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TPS3420: PB2 and TS pin can be left unconnected(NC)?

Jason Hu27
Intellectual 860 points
Part Number: TPS3420
Other Parts Discussed in Thread: TPS3421, TPS3422

Dear Experts, please refer to below schematic. I have some design questions about TPS3420. Please give me some suggestions. Best regards.

(1) If I just use single channel (PB1) to assert a reset low, the other input pin (PB2) should be connected to GND(ground)? Is it OK that PB2 is left unconnected(NC)?

(2) If I just use single channel (PB1) to assert a reset low, external pullup resistance on PB1 is necessary? Can I just connect a push botton  to GND without pullup resistance?

(3) Is it OK that TS pin is left unconnected(NC)?  

  • 0
    TI__Expert 3300 points

    Hi Jason,

    1) The TPS3420. TPS3421 is a dual-channel device with an output that asserts when both inputs (PB1 and PB2) are held low for the push-button timer duration, and deasserts when either input PBx is released.

    2) The TPS3422 has only one input: PB1. This input has an internal pullup resistor to VCC. Depending on your application you may want to consider add resistor

    (Please refer the datasheet Typical application to see more option how PB1 is connected. )

    3) You need to connect Vcc or ground. So you can set the reset time duration 

    Best Regards,

    Sila Atalar

  • 0 in reply to Sila Atalar
    Intellectual 860 points

    Hi Sila, depend my application, tRST is not a fixed time, but instead depends on one of the PB pins going high. So, I must choice TPS3420. But I just use single channel (PB1) to assert a reset low, the other input pin (PB2) should be connected to GND(ground)? Is it OK that PB2 is left unconnected(NC)? If I just use single channel (PB1) to assert a reset low, external pullup resistance on PB1 is necessary?

  • +1 in reply to Jason Hu27
    Intellectual 860 points

    Hi Sila,  if PB2 should be connected to GND(ground), a pull down resistor is necessary? Or, the PB2 can connected to GND(ground) directly without  pull down resistor? Best regards.

  • 0 in reply to Jason Hu27
    TI__Expert 3300 points

    Hi Jason, 

    According to the datasheet  PB1 and PB2 needs to be low until Push-button timer ends so that a reset occurs. It is NOT okay that PB2 is left unconnected. Just directly connect ground. You don't need a resistor for PB2. But you should have a pull up resistor for  PB1. 

    Best Regards,

    Sila Atalar