Texas Instruments TPS53681EVM-002 User manual

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Using the TPS53681EVM-002, Dual Multiphase DC-DC Step-Down Analog
Controller with PMBus™ Interface
SLUUBP7–December 2017
Using the TPS53681EVM-002, Dual Multiphase DC-DC
Step-Down Analog Controller with PMBus™ Interface
This User Guide describes the evaluation module (EVM) for the TPS53681 analog power controller, a
driverless D-CAP+™ multiphase buck controller, which manages several high current phases of the
CSD95490, a NexFet™ Smart Synchronous Buck Power Stage.
Contents
1 Description.................................................................................................................... 1
2 Typical Applications ......................................................................................................... 2
2.1 Features.............................................................................................................. 2
3 Electrical Performance Specifications..................................................................................... 3
4 Schematic..................................................................................................................... 4
5 Test Setup................................................................................................................... 12
5.1 Test and Configuration Software................................................................................ 12
5.2 Test Equipment.................................................................................................... 12
5.3 Recommended Test Setup....................................................................................... 13
6 EVM Configuration Using the Fusion GUI .............................................................................. 14
6.1 Configuration Procedure ......................................................................................... 14
7 Test Procedure ............................................................................................................. 14
7.1 Line/Load Regulation and Efficiency Measurement Procedure............................................. 14
7.2 High Current Operation........................................................................................... 15
7.3 Multiphase/Multi-rail Configurations............................................................................. 16
7.4 On-Board Transient Load Operation............................................................................ 16
7.5 Efficiency ........................................................................................................... 17
7.6 Equipment Turn-on and Shutdown.............................................................................. 18
8 Performance Data and Typical Characteristic Curves................................................................. 19
9 EVM Assembly Drawing .................................................................................................. 24
10 Bill of Materials ............................................................................................................. 26
11 Fusion GUI.................................................................................................................. 30
1 Description
The TPS53681EVM implements a typical application for a low-voltage, high current dual output power
converter, operating from a nominal 12-V input rail to produce a 0.9-V output rail at up to 294 A of load
current and a 0.8-V rail at up to 47 A. The EVM includes test points for evaluating the performance of the
TPS53681 controller and CSD95490 power stages.
For ease of evaluation, the EVM requires only one (12-V) input supply and an output load to get started
with testing, however the user can opt to independently provide 5-V for greater control over the Power
Stage voltage. With the addition of the Fusion Digital Power™ Designer software, the EVM’s PMBus™
interface allows access to the controller NVM for evaluation of additional configuration, control and
monitoring possibilities. Refer to the TPS53681 datasheet (SLUSCT1) for complete information on
configuring multi-phase operation with this controller.

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2 Typical Applications
• High current ASIC and FPGA core power in the following equipment:
– Wired and Wireless Networking
– Enterprise Server and Storage Networks
– Test & Measurement
– Smart Grid Infrastructure
– Aerospace and Defense
– Merchant Power Supplies
2.1 Features
• Dual regulated high current outputs
• Programmable settings available through PMBus™ interface
– Output voltage trim
– Output voltage margin levels (High / Low) within a maximum range
– UVLO protection threshold
– Soft-start slew-rate
– Device enable and disable
– Overcurrent warning and fault limits
– SW frequency
– BOOT voltage
– Monitoring of input & output voltage, current, power, and power stage temperature
• Convenient test points for probing critical waveforms

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3 Electrical Performance Specifications
Table 1. TPS53681EVM Electrical Performance Specifications
PARAMETER TEST CONDITIONS MIN TYP MAX UNITS
INPUT CHARACTERISTICS
VIN Voltage range 10 12 14 V
IIN(max) Maximum input current VIN = 12 V, IOUTA = 294 A, IOUTB =
47 A 30 A
No load input current VIN = 12 V, IOUTA = 0 A, IOUTB = 0 A, Dynamic Phase Shedding
disabled 330 mA
OUTPUT CHARACTERISTICS
VOUT Output voltage RAIL A 0.9 V
RAIL B 0.8 V
IOUT Output load current RAIL A (6-phase mode) 0 294 A
RAIL B (2-phase mode) 0 47 A
Output voltage load regulation 0 A ≤IOUTA ≤294 A 0.15%
0 A ≤IOUTB ≤47 A 0.15%
VRIPPLE Output voltage ripple VIN = 12 V, IOUTA = 150 A 4 mVpp
VIN = 12 V, IOUTB = 45 A 5 mVpp
Output overcurrent protection
(OCP) RAIL A 382.5 A
SYSTEMS CHARACTERISTICS
fSW Rail A Switching frequency VIN = 12 V 500 kHz
Rail A Peak efficiency VIN = 12 V, IOUTA = 90 A 93.0%
Rail A Full-load efficiency VIN = 12 V, IOUTA = 294 A 87.5%
Rail B Switching frequency VIN = 12 V 500 kHz
Rail B Peak efficiency VIN = 12 V, IOUTB = 25 A 91.8%
Rail B Full-load efficiency VIN = 12 V, IOUTB = 47 A 90.6%
TAOperating temperature 25 ºC

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4 Schematic
Figure 1. TPS53681EVM - Controller Schematic

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Figure 2. TPS53681EVM - Rail A Power Stages 1-3-5 Schematic

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Figure 3. TPS53681EVM - Rail A Power Stages 2-4-6 Schematic

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Figure 4. TPS53681EVM - Rail B Power Stages Schematic

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Figure 5. TPS53681EVM - AUX Voltages Schematic

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Figure 6. TPS53681EVM - Helper Circuits and Indicators Schematic

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Figure 7. TPS53681EVM - Input and Output Filter Schematic

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Figure 8. TPS53681EVM - On Board Transient Load Schematic

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5 Test Setup
5.1 Test and Configuration Software
The Texas Instruments Fusion Digital Power Designer software can expand the functionality of the EVM.
To download this software, visit the Fusion Digital Power Software page.
5.1.1 Description
The Fusion Digital Power Designer is a graphical user interface (GUI) used to configure, control and
monitor the TPS53681 controller on the EVM. The software uses the PMBus™ protocol to communicate
with the controller over a serial bus by way of the TI USB-to-GPIO Adapter.
5.1.2 TI Fusion Digital Power Designer Features
The software offers these features:
• Turn on or off the power supply output, either through the hardware control line or the PMBus™
Operation command.
• Monitor real-time data. Items such as input voltage, input current, output voltage, output current,
temperature, warnings and faults are continuously monitored and displayed by the GUI.
• Configure common operating characteristics such as output voltage trim and margin, VIN UVLO, soft-
start slew rate, switching frequency, and warning and fault thresholds.
5.2 Test Equipment
5.2.1 Voltage Sources
Only one DC input voltage sources is needed (VIN). The VIN input voltage source should be a 0 V to 14 V
variable DC source capable of supplying 40 Adc. Connect VIN to terminals J6 and J7 as shown in
Figure 9.
For greater control during testing, one can remove jumpers from J2 and J4 to bypass the onboard 5-V
power supply. This external supply should be limited to 1 Adc.
5.2.2 Multimeters
It is recommended to use two separate multimeters, one meter to measure VIN and the other to measure
VOUT.
5.2.3 Output Load
An electronic load is recommended for the test setup shown in Figure 9. To observe the Rail A at full load
the electronic load should be capable of sinking 294 A at 0.9-V (Rail B, 47 A at 0.8-V).
5.2.4 Oscilloscope
Use an oscilloscope to measure output noise and ripple. Use a coaxial cable to measure output ripple
across the output ceramic capacitors.
5.2.5 Fan
During prolonged operation at high load (More than 100 A), it is necessary to provide forced air cooling
with a small fan aimed at the EVM. Maintain the temperature of the devices on the EVM under 115°C.
5.2.6 USB-to-GPIO Interface Adapter
A communications adapter is required between the EVM and the host computer. This EVM is designed to
use the Texas Instruments USB-to-GPIO adapter connected to J12. To purchase this adapter visit the TI
USB-to_GPIO tool page.

GND 12VIN
VOUTA+
VOUTB+
GND
GND
5VIN*
GND
*IF EXTERNAL
SOURCE IS USED
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5.2.7 Recommended Wire Gauge
(1) Total length of wire less than 4 feet (2 feet input or output, 2 feet return).
Table 2. Recommended Wire Gauge
VOLTAGE (V) CONNECT RECOMMENDED
WIRE SIZE
MAXIMUM TOTAL WIRE LENGTH (1)
(FEET)
RETURN INPUT OUTPUT
12 VIN to J6, GND to J7 2 x AWG #8
2
2 n/a
5 (if J2 open) 5VIN to J1 2 x AWG #18 2 n/a
0.9 Load+ to T1, T2, and T3,
Load- to T4, T5, and T6 6 × AWG #4 n/a 2
0.8 Load+ to T7 and T8,
Load- to T9 and T10 4 × AWG #8 n/a 2
5.3 Recommended Test Setup
Figure 9 shows the recommended test setup, which includes VIN input voltage source(s) and output load.
Figure 9. TPS53681EVM Recommended Test Setup

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6 EVM Configuration Using the Fusion GUI
The controller on this EVM leaves the factory pre-configured. Table 3 lists some key factory configuration
parameters from the configuration file.
Table 3. Key Factory Configuration Parameters
CMD NAME PMBus
COMMAND
CODE
HEX VALUE PHYSICAL
SETTING COMMENTS
VIN_ON 0x35 0xF029 10.25 V Input voltage turn on threshold
Rail A IOUT_OC_FAULT_LIMIT 0x46 0x017E 382.00 A Rail A OC fault level
Rail A IOUT_OC_WARN_LIMIT 0x4A 0x00FF 255.0 A Rail A OC warning level
Rail B IOUT_OC_FAULT_LIMIT 0x46 0x005A 135.00 A Rail B OC fault level
Rail B IOUT_OC_WARN_LIMIT 0x4A 0x0087 90.0 A Rail BOC warning level
ON_OFF_CONFIG 0x02 0x17 Control Pin only Power is converted when the control
pin is active
OT_FAULT_LIMIT 0x4F 0x0073 115 °C OT fault level
OT_WARN_LIMIT 0x51 0x0069 105 °C OT warning level
Rail A Max Num Phases 0xE4 0x05 6 Phase Rail number of phases
FSW 0x33 0x01F4 500kHz Switching frequency
Rail A VBOOT 0xDB 0x83 0.900V Rail A VBOOT voltage
Rail B VBOOT 0xDB 0x6F 0.800V Rail B VBOOT voltage
To configure the EVM with other than the factory settings shown in Table 3, use the TI Fusion Digital
Power Designer software for reconfiguration. Be sure to apply input voltage to the EVM prior to launching
the software. This sequence ensures that the controller and GUI recognize each other.
6.1 Configuration Procedure
1. Connect USB-to-GPIO adaptor to J12.
2. Apply the input power source VIN to the EVM. Refer to Figure 9.
3. Ensure that the controller is receiving 3.3-V (either through the onboard LDOs or an external supply)
4. Launch the Fusion GUI software.
5. Configure the EVM operating parameters as desired.
7 Test Procedure
7.1 Line/Load Regulation and Efficiency Measurement Procedure
1. Set up EVM as shown in Figure 9.
2. Ensure the electronic load is set to draw 0 Adc.
3. Check to see if jumpers are in desired configuration (Refer to Table 4)
4. Increase VIN from 0-V to 12-V.
5. Change the relevant switch to ON position (S1 for Rail A, S2 for Rail B).
6. Turn on the external fan if necessary (When driving a load above 50A).
7. Vary the load from 0 Adc to 294 Adc for Rail A (0 Adc to 47 Adc for Rail B) Ensure VOUT remains in
regulation as defined in Table 1.
8. Vary VIN from 10-V to 14-V. Ensure VOUT remains in regulation as defined in Table 1.
9. Decrease the load to 0 A.
10. Change relevant switch to OFF position (S1 for Rail A, S2 for Rail B).
11. Decrease VIN to 0 V.
12. Shut down the external fan if in use.

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Table 4. Connector Functions
CONNECTOR DESCRIPTION
J1 5VIN External Supply Input
J2 5VIN Supply Selector (Closed by Default to Activate Internal 5VIN Supply)
J4 Internal 5VIN Supply Input (Closed by Default to Activate Internal 5VIN Supply)
J6 VIN + Connector
J7 VIN - Connector
J8 PWM Configuration Connector (Default Pin 2-3 Shorted for 6+2 Configuration)
J9 Reset (Open by Default)
J10 CSP Configuration Connector (Default Pin 2-3 Shorted for 6+2 Configuration)
J11 VOUTA Sense (Leave Open!)
J12 PMBUS Connector
J13 VOUTB Sense (Leave Open!)
J14 VOUTA Onboard Transient Load Signal Generator Selector (Open by default)
J15 VOUTB Onboard Transient Load Signal Generator Selector (Open by default)
J16 VOUTAOutput Measurement Point (Leave Open!)
J17 VOUTB Output Measurement Point (Leave Open!)
T1,T2.T3 VOUTA + Connectors
T4,T5,T6 VOUTA - Connectors
T7, T8 VOUTB + Connectors
T9, T10 VOUTB - Connectors
7.2 High Current Operation
When operating at with loads larger than 100A, one must provide ample cooling to the board, particularly
towards the CSD95490 power stages. Provide at least 100CFM of airflow over the power stages to keep
the board within its thermal limits. By default, this board will stop delivering a switching signal to power
stages when they reach a temperature above 115°C.
Similarly, when using the onboard transient load, one mustn't use a duty cycle wider than 20%, otherwise
the load resistors will overheat.
A VIN =12 V, VOUT = 0.9 V, IOUT=294A
Figure 10. Thermal Picture of TPS53681 EVM. Rail A with Full Load Cooled at 100CFM

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7.3 Multiphase/Multi-rail Configurations
This board is set up in a 6+2 configuration by default (Rail A with six phases, Rail B with two). If one
wishes to change to other configurations consult Table 5. For more information on setting the number of
phases on Rail B, please refer to SLUSCT1, section 7.3.1.5.
Table 5. Phase-Rail Configurations
NUMBER OF PHASES ACTIVE ON
RAIL A NUMBER OF PHASES
ACTIVE ON
RAIL B
STATE OF
JUMPER J8 STATE OF JUMPER J10 CSP RESISTORS TO POPULATE
1 0 Short Pin 2-3 Short Pin 2-3 R29=0Ω, R35=10kΩ
2 0 Short Pin 2-3 Short Pin 2-3 R30=0Ω, R35=10kΩ
3 0 Short Pin 2-3 Short Pin 2-3 R31=0Ω, R35=10kΩ
4 0 Short Pin 2-3 Short Pin 2-3 R32=0Ω, R35=10kΩ
5 0 Short Pin 2-3 Short Pin 2-3 R33=0Ω, R35=10kΩ
6 0 Short Pin 2-3 Short Pin 2-3 R35=10kΩ
1 1 Short Pin 2-3 Short Pin 2-3 R29=0Ω, R38=0Ω
2 1 Short Pin 2-3 Short Pin 2-3 R30=0Ω, R38=0Ω
3 1 Short Pin 2-3 Short Pin 2-3 R31=0Ω, R38=0Ω
4 1 Short Pin 2-3 Short Pin 2-3 R32=0Ω, R38=0Ω
5 1 Short Pin 2-3 Short Pin 2-3 R33=0Ω, R38=0Ω
6 1 Short Pin 2-3 Short Pin 2-3 R38=0Ω, R41=0Ω
1 2 Short Pin 2-3 Short Pin 2-3 R29=0Ω, R41=0Ω
2 2 Short Pin 2-3 Short Pin 2-3 R30=0Ω, R41=0Ω
3 2 Short Pin 2-3 Short Pin 2-3 R31=0Ω, R41=0Ω
4 2 Short Pin 2-3 Short Pin 2-3 R32=0Ω, R41=0Ω
5 2 Short Pin 2-3 Short Pin 2-3 R33=0Ω, R41=0Ω
6 2 Short Pin 2-3 Short Pin 2-3 -
1 3 Short Pin 1-2 Short Pin 1-2 R29=0Ω
2 3 Short Pin 1-2 Short Pin 1-2 R30=0Ω
3 3 Short Pin 1-2 Short Pin 1-2 R31=0Ω
4 3 Short Pin 1-2 Short Pin 1-2 R32=0Ω
5 3 Short Pin 1-2 Short Pin 1-2 -
7.4 On-Board Transient Load Operation
1. Set up EVM as shown in Figure 9.
2. Place Jumper J14 (J15 for Rail B) in order to provide drive signal from onboard 555 timer (~1.2 kHz,
8% Duty cycle) or inject drive signal in TP52 (T53 for Rail B) from signal generator. Take care not to
exceed 20% duty cycle if using external signal generator.
3. Turn ON one or more "banks" of load resistors with S3 (S4 for Rail B). At the default output voltages,
each "Bank" on Rail A adds 37.5A to the transient load. Likewise each "bank" on Rail B adds 23 A.
4. To best observe transient effects, measure voltage across J16 (J17 for Rail B)
5. Turn OFF S3 (or S4) when finished observing transient effects.
6. Disconnect J14 (or J15) or turn off signal generator output.

VIN
GND
VOUT
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7.5 Efficiency
In order to observe the efficiency of the power train on the EVM, it is important to measure the input and
output voltages at specific locations on the input and output capacitors nearest the power-stages. This is
necessary to prevent the inclusion of losses that are not specifically related to the power train itself, such
as losses incurred by the voltage drop in the copper traces or in the input and output connectors. It is
recommended that voltage measurements are measured with reference to the same ground.
Input current can be measured at any point in the input wires, and output current can be measured
anywhere in the output wires of the output being measured.
Figure 11 shows the measurement points that were used for the input voltage and output voltage. Using
these measurement points results in an efficiency derivation which does not include losses due to the
connectors and PCB traces.
Also make sure to provide the 5-V gate drive voltage separately through J1 (leaving J2 and J4 open) if
one wishes to observe efficiency independent of gate-drive and controller losses. R1, R2, R5, and R10 are
installed as shunts to help the user measure current in the auxiliary and drive circuits.
Figure 11. Test Setup for Efficiency Measurement

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7.6 Equipment Turn-on and Shutdown
7.6.1 Turn-on Sequence
1. If using an external 5 V source (J2 and J4 left open), turn on input power supply and increase 5VIN to
5 V
2. Turn on input power supply VIN and increase VIN above 10.5 V.
3. Switch S1 (S2 for Rail B) to ‘ON’ position.
4. Adjust load current as desired.
5. Turn on external fan if necessary.
7.6.2 Shutdown Sequence
1. Reduce the load current to 0 A.
2. Switch S1 (or S2) to ‘OFF’ position.
3. Reduce input voltage to 0 V and shut down input power supply VIN, then 5VIN if used.
4. Shut down the external fan if in use.

IOUT (A)
VOUT (V)
0 50 100 150 200 250 300
0.8985
0.8987
0.8989
0.8991
0.8993
0.8995
0.8997
0.8999
0.9001
TPS5
IOUT (A)
VOUT (A)
0 10 20 30 40 50
0.798
0.7983
0.7986
0.7989
0.7992
0.7995
0.7998
0.8001
TPS5
IOUT (A)
Efficiency (%)
0 10 20 30 40 50
0.7
0.75
0.8
0.85
0.9
0.95
1
TPS5
IOUT (A)
Efficiency (%)
0 50 100 150 200 250 300
70%
75%
80%
85%
90%
95%
100%
TPS5TPS5
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8 Performance Data and Typical Characteristic Curves
Figure 12 through Figure 17 show performance curves for the TPS53681EVM.
The waveforms and bode plots shown below were made after making the following changes from the
default settings using our Fusion Digital Power Software .
Rail A Setting Change
• [Figure 48,Transients] AC_LL: 0.2500mΩ
Rail B Setting Changes
• [Figure 48,Transients] AC_GAIN: 2.00 *x
• [Figure 48,Transients] AC_LL: 0.2500mΩ
• [Figure 48,Transients] INT_Time: 02µs
• [Figure 48,Transients] INTGAIN: 2.00*x
• [Figure 46, Static] IOUT_MAX: 47A
These changes can either be done manually, as described in the Section 11 section or one can download
a complete, reconfigured .xml configuration file from the TPS53681EVM webpage, and upload it to the
device as shown here .
VOUT = 0.9 V, VIN =12 V VOUT = 0.8 V, VIN =12 V
Figure 12. VOUT A Power Stage Efficiency Figure 13. VOUT B Power Stage Efficiency
VOUT = 0.9 V, VIN =12 V VOUT = 0.8 V, VIN =12 V
Figure 14. VOUT A Load Regulation Figure 15. VOUT B Load Regulation

Frequency (Hz)
Gain (dB)
Phase (q)
1000 2000 5000 10000 100000 1000000
-100 -200
-80 -160
-60 -120
-40 -80
-20 -40
0 0
20 40
40 80
60 120
80 160
100 200
RAIL
Gain
Phase
Frequency (Hz)
Gain (dB)
Phase (q)
1000 2000 5000 10000 100000 1000000
-100 -200
-80 -160
-60 -120
-40 -80
-20 -40
0 0
20 40
40 80
60 120
80 160
100 200
RAIL
Gain
Phase
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VIN = 12 V VOUT = 0.9 V IOUT = 50 A VIN = 12 V VOUT = 0.8 V IOUT = 45 A
Figure 16. VOUT A Bode Plot Figure 17. VOUT B Bode Plot