Power off ft232rl or ftdi with a transistor

Other Hardware 3rd Party Boards
1

Hi,

Want to make some circuit with the lower consumption possible.

How can i power off a ft232rl or ftdi with a 2n2222 transistor when nothing is plugged to the usb?

Can i use 5V of the USBP pin connected to the base of the 2n2222 transistor with a resistor to power on/off the ft232rl chip?

collector connected to the gnd pin of the ft232rl
emitter connected to the gnd

is there any easy way to power off/on the ftdi chip?

thanks in advance

2

Better way is to use a Logic level, Low Rds, P-channel MOSFET between power and FTDI Vcc pin.
Bring the uC TX to the FTDI low before turning off the MOSFET (with a high signal on the MOSFET gate) so that power from the TX pin does not keep the FTDI chip running via internal leakage currents.

3

DC Input Voltage – High Impedance Bidirectionals: -0.5 to + (VCC +0.5) V
DC Input Voltage – All Other Inputs: -0.5 to + (VCC +0.5) V

So: bring any uC outputs to the FT232R low before removing power.

4

Just don't connect the FTDI chip to the board 5v, only power it from the USB and protect the Rx pin from parasitically powering the chip.

Or do you also want the USB to power the board when it's plugged in?

Rob

5

Hi all

You have good ideas. :slight_smile: Thanks

I have some questions

  • how can i use P-channel MOSFET between power and FTDI Vcc pin? Is there a circuit somewhere?

  • how can i protect the Rx pin from parasitically powering the chip

i want to connect usb to charge a lipo, if i unplug the usb, how can i avoid powering the ftdi?

thanks in advance

6

Here is a circuit I've used before, D4 blocks current from the CPUs Tx pin and stops it powering up the FTDI through the internal ESD diodes.

This is only required if the CPUs Tx pin remains at a high state, if you can detect that the USB is not connected you can either drive that pin low or make it an input. In either case it won't power the FTDI.

Rob

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7

Speaking of Schottky diodes, just use one between the USB power (including the FTDI chip) and the main processor. Simple as that - the primary power for the FTDI is only there if the USB interface is plugged in (including a passive charger with no actual USB interface).

Previous comments for parasitic powering apply.