TPS629210-Q1: IBB current limit calculation

Hi Dice,

Good question. It should be low-side FET current limit.

If the IL(max) exceeds the Low-side FET current limit but not exceeds the high-side FET current limit, the device would not protect itself immediately. However, when the high-side FET off and low-side FET on, the high-side FET would not be turned on until the inductor current decreases below the low-side FET current limit which would influence the duty and output voltage by this protection behavior. Here using the low-side FET current limit is just to ensure the duty and output voltage would not be influenced by any protection of the device under IBB application.

Hi Dice,

The "Low-side FET current limit" is triggered when inductor current is high than the limit value. The low-side FET would keep on to decrease the inductor current until it reach the limit value as below waveform FYR. So it's indeed valley current. When this is triggered, the output voltage usually decrease due to more off-time.

However, the purpose of this IBB calculation is to ensure that the peak inductor current would not exceed the "Low-side FET current limit" value so that no protection would be triggered and the device could performance well with correct output voltage.