UCC27524: Questions for the ENA voltage of the UCC27524.

Hi Marsh,

Marsh Cai said:

1, if left floating, what voltage of the ENA will be?

It should pull to VDD. 

Marsh Cai said:

2, if disconnect from MCU, but with a 1nF connected to gnd. what voltage will the ENA be? in my understanding, it will be charged to VDD, right? But i see a stable 5V on this pin, can you help to explain?

It should be VDD. I double-checked on a board and it pulled to VDD for me when I left it floating, I can also measure about 200k from EN to VDD with an ohmmeter. Can you check your setup? Also, are you using UCC27524 or UCC27524A? I checked on the non-A version. 

Marsh Cai said:

3, What configuration would you recommend, if we plan use DSP GPIO to drive the ENA directly.

It depends on the voltage rating and structure of your GPIO pin. If it is open-drain, there is a possibility for the EN voltage to reach VDD which may be too high for your DSP. If you are concerned about this, you can add a pullup to 3.3/5V via a <=10kΩ pullup. this will overpower the device's pullup. You could also use a pulldown or a zener diode. 

There is a chance that the GPIO pin is push-pull, or has some ESD path when the voltage exceeds the DSP's VDD. There is a good chance you can just drive the EN pin directly with no pullups or pulldown without issue, but I would check carefully. 

Thanks,

Alex M.