TPS61088: output start up ripple

Howard Zou

Part Number: TPS61088

Hi,

my customer designed the schematic below to convert 5V input to 5.9V output. 9f for ceramic and 9g for resistor means not soldered.

But they find that the output will have large ripple during startup. Blue line below.

The other 3 signals are generated from the 5.9V output so they can be ignored.

Why are there ripple during startup?

over 5 years ago

0 Helen chen over 5 years ago

TI__Mastermind 40080 points

Dear Sir,

Vin=5V and Vo=5.9V is really too close. Please change the operation frequency to 300kHz.

And when Vo and Vin is too close, it is more easy to cause stability issue. So please change Rcomp=R116 from 17.4k to 5.11k then double check the start up performance.

0 Howard Zou over 5 years ago in reply to Helen chen

TI__Genius 12365 points

Helen,

we've tried to reduce the frequency to 277k and it doesn't help. We also tried to raise the output voltage to 8V and it doesn't help eithere.

We can see that VOUT ripple happens before the SW start switching so I don't think it's related to stability.

The ripple always happen when VOUT reaches around 4.2V, even when we raise the output voltage to 8V, there will be ripple when Vout increase to 4.2V before it reaches 8V.