TPS40200: Turning output on/off with logic signal

John McClure

Part Number: TPS40200

I wish to use a 5V logic signal to control the TPS40200 - 0V turning the outputs off, 5V turning it on.

-Can I reliably do this by driving the SS pin low (for OFF) or leaving it floating (for ON)?

-Can I do this by placing a P-channel MosFET above the VDD pin? My only concern with this is that the small voltage drop across the MosFET would throw off the ISNS detection - will this cause problems?

-I can do this by placing a high-current P-channel MosFET to disconnect the entire circuit from power, but wish to avoid this due to PCB layout space constraints.

Thank you!

over 6 years ago

0 Frank De Stasi over 6 years ago

TI__Guru 71985 points

The SS pin is meant to be used as an on/off control as well as soft-start. You would use an open drain NMOS with drain
to SS pin and source to ground. As long as the MNOS you select will pull down the SS pin to 100mV or below, the device will
shut down. Choose an NMOS will low leakage and a small enough Rdson to reliably pull down the SS bin below the start threshold.

0 John McClure over 6 years ago in reply to Frank De Stasi

Prodigy 90 points

Thank you. What is the output impedance, or internal pullup value, that I must overcome to pull this pin low? I must know this in order to select an appropriately small Rdson value for the pull-down MosFET.

0 Frank De Stasi over 6 years ago in reply to John McClure

TI__Guru 71985 points

Based on the data sheet the pull up resistor an vary from 65k to 170k, with a maximum of 8V on the top of the resistor.

0 John McClure over 6 years ago in reply to Frank De Stasi

Prodigy 90 points

I will implement the solution you suggested. Thank you!

Power management

Power management forum

TPS40200: Turning output on/off with logic signal