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Does Adafruit's bq24074 need a resistor for the PGOOD pin?
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Does Adafruit's bq24074 need a resistor for the PGOOD pin?

by mcandre on Sat Jun 12, 2021 8:26 pm

I am impressed by how Adafruit automatically often bundles the necessary capacitors and resistors for many popular IC's. Some of the pins are automatically protected this way, including the Charge Enable (CE) pin. However, I am unable to get a clear answer on whether the PGOOD pin is also automatically resistor-protected with anything in the 1 k Ohm - 100 k Ohm range.

See the conflicting documentations:

* https://www.ti.com/lit/ds/symlink/bq24074.pdf
* https://learn.adafruit.com/adafruit-bq2 ... ut/pinouts

Do Adafruit users need to buy a separate resistor for PGOOD or not?

mcandre
 
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Re: Does Adafruit's bq24074 need a resistor for the PGOOD pi

by sj_remington on Sat Jun 12, 2021 10:32 pm

The /pgood pin is active low, and you must not exceed the absolute maximum sink current of 15 mA.

In practice that means the sink current into /pgood should be well below 15 mA at all times. Design your circuit accordingly. If you are using the Adafruit breakout, the schematic diagram shows a 10K current limiting resistor (R11) and LED between "OUT" and /pgood.

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Re: Does Adafruit's bq24074 need a resistor for the PGOOD pi

by mcandre on Sat Jun 12, 2021 10:54 pm

Are you saying to connect PGOOD to bq24074's own OUT pin? Is that required for normal charging, normal load to work?

I want to setup my schematic so that the Arduino is able to behave differently depending on daytime vs nighttime. Is PGOOD not for such a query?

Should I connect another wire to the solar cell positive terminal and clamp that with a buck or resister to an appropriate 3.3V / 5V GPIO pin?

mcandre
 
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Re: Does Adafruit's bq24074 need a resistor for the PGOOD pi

by sj_remington on Sat Jun 12, 2021 10:59 pm

Are you using Adafruit's breakout, or not?

If you are, why not take a look the schematic diagram?
https://cdn-learn.adafruit.com/assets/a ... 1600203224

It is really not clear what you are asking, or why.

From the device data sheet:

9.3.5.7 Status Indicators (PGOOD, CHG)
The BQ2407x contains two open-drain outputs that signal its status. The PGOOD output signals when a valid
input source is connected. PGOOD is low when (VBAT + VIN(DT)) < VIN < VOVP. When the input voltage is outside
of this range, PGOOD is high impedance.

sj_remington
 
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Re: Does Adafruit's bq24074 need a resistor for the PGOOD pi

by mcandre on Sun Jun 13, 2021 12:14 am

Ah, I can see from that internal schematic that PGOOD is to use such a resistor and diode.

I am interpreting the schematic as saying that these components are built into the product rather than user-supplied.

Allow me to clarify my questions further. My high level goal is to make a solar powered lantern. This lantern will turn on LEDs on at night and turn off the LEDs during the day.

In order to implement this day/night control, I figure the PGOOD pin basically has the information available for whether the sun has set or not.

My low level goal is to understand the interface details for this pin. The data sheet, the Adafruit product page, the internal schematic, and the online forums each tell a slightly different story for how this device works. I dunno, I'm new here. I just want a TTL signal to indicate to my microcontroller sun versus no sun.

If I can extract this signal from PGOOD or another pin on this charger, that would really help my lantern design to progress.

A separate question involves voltage limits for PGOOD. I am not sure whether it is safe to wire directly to GPIO input on a 3.3V Arduino Pro Mini. Would PGOOD require a 5V boost to wire to 5V Pro Mini? I wish to know the right way.

mcandre
 
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Joined: Fri Jun 11, 2021 5:25 pm

Re: Does Adafruit's bq24074 need a resistor for the PGOOD pi

by sj_remington on Sun Jun 13, 2021 11:06 am

The PGOOD output may do what you want, but it reports "power good", not day versus night. A simple LDR/resistor sensor would do the latter.

Since the pin is open drain, the naked chip requires a pullup resistor to produce a logic signal. The edge connector allows access to the pin on the Adafruit board, which has the LED and 10K resistor to perform the pullup function.

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Please be positive and constructive with your questions and comments.