TPS65100 Power Up / Start Up Problem

Fred Sauer

Other Parts Discussed in Thread: TPS65100, PTN78060W, TPS65100EVM-030

I am having issues with the TPS65100 during startup. We have built a couple 100 modules with no problems. I am searching the components to see if we have a bad part. When operating, the output voltages are all correct.

Vin = 3.30

AVDD (Vo1) = 10.8

VGH (Vo3) = 16.2

VGL (Vo2) = -7.12

VCOM = 4.16

The Vin is V33 and comes from a TI PTN78060W 3 Amp switching regulator. At key ON, in a failure mode, the AVDD voltage is 8.60 for some 1-3 seconds and then the TPS65100 will turn OFF. On the scope, you can see the startup of AVDD is either good or bad within the first 2.5 mSec. You can see the voltage ramp and break at 8.6 or ramp to 10.4. The LCD load is measured at 50 mAmp max. When the TPS65100 turns ON in a failure mode it is indicated almost immmediatly by the system current draw. When the TPS65100 works, the module will draw 225 mAmp. When the TPS is going to start with a bad AVDD voltage, the module current draw is 348 mAmp and then drops to 200 mAmp when the TPS shuts off.

1007.32007-901C Schematic.pdf

over 10 years ago

0 Fred Sauer over 10 years ago

Prodigy 100 points

The parts on the failing boards are all correct and per the schematic I attached to the original input.

0 Brigitte over 10 years ago

TI__Guru 61695 points

Hello Fred,

The undervoltage protection of this IC is just activated if all outputs have been at least once above the power good threshold, so I expect that the thermal shutdown is turning the IC off. Would you please check if the IC gets hot when the wrong output voltage is happening?

Your input capacitance is very limited with just a 2.2uF capacitor. You might check if the problem is getting better when adding there 2*10uF in parallel to C77.

Please check the 3.3V while the AVDD is 8.6V to check if there is an issue with the input voltage. Maybe the current drawn from the 3.3V rail prevents the PTN78060W to start properly. This problem can be overcome by adding some delay to the EN pin of TPS65100.

According to the datasheet C64 should be 6.8pF and not 15pF.

Another possibility could be some stability issues, you could check if the problem is gone with changing C74 to 2.2nF and/or reducing R58 to 10k or even lower.

The above checks and changes are listed according the likelyhood of being the root cause. If all of these are not helping to solve the issue, it is essential to get measurements of all output voltages, the input voltage and if possible the currents when the problem occurs.

Best regards,
Brigitte

0 Fred Sauer over 10 years ago in reply to Brigitte

Prodigy 100 points

I have made updates to two units with the addition of 22uF at C77 and changed C64 to 7.5pF. Attached is another scope shot with VGL and Vdd.

6428.TEK0003.TIFe VGL started at

0 Brigitte over 10 years ago in reply to Fred Sauer

TI__Guru 61695 points

Hello Fred,

Please excuse the delay in answer. Do you still have issues with the TPS65100?

I do not fully understand the last post.

Best regards,
Brigitte

0 user4625485 over 8 years ago in reply to Brigitte

Prodigy 80 points

Bonjour,

When I put the input voltage to 5V , all outputs are 5V . While normally I should have 13V , -7V , 3.3V and 23V

I do not know what to do?

0 Ilona over 8 years ago in reply to user4625485

TI__Expert 8010 points

Hello,

Did you set the EN- pin to VIN? If yes, can you share your schematic with me?

Thank you,
Ilona

0 user4625485 over 8 years ago in reply to Ilona

Prodigy 80 points

0 user4625485 over 8 years ago in reply to user4625485

Prodigy 80 points

Hello
The pin " enable" is connected to the input

0 user4625485 over 8 years ago in reply to user4625485

Prodigy 80 points

Output " vo1 " we always 5v

0 Ilona over 8 years ago in reply to user4625485

TI__Expert 8010 points

Hello,

Maybe we have a misunderstanding here. Are you using the TPS65100EVM-030 for your evaluation or is this request concerning your own design?
Can you detail more about your application that this part is implemented for?

Thanks,
Ilona

0 user4625485 over 8 years ago in reply to Ilona

Prodigy 80 points

I used the " TPS65100" to manage a lcd screen

0 Ilona over 8 years ago in reply to user4625485

TI__Expert 8010 points

Is this request the same as the original question from Fred Sauer? Otherwise I would open a new post that only deals with your current request.

Thank you,
Ilona

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TPS65100 Power Up / Start Up Problem