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About the data sheet of BQ27421

Masami Michino
Genius 5070 points
Other Parts Discussed in Thread: BQ27421-G1

Dear, All

Customers are considering using BQ27421.
The customer has two questions.

The first is about "Figure 9. Application Schematic" in the data sheet Page 15.
In the circuit diagram, BIN PIN is connected to 2 pin of J3 via a 10 kΩ resistor.
One pin of J3 is connected to VDD and 3 pin is connected to EXT_VCC.
From here, BIN PIN seems to connect to VDD or EXT_VCC through 10 kΩ.
This does not match the explanation of the item of BIN of "Pin Functions" in the data sheet Page 3.
Please tell me the intention of the circuit diagram.
The second is about "Figure 13. bq27421-G1 Board Layout Example" of the data sheet Page 19.

Although BIN PIN is connected to VDD via Rbin, in the explanatory note it is described as pulldown with 10 kΩ.
Please tell me this intention.

Thanks, Masami M.

  • 0
    TI__Guru 51466 points
    1. The schematics on page 15 should have a 1.8MOhm resistor instead.

    2. Rbin is the 1.8MOhm pull-up resistor. If you remove the battery pack then Rbin will pull up BIN to VDD (logic 1) and the gauge detects that the pack was removed. If you insert the battery pack, the thermistor (typ. 10k) will pull down BIN to almost GND (because the 10k is so much smaller than 1.8M) and the gauge detects that a battery pack was inserted.

    The note just says that if the pack doesn't have a 10k thermistor then you should use a 10k resistor to GND instead of the 1.8M (Rbin) to VDD so that the gauge always thinks that the pack in inserted when the gauge is powered up (this effectively disables the detection circuit).
  • 0 in reply to Dominik Hartl11
    Genius 5070 points


    Hi, Dominik-san,

    Thank you for your reply.
    I answered to the customer.

    Thanks, Masami M.