TPS3808: C_LRESET capacitor value

Oba

Part Number: TPS3808

Hello,

My customer has a question for TPS3808.
Now they put a 100pF capacitor for C_LRESET (capacitor connected to the RESET pin) and want to change it to 10,000pF to improve noise immunity.

But increasing capacitor value means that it would cause a kind of short condition (overcurrent condition) on RESET pin even though it is a short time.
They are concerting about this condition and if it would damage the device.

How big capacitor can be connected to RESET pin?
Is 10,000pF no problem?

Regards,
Oba

over 2 years ago

0 Jake F over 2 years ago

TI__Intellectual 1210 points

Hi Oba-san,

Shown in Figure 7-8, the resistance as seen into the RESET pin is approximately 85-90 Ohms for VDD=3.3V, so 10nF would be fine to use.

Jake

0 Oba over 2 years ago in reply to Jake F

TI__Genius 15750 points

Hello Jake,

Thanks for your answer.

If Rds_ON is 85 ohm, current is about 59mA@VCC=5V which is over the absolute max 5mA even though a short time.

How to think about it?

Regards,
Oba

+1 Jake F over 2 years ago in reply to Oba

TI__Intellectual 1210 points

Hi Oba-san,

You are correct in thinking about it like this. The abs max current of the RESET pin is specced for a DC current, whereas discharging a cap is a transient.

It still should be fine, but if additional precautions are to be taken, adding a series resistance to the pin to further reduce the current is my recommendation.

Jake

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TPS3808: C_LRESET capacitor value