TPS54328: The minimum slow start time

Liu Yang

Part Number: TPS54328

Hi Team,

Please help me answer the follow question, thank you so much.

I am using TPS54328 to generate 5V to 3.3V. Current output 3.3V rise time is a problem. At present, a 3.3 nF capacitor is connected to the SS pin for soft start(according to datasheet). What is the minimum value of the capacity of the capacitor that can be connected to the SS pin and the minimum time that can be set for soft start?

Best Regards,

Tom.Liu

over 5 years ago

0 Iven Su over 5 years ago

TI__Expert 8245 points

Hi,

The minimum start time might be limited by the charging current of output capacitors which might trigger current limit when you try a smaller soft-start capacitor. So its minimum value is also determined by your output capacitors, thanks.

0 Liu Yang over 5 years ago in reply to Iven Su

TI__Expert 5945 points

Hi,

Slow start time tss is calculated by Equation 2 in datasheet.

I want to know what is the minimum value of the soft-start capacitor C6, so I can calculate the minimum start time.

In [8.2 Typical Application], C6 is 3300uF.

Best Regards,

Tom.Liu

0 Iven Su over 5 years ago in reply to Liu Yang

TI__Expert 8245 points

Hi,

A reconmended minimum value of the soft-start capacitor is 1nF based on normal working conditions. The Equation just works on a resonable range, you maynot get a start time small enough just by changing the soft-start capacitor. Thanks.

0 Liu Yang over 5 years ago in reply to Iven Su

TI__Expert 5945 points

Hi Iven,

I'm sorry for trouble you again.

Could you give me some device which soft start time smaller than TPS54328?

Best Regards,

Tom.Liu

0 Liu Yang over 5 years ago in reply to Liu Yang

TI__Expert 5945 points

Hi Iven,

I'm so sorry for this, but I would be grateful if you can answer my question above.

Best Regards,

Tom.Liu

0 Iven Su over 5 years ago in reply to Liu Yang

TI__Expert 8245 points

Hi,

We often recommend 1nF as the minimum value of the soft-start capacitor for these similar devices. As I said the time's highly depended on your circuits not the device. Thanks.

Power management

Power management forum

TPS54328: The minimum slow start time