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FRA response to TI TPS55340 evm

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A Cleverscope CS328A system combined with a Jensen VB-1BB isolation transformer enables frequency response analysis (FRA) of the TI TPS55340EVM-148, offering a stable, non-invasive method to measure power supply gain and phase margins directly on the board..

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  • Special Features
  • Specification

The Cleverscope FRA method injects a small AC signal across a modified 50-ohm resistor (R3) in the feedback loop of the TPS55340 EVM. The response is measured using two scope channels and a 14-bit ADC with filtering enabled to reduce noise.

The CS328A’s internal signal generator is isolated via a 1:1 transformer and a 20 dB attenuator to deliver a clean signal. Measurements are processed using log frequency sweep (20 steps/decade), Fourier transform, and peak averaging with interpolation. This setup reveals phase margins and gain behavior critical to assessing stability in real-world operating conditions (e.g., Vin at 8V, 12V, and 24V under 1A and 2.5A loads).

The Cleverscope results consistently matched those from TI's own network analyzer and Venable's system, confirming the accuracy and usefulness of this setup.

  • Enables real-time Gain/Phase measurement in switching noise environments

  • Injects minimal signal (10–13 mV) for non-disruptive testing

  • Uses synchronous sweep and narrow band correlation for accurate readings

  • Compatible with isolated flyback converters like TPS55340

  • Application software (v4.672) supports auto step and adaptive sweep

  • Matches results of TI and Venable analyzers with high fidelity

Parameter Value/Description
Instrument Cleverscope CS328A
Transformer Jensen VB-1BB (1:1 video isolation)
Test Signal Amplitude ~11–13 mV peak
Sweep Frequency Range 7.6 Hz to 200 kHz (Log sweep, 20 steps/decade)
Channels Used A = TP6 (input), B = TP2 (output)
Load Conditions 1A and 2.5A using 5Ω and 2Ω resistors
Power Input Levels 8V (Low), 12V (Nominal), 24V (High)
Phase Margin (12V, 2.5A) 60° at 6.8 kHz (Unity Gain)
Gain Margin -13.1 dB at 25.6 kHz (0° Phase)
ADC 14-bit with 1.28 μs moving average filter
Windowing Hanning window for spectrum analysis
FRA FOM Range Optimal at 0.2–10
Software Version Cleverscope App v4.672