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LM5160-Q1
SNVSAE4C – JULY 2015 – REVISED OCTOBER 2018
LM5160-Q1 Wide Input 65-V, 2-A Synchronous Buck / Fly-Buck™ DC/DC Converter
1 Features
2 Applications
•
•
•
•
1
•
•
•
•
•
•
•
•
•
•
•
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AEC-Q100 Qualified for Automotive Applications
– Temperature Grade 1: –40°C ≤ TA ≤ 125°C
– HBM ESD Classification Level 2
– CDM ESD Classification Level C5
Wide 4.5-V to 65-V Input Voltage Range
Integrated High-Side and Low-Side Switches
– No External Schottky Diode Required
2-A Maximum Load Current
Meets CISPR 25 EMI Standard
Adaptive Constant On-Time Control
– No External Loop Compensation
– Fast Transient Response
Selectable Forced PWM or DCM Operation
– FPWM Supports Multi-Output Fly-Buck™
Nearly Constant Switching Frequency
– Resistor Adjustable up to 1 MHz
Programmable Soft-Start Time
Prebiased Start-Up
±1% Feedback Voltage Reference
Inherent Protection Features for Robust Design
– Peak Current Limiting Protection
– Adjustable Input UVLO and Hysteresis
– VCC and Gate Drive UVLO Protection
– Thermal Shutdown Protection With Hysteresis
14-Pin HTSSOP Package, 0.65-mm Pitch
Create a Custom Design Using the LM5160-Q1
With the WEBENCH® Power Designer
Automotive DC/DC Converter
IGBT Gate Drive Bias Supply
Low-Power Isolated DC/DC (Fly-Buck)
3 Description
The LM5160-Q1 is a 65-V, 2-A synchronous stepdown converter with integrated high-side and low-side
MOSFETs. The adaptive constant on-time control
scheme requires no loop compensation and supports
high step-down ratios with fast transient response. An
internal feedback amplifier maintains ±1% output
voltage regulation over the entire operating
temperature range. The on-time varies inversely with
input voltage resulting in nearly constant switching
frequency.
Peak and valley current limit circuits protect against
overload conditions. The undervoltage lockout
(EN/UVLO) circuit provides independently adjustable
input undervoltage threshold and hysteresis. The
LM5160-Q1 is programmed through the FPWM pin to
operate in continuous conduction mode (CCM) from
no load to full load or to automatically switch to
discontinuous conduction mode (DCM) at light load
for higher efficiency. Forced CCM operation supports
multiple-output and isolated Fly-Buck applications
using a coupled inductor.
The LM5160-Q1 is qualified to automotive AEC-Q100
grade 1 and is available in 14-pin HTSSOP package
with 0.65-mm pin pitch.
Device Information(1)
PART NUMBER
LM5160-Q1
PACKAGE
BODY SIZE (NOM)
HTSSOP (14)
4.40 mm × 5.00 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Typical Synchronous Buck Application Circuit
Typical Fly-Buck Application Circuit
VIN
VIN
VOUT(SEC)
BST
VOUT
LM5160-Q1
VIN
VIN
BST
SW
LM5160-Q1
RON
SW
RON
EN/UVLO
VCC
SS
AGND
VOUT(PRI)
FB
EN/UVLO
VCC
FPWM
PGND
FB
SS
AGND
FPWM
PGND
1
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.
LM5160-Q1
SNVSAE4C – JULY 2015 – REVISED OCTOBER 2018
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Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
4
6.1
6.2
6.3
6.4
6.5
6.6
6.7
4
4
4
5
5
6
7
Absolute Maximum Ratings .....................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Switching Characteristics ..........................................
Typical Characteristics .............................................
Detailed Description ............................................ 10
7.1
7.2
7.3
7.4
Overview ................................................................
Functional Block Diagram .......................................
Feature Description ................................................
Device Functional Modes .......................................
10
10
11
14
8
Application and Implementation ........................ 15
8.1 Application Information............................................ 15
8.2 Typical Applications ................................................ 16
8.3 Do's and Don'ts ...................................................... 24
9 Power Supply Recommendations...................... 25
10 Layout................................................................... 26
10.1 Layout Guidelines ................................................ 26
10.2 Layout Example ................................................... 26
11 Device and Documentation Support ................. 27
11.1
11.2
11.3
11.4
11.5
11.6
11.7
Device Support......................................................
Documentation Support ........................................
Receiving Notification of Documentation Updates
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
27
27
28
28
28
28
29
12 Mechanical, Packaging, and Orderable
Information ........................................................... 29
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision B (November 2017) to Revision C
Page
•
Changed Features ................................................................................................................................................................. 1
•
Changed front page schematics............................................................................................................................................. 1
•
Changed Pinout Drawing........................................................................................................................................................ 3
•
Changed ESD Ratings ........................................................................................................................................................... 4
•
Changed Function Block Diagram........................................................................................................................................ 10
•
Changed Power Supply Recommendations......................................................................................................................... 25
•
Changed Related Documentation ....................................................................................................................................... 27
Changes from Revision A (November 2015) to Revision B
Page
•
Updated AEC-Q100 qualified bullet points ............................................................................................................................. 1
•
Deleted the lead temperature from the Absolute Maximum Ratings table ............................................................................ 4
•
Moved the Ripple Configuration section to the Application Information section .................................................................. 15
•
Changed the Application Performance Plots title to Application Curves in both typical application sections ...................... 20
•
Added layout details with LM5160-Q1 HTSSOP-14 package ............................................................................................. 26
•
Changed the Electrostatic Discharge Caution statement..................................................................................................... 28
Changes from Original (July 2015) to Revision A
•
2
Page
Changed current limit off-timer in the Electrical Characteristics to 16.................................................................................... 5
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SNVSAE4C – JULY 2015 – REVISED OCTOBER 2018
5 Pin Configuration and Functions
PWP PowerPAD™ Package
14-Pin HTSSOP
Top View
AGND
1
14
NC
PGND
2
13
SW
VIN
3
12
SW
EN/UVLO
4
11
BST
10
VCC
LM5160-Q1
THERMAL
PAD
RON
5
SS
6
9
FB
NC
7
8
FPWM
Pin Functions
PIN
I/O (1)
DESCRIPTION
NO.
NAME
1
AGND
—
Analog Ground. Ground connection of internal control circuits.
2
PGND
P
Power Ground. Ground connection of the internal synchronous rectifier FET.
3
VIN
P
Input supply connection. Operating input range is 4.5 V to 65 V.
4
EN/UVLO
I
Precision enable. Input pin of undervoltage lockout (UVLO) comparator.
5
RON
I
On-time programming pin. A resistor between this pin and VIN sets the switch on-time as a function of
input voltage.
6
SS
I
Soft-start. Connect a capacitor from SS to AGND to control output rise time and limit overshoot.
8
FPWM
I
Forced PWM logic input pin. Connect to AGND for discontinuous conduction mode (DCM) with light
loads. Connect to VCC for continuous conduction mode (CCM) at all loads and Fly-Buck configuration.
9
FB
I
Feedback input of voltage regulation comparator.
10
VCC
O
Internal high voltage start-up regulator bypass capacitor pin.
11
BST
P
Bootstrap capacitor pin. Connect a capacitor between BST and SW to bias gate driver of high-side buck
FET.
12,13
SW
P
Switch node. Source connection of high-side buck FET and drain connection of low-side synchronous
rectifier FET.
7,14
NC
—
No Connection.
—
EP
—
Exposed Pad. Connect to AGND and printed-circuit board ground plane to improve power dissipation.
(1)
P = Power, G = Ground, I = Input, O = Output.
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6 Specifications
6.1 Absolute Maximum Ratings
Over the recommended operating junction temperature of –40°C to 150°C (unless otherwise noted). (1) (2)
Input voltages
MIN
MAX
VIN to AGND
–0.3
70
EN/UVLO to AGND
–0.3
70
RON to AGND
–0.3
70
BST to AGND
–0.3
84
VCC to AGND
–0.3
14
FPWM to AGND
–0.3
14
SS to AGND
–0.3
7
FB to AGND
–0.3
7
BST to SW
–0.3
14
BST to VCC
Output voltages
UNIT
V
70
SW to AGND
–1.5
SW to AGND (20-ns transient)
V
70
–3
Operating junction temperature, TJ (3)
–40
150
°C
Storage temperature, Tstg
–65
150
°C
(1)
(2)
(3)
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.
If Military/Aerospace specified devices are required, contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
High junction temperatures degrade operating lifetimes. Operating lifetime is derated for junction temperatures greater than 125°C.
6.2 ESD Ratings
VALUE
V(ESD)
(1)
Electrostatic
discharge
Human-body model (HBM), per AEC Q100-002 (1)
Charged-device model (CDM), per AEC Q100-011
UNIT
±2000
All pins
V
±750
AEC Q100-002 indicates HBM stressing is done in accordance with the ANSI/ESDA/JEDEC JS-001 specification.
6.3 Recommended Operating Conditions
Over the recommended operating junction temperature of –40°C to 150°C (unless otherwise noted). (1)
VIN input voltage
MIN
MAX
4.5
65
IOUT output current
Operating junction temperature
(1)
4
-40
UNIT
V
2
A
150
°C
Recommended Operating Ratings are conditions under the device is intended to be functional. For specifications and test conditions,
see Electrical Characteristics.
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6.4 Thermal Information
LM5160-Q1
THERMAL METRIC (1)
PWP (HTSSOP)
UNIT
14 PINS
RθJA
Junction-to-ambient thermal resistance
39.3
°C/W
RθJCbot
ψJB
Junction-to-case (bottom) thermal resistance
2.0
°C/W
Junction-to-board thermal characteristic parameter
19.3
°C/W
RθJB
Junction-to-board thermal resistance
19.6
°C/W
RθJCtop
Junction-to-case (top) thermal resistance
22.8
°C/W
ψJT
Junction-to-top thermal characteristic parameter
0.5
°C/W
(1)
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics report.
6.5 Electrical Characteristics
Typical values correspond to TJ = 25°C. Minimum and maximum limits apply over TJ = –40°C to 125°C. Unless otherwise
stated, VIN = 24 V. (1) (2)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
SUPPLY CURRENT
ISD
Input shutdown current
VIN = 24 V, VEN/UVLO = 0 V
50
90.7
µA
IOP
Input operating current
VIN = 24 V, VFB = 3 V, non-switching
2.3
2.84
mA
VCC
Bias regulator output
VIN = 24 V, ICC = 20 mA
7.5
8.52
VCC
Bias regulator current limit
VIN = 24 V
VCC(UV)
VCC undervoltage threshold
VVCC rising
3.98
VCC(HYS)
VCC undervoltage hysteresis
VVCC falling
185
VCC(LDO)
VIN – VCC dropout voltage
VIN = 4.5 V, IVCC = 20 mA
165
VCC SUPPLY
6.47
30
V
mA
4.1
V
mV
260
mV
HIGH-SIDE FET
RDS(ON)
High-side on-state resistance
VBST – VSW = 7 V, ISW = 1 A
0.29
BST(UV)
Bootstrap gate drive UV
VBST – VSW rising
2.93
BST(HYS)
Gate drive UV hysteresis
VBST – VSW falling
200
mV
ISW = 1 A
0.13
Ω
Ω
3.6
V
LOW-SIDE FET
RDS(ON)
Low-side on-state resistance
HIGH-SIDE CURRENT LIMIT
ILIM
(HS)
High-side current limit threshold
2.125
2.875
100
A
Current limit response time
ILIM
TOFF1
Current limit forced off-time
VFB = 0 V, VIN = 65 V
16
29
39.8
µs
TOFF2
Current limit forced off-time
VFB = 1 V, VIN = 24 V
2.18
3.5
5.12
µs
1.9
2.5
3
A
(HS)
threshold detect to FET turnoff
2.5
TRES
ns
LOW-SIDE CURRENT LIMIT
ISOURCE(LS)
Sourcing current limit
ISINK(LS)
Sinking current limit
5.4
A
DIODE EMULATION
VFPWM(LOW)
FPWM input logic low
VIN = 24 V
VFPWM(HIGH)
FPWM input logic high
VIN = 24 V
IZX
Zero cross detect current
FPWM = AGND (diode emulation)
1
3
V
V
0
mA
REGULATION COMPARATOR
VREF
FB regulation level
VIN = 24 V
I(Bias)
FB input bias current
VIN = 24 V
(1)
(2)
1.975
1.995
2.015
V
100
nA
All minimum and maximum limits are specified by correlating the electrical characteristics to process and temperature variations and
applying statistical process control.
The junction temperature (TJ in °C) is calculated from the ambient temperature (TA in °C) and power dissipation (PD in Watts) as follows:
TJ = TA + (PD • RθJA) where RθJA (in °C/W) is the package thermal impedance provided in Thermal Information.
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Electrical Characteristics (continued)
Typical values correspond to TJ = 25°C. Minimum and maximum limits apply over TJ = –40°C to 125°C. Unless otherwise
stated, VIN = 24 V.(1)(2)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
ERROR CORRECTION AMPLIFIER and SOFT START
GM
Error amp transconductance
VFB = VREF ± 10 mV
IEA(Source)
Error amp source current
VFB = 1 V, VSS = 1 V
7.62
10.2
105
12.51
µA/V
µA
IEA(Sink)
Error amp sink current
VFB = 5 V, VSS = 2.25 V
7.46
10
12.2
µA
V(SS-FB)
VSS – VFB clamp voltage
VFB = 1.75 V, CSS= 1 nF
ISS
Soft-start charging current
VSS = 0.5 V
7.63
10.2
12.5
µA
1.213
1.24
1.277
V
15
20
25
µA
0.28
0.35
135
mV
ENABLE/UVLO
VUVLO (TH)
UVLO threshold
VEN/UVLO rising
IUVLO(HYS)
UVLO hysteresis current
VEN/UVLO = 1.4 V
VSD(TH)
Shutdown mode threshold
VEN/UVLO falling
VSD(HYS)
Shutdown threshold hysteresis
VEN/UVLO rising
V
47
mV
THERMAL SHUTDOWN
TSD
Thermal shutdown threshold
175
°C
TSD(HYS)
Thermal shutdown hysteresis
20
°C
6.6 Switching Characteristics
Typical values correspond to TJ = 25°C. Minimum and maximum limits apply over TJ = –40°C to 125°C. Unless otherwise
stated, VIN = 24 V. (1)
MIN
TYP
MAX
UNIT
MINIMUM OFF-TIME
TOFF-MIN
Minimum off-time, VFB = 0 V
170
ns
ON-TIME GENERATOR
TON1
VIN = 24 V, RON = 100 kΩ
312
428
520
ns
TON2
VIN = 24 V, RON = 200 kΩ
625
818
1040
ns
TON3
VIN = 8 V, RON = 100 kΩ
937
1247
1563
ns
TON4
VIN = 65 V, RON = 100 kΩ
132
176
220
ns
(1)
6
All minimum and maximum limits are specified by correlating the electrical characteristics to process and temperature variations and
applying statistical process control.
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6.7 Typical Characteristics
100
100
90
90
80
80
Efficiency (%)
Efficiency (%)
TA = 25°C, unless otherwise noted. Please refer to Typical Applications for circuit designs.
70
60
50
40
70
60
50
40
Vin = 18V
Vin = 24V
Vin = 48V
30
Vin = 12V
Vin = 24V
Vin = 48V
30
20
20
0
0.2
0.4
VOUT = 10 V
L = 47 µH
0.6
0.8
1
Load Current (A)
1.2
1.4
1.6
0
RON = 200 kΩ
0.2
0.4
0.6
0.8
1
Load Current (A)
VOUT = 5 V
L = 100 µH
Figure 1. Efficiency at 500 kHz
1.2
1.4
1.6
RON = 215 kΩ
Figure 2. Efficiency at 250 kHz
100
100
FPWM = 0
50
Efficiency (%)
Efficiency (%)
90
FPWM = 1
80
70
IO = 0.5A
IO = 1A
IO = 1.5A
Vin = 12V
Vin = 24V
Vin = 48V
20
0.005
60
0.01
0.05
0.1
Load Current (A)
VOUT = 5 V
L = 47 µH
0.5
5
1 1.5
RON = 169 kΩ
15
25
VOUT = 5 V
L = 47 µH
Figure 3. Efficiency CCM vs DCM at 300 kHz
35
45
Input Voltage (V)
55
65
RON = 169 kΩ
Figure 4. Efficiency vs Input Voltage at 300 kHz
8
8
7
6
Vcc Voltage (V)
Vcc Voltage (V)
6
4
5
4
3
2
2
1
0
0
0
2
4
6
8
Input Voltage (V)
10
12
14
0
0.01
0.02
0.03
0.04
Icc Current (A)
0.05
0.06
VIN = 24 V
Figure 5. VCC vs VIN
Figure 6. VCC vs ICC
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Typical Characteristics (continued)
TA = 25°C, unless otherwise noted. Please refer to Typical Applications for circuit designs.
2000
Vin = 12V
Vin = 24V
Vin = 48V
Vin = 65V
25
22.5
20
1000
On - Time (ns)
Peak Current LImit Off-Timer (Ps)
27.5
17.5
15
12.5
10
500
7.5
100
5
Ron = 200k:
Ron = 169k:
Ron = 100k:
2.5
0
0
0.2
0.4
0.6 0.8
1
1.2 1.4
Feedback Voltage (V)
1.6
1.8
50
10
2
15
20
25
30
35
40
Input Voltage (V)
45
50
55
60
VOUT = 5 V
Figure 8. TON vs VIN
4
650
3.5
Operating Current (mA)
Switching Frequency (kHz)
Figure 7. TOFF (ILIM) vs VFB
750
550
450
350
250
Ron = 169k:
Ron = 100k:
Ron = 200k:
150
50
10
15
20
25
30
35
40
Input Voltage (V)
45
50
55
3
2.5
2
1.5
1
10
60
15
20
25
VOUT = 5 V
50
55
60
Figure 10. IIN vs VIN (Operating, Non-Switching)
4
2.05
3.25
2.025
Reference Voltage (V)
Gate Drive UVLO Threshold (V)
45
VFB = 3 V
Figure 9. Switching Frequency vs VIN
2.5
1.75
2
1.975
Falling
Rising
1
-50
-25
0
25
50
75
100
Junction Temperature (oC)
125
150
1.95
-50
VIN = 24 V
-25
0
25
50
75
100
Junction Temperature (oC)
125
150
VIN = 24 V
Figure 11. Gate Drive UVLO vs Temperature
8
30
35
40
Input Voltage (V)
Figure 12. Reference Voltage vs Temperature
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Typical Characteristics (continued)
TA = 25°C, unless otherwise noted. Please refer to Typical Applications for circuit designs.
60
Input Shutdown Current (PA)
Input Operating Current (mA)
2.5
2.25
2
1.75
1.5
-50
-25
0
25
50
75
100
Junction Temperature (oC)
125
55
50
45
40
35
30
-50
150
-25
0
VIN = 24 V
Figure 13. Input Operating Current vs Temperature
150
Figure 14. Input Shutdown Current vs Temperature
3
4.1
Current Limit (A)
2.75
3.95
3.8
2.5
2.25
3.65
Falling
Rising
3.5
-50
-25
0
25
50
75
100
Junction Temperature (oC)
125
High Side FET
Low Side FET
2
-50
150
-25
0
VIN = 24 V
125
150
Figure 16. Current Limit vs Temperature
0.45
2.5
0.35
FET RDSON
3
2
0.25
0.15
1.5
Rising
Falling
1
-50
25
50
75
100
Junction Temperature (oC)
VIN = 24 V
Figure 15. VCC UVLO vs Temperature
FPWM Threshold (V)
125
VIN = 24 V
4.25
Vcc UVLO Threshold (V)
25
50
75
100
Junction Temperature (oC)
-25
0
25
50
75
100
Junction Temperature (oC)
125
150
High Side FET
Low Side FET
0.05
-50
-25
ISW = 200 mA
VIN = 24 V
Figure 17. FPWM Threshold vs Temperature
0
25
50
75
100
Junction Temperature (oC)
125
150
D001
VIN = 24 V
Figure 18. Switch Resistance vs Temperature
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7 Detailed Description
7.1 Overview
The LM5160-Q1 step-down synchronous switching regulator features all the functions needed to implement a
low-cost, efficient buck converter capable of supplying 2 A to the load. This high voltage regulator contains 65-V
N-channel buck and synchronous rectifier switches and is available in a 14-pin HTSSOP package with 0.65-mm
pin pitch. The regulator operation is based on an adaptive constant on-time control architecture where the ontime is inversely proportional to input voltage VIN. This feature maintains a relatively constant operating frequency
with load and input voltage variations. A constant on-time switching regulator requires no loop compensation
resulting in fast load transient response. Peak current limit detection circuit is implemented with a forced off-time
during current limiting which is inversely proportional to voltage at the feedback pin, VFB and directly proportional
to VIN. Varying the current limit off-time with VFB and VIN ensures short-circuit protection with minimal current limit
foldback. The LM5160-Q1 can be applied in numerous end equipment systems requiring efficient step-down
regulation from higher input voltages. This regulator is well-suited for 24-V industrial systems as well as 48-V
telecom and PoE voltage ranges. The LM5160-Q1 integrates an undervoltage lockout (EN/UVLO) circuit to
prevent faulty operation of the device at low input voltages and features intelligent current limit and thermal
shutdown to protect the device during overload or short circuit.
7.2 Functional Block Diagram
LM5160-Q1
VIN
VIN
VCC
REGULATOR
RUV2
CIN
VCC UVLO
20µA
CVCC
EN/UVLO
STANDBY
THERMAL
SHUTDOWN
VIN
RUV1
VCC
1.24V
SHUTDOWN
BST
BIAS
REGULATOR
0.35V
RON
VIN
RON
VOUT
ON/OFF
TIMERS
SS
FEEDBACK
COMPARATOR
CSS
CBST
DISABLE
COT
CONTROL
LOGIC
L
SW
VCC
VOUT
RESR
RFB2
FB
2V
RFB1
AGND
GM
ERROR
AMP
PGND
CURRENT
LIMIT TIMER
COUT
CURRENT LIMIT
COMPARATOR
+
VILIM
FPWM
DIODE
EMULATION
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7.3 Feature Description
7.3.1 Control Circuit
The LM5160-Q1 step-down switching regulator employs a control principle based on a comparator and a oneshot timer, with the output voltage feedback (FB) compared to the voltage at the soft-start (SS) pin (VSS). If the
FB voltage is below VSS, the internal buck switch is turned on for a conduction time determined by the input
voltage and the one-shot programming resistor (RON). Following the on-time, the buck switch must stay off for the
off-time forced by the minimum off-time one-shot. The buck switch remains off until the FB voltage falls below the
SS voltage again, when it turns back on for another on-time interval.
During a rapid start-up or when the load current increases suddenly, the regulator operates with minimum offtime per cycle. When regulating the output in steady-state operation, the off-time automatically adjusts to
produce the SW voltage duty cycle required for output voltage regulation.
When in regulation, the LM5160-Q1 operates in continuous conduction mode at heavy load currents. If FPWM is
connected to ground or left floating, the regulator operates in discontinuous conduction mode at light load with
the synchronous rectifier FET in diode emulation. With sufficient load, the LM5160-Q1 operates in continuous
conduction mode with the inductor current never reaching zero during the off-time of the high-side FET. In this
mode the operating frequency remains relatively constant with load and line variations. The minimum load
current for continuous conduction mode is one-half the inductor’s ripple current amplitude. The operating
frequency is programmed by the resistor connected from VIN to RON and can be calculated from Equation 1
with RON expressed in Ohms.
VOUT
Fsw
Hz
RON u 1u 10 10
(1)
In discontinuous conduction mode, current through the inductor ramps up from zero to a peak value during the
on-time, then ramps back to zero before the end of the off-time. The next on-time interval starts when the voltage
at FB falls below VSS. When the inductor current is zero during the high-side FET off-time, the load current is
supplied by the output capacitor. In this mode, the operating switching frequency is lower than the continuous
conduction mode switching frequency and the frequency varies with load. Discontinuous conduction mode
maintains conversion efficiency at light loads because the switching losses reduce with the decrease in load and
frequency.
The output voltage is set by two external resistors (RFB1, RFB2). Calculate the regulated output voltage from
Equation 2.
VREF u (RFB2 RFB1 )
VOUT
V
RFB1
where
•
VREF = 2 V (typical) is the feedback reference voltage.
(2)
7.3.2 VCC Regulator
The LM5160-Q1 contains an internal high-voltage linear regulator with a nominal output voltage of 7.5 V (typical).
The VCC regulator is internally current limited to 30 mA (minimum). This regulator supplies power to internal
circuit blocks including the synchronous FET gate driver and the logic circuits. When the VCC voltage reaches
the undervoltage lockout (VCC(UV)) threshold of 3.98 V (typical), the IC is enabled. An external capacitor at the
VCC pin stabilizes the regulator and supplies transient VCC current to the gate drivers. An internal diode
connected from VCC to BST replenishes the charge in the high-side gate drive bootstrap capacitor when the SW
voltage is low.
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Feature Description (continued)
7.3.3 Regulation Comparator
The feedback voltage at the FB pin is compared to the SS pin voltage VSS. In normal operation when the output
voltage is in regulation, an on-time interval is initiated when the voltage at FB pin falls below VSS. The high-side
buck switch stays on for a pre-defined on-time causing the FB voltage to rise. After the on-time interval expires,
the high-side switch remains off until the FB voltage falls below VSS. During start-up, the FB voltage is below VSS
at the end of each on-time interval and the high-side switch turns on again after the minimum forced off-time of
170 ns (typical). When the output is shorted to ground (VFB = 0 V), the high-side peak current limit is triggered,
the high-side FET is turned off and remains off for a period determined by the current limit off-timer. See Current
Limit for additional information.
7.3.4 Soft Start
The soft-start feature of the LM5160-Q1 allows the converter to gradually reach a steady-state operating point,
thereby reducing start-up stresses and current surges. When the EN/UVLO voltage is above the EN/UVLO
standby threshold VUVLO(TH) = 1.24 V (typical) and the VCC voltage exceeds the VCC undervoltage threshold,
VCC(UV) = 3.98 V (typical) , an internal 10-µA current source charges the external capacitor at the SS pin (CSS)
from 0 V to 2 V. The voltage at SS is the noninverting input of the internal FB comparator. The soft-start interval
ends when the SS capacitor is charged to the 2-V reference level. The ramping voltage at SS produces a
controlled, monotonic output voltage start-up. Use a minimum soft-start capacitance of 1 nF for all applications.
7.3.5 Error Amplifier
The LM5160-Q1 provides a transconductance (GM) error amplifier that minimizes the difference between the
reference voltage (VREF) and the average feedback (FB) voltage. This amplifier reduces the load and line
regulation errors that are common in constant on-time regulators. The soft-start capacitor CSS provides
compensation for this error correction loop. The soft-start capacitor must be greater than 1 nF to ensure stability.
7.3.6 On-Time Generator
The on-time of the LM5160-Q1 high-side MOSFET is determined by the RON resistor and is inversely
proportional to the input voltage (VIN). The inverse relationship with VIN results in a nearly constant frequency as
VIN is varied. Calculate the on-time from Equation 3 with RON expressed in Ohms.
TON
RON u 1u 10
VIN
10
s
(3)
To set a specific continuous conduction mode switching frequency (FSW expressed in Hz), determine the RON
resistor from Equation 4.
VOUT
:
RON
FSW u 1u 10 10
(4)
RON must be selected for a minimum on-time (at maximum VIN) greater than 150 ns for proper operation. This
minimum on-time requirement limits the maximum switching frequency of applications with relatively high VIN and
low VOUT.
7.3.7 Current Limit
The LM5160-Q1 provides an intelligent current limit off-timer that adjusts the off-time to reduce the foldback in
the current limit. If the peak value of the current in the buck switch exceeds 2.5 A (typical), the present on-time
interval is immediately terminated and a non-resettable off-timer is initiated. The length of the off-time is
controlled by the FB voltage and the input voltage VIN. As an example, when VFB = 0 V and VIN = 24 V, the offtime is set to 10 µs. This condition occurs if the output is shorted or during the initial phase of start-up. In cases
of output overload where the FB voltage is greater than zero volts (a soft short), the current limit off-time is
reduced. Decreasing the off-time during less severe overloads reduces the current limit foldback, overload
recovery time, and start-up time. Calculate the current limit off-time using Equation 5.
5VIN
TOFF(CL)
Ps
24VFB 12
(5)
12
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Feature Description (continued)
7.3.8 N-Channel Buck Switch and Driver
The LM5160-Q1 integrates an N-channel buck switch and associated floating high-side gate driver. The gate
driver circuit works in conjunction with an external bootstrap capacitor and an internal high voltage bootstrap
diode. A 10-nF or larger ceramic capacitor connected between BST and SW provides the voltage to the high-side
driver during the buck switch on-time. During the off-time, the SW node is pulled down to approximately 0 V and
the bootstrap capacitor charges from VCC through the internal bootstrap diode. The minimum off-time of 170 ns
(typical) provides a minimum time each cycle to recharge the bootstrap capacitor.
7.3.9 Synchronous Rectifier
The LM5160-Q1 provides an internal low-side synchronous rectifier N-channel FET. This low-side FET provides
a low resistance path for the inductor current when the high-side FET is turned off.
With the FPWM pin connected to ground or left floating, the LM5160-Q1 synchronous rectifier operates in diode
emulation mode. Diode emulation enables the pulse-skipping during light load conditions. This leads to a
reduction in the average switching frequency at light loads. Switching losses and FET gate driver losses, both of
which are proportional to switching frequency, are significantly reduced and efficiency is improved. This pulseskipping mode also reduces the circulating inductor currents and losses associated with a continuous conduction
mode (CCM).
When FPWM is pulled high, diode emulation is disabled. The inductor current can flow in either direction through
the low-side FET, resulting in CCM operation with nearly constant switching frequency. A negative sink current
limit circuit limits the current that can flow into SW and through the low-side FET to ground. In a buck regulator
application, large negative current typically only flows from VOUT to SW if VOUT is lifted above the output
regulation setpoint.
7.3.10 Enable / Undervoltage Lockout (EN/UVLO)
The LM5160-Q1 contains a dual-level undervoltage lockout (EN/UVLO) circuit. When the EN/UVLO voltage is
below 0.35 V, the regulator is in a low-current shutdown mode. When the EN/UVLO voltage is greater than 0.35
V (typical) but less than 1.24 V (typical), the regulator is in standby mode. In standby mode, the VCC bias
regulator is active but converter switching remains disabled. When the voltage at the VCC exceeds the VCC
rising threshold, VCC(UV) = 3.98 V (typical), and the EN/UVLO voltage is greater than 1.24 V, normal switching
operation begins. Use an external resistor voltage divider from VIN to GND to set the minimum operating voltage
of the regulator.
EN/UVLO hysteresis is implemented with an internal 20 µA (typical) current source (IUVLO(HYS)) that is switched
on or off into the impedance of the EN/UVLO pin resistor divider. When the EN/UVLO threshold is exceeded, the
current source is activated to effectively raise the voltage at the EN/UVLO pin. The hysteresis is equal to the
value of this current times the upper resistance of the resistor divider, RUV2. See Functional Block Diagram.
7.3.11 Thermal Protection
The LM5160-Q1 must be operated such that the junction temperature does not exceed 150°C during normal
operation. An internal thermal shutdown circuit is provided to protect the LM5160-Q1 in the event of higher than
normal junction temperature. When activated, typically at 175°C, the controller is forced into a low-power reset
state, disabling the high-side buck switch and the VCC regulator. This feature prevents catastrophic failures from
accidental device overheating. When the junction temperature falls below 155°C (typical hysteresis of 20°C), the
VCC regulator is enabled and operation resumes.
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7.4 Device Functional Modes
7.4.1 Forced Pulse Width Modulation (FPWM) Mode
The Synchronous Rectifier section gives a brief introduction to the LM5160-Q1 diode emulation feature. The
FPWM pin allows the power supply designer to select either CCM or DCM operation at light loads. When FPWM
is connected to ground or left floating (FPWM = 0), a pulse-skipping mode and a zero-cross current detector
circuit are enabled. The zero-cross detector turns off the low-side FET when the inductor current falls to zero (IZX,
see Electrical Characteristics). This feature allows the LM5160-Q1 regulator to operate in DCM mode at light
loads. In the DCM state, the switching frequency decreases with lighter loads.
If FPWM is pulled high (FPWM connected to VCC), the LM5160-Q1 operates in CCM even at light loads. This
option allows the synchronous rectifier FET to conduct until the start of the next high-side switch cycle. The
inductor current drops to zero and then reverse direction (negative direction through inductor), passing from drain
to source of the low-side FET. The current flows continuously until the FB comparator initiates another high-side
switch on-time. CCM operation reduces efficiency at light load but improves the transient response to step load
changes and provides nearly constant switching frequency.
Table 1. FPWM Pin Mode Summary
FPWM PIN CONNECTION
LOGIC STAGE
DESCRIPTION
GND or Floating (High Z)
0
The FPWM pin is grounded or left floating. DCM enabled at light
loads.
VCC
1
The FPWM pin is connected to VCC. The LM5160-Q1 then
operates in CCM mode at light loads.
7.4.2 Undervoltage Detector
The following table summarizes the dual threshold levels of the undervoltage lockout (EN/UVLO) circuit
explained in Enable / Undervoltage Lockout (EN/UVLO).
Table 2. UVLO Pin Mode Summary
EN/UVLO PIN
VOLTAGE
VCC REGULATOR
MODE
< 0.35 V
Off
Shutdown
VCC regulator disabled. High-side and lowside FETs disabled.
0.35 V to 1.24 V
On
Standby
VCC regulator enabled. High-side and lowside FETs disabled.
VCC < VCC(UV)
Standby
VCC regulator enabled. High-side and lowside FETs disabled.
VCC > VCC(UV)
Operating
VCC regulator enabled. Switching enabled.
> 1.24 V
DESCRIPTION
If input UVLO is not required, EN/UVLO can be driven by a logic signal as an enable input or connected directly
to VIN. If EN/UVLO is directly connected to VIN, the regulator begins switching when VCC(UV) = 3.98 V (typical) is
satisfied.
14
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8 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. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
The LM5160-Q1 is a synchronous buck or Fly-Buck DC/DC converter designed to operate over wide input
voltage and output current ranges. LM5160-Q1 quick-start calculator tools are available for download to design a
single-output synchronous buck converter or an isolated dual-output Fly-Buck converter. For a detailed design
guide of the Fly-Buck converter, refer to AN-2292 Designing an Isolated Buck (Fly-Buck) Converter application
report (SNVA674). Alternatively, use online WEBENCH software to create a complete buck or Fly-Buck design
and generate the bill of materials, estimated efficiency, solution size and cost of the complete solution.
Typical Applications describes a few application circuits using the LM5160-Q1 with detailed, step-by-step design
procedures.
8.1.1 Ripple Configuration
The LM5160-Q1 uses an adaptive constant on-time (COT) control scheme in which the PWM on-time is set by a
one-shot timer and the off-time is set by the feedback voltage (VFB) falling below the reference voltage.
Therefore, for stable operation, the feedback voltage must decrease monotonically in phase with the inductor
current during the off-time. Furthermore, this change in feedback voltage (VFB) during the off-time must be large
enough to dominate any noise present at the feedback node.
Table 3 presents three different methods for generating appropriate voltage ripple at the feedback node. Type 1
and Type 2 ripple circuits couple the ripple from the output of the converter to the feedback node (FB). The
output voltage ripple has two components:
1. Capacitive ripple caused by the inductor ripple current charging or discharging the output capacitor.
2. Resistive ripple caused by the inductor ripple current flowing through the ESR of the output capacitor and
R3.
Table 3. Ripple Configurations
TYPE 1
TYPE 2
TYPE 3
Lowest Cost
Reduced Ripple
Minimum Ripple
VOUT
VOUT
L1
VOUT
L1
L1
R FB2
Cff
R FB2
R3
To FB
RA
R3
R FB1
GND
R FB1
GND
25 mV u VO
R3 t
VREF u 'IL1, min
COUT
R FB2
CB
To FB
C OUT
CA
C OUT
To FB
R FB1
GND
Cff t
5
FSW u (RFB2 IIRFB1 )
R A CA d
(6) R t 25 mV
3
'IL1, min
(VIN, min
VO ) u TON(@ VIN, min )
25mV
(8)
(7)
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The capacitive ripple is out-of-phase with the inductor current. As a result, the capacitive ripple does not
decrease monotonically during the off-time. The resistive ripple is in phase with the inductor current and
decreases monotonically during the off-time. The resistive ripple must exceed the capacitive ripple at output
(VOUT) for stable operation. If this condition is not satisfied, unstable switching behavior is observed in COT
converters with multiple on-time bursts in close succession followed by a long off-time.
Type 3 ripple method uses a ripple injection circuit with RA, CA and the switch-node (SW) voltage to generate a
triangular ramp. This ramp is then AC-coupled into the feedback node (FB) using coupling capacitor CB. Because
this circuit does not use the output voltage ripple, it is suited for applications where low output voltage ripple is
imperative. For more information on each ripple generation method, refer to the AN-1481 Controlling Output
Ripple & Achiev ESR Indep Constant On-Time Regulator Designs application note.
8.2 Typical Applications
For step-by-step design procedure, circuit schematics, bill of materials, PCB files, simulation and test results of
an LM5160-powered implementation, refer to Wide-Input Isolated IGBT Gate-Drive Fly-Buck Power Supply for
Three-Phase Inverters reference design.
8.2.1 LM5160-Q1 Synchronous Buck (10-V to 60-V Input, 5-V Output, 1.5-A Load)
A typical application example is a synchronous buck converter operating from a wide input voltage range of 10 V
to 65 V and providing a stable 5-V output voltage with output current capability of 1.5 A. Figure 19 shows the
complete schematic for a typical synchronous buck application circuit. The components are labeled by numbers
instead of the descriptive name used in the previous sections. For example, R3 represents RON and so forth.
Figure 19. LM5160-Q1 Synchronous Buck Application Circuit
NOTE
This and subsequent design examples are provided herein to showcase the LM5160-Q1
converter in several different applications. Depending on the source impedance of the
input supply bus, an electrolytic capacitor may be required at the input to ensure stability,
particularly at low input voltage and high output current operating conditions. See Power
Supply Recommendations for more detail.
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8.2.1.1 Design Requirements
Table 4 summarizes the operating parameters:
Table 4. Design Parameters
DESIGN PARAMETER
EXAMPLE VALUE
Input voltage range
10 V to 65 V
Output
5V
Load current
1.5 A
Nominal switching frequency
300 kHz
Light-load operating mode
CCM, FPWM = VCC
8.2.1.2 Detailed Design Procedure
8.2.1.2.1 Custom Design With WEBENCH® Tools
Click here to create a custom design using the LM5160-Q1 device with the WEBENCH® Power Designer.
1. Start by entering the input voltage (VIN), output voltage (VOUT), and output current (IOUT) requirements.
2. Optimize the design for key parameters such as efficiency, footprint, and cost using the optimizer dial.
3. Compare the generated design with other possible solutions from Texas Instruments.
The WEBENCH Power Designer provides a customized schematic along with a list of materials with real-time
pricing and component availability.
In most cases, these actions are available:
• Run electrical simulations to see important waveforms and circuit performance
• Run thermal simulations to understand board thermal performance
• Export customized schematic and layout into popular CAD formats
• Print PDF reports for the design, and share the design with colleagues
Get more information about WEBENCH tools at www.ti.com/WEBENCH.
8.2.1.2.2 Feedback Resistor Divider - RFB1, RFB2
With the required output voltage setpoint at 5 V and VFB = 2 V (typical), calculate the ratio of R6 (RFB1) to R5
(RFB2) using Equation 9.
RFB2 VOUT
1
RFB1 VREF
(9)
The resistor ratio calculates to be 3:2. Choose standard values of R6 (RFB1) = 2 kΩ and R5 (RFB2 ) = 3.01 kΩ.
Higher or lower values can be used as long as a ratio of the 3:2 is maintained.
8.2.1.2.3 Switching Frequency - RON
The duty cycle required to maintain output regulation at the minimum input voltage restricts the maximum
switching frequency of the LM5160-Q1. The maximum value of the minimum forced off-time, TOFF,min, limits the
duty cycle and therefore the switching frequency. Calculate the maximum frequency that avoids output dropout at
minimum input voltage using Equation 10.
VIN, min VOUT
FSW, max (@ VIN, min )
VIN, min u TOFF, min (ns)
(10)
For this design example, the maximum frequency based on the minimum off-time limitation of TOFF,min (typical) =
170 ns is calculated as FSW,max(@VIN,min) = 2.9 MHz. This value is well above 1 MHz, the maximum possible
operating frequency of the LM5160-Q1.
At maximum input voltage the maximum switching frequency of the LM5160-Q1 is restricted by the minimum ontime, TON,min which limits the minimum duty cycle of the converter. Calculate the maximum frequency at
maximum input voltage using Equation 11.
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VOUT
VIN, max u TON, min (ns)
(11)
Using Equation 11 and TON,min (typical) = 150 ns, the maximum achievable switching frequency is
FSW,max(@VIN,min) = 514 kHz. Taking this value as the maximum possible switching frequency over the input
voltage range for this application, choose a nominal switching frequency of FSW = 300 kHz for this design. The
value of resistor RON sets the nominal switching frequency based on Equation 12.
VOUT
:
RON
FSW u 1u 10 10
(12)
For this particular application with FSW = 300 kHz, RON calculates to be 167 kΩ. Selecting a standard value for
R3 (RON) = 169 kΩ (±1%) results in a nominal frequency of 296 kHz. The resistor value may need to adjusted
further in order to achieve the required switching frequency as the switching frequency in COT converters varies
slightly (±10%) with input voltage and/or output current. Operation at a lower nominal switching frequency results
in higher efficiency but increases the inductor and capacitor values leading to a larger total solution size.
8.2.1.2.4 Inductor - L
Select the inductor to limit the inductor ripple current between 20 and 40 percent of the maximum load current.
Calculate the minimum value of the inductance required in this application from Equation 13.
VO u (VIN, max VO )
Lmin
VIN, max u FSW u IO, max u 0.4
(13)
Based on Equation 13, determine the minimum value of the inductance as 26 µH for VIN = 65 V (maximum) and
inductor ripple current equal to 40 percent of the maximum load current. Allowing some margin for inductance
variation with current, select a higher standard value of L1 (L) = 47 µH for this design.
The peak inductor current at maximum load must be smaller than the minimum current limit threshold of the highside FET, as given in Electrical Characteristics table. Determine the inductor ripple current at any input voltage
using Equation 14.
VO u (VIN VO )
'IL
VIN u FSW u L
(14)
Calculate the peak-to-peak inductor ripple current as 180 mA and 332 mA at the minimum and maximum input
voltages, respectively. Determine the maximum peak inductor current in the buck FET using Equation 15.
'IL, max
IL(peak) IO, max
(15)
2
In this design with an output current of 1.5 A, the maximum peak inductor current is calculated to be
approximately 1.67 A, which is less than the high-side FET minimum current limit threshold.
The saturation current of the inductor must also be carefully considered. The peak value of the inductor current is
bound by the high-side FET current limit during overload or short circuit conditions. Based on the high-side FET
current limit specification in Electrical Characteristics, select an inductor with saturation current rating above
2.875 A.
8.2.1.2.5 Output Capacitor - COUT
Select the output capacitor to limit the capacitive ripple at the output of the regulator. Maximum capacitive ripple
is observed at maximum input voltage. The output capacitance required for a ripple voltage ∆VO across the
capacitor is given by Equation 16.
'IL, max
COUT
8 u FSW u 'VO, ripple
(16)
Substituting ∆VO, ripple = 10 mV gives COUT = 14 µF. Two standard 10-µF ceramic capacitors in parallel (C8, C9)
are selected. An X7R type capacitor with a voltage rating 16 V or higher must be used for COUT (C8, C9) to limit
the reduction of capacitance due to DC bias voltage.
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8.2.1.2.6 Series Ripple Resistor - RESR
Select the series resistor such that sufficient ripple is injected at the feedback node (FB). The ripple voltage
produced by RESR is proportional to the inductor ripple current. Therefore, select RESR based on the lowest
inductor ripple current occurring at minimum input voltage. Calculate RESR usingEquation 17.
25 mV u VO
RESR t
VREF u 'IL, min
(17)
With VO = 5 V, VREF = 2 V and ΔIL, min = 180 mA (at VIN, min= 10 V) as calculated in Equation 14, Equation 17
requires an RESR greater than or equal to 0.35 Ω. Selecting R7 (RESR) = 0.47 Ω results in approximately 150 mV
of maximum output voltage ripple at VIN,max. For applications requiring lower output voltage ripple, use Type II or
Type III ripple injection circuits as described in Ripple Configuration.
8.2.1.2.7 VCC and Bootstrap Capacitors - CVCC, CBST
The VCC capacitor charges the bootstrap capacitor during the off-time of the high-side switch and powers
internal logic circuits and the low-side sync FET gate driver. The bootstrap capacitor biases the high-side gate
driver during the high-side FET on-time. Recommended values for C5 (CVCC) and C4 (CBST) are 1 µF and 10 nF,
respectively. Both must be high-quality X7R ceramic capacitors.
8.2.1.2.8 Input Capacitor - CIN
The input capacitor must be large enough to limit the input voltage ripple to an acceptable level. Equation 18
provides the input capacitance CIN required for a worst-case input ripple of ∆VIN, ripple.
IO, max u D u (1 D)
CIN
'VIN, ripple u FSW
(18)
CIN (C1, C10) supplies most of the switch current during the on-time to limit the voltage ripple at the VIN pin. At
maximum load current, when the buck switch turns on, the current into the VIN pin quickly increases to the valley
current of the inductor ripple and then ramps up to the peak of the inductor ripple during the on-time of the highside FET. The average current during the on-time is the output load current. For a worst-case calculation, CIN
must supply this average load current during the maximum on-time, without letting the voltage at VIN drop more
than the desired input ripple. For this design, the input voltage drop is limited to 0.5 V and the value of CIN is
calculated using Equation 18.
Based on Equation 18, the value of the input capacitor is determined as approximately 2.5 µF at D = 0.5. Taking
into account the decrease in capacitance with applied voltage, two standard value 2.2-µF, 100-V, X7R ceramic
capacitors are selected for C1 and C10. The input capacitors must be rated for the maximum input voltage under
all operating and transient conditions.
A third input capacitor C2 may be needed in this design as a bypass path for the high-frequency components of
input switching current. The value of C2 is 0.1 µF and this bypass capacitor must be placed directly across VIN
and PGND (pins 3 and 2) near the IC. The CIN values and location are critical to reducing switching noise and
transients.
8.2.1.2.9 Soft-Start Capacitor - CSS
The capacitor at the SS pin determines the soft-start time, that is, the time for the output voltage to reach its final
steady-state value. Determine the SS capacitor value from Equation 19:
ISS u TStartup
CSS
VSS
(19)
With C3 (CSS) set at 22 nF and VSS = 2 V, ISS = 10 µA, TStartup is approximately 4 ms.
8.2.1.2.10 EN/UVLO Resistors - RUV1, RUV2
The UVLO resistors R1 (RUV2) and R2 (RUV1) set the input undervoltage lockout threshold and hysteresis
according to Equation 20 and Equation 21.
VIN(HYS) IUVLO(HYS) u RUV2
(20)
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VIN, UVLO(rising)
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§ RUV2 ·
VUVLO(TH) ¨ 1
¸
RUV1 ¹
©
(21)
From the Electrical Characteristics table, IUVLO(HYS) = 20 µA (typical). To design for a VIN rising threshold (VIN,
UVLO(rising)) of 10 V and hysteresis of 2.5 V, Equation 20 and Equation 21 yield RUV1 = 17.98 kΩ and RUV2 = 125
kΩ. Selecting 1% standard values of R2 (RUV1) = 18.2 kΩ and R1 (RUV2) = 127 kΩ result in UVLO rising
threshold and hysteresis voltages of 9.89 V and 2.54 V, respectively.
8.2.1.3 Application Curves
5.025
100
90
80
70
Efficiency (%)
Output Voltage (V)
5.015
5.005
4.995
Vin = 12V
4.985
Vin = 24V
Vin = 48V
4.975
0.00
0.25
0.50
0.75
1.00
Load Current (A)
20
1.25
1.50
60
50
40
30
Vin = 12V
20
Vin = 24V
10
0
0.00
Vin = 48V
0.25
0.50
0.75
1.00
1.25
Load Current (A)
C002
1.50
1.75
C001
Figure 20. Load Regulation
Figure 21. Efficiency vs IOUT
Figure 22. EN/UVLO Start-Up at VIN= 24 V and IOUT = 1 A
Figure 23. Prebias Start-Up at VIN= 48 V and RLOAD = 3 Ω
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Figure 24. EN/UVLO Start-Up at VIN= 24 V and
RLOAD = 100 Ω
Figure 25. Start-Up at VIN= 48 V and RLOAD = 10 Ω
iLIND (500 mA/div)
VSW (20 V/div)
VSS (2 V/div)
VOUT (5 V/div)
Time = 50 µs/div)
Figure 26. Load Transient (300 mA – 1.5 A) at VIN = 24 V
With Type 3 Ripple Configuration
Figure 27. Output Short-Circuit at VIN = 48 V
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8.2.2 LM5160-Q1 Isolated Fly-Buck (18-V to 32-V Input, 12-V, 4.5-W Isolated Output)
For technical solutions, industry trends, and insights for designing and managing power supplies, please refer to TI's
Power House blog series.
Below is an application example of an isolated Fly-Buck converter that operates over an input voltage range of
18 V to 32 V. It provides a stable 12-V isolated output voltage with an output power capability of 4.5 W. Figure 28
shows the complete schematic of the Fly-Buck application circuit.
Figure 28. LM5160-Q1 12-V, 4.5-W Fly-Buck Converter Schematic
8.2.2.1 LM5160-Q1 Fly-Buck Design Requirements
This LM5160-Q1 Fly-Buck application example is designed to operate from a 24-V DC supply with line variations
from 18 V to 32 V. The example provides a space-optimized and efficient 12-V isolated output solution with
secondary load current capability from 0 mA to 400 mA. The primary side remains unloaded in this application.
The switching frequency is set at 300 kHz (nominal). This design achieves greater than 88% peak efficiency.
Table 5. Design Parameters
DESIGN PARAMETER
EXAMPLE VALUE
Input voltage range
18 V to 32 V
Isolated output
12 V
Isolated load current range
0 mA to 400 mA
Nominal switching frequency
300 kHz
Peak Efficiency
88%
8.2.2.2 Detailed Design Procedure
The Fly-Buck converter design procedure closely follows the buck converter design outlined in LM5160-Q1
Synchronous Buck (10-V to 60-V Input, 5-V Output, 1.5-A Load). The selection of primary output voltage,
transformer turns ratio, rectifier diode, and output capacitors are covered here.
8.2.2.2.1 Selection of VOUT1 and Turns Ratio
The primary-side output voltage of a Fly-Buck converter must be no more than one half of the minimum input
voltage. For a minimum VIN of 18 V, the primary output voltage (VOUT) must be no higher than 9 V. To generate
an isolated output voltage of VOUT(ISO) = 12 V, a transformer turns ratio of 1 : 1.5 (N1 : N2) is selected. Using this
turns ratio, calculate the required primary output voltage VOUT using Equation 22.
22
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VOUT
VOUT(ISO)
0.7 V
1.5
8.47 V
(22)
The 0.7 V subtracted from VOUT(ISO) represents the forward voltage drop of the secondary rectifier diode. Fine
tuning the primary side VOUT1 may be required to account for voltage errors due to the leakage inductance of the
transformer and the resistance of the transformer windings and the low-side MOSFET of the LM5160-Q1.
8.2.2.2.2 Secondary Rectifier Diode
The secondary rectifier diode must block the maximum input voltage multiplied by the transformer turns ratio.
Determine the minimum diode reverse voltage VR(diode) rating from Equation 23.
N2
VR(diode) VIN(max) u
VOUT(ISO) 32 V u 1.5 12 V 60 V
(23)
N1
Select a diode with 60 V or higher reverse voltage rating for this application. If the input voltage (VIN) has
transients above the normal operating maximum input voltage of 32 V, then the worst-case transient input
voltage must be used in the diode voltage calculation given by Equation 23.
8.2.2.2.3 External Ripple Circuit
A Type 3 ripple circuit is required for Fly-Buck converter applications. The design procedure for ripple
components is identical to that in a buck converter. See Ripple Configuration for ripple design information.
8.2.2.2.4 Output Capacitor - COUT2
The Fly-Buck output capacitor conducts higher ripple current than a buck converter output capacitor. Calculate
the capacitive ripple for the isolated output capacitor based on the time the rectifier diode is off. During this time
the entire output current is supplied by the output capacitor. Calculate the required capacitance for a worst-case
VOUT2 (VOUT(ISO)) ripple voltage using Equation 24.
COUT2
IOUT2 § VOUT1 · 1
¨
¸u
'VOUT2 ¨© VIN(MIN) ¸¹ fsw
where
•
ΔVOUT2 is the target ripple at the secondary output.
(24)
Equation 24 is an approximation and ignores the ripple components associated with ESR and ESL of the output
capacitor. For a ΔVOUT2 = 100 mV, Equation 24 requires COUT2 = 6.5 µF. When selecting a ceramic capacitor,
consider its voltage coefficient to ensure sufficient capacitance at the output voltage operating point.
8.2.2.3 Application Curves
Isolated Sec. Output Voltage (V)
14
13
12
11
10
Vin = 18V
9
Vin = 24V
Vin = 32V
8
0.0
0.1
0.2
0.3
Secondary Load Current (A)
0.4
0.5
C002
Figure 30. Efficiency vs IOUT2
Figure 29. Load Regulation
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VSW (20 V/div)
VD1-ISOGND (20 V/div)
iLSEC (500 mA/div)
iLPRI (500 mA/div)
Time = 1 µs/div
Figure 31. Primary Switch Node at VIN = 24 V
and IOUT2 = 200 mA
Figure 32. Load Transient at IOUT2 = 100 mA - 300mA
VOUT1 (10 V/div)
VOUT2 (10 V/div)
iLPRI (2 A/div)
Time = 100 µs/div
Figure 33. VIN Start-Up at IOUT2 = 200 mA
Figure 34. Secondary Short at IOUT2 = 600mA
and IOUT1 = 200mA
8.3 Do's and Don'ts
As mentioned earlier in Soft Start, the SS capacitor CSS must always be more than 1 nF in both buck and FlyBuck converter applications. Apart from determining the start-up time, this capacitor serves as the external
compensation of the internal GM error amplifier. A minimum value of 1 nF is necessary to maintain stability. The
SS pin must not be left floating.
The VCC pin of the LM5160-Q1 must not be biased with an external voltage source. When an improved
efficiency requirement warrants an external VCC bias, the LM5160A must be used.
24
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9 Power Supply Recommendations
The LM5160-Q1 DC/DC converter is designed to operate from a wide input voltage range of 4.5 V to 65 V. The
characteristics of the input supply must be compatible with the Absolute Maximum Ratings and Recommended
Operating Conditions tables. In addition, the input supply must be capable of delivering the required input current
to the fully-loaded regulator. Estimate the average input current with Equation 25.
POUT
VIN ˜ K
IIN
where
•
η is the efficiency
(25)
If the regulator is connected to an input supply through long wires or PCB traces with a large impedance, take
special care to achieve stable performance. The parasitic inductance and resistance of the input cables may
have an adverse affect on converter operation, particularly during operation at low input voltage. The parasitic
inductance in combination with the low-ESR ceramic input capacitors form an underdamped resonant circuit.
This circuit can cause overvoltage transients at VIN each time the input supply is cycled on and off. The parasitic
resistance causes the input voltage to dip during a load transient. The best way to solve such 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 the electrolytic capacitors helps to damp the input resonant circuit and
reduce any voltage overshoots. A capacitance in the range of 10 µF to 47 µF is usually sufficient to provide input
parallel damping and helps to hold the input voltage steady during large load transients.
An EMI input filter is often used in front of the regulator that, unless carefully designed, can lead to instability as
well as some of the effects mentioned above. The application report Simple Success with Conducted EMI for
DC-DC Converters (SNVA489) provides helpful suggestions when designing an input filter for any switching
regulator.
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10 Layout
10.1 Layout Guidelines
A proper layout is essential for optimum performance of the circuit. In particular, observe the following guidelines:
• CIN: The loop consisting of input capacitor (CIN), VIN pin and PGND pin carries the switching current. The
input capacitor must be placed close to the IC, directly across VIN and PGND pins, and the connections to
these two pins must be direct to minimize the switching power loop area. In general, it is not possible to place
all of input capacitances near the IC. A good layout practice includes placing the bulk capacitor(s) as close as
possible to the VIN pin (see Figure 35). A bypass capacitor measuring 0.1 µF must be placed directly across
VIN and PGND (pin 3 and 2, respectively), as close as possible to the IC while complying with all layout
design rules.
• CVCC and CBST: The VCC and bootstrap (BST) bypass capacitors supply switching currents to the high-side
and low-side gate drivers. These two capacitors must also be placed as close to the IC as possible, and the
connecting trace length and loop area must be minimized (see Figure 35).
• The feedback trace carries the output voltage information and a small ripple component that is necessary for
proper operation of the LM5160-Q1. Therefore, take care while routing the feedback trace to avoid coupling
any noise into this pin. In particular, the feedback trace must be short and not run close to magnetic
components, or parallel to any other switching trace.
• SW trace: The SW node switches rapidly between VIN and GND every cycle and is therefore a source of
noise. The SW node copper area must be minimized. In particular, the SW node must not be inadvertently
connected to a copper plane or pour.
10.2 Layout Example
VIN
AGND
CIN
CIN
SW
PGND
SW
CBST
LM5160
VIN
BST
EN/
UVLO
VCC
VOUT
THERMAL
PAD
RON
FB
SS
FPWM
CVCC
RFB2
RFB1
Figure 35. Placement of Bypass Capacitors
26
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11 Device and Documentation Support
11.1 Device Support
11.1.1 Third-Party Products Disclaimer
TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT
CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES
OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER
ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE.
11.1.2 Development Support
For development support, see the following:
• LM5160 Buck Converter Quick-start Calculator
• LM5160 Fly-Buck Converter Quick-start Calculator
• LM5160 PSpice Transient Model
• LM5160 Unencrypted PSpice Transient Model
• LM5160 TINA-TI Fly-Buck Reference Design
• For TI's reference design library, visit TIDesigns
• For TI's WEBENCH Design Environment, visit the WEBENCH® Design Center
• To view a related device of this product, see the LM5161-Q1 100-V, 1-A synchronous buck converter
11.1.2.1 Custom Design With WEBENCH® Tools
Click here to create a custom design using the LM5160-Q1 device with the WEBENCH® Power Designer.
1. Start by entering the input voltage (VIN), output voltage (VOUT), and output current (IOUT) requirements.
2. Optimize the design for key parameters such as efficiency, footprint, and cost using the optimizer dial.
3. Compare the generated design with other possible solutions from Texas Instruments.
The WEBENCH Power Designer provides a customized schematic along with a list of materials with real-time
pricing and component availability.
In most cases, these actions are available:
• Run electrical simulations to see important waveforms and circuit performance
• Run thermal simulations to understand board thermal performance
• Export customized schematic and layout into popular CAD formats
• Print PDF reports for the design, and share the design with colleagues
Get more information about WEBENCH tools at www.ti.com/WEBENCH.
11.2 Documentation Support
11.2.1 Related Documentation
For related documentation see the following:
• LM5160A, LM5160 Buck EVM User's Guide (SNVU441)
• LM5160 Fly-Buck (Isolated Buck) User’s Guide (SNVU408)
• AN-2292 Designing an Isolated Buck (Fly-Buck) Converter (SNVA674)
• AN-1481 Controlling Output Ripple & Achieving ESR Independence in Constant ON-Time Regulator Designs
(SNVA166)
• TI Designs:
– High Resolution, Fast Startup Analog Front End for Air Circuit Breaker Reference Design (TIDUB80)
– Wide-Input Isolated IGBT Gate-Drive Fly-Buck Power Supply for Three-Phase Inverters (TIDU670)
– Input Protection and Backup Supply Reference Design for 25W PLC Controller Unit (TIDUCC7)
– Non-Isolated RS-485 to Wi-Fi Bridge with 24 VAC Power Reference Design (TIDUA48)
– Isolated RS-485 to Wi-Fi Bridge with 24 VAC Power Reference Design (TIDUA49)
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Documentation Support (continued)
•
•
•
•
•
•
– Dual-Output Isolated Fly-Buck Reference Design With an Ultra-Small Coupled Inductor (TIDUC31)
– 2.5W Bipolar Isolated Fly-Buck Ultra-Compact Reference Design (TIDUCA3)
– Small Footprint Isolated DC/DC Converter for Analog Input Module Reference Design (TIDUBR7)
– 2.3 nV/√Hz, Differential, Time Gain Control (TGC) DAC Reference Design for Ultrasound (TIDUD38)
– Leakage Current Measurement Reference Design for Determining Insulation Resistance (TIDU873)
– Class 3 Isolated Fly-Buck Power Module for PoE Application Reference Design (TIDU779)
– Thermal Protection Reference Design of IGBT Modules for HEV/EV Traction Inverters (TIDUBJ2)
White Papers:
– Designing Isolated Rails on the Fly With Fly-Buck Converters
– Valuing Wide VIN, Low-EMI Synchronous Buck Circuits for Cost-Effective, Demanding Applications
– An Overview of Conducted EMI Specifications for Power Supplies
– An Overview of Radiated EMI Specifications for Power Supplies
Power House Blogs:
– Fly-Buck: Frequently Asked Questions (FAQs)
– Lower EMI and Quiet Switching With the Fly-Buck Topology
– Fly-Buck Converter PCB Layout Tips
– When is Fly-Buck the Right Choice for Your Isolated Power Needs?
– How to Design for EMC and Isolation With Fly-Buck Converters
– Create a Fly-Buck Converter in WEBENCH® Power Designer
AN-2162: Simple Success with Conducted EMI from DC-DC Converters (SNVA489)
Automotive Cranking Simulator User's Guide (SLVU984)
Using New Thermal Metrics (SBVA025)
Semiconductor and IC Package Thermal Metrics (SPRA953)
11.3 Receiving Notification of Documentation Updates
To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper
right corner, click on Alert me 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.
11.4 Community Resources
The following links connect to TI community resources. Linked contents are 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.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
11.5 Trademarks
Fly-Buck, E2E are trademarks of Texas Instruments.
WEBENCH is a registered trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
11.6 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.
28
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11.7 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
12 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 OPTION ADDENDUM
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10-Dec-2020
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)
LM5160QPWPQ1
ACTIVE
HTSSOP
PWP
14
94
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 125
5160
QPWPQ1
LM5160QPWPRQ1
ACTIVE
HTSSOP
PWP
14
2500
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 125
5160
QPWPQ1
LM5160QPWPTQ1
ACTIVE
HTSSOP
PWP
14
250
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 125
5160
QPWPQ1
(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