TPSM82864A: Falling transition time at VIN

Arkadi shap

Intellectual 650 points

Part Number: TPSM82864A

Hi,

In the section 7.3 in the datasheet there is a limitation on VIN falling ramp.

The falling slew rate of VIN should be limited if VIN goes below VUVLO - 10mV/us.

I have

What will happen if the ramp will be faster?

When VIN goes below UVLO, the DCDC stops operating. Why the ramp is important if the DCDC is off?

Best Regards,

Arkadi

8 months ago

0 Chris Glaser 8 months ago

TI__Guru*** 145990 points

Hi Arkadi,

In general for many devices, very fast slew rates of the supply voltage can cause issues with the internal logic and supply rails.

I have not seen a customer have an issue with this limit in their application. If Vin is kept low for a decent amount of time, the residual charge on internal nodes will leak off and the device will have a full and proper reset.

Chris

0 Arkadi shap 8 months ago in reply to Chris Glaser

Intellectual 650 points

Hi Chris,

Thank you for your answer.

You mean that if the falling slew rate will be faster than 10mV/us, but the period of time that VIN will be low, it will not cause any problems.

Is it correct?

What is this period of time?

Regards,

Arkadi

0 Chris Glaser 8 months ago in reply to Arkadi shap

TI__Guru*** 145990 points

Yes, if you exceed that slew rate, you should keep Vin at 0V for some time before going back up again. The time it needs to remain low is not defined, since it depends on internal parasitics, etc.

How is Vin removed and applied in your system?

Chris

0 Arkadi shap 8 months ago in reply to Chris Glaser

Intellectual 650 points

In a proper operation it will be removed for a long time, but we want to operate correct in unexpected situations...

+1 Chris Glaser 8 months ago in reply to Arkadi shap

TI__Guru*** 145990 points

Fully discharging Vin (down to 0V) also gives a proper reset. This is normally the case in most systems.

I've not seen this be an issue at any customer before.

Chris

0 Arkadi shap 8 months ago in reply to Chris Glaser

Intellectual 650 points

Thank you very much!

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TPSM82864A: Falling transition time at VIN