Tool/software:
Hello,
I observed an abnormal waveform in the power-off sequence of the TPSM86638.
I strongly believe this is due to the hiccup mode being triggered, but I am unable to confirm this because the actual tUVP_HICCUP does not match the value listed in the datasheet.
Therefore, I would appreciate your input on where my understanding may be incorrect.
First, I will attach a diagram of the abnormal waveform. The yellow line represents the 24V input, and the green line represents the 12V output.
I will also attach the surrounding circuit diagram.
The actual tUVP_HICCUP I observed is 34ms.
According to the datasheet, tUVP_HICCUP is listed as 10.5 * tss (p.6).
From equation (2) on p.15, tss is calculated as (22nF) * (0.6V) / (0.6μA) = 2.2ms.
Therefore, tUVP_HICCUP = 10.5 * 2.2ms = 23.1ms, which does not match the actual tUVP_HICCUP observed.
Is my thinking incorrect?
Additionally, since tUVP_HICCUP = 10.5 * tss and tss is determined by the charge time of the SS pin voltage, I assumed that tUVP_HICCUP corresponds to repeating the charge and discharge cycle of the SS pin 10.5 times.
For reference, I also measured the output voltage and SS pin voltage during power-off.
The yellow line represents the output voltage, and the green line represents the SS pin voltage.
It seems that the hiccup mode recovery occurs every time the SS pin completes exactly 8 charge and discharge cycles. Is this behavior expected for the IC?
Best Regards
keiju
