TPS25985: glitch in V(OUT), but V(DVDT) looks smooth

JSR

Part Number: TPS25985

Tool/software:

Hello, please see above the scope trace of the TPS259850:

yellow trace: V(IN)
blue trace: V(DVDT)
purple trace: V(OUT)

Good: V(DVDT), blue, starts rising smoothly when ENABLE, not shown, goes high. This looks as expected.
Bad: V(OUT), purple, makes a sudden jump while V(DVDT) is still low. It seems like the FET is being turned on temporarily by some other mechanism. I did not expect this.

Does the TPS25985 have some other functionality that would turn on the FET while V(DVDT) is still low?

over 1 year ago

0 Kunal Goel over 1 year ago

TI__Guru* 79181 points

Hi JSR,

I will check and get back on this.

Regards

Kunal Goel

0 JSR over 1 year ago in reply to Kunal Goel

Prodigy 30 points

Great, thanks!

0 Kunal Goel over 1 year ago in reply to JSR

TI__Guru* 79181 points

Hi Jsr,

When VIN slew rate is very high then there can be internal FET CDG to CGS coupling causing VOUT to jump.

Regards

Kunal Goel

0 JSR over 1 year ago

Prodigy 30 points

Thanks Kunal,

High slew rate on VIN makes good sense for causing the first bump in VOUT that happens just as VIN is starting its ramp. Thanks, that makes total sense.

Any ideas about the second jump in VOUT that happens just as V(DVDT) (blue) is starting its ramp? At that point VIN (yellow) is fully settled.