Texas Instruments LM5161PWPBKEVM User manual

LM5161PWPBKEVM Buck Evaluation Module
User's Guide
Literature Number: SNVU504A
August 2016–Revised August 2016

2SNVU504A–August 2016–Revised August 2016
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Table of Contents
Contents
1 Introduction......................................................................................................................... 5
2 EVM Description and Performance Specifications.................................................................... 5
3 Test Setup and Operation ..................................................................................................... 5
3.1 Recommended Test Setup ............................................................................................. 5
3.2 Operation.................................................................................................................. 6
4 Typical Performance Curves ................................................................................................. 7
5 LM5161 Buck EVM Schematic.............................................................................................. 11
6 LM5161 Buck EVM Bill of Materials....................................................................................... 12
7 LM5161 Buck EVM PCB Layout............................................................................................ 12
Revision History.......................................................................................................................... 14

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List of Figures
List of Figures
1 Buck EVM Setup............................................................................................................. 6
2 Load Regulation.............................................................................................................. 7
3 Line Regulation .............................................................................................................. 7
4 Efficiency vs. IOUT ............................................................................................................ 7
5 Efficiency Comparison Between Forced CCM and DCM .............................................................. 7
6 Startup at Full Load.......................................................................................................... 7
7 Steady State at VIN = 48 V and FPWM = 0 (no load) .................................................................. 7
8 Steady State at VIN = 48 V and FPWM = 1 (no load) .................................................................. 8
9 EN/UVLO Startup/Shutdown at Full Load ................................................................................ 8
10 Pre-Bias Startup at No Load ............................................................................................... 8
11 Load Transient (ILoad = No Load to Full Load to No Load) in DCM .................................................... 8
12 Load Transient (ILoad = No Load to Full Load) in DCM................................................................... 8
13 Load Transient (ILoad = Full Load to No Load) in DCM................................................................... 8
14 Load Transient (ILoad = No Load to Full Load to No Load) in CCM .................................................... 9
15 Load Transient (ILoad = No Load to Full Load) in CCM................................................................... 9
16 Load Transient (ILoad = Full Load to No Load) in CCM................................................................... 9
17 Short Circuit (ILoad = Full Load to Short to Full Load) .................................................................... 9
18 Short Circuit (ILoad = Full Load to Short) ................................................................................... 9
19 Line Transient (36VIN-100VIN-72VIN)....................................................................................... 9
20 LM5161 Synchronous Buck EVM Schematic........................................................................... 11
21 EVM Component View with LM5161 .................................................................................... 12
22 EVM Top Copper View with LM5161 ................................................................................... 12
23 EVM Bottom Copper View with LM5161 ............................................................................... 12
24 EVM Top Solder Mask with LM5161 .................................................................................... 12

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List of Tables
List of Tables
1 LM5161 Buck EVM Specifications......................................................................................... 5
2 FPWM Pin Mode............................................................................................................. 7
3 LM5161 Buck EVM Bill of Materials for 300 kHz Configuration...................................................... 12

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LM5161 Buck EVM User’s Guide
User's Guide
SNVU504A–August 2016–Revised August 2016
LM5161 Buck EVM User’s Guide
1 Introduction
The LM5161 evaluation module (EVM) is designed to showcase the performance of the LM5161
synchronous buck DC/DC buck converter. The purpose of the user's guide is to highlight the
specifications, setup instructions, complete application schematic, bill of materials (BOM), and typical
performance curves of the EVM. The LM5161 is supported by WEBENCH®Designer and unencrypted
PSpice simulation models. Furthermore, the reader can use the LM5161 Quick-start calculator to optimize
component selection and examine estimated efficiency performance across wide line and load ranges.
The LM5161 device name is used generically throughout this document and represents both the LM5161
and the LM5161-Q1, unless stated otherwise.
2 EVM Description and Performance Specifications
The LM5161 Buck evaluation board provides a fully functional buck regulator, employing the constant ON-
time (COT) control scheme. This provides a 12 V output over an input voltage range of 15 V to 80 V with
output current rated up to 1 A. The application schematic of the EVM has been set up to operate from a
nominal 48-V input supply. The switching frequency is set to approximately 300 kHz. The board is
designed to demonstrate a synchronous buck with small solution size for 12 W wide VIN applications.
Table 1. LM5161 Buck EVM Specifications
ORDERABLE NAME VIN VOUT IOUT EFFICIENCY
LM5161PWPBKEVM 15 V–80 V 12 V 0 A –1 A 94%
3 Test Setup and Operation
This section describes the connectors, the test points and the jumpers in the EVM.
3.1 Recommended Test Setup
3.1.1 Input/Output Connector Description
J1 – Input is the power input terminal for the converter. The terminal block provides an input VIN (+) and
ground (-) connection to allow the user to attach the EVM to a power supply.
J2 – Output is the regulated output voltage terminal for the converter. The terminal block provides a VOUT
(+) and ground (-) connection to allow the user to attach the EVM to a load.
J3 – (EN) allows the user to remotely shutdown/startup LM5161.
J4 – (VOUT to VCC connection) allows the user to check for the operation with and without the external VCC
connection (VCC pin diode connected to VOUT)
JP1 –MODE pin allows the user to select between forced CCM (FPWM = 1) and DCM (FPWM = 0)
operation. See Section 3.2 and Table 2 for more details.

UV2
IN,UVLO(rising) UVLO(TH) UV1
R
V V 1 R
§ ·

¨ ¸
© ¹
IN(HYS) UVLO(HYS) UV2
V I Ru
OUT
FB2
FB1 REF
V
R1
R V

OUT
SW 10 ON
V
F Hz
1.008 x10 x R

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LM5161 Buck EVM User’s Guide
Figure 1. Buck EVM Setup
3.2 Operation
In order to maintain proper operation of the LM5161PWPBKEVM, the input voltage applied across J1
should be gradually increased. The load at the output (J2) should not exceed 1 A. The inductor L2 used in
this board is optimized for small solution size. The saturation current rating (ISAT) of the inductor should be
higher than the LM5161 integrated high-side FET peak current-limit threshold of 1.9 A (max.).
The nominal switching frequency (in Hz) can be set using the RON (R1 in the EVM) resistor, as shown in
Equation 1:
(1)
The output voltage is set by using the feedback divider resistors R8 (RFB1) and R7 (RFB2) in the EVM by
using Equation 2:
(2)
The EN/UVLO resistors R9 (RUV1) and R3 (RUV2) in the EVM sets the input undervoltage lockout threshold
and the EN/UVLO hysteresis according to Equation 3:
(3)
and,
(4)
where IUVLO(HYS) = 20 µA and VUVLO(TH) = 1.24 V.
Table 2 summarizes the LM5161 Buck EVM Jumper (JP1) settings that determine the desired modes of
operation.
•Forced continuous conduction mode (CCM) or FPWM
•Discontinuous conduction mode (DCM)

Load Current (A)
Output Voltage (V)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
11.88
11.9
11.92
11.94
11.96
11.98
12
12.02
12.04
12.06
12.08
12.1
12.12
Ext-VCC
FPWM = 1 VIN = 24 V
VIN = 48 V
VIN = 60 V
Input Voltage (V)
Output Voltage (V)
15 20 25 30 35 40 45 50 55 60
11.88
11.9
11.92
11.94
11.96
11.98
12
12.02
12.04
12.06
12.08
12.1
12.12
Ext-VCC
FPWM = 1 IOUT = 0 A
IOUT = 0.5 A
IOUT = 1 A
www.ti.com Typical Performance Curves
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LM5161 Buck EVM User’s Guide
When selecting the FPWM mode, the LM5161 needs an external feedback ripple injection circuit (Type 3)
or the external ESR resistor (Type 1) on board, for normal operation. The correct values for the external
ESR resistor (R4 in the EVM) in series with the output capacitors (C10, C11) or for the external ripple
injection circuit (R6,C7 and C10), depending on which ripple injection scheme (Type 1 or Type 3) is used,
are calculated based on the formulae mentioned in the LM5161 datasheet. See application note AN-1481
for more details for each ripple generation method.
When selecting the DCM mode setting using the Jumper (JP1) see Table 2, the internal emulated ripple
mode is enabled. When operating in this mode, there is no need to add the external ESR resistor in series
with the output capacitors or the external ripple injection circuit (see Section 7 for more details). The
internal emulated ripple is sufficient to maintain steady-state and dynamic stability while operating in this
mode. In a typical buck application at TJ> 125°C and FPWM = 0, with the input voltage VIN > 72 V and
the VCC externally supplied add a BST resistor, R2 (recommended > 3Ω) in series with the BST capacitor
(see Figure 21). This protects the internal bootstrap diode during a full load transient operation.
An external voltage can be supplied to the VCC pin in the range of 9 V to 13 V, for improved efficiency
requirements. In that case, the diode D1 must be appropriately populated. The user can keep diode D1
populated on board and install/uninstall the jumper J4 in order to estimate the difference in efficiency, with
and without the external VCC supply. More details about the diode D1 are given in the Section 6.
Table 2. FPWM Pin Mode
JP1 Setting Logic Stage Description
DCM or Floating (High Z) (Pin 2 - Pin 3:
DCM) 0The FPWM pin is grounded or left floating. Populate
resistor R2 appropriately. DCM with the pulse
skipping mode at light load enabled. No external
ripple injection circuit needed.
FPWM (VCC) (Pin 2 - Pin 1: FPWM) 1 The FPWM pin is connected to VCC. External Ripple Injection circuit needed. CCM mode enabled over the
entire load range.
4 Typical Performance Curves
VOUT - VCC diode
connected FPWM = 1 FSW = 300kHz
Figure 2. Load Regulation
VOUT - VCC diode
connected FPWM = 1 FSW = 300kHz
Figure 3. Line Regulation

Load Current (A)
Efficiency (%)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
75
80
85
90
95
100
Ext-VCC
Int-VCC
FPWM = 1 VIN = 24 V
VIN = 48 V
VIN = 60 V
Load Current (A)
Efficiency (%)
0.04 0.07 0.1 0.2 0.3 0.4 0.5 0.7 1
40
50
60
70
80
90
100
FPWM = 1
FPWM = 0
VIN = 24 V
VIN = 48 V
VIN = 60 V
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VOUT = 12 V FPWM = 1 FSW = 300kHz
Figure 4. Efficiency vs. IOUT
VOUT - VCC diode
connected FSW = 300kHz VOUT = 12 V
Figure 5. Efficiency Comparison Between Forced CCM and
DCM
VIN = 48 V FSW = 300kHz FPWM = 1 VOUT - VCC
diode
connected
Figure 6. Startup at Full Load
Figure 7. Steady State at VIN = 48 V and FPWM = 0
(no load)
Figure 8. Steady State at VIN = 48 V and FPWM = 1
(no load)
VIN = 48 V FSW = 300kHz FPWM = 1 VOUT - VCC
diode
connected
Figure 9. EN/UVLO Startup/Shutdown at Full Load

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LM5161 Buck EVM User’s Guide
VIN = 48 V FSW = 300kHz FPWM = 1 VOUT - VCC
diode
connected
Figure 10. Pre-Bias Startup at No Load
VIN = 48 V FPWM = 0 FSW = 300kHz
Figure 11. Load Transient (ILoad = No Load to Full Load to
No Load) in DCM
VIN = 48 V FPWM = 0 FSW = 300kHz VOUT = 12 V
Figure 12. Load Transient (ILoad = No Load to Full Load) in
DCM
VIN = 48 V FPWM = 0 FSW = 300kHz VOUT = 12 V
Figure 13. Load Transient (ILoad = Full Load to No Load) in
DCM
VIN = 48 V FPWM = 1 FSW = 300kHz VOUT = 12 V
Figure 14. Load Transient (ILoad = No Load to Full Load to
No Load) in CCM
VIN = 48 V FPWM = 1 FSW = 300kHz VOUT = 12 V
Figure 15. Load Transient (ILoad = No Load to Full Load) in
CCM

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LM5161 Buck EVM User’s Guide
VIN = 48 V FPWM = 1 FSW = 300kHz VOUT = 12 V
Figure 16. Load Transient (ILoad = Full Load to No Load) in
CCM
VIN = 48 V FSW = 300kHz VOUT = 12 V
Figure 17. Short Circuit (ILoad = Full Load to Short to Full
Load)
VIN = 48 V FSW = 300kHz VOUT = 12 V
Figure 18. Short Circuit (ILoad = Full Load to Short)
FSW = 300kHz VOUT = 12 V ILoad = 500 mA
Figure 19. Line Transient (36VIN-100VIN-72VIN)