TPS51916 VTT overshoot at power down

Hirotsugu Kobayashi

Other Parts Discussed in Thread: TPS51916, TPS51116

Hi All,
Our customer found the VTT overshoot at power down.
Please see attached file. CH1 is VIN, CH2 is VDDQ, CH3 is VTT.
VTTREF output is correct and no overshoot, but VTT output is overshoot a moment.

Is this phenomenon right?

TPS51916 is used in the following condition.
Vin is 5V, S3 and S5 are tied to Vin, VDDQ is 1.5V, VTT is 0.75V.

Best regards,

over 8 years ago

0 Hirotsugu Kobayashi over 8 years ago

Mastermind 8485 points

Hello,

Please someone answer my question.
This phenomenon occurs only in TPS51916, It's doesn't occur in TPS51116.
Is there difference in the structure of VTT?

Best Regards.

0 JohnTucker over 8 years ago in reply to Hirotsugu Kobayashi

TI__Guru**** 191445 points

I'm not sure why that would be. The two devices seem similar in the Vtt LDO implementation. Let me see if I can find someone who knows the two devices well.

0 Bill Lin over 8 years ago

TI__Prodigy 500 points

1. VTT output current changes from heavy load to light load in a rapid manner during it discharges, that is why you see VTT peak, for tps51916 as far as peak not exceed 3.5v it is safe
2. suggest you using the tracking discharge mode, which discharges faster than non-tracking mode
3. increasing the VTT output capacitance also help reduce the peak

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TPS51916 VTT overshoot at power down