TPS2115A: What resistor to use for R1?

Hi Art, 

Art Mecina said:

Our customer wanted to know what resistor to use for R1 (stat PU) listed in the datasheet. It doesn't indicate what resistance pulls it low. Presumably the PU needs to be a higher resistance. So it pulls up if stat is High-Z, and pulls low if stat is low.

status pin is open drain output. When STATUS pin pulls down, the internal fet with drain connectedhas very low resistance and you essentially can consider it as a short to ground. the R1 pullup just ensures that ST pin can go high. When st pulls down we dont want it to be small due to divider effect and we dont want unecessary current sonsumption. and you don't want it huge like 10s of Mohm which could have RC effect. 

With that said, the rule of thumb is pullups are nearly always around, or exactly 10k, this is the sweet spot and we use 10kohm pullup on our EVM. 

Recommend to just use 10k

Art Mecina said:

In addition, what would cause Input 2 to not be active, even with D0 and D1 set low? On his design  Input 1 works when D0 is high, as expected. However only part of Input 2's voltage is being passed through.

If D0/D1 are both LOW, then IN2 will be switched to output unless the input is invalid/doesn't meet UVLO conditions. 

Could you please provide us more information about input and load conditions.

If possible, Scope shots would be great, of VIN1, VIN2, OUT, and D0/D1 settings. 

Best

Dimitri