TPS40400EVM-351 contains a 49.9-Ω series resistor in the feedback loop for loop response analysis.
- Set up EVM as described in Section 5.3 and Figure 5-2.
- Connect isolation transformer to test points marked TP13 and TP15.
- Connect input signal amplitude measurement probe (channel A) to TP13. Connect output signal amplitude measurement probe (channel B) to TP15.
- Connect ground lead of channel A and channel B to TP14 and TP16.
- Inject 40-mV or less signal through the isolation transformer.
- Sweep the frequency from 100 Hz to 1 MHz with 10-Hz or lower post filter. The control loop gain and phase margin can be measured.
- Disconnect isolation transformer from bode plot test points before making other measurements (Signal injection into feedback may interfere with accuracy of other measurements).