TPS22965: Discharge FET function

Michiaki Tanii

Expert 4610 points

Part Number: TPS22965

Could you kindly advise the conditions that discharge FET is off ?

Our customer see the below phenomenon.

- VBIAS : 5V

- VIN : 3.3V

- Cload : 250uF

- CT : 500pF

It takes about 30 sec to drop to 0V at Vout pin even if VON is turned off.

In our understanding, Vout should be 0V for about 100m sec if discharge FET was worked properly.

We would much appreciate if we get your any comments.

Thank you and best regards,

Michiaki

over 5 years ago

0 Shreyas Dmello over 5 years ago

TI__Mastermind 32650 points

Tanii-san,

For TPS22965, the QOD is ON whenever the switch is OFF. This QOD feature is not available on TPS22965N.

Could you please share a scopeshot of this event as 30 seconds is a very long discharge time. I would like to see Vin, Vout and ON.

0 Michiaki Tanii over 5 years ago in reply to Shreyas Dmello

TI__Expert 4610 points

Could you provide the saturation characteristics for discharge FET ?

If no, could I show the saturation characteristics of Nch FET such as CSDxxxx as reference ?

Thank you and best regards,

Michiaki

0 Shreyas Dmello over 5 years ago in reply to Michiaki Tanii

TI__Mastermind 32650 points

Tanii-san,

Please share a scopeshot of the actual discharge event and a schematic. This is because there might be system considerations that could affect this. Has the customer been able to reproduce this issue on an EVM?

0 Michiaki Tanii over 5 years ago in reply to Shreyas Dmello

TI__Expert 4610 points

Hi Shreyas,

I understand what you said but customer would like to confirm if RDS_on is changed by VBIAS and VIN dramatically.

In my understanding, RDS_ON would be affected by VBIAS not VIN.

Customer already has found the leak current from another circuit but just would like to confirm on the above.

Thank you and best regards,

Michiaki

0 Shreyas Dmello over 5 years ago in reply to Michiaki Tanii

TI__Mastermind 32650 points

Tanii-san,

ON resistance is more dependent on Vbias than Vin. There will be slight changes in on resistance over varying Vin for a fixed Vbias.

On the other hand, there will be a noticeable change in on resistance for a fixed Vin at different Vbias.

0 Michiaki Tanii over 5 years ago in reply to Shreyas Dmello

TI__Expert 4610 points

Hi Shreyas,

Could you provide the saturation characteristics for discharge FET ?

If no, could I show the saturation characteristics of Nch FET such as CSDxxxx as reference ?

Thank you and best regards,

Michiaki

0 Timothy Logan over 5 years ago in reply to Michiaki Tanii

TI__Mastermind 34935 points

Tanii-san,

We do not provide the saturation characteristics of the internal Nch FET.

Specifically is there a data point you were looking for?

Power management

Power management forum

TPS22965: Discharge FET function