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BQ79616-Q1: BQ79616 UART RX Pin: Direct Pull-Up to CVDD or Through Resistor?

Batuhan Yavasoglu
Prodigy 220 points
Part Number: BQ79616-Q1
Other Parts Discussed in Thread: BQ79616, USB2ANY

Hello,

I am designing a BMS with the BQ79616 and I'm currently setting up the UART communication lines, specifically for the RX pin.

Based on the datasheet's instructions:

"The UART interface requires that RX is pulled up to CVDD through a resistor on the base device. The RX is pulled up on the device side. Do not leave RX unconnected. Ensure RX is connected directly to CVDD for stack devices."

I am seeking clarity on the following:

  1. Should I pull up the RX pin directly to CVDD without a resistor, or should I use a resistor for the pull-up?
  2. If a resistor is recommended, what would be the appropriate value for it? Would a 100k resistor be suitable?

Thank you for your guidance on this matter.

My design is below.

Best regards, Batuhan

  • +1
    TI__Expert 7000 points

    Hi Batuhan,

    Batuhan Yavasoglu said:
    Should I pull up the RX pin directly to CVDD without a resistor, or should I use a resistor for the pull-up?

    A resistor is recommended if you intend to use RX and TX for UART communication. Shorting RX to CVDD will disable the use of RX and TX pins for UART.

    Batuhan Yavasoglu said:
    If a resistor is recommended, what would be the appropriate value for it? Would a 100k resistor be suitable?

    A 100k resistor is suitable. On the EVM, we use a 100k resistor between RX and CVDD. To disable UART, the EVM has Jumper J1 which can short RX and CVDD when populated.

    Regards,

    David

  • 0 in reply to David Ray
    Prodigy 220 points

    Thank you for your response. I referance EVM. what about RX MC can you explain the 100R?

  • 0 in reply to Batuhan Yavasoglu
    TI__Expert 7000 points

    Hi Batuhan,

    If you are referencing RX_C:

    This is because J3 is for an FTDI cable which is a second way to talk to the EVM. In the case that the user is using both a USB2ANY and FTDI cable, the 100 ohm resistor is to limit the current between the two voltage sources (USB2ANY's 5V line & FTDI's 5V line). If you are using only 1 form of UART communication, then you do not need this resistor.

    Regards,

    David