SNVA962 December   2020 TPSM5601R5H

 

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4.2 System Loop Stability

Stability is an important factor in the system when adding more output capacitance. The guideline for a stable design is a desired phase margin of at least 45°. In extreme conditions too much output capacitance added to the system results in a lowered bandwidth and phase margin less than 45°. Table 4-1 shows the phase margin for each output voltage selection measured from the original BOM (COUT = 2 × 4.7 µF) of the TPSM5601R5HEVM.

Table 4-1 Phase Margin of IBB TPSM5601R5H
VIN (V) VOUT (V) IOUT (A) Fcrossover (kHz) Phase Margin (°)
24 –2.5 1.35 19.13 54.4
24 –3.3 1.3 19.03 57.0
24 –5 1.24 18.15 54.7
24 –12 1.0 13.90 54.3
24 –15 0.92 12.22 53.7

Additionally, too much output capacitance can falsely trigger hiccup-mode in the TPSM5601R5H. After start-up, hiccup mode is a feature in the module that protects the device against output short-circuit conditions. In this mode the high-side and low-side MOSFETs power off and wait for a fixed hiccup time interval before restarting the device operation. Larger output capacitance results a longer charge time of the capacitors to meet the desired output voltage. The device can see this as a false short circuit condition and trigger hiccup mode.