Test Set UP
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3.3.3
Channel 1 Loop Analysis (TP5, TP6, TP7 and TP8)
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 (30mV 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)
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)
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)
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)
TPS54291EVM-431 contains a 51
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 (30mV 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)
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)
4
Test Set UP
4.1
Equipment
4.1.1
Voltage Source
V
IN
The input voltage source (V
IN
) should be a 0-15V variable DC source capable of 2Adc. Connect V
IN
to J1
as shown in
4.1.2
Meters
A1: 0-2Adc, ammeter
6
Using the TPS54291EVM-431 A 12V Input, 3.3V 1.5A and 1.2V 2.5A
SLVU356 – January 2010
Synchronous Buck Converter
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