TPS65131: Maximum Output capacitor value

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Guru 21045 points

Part Number: TPS65131

Hi Team,

We have two questions.

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[Q1]

Could you please let us know the maximum output capacitor value?

We understand that Output capacitor is “4 x 4.7 uF, ceramic, 25 V, X7R” in Typical Application.

However, we would like to add 47uF of VPOS output capacitor because Input capacitor of LDO is connected behind VPOS.

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[Q2]

We are evaluating TPS65131 at VIN=5V, VNEG=-15V, VPOS=+15V, IOUT=around 100mA.

-If VPOS output capacitor is “4 x4.7uF”, VPOS startup is normal.

-If VPOS output capacitor is “4 x4.7uF + 47uF”, VPOS startup is abnormal (Switching stop.)

We guess that abnormal startup issue is output capacitor value.

However, we can't understand the mechanism of problem occurrence.

Could you please let us know if you have any concern?

[Image of the measurement waveform]

Regards,

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over 5 years ago

0 Costin Cazana over 5 years ago

TI__Expert 4940 points

Hi,

I have notified our expert regarding this topic. Please expect a response by 5/1/20.

Regards,

Costin

0 Hide over 5 years ago in reply to Costin Cazana

Guru 21045 points

Hi Costin-san,

Thank you for your prompt reply.

I’m looking forward to hearing from you.

Regards,

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0 Liaqat Khan over 5 years ago

TI__Mastermind 18550 points

Hello Hide,

As you have noticed, recommended capacitance in the datasheet at boost output is up to 22uF but we have tested the device with up to 33uF, ceramic X5R/X7R capacitor. We have not done validation for higher capacitance than this. I suspect may be some instability in the control loop at very high capacitance. I would not recommend capacitance higher than 33uF.

Kind Regards,

Liaqat

0 Hide over 5 years ago in reply to Liaqat Khan

Guru 21045 points

Hi Liaqat-san,

Thank you for the detail information.

I greatly appreciate your cooperation.

Regards,

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TPS65131: Maximum Output capacitor value