3.3.3 Channel 1 Loop Analysis (TP5, TP6, TP7, and TP8)
The TPS54291EVM-431 contains a 51-Ω series resistor (R1) in the feedback loop to allow for matched
impedance signal injection into the feedback for loop response analysis. An isolation transformer should be
used to apply a small (30 mV or less) signal across R1 through TP6 and TP8. By monitoring the AC injection
level at TP8 and the returned AC level at TP6, the power supply loop response can be determined.
3.3.4 Channel 1 Switching Waveforms (TP9 and TP10)
The TPS54291EVM-431 provides a surface test pad and a local ground connection (TP10) for the monitoring
of the channel 1 power stage switching waveform. Connect an oscilloscope probe to TP9 to monitor the switch
node voltage for channel 1. Test pads are used on the switch nodes to minimize radiated noise from the switch
node.
3.3.5 TPS54291 IC Ground (TP11)
The TPS54291EVM-431 provides a test point for the IC ground. To measure IC pin voltages, connect the ground
of the oscilloscope probe to TP11.
3.3.6 Channel 2 Switching Waveforms (TP12 and TP13)
The TPS54291EVM-431 provides a surface test pad and a local ground connection (TP13) for the monitoring of
the channel 1 power stage switching waveform. Connect an oscilloscope probe to TP12 to monitor the switch
node voltage for channel 1. Test pads are used on the switch nodes to minimize radiated noise from the switch
node.
3.3.7 Channel 2 Loop Analysis (TP14, TP15, TP16, and TP17)
The TPS54291EVM-431 contains a 51-Ω series resistor (R13) in the feedback loop to allow for matched
impedance signal injection into the feedback for loop response analysis. An isolation transformer should be used
to apply a small (30 mV or less) signal across R13 through TP14 and TP16. By monitoring the AC injection level
at TP14 and the returned AC level at TP16, the power supply loop response can be determined.
3.3.8 Output Voltage Monitoring (TP18 and TP19)
The TPS54291EVM-431 provides two test points for measuring the voltage generated by the module. This
allows the user to measure the actual module output voltage without losses from output cables and connector
losses. All output voltage measurements should be made between TP18 and TP19. To use TP18 and TP19,
connect a voltmeter positive terminal to TP18 and negative terminal to TP19. For output ripple measurements,
TP18 and TP19 allow a user to limit the ground loop area by using the tip and barrel measurement technique
shown in
. All output ripple measurements should be made using the tip and barrel measurement.
Even this tip and barrel measurement technique increases the measured switch edge noise. For improved
output ripple measurement, measure the output ripple at the output capacitor (C17).
Schematic
6
TPS54291 Step-Down Converter Evaluation Module User's Guide
SLVU356A – JANUARY 2010 – REVISED OCTOBER 2021
Copyright © 2021 Texas Instruments Incorporated
