BQ25895: how to connect OTG pin if the customer doesn't need OTG function?

Howard Zou

Genius 12365 points

Part Number: BQ25895

Can I connect it directly to GND?

over 5 years ago

0 Paul Yeh over 5 years ago

TI__Genius 14755 points

Howard,
Yes, if you don't need OTG function, you can connect OTG pin to ground.
Thanks

0 Howard Zou over 5 years ago in reply to Paul Yeh

TI__Genius 12365 points

Paul,
do I need a resistor to connect to GND? what's the proper value?
Besides, generally speaking, why we always connect pin to GND through a resistor?

0 Paul Yeh over 5 years ago in reply to Howard Zou

TI__Genius 14755 points

Howard,
To use resistor connect to ground, I think the purpose is it will be easier for engineer to evaluate boost mode if they want to enable OTG function.
As for pull down resistor, I think 10kohm should be ok.
Thanks

0 Howard Zou over 5 years ago in reply to Paul Yeh

TI__Genius 12365 points

Paul,
how about PMID pin.
Could it be floating when OTG is not needed?

0 Paul Yeh over 5 years ago in reply to Howard Zou

TI__Genius 14755 points

Howard,
PMID pin is bulk converter's input and boost mode output pin, so you must put bulk caps closed to this pin.
In general, there should be 40uF cap at least.
Thanks

0 Howard Zou over 5 years ago in reply to Paul Yeh

TI__Genius 12365 points

Paul,

In datasheet page 31 it says "the host has to reset the watchdog timer by writing 1 to WD_RST bit before the watchdog timer expires"

So write I2C without writing 1 to WD_RST will not reset the watchdog timer, right?

0 Paul Yeh over 5 years ago in reply to Howard Zou

TI__Genius 14755 points

Hi,
Yes, your comment is correct. Watchdog timer purpose is to avoid host is hangup, so if host access BQ25895 register via I2C within watchdog timer then BQ25895 will not reset register to default.
Thanks

0 Howard Zou over 5 years ago in reply to Paul Yeh

TI__Genius 12365 points

No.
what I meant is that if host access BQ25895 register via I2C without writing 1 to WD_RST when watchdog timer counts to 5s, the watchdog timer will still be 5s, it will not reset to 0s and start a new count cycle. Right?

0 Joel Hernandez II over 5 years ago in reply to Howard Zou

TI__Mastermind 25800 points

Hey Howard,

You are correct. The watchdog timer expiration will be reported as a fault. As Paul mentioned, the registers will be reset to their default values (with exception to the input related registers). Until you make a host-controlled change to the registers, the charger will remain in "Default Mode". Writing to the registers exits "Default Mode" and enters "Host Mode" and will restart the watchdog timer.

Regards,
Joel H

0 Howard Zou over 5 years ago in reply to Joel Hernandez II

TI__Genius 12365 points

Joel,
So let's say it's already in "host mode", and the watchdog timer is counting.
Now if I write registers again, but I don't write 1 to WD_RST bit, will the watchdog timer restart?

0 Joel Hernandez II over 5 years ago in reply to Howard Zou

TI__Mastermind 25800 points

Hey Howard,

In this case, you are letting the Watchdog timer expire without resetting, even if you wrote to the registers.

This would not restart the watchdog timer. It would actually cause it to expire, forcing a fault flag, and also place the charger back into default mode.

Regards,
Joel H

Power management

Power management forum

BQ25895: how to connect OTG pin if the customer doesn't need OTG function?