramic input capacitor or capacitors. Use Equation 11
to calculate the approximate RMS current. This value must be checked against the manufacturers' maximum
ratings.
IRMS #
IOUT
2
(11)
9.2.2.6 CBOOT
The LM636x5D-Q1 requires a bootstrap capacitor to be connected between the BOOT pin and the SW pin. This
capacitor stores energy that is used to supply the gate drivers for the power MOSFETs. A high-quality ceramic
capacitor of 220 nF and at least 16 V is required.
9.2.2.7 VCC
The VCC pin is the output of the internal LDO used to supply the control circuits of the regulator. This output
requires a 1-µF, 16-V ceramic capacitor connected from VCC to PGND for proper operation. In general, this
output must not be loaded with any external circuitry. However, this output can be used to supply the pullup for
the RESET function and as a logic supply for the various control inputs of the device. A value of 100 kΩ is a
good choice for the RESET flag pullup resistor. The nominal output voltage on VCC is 5 V.
28
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9.2.2.8 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 Figure 9-3. The input voltage at which the device turns on is
designated as VON while the turnoff voltage is VOFF. First, a value for RENB is chosen in the range of 10 kΩ to
100 kΩ. Then, Equation 12 is used to calculate RENT and VOFF.
VIN
RENT
EN
RENB
Figure 9-3. Setup for External UVLO Application
RENT
§ V
RENB ˜ ¨ ON
© VEN H
VOFF
VEN
L
·
1¸
¹
§ V
·
˜ ¨ ON ¸
© VEN H ¹
(12)
where
•
•
VON = VIN turnon voltage
VOFF = VIN turnoff voltage
9.2.2.9 Maximum Ambient Temperature
As with any power conversion device, the LM636x5D-Q1 dissipates internal power while operating. The effect
of this power dissipation is to raise the internal temperature of the converter above ambient. The internal die
temperature (TJ) is a function of the ambient temperature, the power loss, and the effective thermal resistance,
RθJA, of the device, and PCB combination. The maximum internal die temperature for the LM636x5D-Q1 must
be limited to 150°C. This establishes a limit on the maximum device power dissipation and, therefore, the
load current. Equation 13 shows the relationships between the important parameters. It is easy to see that
larger ambient temperatures (TA) and larger values of RθJA reduce the maximum available output current. The
converter efficiency can be estimated by using the curves provided in this data sheet. Note that these curves
include the power loss in the inductor. If the desired operating conditions cannot be found in one of the curves,
then interpolation can be used to estimate the efficiency. Alternatively, the EVM can be adjusted to match the
desired application requirements and the efficiency can be measured directly. The correct value of RθJA is more
difficult to estimate. As stated in the Semiconductor and IC Package Thermal Metrics Application Report, the
value of RθJA given in the Section 7.4 table is not valid for design purposes and must not be used to estimate the
thermal performance of the application. The values reported in that table were measured under a specific set of
conditions that are rarely obtained in an actual application. The data given for RθJC(bott) and ΨJT can be useful
when determining thermal performance. See the Semiconductor and IC Package Thermal Metrics Application
Report for more information and the resources given at the end of this section.
IOUT
MAX
TJ TA
1
K
˜
˜
R TJA
1 K VOUT
(13)
where
•
η = efficiency
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The effective RθJA is a critical parameter and depends on many factors such as the following:
•
•
•
•
•
•
Power dissipation
Air temperature/flow
PCB area
Copper heat-sink area
Number of thermal vias under the package
Adjacent component placement
The HTSSOP and the DRR0012 package use a die attach paddle, or "thermal pad" (DAP), to provide a place
to solder down to the PCB heat-sinking copper. This provides a good heat conduction path from the regulator
junction to the heat sink and must be properly soldered to the PCB heat sink copper. Typical examples of RθJA
versus copper board area can be found in Figure 9-4 and Figure 9-5. The copper area given in the graph is for
each layer. The top and bottom layers are 2-oz. copper each, while the inner layers are 1 oz. Figure 9-6 shows
a typical curve of maximum output current versus ambient temperature. This data was taken with a device and
PCB combination, giving an RθJA of approximately 30°C/W. Remember that the data given in these graphs
are for illustration purposes only, and the actual performance in any given application depends on all of the
previously mentioned factors.
40
4L, 0.9W
4L, 2W
2L, 0.9W
2L, 2W
37.5
35
RTJA (qC/W)
32.5
30
27.5
25
22.5
20
17.5
15
0
20
40
60
80
100
Copper Area (cm2)
120
140
160
180
thet
Figure 9-4. Typical RθJA versus Copper Area for the HTSSOP Package
55
2L, 0.9W
2L, 2W
4L, 0.9W
4L, 2W
50
45
RTJA (qC/W)
40
35
30
25
20
15
0
20
40
60
80
100
Copper Area (cm2)
120
140
160
180
Thet
Figure 9-5. Typical RθJA vs Copper Area for the WSON Package
30
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3
Maximum Output Current (A)
2.5
2
1.5
1
0.5
0
0
10
20
30
40
50
60
70
80
90
100
Ambient Temperature (qC)
110
120
130
140
150
160
dera
Figure 9-6. Maximum Output Current versus Ambient Temperature VIN = 12 V, VOUT = 5 V, ƒSW = 2.1 MHz,
RθJA = 30°C/W
The following resources can be used as a guide to optimal thermal PCB design and estimating RθJA for a given
application environment:
•
•
•
•
•
AN-2020 Thermal Design By Insight, Not Hindsight Application Report
A Guide to Board Layout for Best Thermal Resistance for Exposed Pad Packages Application Report
Semiconductor and IC Package Thermal Metrics Application Report
Thermal Design Made Simple with LM43603 and LM43602 Application Report
Using New Thermal Metrics Application Report
9.2.3 Full Feature Design Example
The schematic in Figure 9-7 shows a typical application using all of the features of the LM636x5D-Q1. This
example provides a 12-V output at 2.5 A from an input of 24 V. Components are calculated using the equations
and procedures found in Section 9.2.2.
L
VIN
VIN
24 V
10 µF
VOUT 12 V
SW
8.2 µH
CIN
2.5 A
CBOOT
CHF
220 nF
COUT
BOOT
PGND
2x 22 µF
0.22 µF
AGND
100 NŸ
*
SYNC/
MODE
FB
EN
µC
RESET
VCC
VSEL
9.09 NŸ
RT
100 NŸ
CVCC
1 µF
10 NŸ
15.8 k
fSW= 1 MHz
*
Optional component
Figure 9-7. Full-Featured Design Example VIN = 24 V, VOUT = 12 V, IOUT = 2.5 A, ƒSW = 1 MHz
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9.2.4 Application Curves
100
95
95
90
90
85
Efficiency (%)
Efficiency (%)
Unless otherwise specified, the following conditions apply: VIN = 13.5 V, TA = 25°C. Table 9-4 shows the circuit with the
appropriate BOM from Figure 9-44.
85
80
75
65
0.001
LM63625
0.01
0.1
Output Current (A)
VOUT = 5 V
1
75
70
8V
13.5V
18V
24V
70
80
60
0.001
5
ƒSW = 400 kHz
(AUTO)
LM63625
95
95
90
Efficiency (%)
Efficiency (%)
85
80
75
0.01
0.1
Output Current (A)
VOUT = 5 V
1
75
70
8V
13.5V
18V
24V
60
55
0.001
2
0.01
eff_
ƒSW = 400 kHz
(AUTO)
LM63615
0.1
Output Current (A)
VOUT = 5 V
1
2
eff_
ƒSW = 2100 kHz
(AUTO)
Figure 9-11. Efficiency
95
95
90
90
85
Efficiency (%)
85
Efficiency (%)
ƒSW = 2100 kHz
(AUTO)
80
Figure 9-10. Efficiency
80
75
70
0.01
0.1
Output Current (A)
VOUT = 3.3 V
1
80
75
70
65
8V
13.5V
18V
24V
65
8V
13.5V
18V
24V
60
55
0.001
5
0.01
eff_
ƒSW = 400 kHz
(AUTO)
Figure 9-12. Efficiency
32
5
eff_
65
8V
13.5V
18V
24V
70
LM63625
VOUT = 5 V
1
85
90
60
0.001
0.1
Output Current (A)
Figure 9-9. Efficiency
100
LM63615
0.01
eff_
Figure 9-8. Efficiency
65
0.001
8V
13.5V
18V
24V
65
LM63625
0.1
Output Current (A)
VOUT = 3.3 V
1
5
eff_
ƒSW = 2100 kHz
(AUTO)
Figure 9-13. Efficiency
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9.2.4 Application Curves (continued)
95
95
90
90
85
Efficiency (%)
Efficiency (%)
85
80
75
70
60
0.001
0.01
LM63615
0.1
Output Current (A)
VOUT = 3.3 V
1
75
70
65
8V
13.5V
18V
24V
65
80
8V
13.5V
18V
24V
60
55
0.001
2
0.01
eff_
ƒSW = 400 kHz
(AUTO)
LM63615
VOUT = 3.3 V
Figure 9-14. Efficiency
1
2
eff_
ƒSW = 2100 kHz
(AUTO)
Figure 9-15. Efficiency
3.34
5.06
8V
13.5V
18V
24V
8V
13.5V
18V
24V
3.33
Output Voltage (V)
5.05
Output Voltage (V)
0.1
Output Current (A)
5.04
5.03
5.02
3.32
3.31
5.01
5
3.3
0
0.5
LM63625
1
1.5
Output Current (A)
VOUT = 5 V
2
2.5
0
ƒSW = 2100 kHz
(AUTO)
LM63625
Figure 9-16. Line and Load Regulation
1
1.5
Output Current (A)
VOUT = 3.3 V
2
2.5
LL_3
ƒSW = 2100 kHz
(AUTO)
Figure 9-17. Line and Load Regulation
3.34
5.06
8V
13.5V
18V
24V
5.05
8V
13.5V
18V
24V
3.33
Output Voltage (V)
5.04
Output Voltage (V)
0.5
LL_5
5.03
5.02
5.01
3.32
3.31
5
3.3
4.99
4.98
3.29
0
0.25
LM63615
0.5
0.75
1
Output Current (A)
VOUT = 5 V
1.25
ƒSW = 2100 kHz
(AUTO)
Figure 9-18. Line and Load Regulation
1.5
0
0.25
LL_5
A.
LM63615
0.5
0.75
1
Output Current (A)
VOUT = 3.3 V
1.25
1.5
LL_3
ƒSW = 2100 kHz
(AUTO)
Figure 9-19. Line and Load Regulation
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10000
10000
1000
1000
Switching Frequency (kHz)
Switching Frequency (kHz)
9.2.4 Application Curves (continued)
100
10
1
0.1
10
1
0.1
5V
3.3V
0.01
1E-6
1E-5
LM63625
0.0001 0.001
0.01
Output Current (A)
VIN = 13.5 V
0.1
1
ƒSW = 2100 kHz
(AUTO)
LM63615
2000
2000
Switching Frequency (kHz)
2250
1750
1500
1250
1000
750
500
0.0001
0.001
0.01
Output Current (A)
VIN = 13.5 V
0.1
1
Fsw_
ƒSW = 2100 kHz
(AUTO)
Figure 9-21. Switching Frequency versus Output Current
2250
0A
2.5A
1750
1500
1250
1000
750
500
0A
2.5A
250
0
0
0
4
8
LM63625
12
16
20
24
Input Voltage (V)
VOUT = 3.3 V
28
32
36
40
0
4
8
12
Fsw_
ƒSW = 2100 kHz
(FPWM)
LM63625
Figure 9-22. Switching Frequency versus Input Voltage
2250
2000
2000
1750
1500
1250
1000
750
500
0A
1.5A
250
16
20
24
Input Voltage (V)
VOUT = 5 V
28
32
40
Fsw_
ƒSW = 2100 kHz
(FPWM)
1750
1500
1250
1000
750
500
0A
1.5A
250
0
36
Figure 9-23. Switching Frequency versus Input Voltage
2250
Switching Frequency (kHz)
Switching Frequency (kHz)
1E-5
Fsw_
250
0
0
LM63615
4
8
12
16
20
24
Input Voltage (V)
VOUT = 3.3 V
28
32
36
40
0
4
8
Fsw_
ƒSW = 2100 kHz
(FPWM)
Figure 9-24. Switching Frequency versus Input Voltage
34
5V
3.3V
0.01
1E-6
5
Figure 9-20. Switching Frequency versus Output Current
Switching Frequency (kHz)
100
LM63615
12
16
20
24
Input Voltage (V)
VOUT = 5 V
28
32
36
40
Fsw_
ƒSW = 2100 kHz
(FPWM)
Figure 9-25. Switching Frequency versus Input Voltage
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9.2.4 Application Curves (continued)
VOUT, 200mV/DIV
VOUT, 200mV/DIV
3.3V
3.3V
Output Current, 1A/DIV
Output Current, 1A/DIV
50µs/DIV
50µs/DIV
0
LM63625
VOUT = 3.3 V
0 A to 2.5 A, 2 µs
FPWM
0
ƒSW = 2100 kHz
LM63615
VOUT = 3.3 V
0 A to 1.5 A, 2 µs
FPWM
Figure 9-26. Load Transient
ƒSW = 2100 kHz
Figure 9-27. Load Transient
VOUT, 200mV/DIV
VOUT, 200mV/DIV
5V
5V
Output Current, 1A/DIV
Output Current, 1A/DIV
50µs/DIV
0
50µs/DIV
0
LM63625
VOUT = 5 V
0 A to 2.5 A, 2 µs
FPWM
ƒSW = 2100 kHz
Figure 9-28. Load Transient
LM63615
VOUT = 5 V
0 A to 1.5 A, 2 µs
FPWM
ƒSW = 2100 kHz
Figure 9-29. Load Transient
VOUT, 100mV/DIV
VOUT, 100mV/DIV
3.3V
3.3V
Output Current, 1A/DIV
Output Current, 1A/DIV
50µs/DIV
50µs/DIV
0
LM63625
VOUT = 3.3 V
1.5 A to 2.5 A, 2 µs
AUTO
ƒSW = 2100 kHz
Figure 9-30. Load Transient
0
LM63615
VOUT = 3.3 V
0.5 A to 1.5 A, 2 µs
AUTO
ƒSW = 2100 kHz
Figure 9-31. Load Transient
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9.2.4 Application Curves (continued)
VOUT, 100mV/DIV
VOUT, 100mV/DIV
5V
5V
Output Current, 1A/DIV
Output Current, 1A/DIV
50µs/DIV
50µs/DIV
0
0
LM63625
VOUT = 5 V
1.5 A to 2.5 A, 2 µs
AUTO
ƒSW = 2100 kHz
LM63615
VOUT = 5 V
0.5 A to 1.5 A, 2 µs
AUTO
Figure 9-32. Load Transient
Figure 9-33. Load Transient
0.4
3
0.35
2.5
Drop-Out Voltage (V)
Drop-Out Voltage (V)
ƒSW = 2100 kHz
0.3
0.25
0.2
2
1.5
1
0.15
0.1
0.5
0.75
1
1.25
1.5
1.75
Output Current (A)
LM63625
2
2.25
0.5
0.5
2.5
0.75
1
1.25
1.5
1.75
Output Current (A)
DO_f
ƒSW = 140 kHz (AUTO)
LM63625
Figure 9-34. Dropout Voltage versus Output Current for -1%
Drop
2
2.25
2.5
DO_f
ƒSW = 1850 kHz (AUTO)
Figure 9-35. Dropout Voltage versus Output Current to 1.85 MHz
0.3
1.5
1.4
1.3
Drop-Out Voltage (V)
Drop-Out Voltage (V)
0.25
0.2
0.15
0.1
1.2
1.1
1
0.9
0.8
0.7
0.6
0.05
0.5
0.6
0.7
0.8
0.9
1
1.1 1.2
Output Current (A)
LM63615
1.3
1.4
1.5
0.6
0.7
DO_f
ƒSW = 140 kHz (AUTO)
Figure 9-36. Dropout Voltage versus Output Current for -1%
Drop
36
0.5
0.5
LM63615
0.8
0.9
1
1.1 1.2
Output Current (A)
1.3
1.4
1.5
DO_f
ƒSW = 1850 kHz (AUTO)
Figure 9-37. Dropout Voltage versus Output Current to 1.85 MHz
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9.2.4 Application Curves (continued)
29
30
29
28
Input Current (uA)
Input Current (PA)
28
27
26
25
27
26
25
24
23
24
5V
3.3V
22
23
5
LM63625
10
15
20
25
Input Voltage (V)
IOUT = 0 A
30
35
40
5
10
Inpu
ƒSW = 2100 kHz
(AUTO)
LM63615
Figure 9-38. Input Supply Current versus Input Voltage
15
20
25
Input Voltage (V)
IOUT = 0 A
Input Current (mA)
0.1
Output Current (mA)
VOUT = 5 V
0.01
0.01
1
Inpu
ƒSW = 2100 kHz
(AUTO)
LM63615
0.1
Output Current (mA)
VOUT = 5 V
1
Inpu
ƒSW = 2100 kHz
(AUTO)
1
Input Current (mA)
Input Current (mA)
ƒSW = 2100 kHz
(AUTO)
Figure 9-41. Input Supply Current versus Output Current
1
0.1
0.1
Output Current (mA)
VOUT = 3.3 V
0.1
13.5V
18V
13.5V
18V
LM63625
Inpu
13.5V
18V
Figure 9-40. Input Supply Current versus Output Current
0.01
0.01
40
0.1
13.5V
18V
LM63625
35
1
0.1
0.01
0.01
30
Figure 9-39. Input Supply Current versus Input Voltage
1
Input Current (mA)
5V
3.3V
0.01
0.01
1
Inpu
ƒSW = 2100 kHz
(AUTO)
Figure 9-42. Input Supply Current versus Output Current
LM63615
0.1
Output Current (mA)
VOUT = 3.3 V
1
Inpu
ƒSW = 2100 kHz
(AUTO)
Figure 9-43. Input Supply Current versus Output Current
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9.2.4 Application Curves (continued)
VOUT
VIN
U1
VIN
CIN
SW
L
CHF
10 µF
CBOOT
EN
220 nF
BOOT
COUT
0.22 µF
SYNC/
MODE
Mode
VSEL
VOUT
FB
Frequency
RT
RESET
VCC
PGND
AGND
100 NŸ
RESET
CVCC
1 µF
Figure 9-44. Circuit for Typical Application Curves
Table 9-4. BOM for Typical Application Curves
FREQUENCY
OUTPUT
CURRENT
COUT
L
U1
3.3 V
400 kHz
2.5 A
3 × 22 µF
6.8 µH, 22 mΩ
LM63625
3.3 V
2100 kHz
2.5 A
3 × 22 µF
2.2 µH, 15 mΩ
LM63625
5V
400 kHz
2.5 A
3 × 22 µF
6.8 µH, 22 mΩ
LM63625
5V
2100 kHz
2.5 A
3 × 22 µF
2.2 µH, 15 mΩ
LM63625
3.3 V
400 kHz
1.5 A
2 × 22 µF
10 µH, 40 mΩ
LM63615
3.3 V
2100 kHz
1.5 A
1 × 10 µF
4.7 µH, 30 mΩ
LM63615
5V
400 kHz
1.5 A
2 × 22 µF
10 µH, 40 mΩ
LM63615
5V
2100 kHz
1.5 A
1 × 10 µF
4.7 µH, 30 mΩ
LM63615
VOUT
(1)
38
(1)
The values in this table were selected to enhance certain performance criteria and may not represent typical values.
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9.2.5 EMI Performance Curves
dBµV
dBµV
EMI results critically depend on PCB layout and test setup. The results given here are typical and given for
information purposes only. Figure 9-45 shows the used EMI filter. The limit lines shown refer to CISPR25 class 5.
PK
AV
PK
AV
0.15 MHz
1 MHz
10 MHz
30 MHz
30 MHz
LM63625DQ
VOUT = 5 V
IOUT = 2.5 A
Dither
ƒSW = 2100 kHz
Figure 9-45. Typical Conducted EMI 0.15 MHz to 30
MHz
80 MHz
LM63625DQ
VOUT = 5 V
IOUT = 2.5 A
Dither
ƒSW = 2100 kHz
Figure 9-46. Typical Conducted EMI 30 MHz to 108
MHz
Input to
Regulator
1.5 µF
Input Supply
100 MHz
A.
0.22 µF
2x 2.2 µF
0.51
1 µF
4.7 µF
Ferrite Bead
Input filter used only for EMI measurements shown in the Section 9.2.5 section.
Figure 9-47. Typical Input EMI Filter
9.3 What to Do and What Not to Do
•
•
•
•
•
•
•
•
Do not exceed the Absolute Maximum Ratings.
Do not exceed the Recommended Operating Conditions.
Do not exceed the ESD Ratings.
Do not allow the EN input to float.
Do not allow the output voltage to exceed the input voltage, nor go below ground.
Do not use the value of RθJA given in the Section 7.4 table to design your application. See Section 9.2.2.9.
Follow all the guidelines and suggestions found in this data sheet before committing the design to production.
TI application engineers are ready to help critique your design and PCB layout to help make your project a
success.
Use a 220-nF capacitor connected directly to the VIN and PGND pins of the device. See Section 9.2.2.5 for
details.
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10 Power Supply Recommendations
The characteristics of the input supply must be compatible with the limits found in Section 7 of this data sheet.
In addition, the input supply must be capable of delivering the required input current to the loaded regulator. The
average input current can be estimated with Equation 14.
IIN
VOUT ˜ IOUT
VIN ˜ K
(14)
where
•
η is the efficiency
If the regulator 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 regulator. 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 regulator. 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 regulator 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 regulator and use an aluminum or tantalum input capacitor in parallel with
the ceramics. The moderate ESR of these types of capacitors help damp the input resonant circuit and reduce
any overshoots. 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.
It is recommended that the input supply must not be allowed to fall below the output voltage by more than
0.3 V. Under such conditions, the output capacitors discharges through the body diode of the high-side power
MOSFET. The resulting current can cause unpredictable behavior, and in extreme cases, possible device
damage. If the application allows for this possibility, then use a Schottky diode from VIN to VOUT to provide a
path around the regulator for this current.
In some cases, a transient voltage suppressor (TVS) is used on the input of regulators. 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 regulator, the output capacitors discharges through the device, as mentioned above.
Sometimes, for other system considerations, an input filter is used in front of the regulator. This can lead to
instability as well as some of the effects mentioned above, unless it is designed carefully. The AN-2162 Simple
Success with Conducted EMI from DCDC Converters User's Guide provides helpful suggestions when designing
an input filter for any switching regulator.
40
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11 Layout
11.1 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 regulator 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 capacitors and power ground, as shown in Figure
11-1. 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. Figure 11-2 and Figure 11-3 show recommended layouts for the critical components of the
LM636x5D-Q1.
1. Place the input capacitors as close as possible to the VIN and PGND terminals. VIN and PGND pins
are adjacent, simplifying the input capacitor placement. Thermal reliefs in this area are not recommended.
2. Place a bypass capacitor for VCC close to the VCC pin. This capacitor must be placed close to the
device and routed with short, wide traces to the VCC and PGND pins. Thermal reliefs in this area are not
recommended.
3. Use wide traces for the CBOOT capacitor. Place CBOOT close to the device with short and wide traces to
the BOOT and SW pins. Thermal reliefs in this area are not recommended.
4. Place the feedback divider as close as possible to the FB pin of the device. If an external feedback
divider is used with the ADJ option, place RFBB, RFBT, and CFF close to the device. The connections to FB
and AGND 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 regulator.
5. Use at least one ground plane in one of the middle layers. This plane acts as a noise shield and also act
as a heat dissipation path.
6. Connect the thermal pad to the ground plane. The thermal pad (DAP) connection must be soldered down
to the PCB ground plane. This pad acts as a heat-sink connection and an electrical ground connection for
the regulator. The integrity of this solder connection has a direct bearing on the total effective RθJA of the
application. Thermal reliefs in this area are not recommended.
7. Provide wide paths for VIN, VOUT, SW, and PGND. Making these paths as wide and direct as possible
reduces any voltage drops on the input or output paths of the converter and maximizes efficiency. Thermal
reliefs in this area are not recommended.
8. Provide enough PCB area for proper heat-sinking. As stated in Section 9.2.2.9, enough copper
area must be used to ensure a low RθJA, commensurate with the maximum load current and ambient
temperature. The top and bottom PCB layers must be made with two-ounce copper and no less than one
ounce. Use an array of heat-sinking vias to connect the thermal pad (DAP) to the ground plane on the
bottom PCB layer. If the PCB design uses multiple copper layers (recommended), these thermal vias can
also be connected to the inner layer heat-spreading ground planes.
9. 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.
See the following PCB layout resources for additional important guidelines:
•
•
•
•
Layout Guidelines for Switching Power Supplies Application Report
Simple Switcher PCB Layout Guidelines Application Report
Construction Your Power Supply- Layout Considerations Seminar
Low Radiated EMI Layout Made Simple with LM4360x and LM4600x Application Report
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VIN
CIN
KEEP
CURRENT
LOOP
SMALL
SW
GND
Figure 11-1. Current Loops With Fast Edges
11.1.1 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. Connect the AGND and PGND pins 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 the thermal pad (DAP) of the device as the
primary thermal path. Use a minimum 4 × 3 array of 10 mil thermal vias to connect the DAP to the system
ground plane heat sink. The vias must be evenly distributed under the DAP. 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.
42
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11.2 Layout Example
Bottom Trace
VIA to Ground Plane
GND
HEATSINK
Top Trace
VOUT
INDUCTOR
COUT
COUT
CIN
CIN
GND
COUT
CBOOT
CBOOT
CIN
RT
EN
VSEL
SYNC/MODE
AGND
FB
RESET
GND
HEATSINK
GND
HEATSINK
CVCC
VIN
VCC
Figure 11-2. Example Layout for HTSSOP Package
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Bottom Trace
VIA to Ground Plane
GND
HEATSINK
Top Trace
VOUT
INDUCTOR
COUT
CIN
CIN
CIN-HF
CBOOT
N/C
VCC
EN
RT
AGND
CVCC
VIN
VSEL
FB
SYNC/
MODE
RESET
GND
HEATSINK
CBOOT
SW
VIN
GND
GND
COUT
GND
HEATSINK
Figure 11-3. Example Layout for WSON Package
44
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Boom Trace
VIA to Ground Plane
GND
HEATSINK
Top Trace
VOUT
INDUCTOR
COUT
CIN
CIN
CBOOT
CVCC
CBOOT
N/C
N/C
EN
VCC
AGND
SYNC/
MODE
N/C
RESET
FB
RFBT
VIN
RFBB
SW
GND
HEATSINK
CIN-HF
VIN
GND
GND
COUT
GND
HEATSINK
Figure 11-4. Example Layout for WSON Package 2nd pinout
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12 Device and Documentation Support
12.1 Documentation Support
12.1.1 Related Documentation
For related documentation see the following:
• Texas Instruments, AN-2020 Thermal Design By Insight, Not Hindsight Application Report
• Texas Instruments, A Guide to Board Layout for Best Thermal Resistance for Exposed Pad Packages
Application Report
• Texas Instruments, Semiconductor and IC Package Thermal Metrics Application Report
• Texas Instruments, Thermal Design Made Simple with LM43603 and LM43602 Application Report
• Texas Instruments, Using New Thermal Metrics Application Report
• Texas Instruments, Layout Guidelines for Switching Power Supplies Application Report
• Texas Instruments, Simple Switcher PCB Layout Guidelines Application Report
• Texas Instruments, Constructing Your Power Supply-layout Considerations Seminar
• Texas Instruments, Low Radiated EMI Layout Made Simple with LM4360x and LM4600x Application Report
12.2 Receiving Notification of Documentation Updates
To receive notification of documentation updates, navigate to the device product folder on ti.com. Click on
Subscribe to updates to register and receive a weekly digest of any product information that has changed. For
change details, review the revision history included in any revised document.
12.3 Support Resources
TI E2E™ support forums are an engineer's go-to source for fast, verified answers and design help — straight
from the experts. Search existing answers or ask your own question to get the quick design help you need.
Linked content is provided "AS IS" by the respective contributors. They do not constitute TI specifications and do
not necessarily reflect TI's views; see TI's Terms of Use.
12.4 Trademarks
PowerPAD™ and TI E2E™ are trademarks of Texas Instruments.
All trademarks are the property of their respective owners.
12.5 Glossary
TI Glossary
This glossary lists and explains terms, acronyms, and definitions.
12.6 Electrostatic Discharge Caution
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled
with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may
be more susceptible to damage because very small parametric changes could cause the device not to meet its published
specifications.
13 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.
46
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Copyright © 2021 Texas Instruments Incorporated
Product Folder Links: LM63615-Q1 LM63625-Q1
PACKAGE OPTION ADDENDUM
www.ti.com
5-Feb-2021
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LM63615DQDRRRQ1
ACTIVE
WSON
DRR
12
3000
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 150
L63615
LM63615DQPWPRQ1
ACTIVE
HTSSOP
PWP
16
2000
RoHS & Green
NIPDAU
Level-3-260C-168 HR
-40 to 150
63615DQ
LM63625DQDRRRQ1
ACTIVE
WSON
DRR
12
3000
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 150
L63625
LM63625DQPWPRQ1
ACTIVE
HTSSOP
PWP
16
2000
RoHS & Green
NIPDAU
Level-3-260C-168 HR
-40 to 150
63625DQ
LM63635DQDRRRQ1
ACTIVE
WSON
DRR
12
3000
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 150
L63635
LM63635DQPWPRQ1
ACTIVE
HTSSOP
PWP
16
2000
RoHS & Green
NIPDAU
Level-3-260C-168 HR
-40 to 150
63635DQ
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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