TPS628503-Q1: [Bosch] VIN unstable

Mingkang Song

Part Number: TPS628503-Q1
Other Parts Discussed in Thread: TPS628502EVM-092, , TPS628502-Q1

Tool/software:

Dear team,

My customer Bosch are using TPS628502EVM-092 and replaced the chip with TPS628503-Q1 for short-circuit testing.
We found that when Vout is short-circuited to ground, the voltage of VIN also becomes very unstable. From the manual, we can see that when overcurrent occurs, the HS switch will be turned off, and then the current of LS will drop, and then HS will be turned on again, which will cause VIN to become unstable.

I would like to ask if the VIN instability we see is caused by the mechanism of HS turn on again? Can this mechanism be turned off? Thanks!

(The picture shows the waveform of Vin when VIN=4V, Vout=1.8V, and Vout is short-circuited. The EVM is the default configuration of TPS628502EVM)

Regards,

Mingkang

4 months ago

0 Farheen 4 months ago

TI__Genius 16940 points

Hello Mingkang,

Let me have a look and get back to you asap.

Thanks,

Farheen

0 Farheen 4 months ago in reply to Farheen

TI__Genius 16940 points

Hello Mingkang,

Just to double check, you are using the official EVM of device BSR-092?

Thanks,

Farheen

0 Mingkang Song 4 months ago in reply to Farheen

TI__Intellectual 2230 points

Hi Farheen,

Yes, we are using official TPS628502EVM-092 and replaced the chip with TPS628503-Q1.

Looking forward to your reply!

Regards,

Mingkang

0 Farheen 4 months ago in reply to Mingkang Song

TI__Genius 16940 points

Hello Mingkang,

I quickly checked in the lab and tested by shorting the output on EVM and I do not see this high frequency noise in Vin:

This looks like high frequency noise which is not coming from device.

Thanks,

Farheen

0 Mingkang Song 4 months ago in reply to Farheen

TI__Intellectual 2230 points

Hi Farheen,

Thanks for your reply.

Just to make sure: are you testing TPS628503-Q1 on the official TPS628502EVM-092?

Thanks!

Regards,

Mingkang

0 Farheen 4 months ago in reply to Mingkang Song

TI__Genius 16940 points

Hello Mingkang,

I have tested on TPS628502-Q1 but it is same family but just rated at 2A and there should not be any difference in terms of short circuit behavior.

Thanks,

Farheen

0 Mingkang Song 4 months ago in reply to Farheen

TI__Intellectual 2230 points

Hi Farheen,

Thanks for your reply!

Farheen said:
I quickly checked in the lab and tested by shorting the output on EVM and I do not see this high frequency noise in Vin:

1. I see that the scale of VIN in your picture is 2V/grid, and the picture I posted before is 100mV/grid, so please help expand the waveform of Vin to 100mV. In addition, the picture I posted before is not high-frequency noise, but 2.22Mhz switching noise.
2. Another question, from your photo, I can see that after Vout is short-circuited, VIN is also disturbed. Is the mechanism shown in the screenshot below taking effect?

It would be better if you could test the TPS628503-Q1 on the official TPS628502EVM-092. Thanks！

Regards,

Mingkang

0 Farheen 4 months ago in reply to Mingkang Song

TI__Genius 16940 points

Hello Minkang,

Understood! It can be because of short, device hits the current limit then the Vout drops but there is still current consumption happening which is making the ripple higher.

But this can not be turned off as it is part of protection circuit. Does this affect the Vin min and max specs?

Thanks,

Farheen

0 Mingkang Song 4 months ago in reply to Farheen

TI__Intellectual 2230 points

Hi Farheen,

Thanks! Could you pls share the waveform that expand Vin to 100mV/grid like I post before?

Regards,

Mingkang

0 Farheen 4 months ago in reply to Mingkang Song

TI__Genius 16940 points

Hello Mingkang,

Today I am out of office because of Electronica. I can check that on Monday and share with you.

Thanks,

Farheen

0 Farheen 4 months ago in reply to Farheen

TI__Genius 16940 points

Hello Mingkang,

Please find the requested:

If you have noticed when it is short input current consumption increases from 17mA to around 600mA..

Thanks,

Farheen

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TPS628503-Q1: [Bosch] VIN unstable