TPS24741: Regarding requirement of external gate capacitance for ensuring MOSFET stability.

Akshat Madaan

Part Number: TPS24741
Other Parts Discussed in Thread: CSD16415Q5,

Tool/software:

Greetings,

We are currently using the TPS24741 IC in a Priority MUXing configuration with CSD16415Q5 external MOSFETs and are encountering certain problems.

According to the part datasheet, we would be requiring an external gate capacitance of around 1.37nF (Cgs,min) to ensure stability. However, even upon choosing 3.3nF as external gate capacitance, when the input voltage is made to rise from 8.4V to 8.5V (which is the undervoltage lockout release that we set) the gate voltage starts oscillating, and the MOSFET heats up excessively. Only upon further increasing the voltage to around 8.8V, the HGATE turns on properly and give a stable output.

In Yellow: IMON pin

In Blue: Output Voltage

Any suggestions/ ideas on as to why this may be happening?

Thanks,

Akshat

9 months ago

0 Avishek Pal 9 months ago

TI__Mastermind 44040 points

Thanks for reaching out. We will get back to you by the end of next week.

0 Akshat Madaan 9 months ago in reply to Avishek Pal

Prodigy 40 points

Hi Avishek! Did you get a chance to look at this issue yet?

0 Avishek Pal 9 months ago in reply to Akshat Madaan

TI__Mastermind 44040 points

I think this is because of the hysteresis on the ENHS pin. When the input voltage is increased to 8.8V level, the device is come out of the UVLO hysteresis.

0 Akshat Madaan 9 months ago in reply to Avishek Pal

Prodigy 40 points

Is there any way this could be related to the inrush timer and power limit at startup? If there is a load current over 3 Amps, these oscillations start happening. The power limit and inrush timer at startup values were all selected with the help of the TPS24741 Calculator tool provided. If this issue is due to hysteresis, could this be improved? Because this does not occur on the MAINS supply line, only on the AUX.

0 Avishek Pal 9 months ago in reply to Akshat Madaan

TI__Mastermind 44040 points

Akshat Madaan said:
Is there any way this could be related to the inrush timer and power limit at startup?

I don't think so.

Akshat Madaan said:
If there is a load current over 3 Amps, these oscillations start happening.

If VIN is more than 8.5V with a load current > 3A, there is no oscillations. Correct?

Akshat Madaan said:
If this issue is due to hysteresis, could this be improved?

Please add 100nF capacitor as shown below.

Akshat Madaan said:
Because this does not occur on the MAINS supply line, only on the AUX.

What are the things different in these two schematics?

0 Akshat Madaan 9 months ago in reply to Avishek Pal

Prodigy 40 points

Added a 100nF capacitor at the point mentioned (had a 22nF capacitor there earlier), observed no change the issue still remains. The only thing different in these two schematics are the UVLO and OVLO thresholds. The oscillations start at 8.58V and continue upto 8.6~8.7V and stop thereafter, if the load current> 3A. Oscillations do not occur at a much lower current, at 1.5-2A they still occur but the voltage band in which they occur is small. The problem arises glaringly at higher currents (>3A)

0 Avishek Pal 9 months ago in reply to Akshat Madaan

TI__Mastermind 44040 points

This is an expected behavior due to UVLO hysteresis. No solution for this.

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TPS24741: Regarding requirement of external gate capacitance for ensuring MOSFET stability.