I am trying to turn a power regulator on and off by it's enable pin. I need a high to turn it on and a low to turn it off. I want it to be turned off at power up so I use a 10K pull-down and make sure the pin is low before I configure as output. Everything works great.
Now I need to move that to a pin expander, MCP23S09. It has open drain outputs, so it doesn't actually make a high, you have to use a pull-up to get a high. It can only make a low. That's no problem on any other pin except this one because it already want's a pull-down. I can't have both.
I have confirmed that the MCP will be configured as input at high impedance when it starts. So if I have a pull-up on there to make the pin capable of giving me a high signal, it's going to turn it on for at least a few hundred milliseconds until I get the MCP configured. I can't have that. It's gotta be off until I turn it on.
How can I solve this conundrum and have a open drain output that can give a high at some point to turn this power on, but can be pulled down to low at startup. Maybe some kind of circuit to invert the logic so my pull-up becomes an OFF signal?