Texas Instruments TPS56121, User Manual, Page: 12 / 28

8.3 Control Loop Gain and Phase Measurement Procedure
1. Follow Section 8.1 to set VIN and LOAD to desired operating condition.
2. Connect isolation transformer to test points TP7 and TP10 as shown in Figure 8-2 .
3. Connect input signal amplitude measurement probe (Channel A) to TP7 as shown in Figure 8-2 .
4. Connect output signal amplitude measurement probe (Channel B) to TP10 as shown in Figure 8-2 .
5. Connect ground lead of Channel A and Channel B to TP8 and TP9 as shown in Figure 8-2 , respectively.
6. Inject 10 mV or less signal through the isolation transformer.
7. Sweep the frequency from 500 Hz to 500 kHz with 10-Hz or lower post filter.
8. Control loop gain can be measured by
ChannelB
20 log
ChannelA
æ ö
´
ç ÷
è ø
.
9. Control loop phase can be measured by the phase difference between Channel A and Channel B.
10. Follow Section
Section 8.1 to power down.
T
I
EXAS
NSTRUMENTS
LOAD
1.0V @
15A
-
+
FAN
V2
-
+
A1
-
+
DC
source
V
IN
V1
-
+
Network
Analyzer
Isolation
Transformer
CHA CHB Output
Figure 8-2. Control Loop Measurement Setup
8.4 Equipment Shutdown
1. Shut down VIN.
2. Shut down LOAD.
3. Shut down fan.
4. Shut down oscilloscope.
Test Procedures www.ti.com
12 TPS56121 Step-Down Converter Evaluation Module User's Guide SLVU445C – MARCH 2011 – REVISED AUGUST 2021
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