MCP73837 Li-ion USB charging

[zerosignal]

Hi there!
First post here - great channel and forum. I would be grateful if someone more experienced could give me some guidance on a circuit I am designing.

I am basing a design on the MCP73837 dual input lithium ion battery charger IC. There is already a great reference design in the A1149 application note http://ww1.microchip.com/downloads/en/AppNotes/01149c.pdf although I am not quite sure how best to set the PROG2 input to select the 500mA USB charging mode without the use of an additional MCU.

I understand that the pin can be driven logic low to select 100mA mode, and that this could be achieved by tieing the input to ground but for a logic high to select 500mA operation can I just tie this input to the power rail at the top of the attached diagram or is this just totally wrong?

The design I am working on is a battery powered Raspberry Pi Zero project for which I rather not have to use a GPIO pin and additional software to drive this input on the charging IC high. I'm reasonably comfortable with the operation of the rest of the design detailed in the application note however.

Any advice on how best to proceed would be greatly appreciated.

Thanks!

[trophosphere]

Tie PROG2 to the positive rail of your USB charging port. Per the datasheet on page 5, the input voltage needs to be at least 0.8Vdd for Vdd = VUSB when input power source is from USB-port.

[zerosignal]

Cool thanks for the response.

I had seen the minimum value and the Vdd changes between Vac and Vusb depending on which sources were present but was unsure on where to tie into this.

There are plenty of designs floating about that tie the input low but none I can see that use the high mode. Simply leaving it low would take days to chatge the a 3000mah battery!

Thanks again.