TPS62740: extending soft-start or limiting in-rush current

Bart

Part Number: TPS62740
Other Parts Discussed in Thread: TPS62821

Hi,

is it possible to extend the softstart period, or alternatively limit inrush current to a bigger extent in some way?

In our application we use TPS62740 with a battery of a big resistance, on the turn on the converter causes the battery supervisor turn off.

If not possible with TPS62740, what other device should we consider?

Thanks for help.

over 6 years ago

0 Alfonso Furio over 6 years ago

TI__Expert 3645 points

Hello,

can you tell me how much output capacitance do you have?

0 Bart over 6 years ago in reply to Alfonso Furio

TI__Expert 6470 points

Hello Alfonso,

it is about 230uF.

The Resistance of the source and switches on the path 2-3Ohm

0 Alfonso Furio over 6 years ago in reply to Bart

TI__Expert 3645 points

Hello,

the big output cap increases the inrush current and the device is running out of our spec. You can test with a lower value of capacitance or you can also try to startup with a lower vout selection and further increase it to the desired value (this also will reduce a bit the inrush).

0 Bart over 6 years ago in reply to Alfonso Furio

TI__Expert 6470 points

Hi Alfonso,

thanks for feedback. The problem is that we can't change the capacitance as it is created by a module component for UWB/BT.

Do you have any recommendation for similar converter that would cope with this level of capacitance at the output?

0 Alfonso Furio over 6 years ago in reply to Bart

TI__Expert 3645 points

Hello,

which is the output capacitance used close to our device. Can you tell me also which is the output current and voltage?

The very low Iq of this device is a fundamental spec?

0 Bart over 6 years ago in reply to Alfonso Furio

TI__Expert 6470 points

Hi Alfonso,

Input voltage 3.7V (Li-Ion)

Vout - 3.3V (fixed)

Iout is very variable in time - from uA range up to 300mA.

Thank you.

0 Alfonso Furio over 6 years ago in reply to Bart

TI__Expert 3645 points

Hello,

what about the Iq? do you need as spec for your application? I just need to filter other devices when I look another part for your application.

0 Bart over 6 years ago in reply to Alfonso Furio

TI__Expert 6470 points

Hi Alfonso,

Iq - the lower the better.

Capacitances at the output are 2x10uF + 100nF - due to possible drop of capacitances of the caps under voltage and temp. changes.

0 Alfonso Furio over 6 years ago in reply to Bart

TI__Expert 3645 points

Hello,
if you use TPS62740, you can only start with a lower setting for Vout and after increase to the target value (3.3V). This will decrease a bit the inrush current.
You can also have a look at this device TPS62821 because has a slower soft start. All the other low Iq devices have a faster soft start.
If you can increase your Iq requirements, tps62810 could be an option since it can manage higher output caps and has a pin for adjustable soft start.

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TPS62740: extending soft-start or limiting in-rush current