TPS40200 loading question

Cam Buskell

Other Parts Discussed in Thread: TPS40200-HT

Hello.

I have built and tested a 5.0V supply with the TPS40200-HT chip based on the SwitcherPro schematic and layout.

I originally built this supply for a 500mA max supply. It is currently being used on a system that draws 40mA (tested on an external power supply).

Here is where the issue arrises:

My supply will provide 5V, but as soon as the load (40mA system above) is connected, my supply voltage drops to 1.2V.

Can you please provide some assistance with this issue?

Thanks.

over 13 years ago

0 Na Kong over 13 years ago

TI__Genius 17240 points

Hi Cam,

Can you share the schematic and layout?

Can you check the switch node waveform at the instance when the load is applied?

Regards,

0 Cam Buskell over 13 years ago in reply to Na Kong

Intellectual 425 points

Hi Na.

Here are the preliminary schematics.

Is there a way I can share my proprietary schematics and layouts with you?

0 Na Kong over 13 years ago in reply to Cam Buskell

TI__Genius 17240 points

Hi Cam,

The compensation in your schematic seems giving non-stable loop. You may try the parameters given in the SwitcherPro.

I also want to confirm that R79 in your circuit is not populated, because it will disable the softstart and the inrush current at startup may trigger overcurrent protection.

If you could give your email address here, we can discuss offline.

Regards,

0 Cam Buskell over 13 years ago in reply to Na Kong

Intellectual 425 points

cbuskell@leespecialties.com

R79 is not populated. I included R79 initially going through the calculations on the datasheet, but have removed it as per SwitcherPro suggestions.

Power management

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TPS40200 loading question