Hi, we have a circuit with the MPQ5069 load switch that isn’t working as expected. Here’s what’s happening:
We have a circuit where the MPQ5069 is supplying 2A to a resistive load and we’ve set a current limit on it of 3A. On turn on I scoped the waveform on the ISET pin and saw that the current limit is exceeded at 0.6V for less than the time set by the TIMER pin before the voltage on the ISET pin falls to 0.4V. After the TIMER triggered by the initial current limit violation passes the MPQ5069 faults and turns the output off and then on again.
However! The data sheet for the MPQ5069 says:
“When the current reaches its over-current limit threshold, a 200µA fault timer current source charges the external capacitor (CT) at the TIMER pin. If the current-limit state ceases before the TIMER pin reaches 1.23V, the MPQ5069 returns to normal operation mode and a low-value resistor discharges CT after the TIMER voltage reaches 1.23V. If the current-limit state continues after the TIMER pin voltage reaches 1.23V, the MOSFET switches off. The subsequent restart procedure then depends on the selected retry configuration.”
So, the chip should enter the normal operation condition after the inrush current ends. However, this does not happen. It seems that if the current limit is exceeded at all when the device is in operation it will turn off.
Is there a work around for this other than just setting very high current limits? I tried increasing the TIMER capacitor value but if the chips sees a current limit fault during inrush it still faults after the timer expired even if the current limit is no longer violated (like milliseconds after).
As far as I can tell this is a silicon bug in the chip which doesn’t have a fix other than setting a very high current limit.