TPS63700 output problem

Vitali Lach

Other Parts Discussed in Thread: TPS63700

Hello,

we’ve got some phenomenon with TPS63700 which is working as -15V inverter.

-15V is used as a bias voltage for photodiodes for the purpose of laser energy measurement.

If the power is off for the hole system for about two days, TPS63700 doesn’t want to start at the first push. After turning power off and on again -15V appears properly.

Please see the attached schematic: do you have some recommendations what he have to improve?

Two years ago we had a similar problem in another schematic where EN was connected to VIN (-15V inverter as well). We found a solution by using a rc element for EN, but applying this method in current project has caused another issue.

I would very much appreciate your help.

Best Regards

Vitali Lach

over 11 years ago

0 Vitali Lach over 11 years ago

Expert 1130 points

I also attached a scope shot:

CH1: EN

CH2: -15V Output

CH3: 5V Input

Best Regards

0 Chris Glaser over 11 years ago in reply to Vitali Lach

TI__Guru**** 150830 points

It looks like there is still some voltage at the -15V net when it is enabled. This 'pre-bias' can cause issues with the startup of the TPS63700, so it is not recommended. You can use a resistor on the output to discharge the output voltage to 0 before starting again.

0 Vitali Lach over 11 years ago in reply to Chris Glaser

Expert 1130 points

Hello Chris,

Thank you very much for that hint; we will try it in the system verification setup

Do you think that more separation of EN and Vin (resistor divider on EN) will also be helpful? I attached a scope shot for better explanation.

Many thanks in advance.

Vitali Lach

0 Chris Glaser over 11 years ago in reply to Vitali Lach

TI__Guru**** 150830 points

Yes, if there is some load that is slowly pulling up the output voltage to 0V, then a delay to the enable threshold would allow more time for this to discharge.

But a better solution, it seems, is to discharge the output. Just a suitable resistor on the output should do this.

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TPS63700 output problem