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BQ27426: Question on BQ27426 reference design

Prodigy 220 points

Replies: 5

Views: 563

Part Number: BQ27426

I was looking in the schematic and layout of this ref design: www.ti.com/.../TIDA-01012

Wireless IoT, Bluetooth® Low Energy, 4½ Digit, 100kHz True RMS Digital Multimeter.  I notice BT1, terminal 2,  the negative terminal (pack-) is not connected to GND node -- the gate of the P-Mosfet (D3).

In fact I don't see the BT1 node 2 anywhere in the layout. Should it not be there?

If I decide to use this part in my design, should I not connect the BT1 battery negative terminal (pack-) to GND and P-Mosfet together? Please advise.

Also, I'll be using 3.3V for I2C interface, should I use 4.7K for I2C pull-up? I already use I2C in my board and has the necessary pull-ups for SDA and SDC, do I need to add additional pull-ups near to

this part  when routing I2C?  I'm considering adding this part to an existing design so I wanted to check to be safe.

Thanks,

- Andy

5 Replies

  • Hi Andy
    I am not sure i am clear on what you mean. BT11 is the battery and node 2 is connected to ground. The pfet allows the battery connect to the system and it appears redundant to me and not necessary except i am missing some thing.
    4.7 k pull-ups should be good with a 3.3V pulll up voltage.
    thanks
    Onyx
  • In reply to Onyx Ahiakwo:

    Hi Onyx,

    Thanks for the info.

    BT1 is the battery connector in the schematic with +ve (term: 1) and -ve terminal (term:2 ). I don't see the -ve terminal is routed or shorted to GND which I was expecting.

    - Andy

  • In reply to Andy Sarangi:

    Hi Andy,

    I am seeing BT2 connected t ground. Are we looking at the  same schematic?

    thanks

    Onyx

  • In reply to Onyx Ahiakwo:

    I don't see this connection (BT1: net2 to GND) in the Altium Layout. That was my question. There I see a pin something called "ALIGN" it is not connected to GND or to BT1: net2. Thanks Onyx for investigating it.
  • In reply to Andy Sarangi:

    Hi Andy,
    Pls go off what is in the schematic as that is what is correct and how the circuit should be connected.
    thanks
    Onyx

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