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TCA4307: pre-charge circuitry work condition at hot-swap insertion when EN pin controlled by GPIO

Zach Xia
Genius 9475 points

Part Number: TCA4307
Other Parts Discussed in Thread: TCA9511A

Hi expert,

In the datasheet, "EN pin is low, TCA4307 disables the bus pre-charge circuitry(after the initial power up)". 

In customer's application, EN pin is controlled by FPGA GPIO with a default pull down external resister, will TCA4307 pre-charge circuitry works or not during initial power up when board hot swap insertion? 

Thanks!

  • 0
    Guru 327600 points

    The pre-charge circuitry does not start immediately at power up (see tPRECHARGE in section 6.7). So the only way to get a charge is to have EN high, i.e., with a pull-up resistor.

  • 0
    TI__Guru* 81641 points

    Hi Zach,

    I believe Clemen's is correct on this one. The functional block diagram also seems to show that the EN directly controls if the pre-charge circuit turns on during initial power up. I'll contact the lead designer for this to be double sure anyways.

    -Bobby

  • 0 in reply to BOBBY
    TI__Genius 9475 points

    Maybe the pre-charge is disabled by the /CONNECT signal at power up, hope you can double check with designer.

  • 0 in reply to Zach Xia
    TI__Guru* 81641 points

    Zach 

    I'm still waiting to hear back from our designer. Normally I'd test this on the bench myself but I'm currently not able to as I currently don't have access to my TCA9511A/TCA4307 EVMs.

    -Bobby

  • 0 in reply to BOBBY
    TI__Guru* 81641 points

    Hi Zach,

    The design engineer just got back to me. It looks like the pre-charge circuit turns on even when the EN pin is held to GND during power up.

    I can double check this on bench in about a week if you want me to triple check. Let me know if you want this.

    -Bobby

  • 0 in reply to BOBBY
    TI__Genius 9475 points

    Hi Bobby,

    Thanks for your support. This should make sense as t_precharge condition is EN=VCC,GND. Better if you can help to test. One further question is, since "the pre-charge circuit turns on even when the EN pin is held to GND during power up", after the power up, will the circuit be on/off? I assume it's off because in normal state, the circuit should be controlled by EN pin. Hence, a test waveform showing the sequence during  power up would be very helpful.  

    BR,

    Zach

  • 0 in reply to Zach Xia
    TI__Guru* 81641 points

    Hi Zach,

    The pre-charge circuit should turn off after you pull the SDA/SCL lines up to Vcc. I'll see if I can do testing on this Friday.

    -Bobby

  • +1 in reply to Zach Xia
    TI__Guru* 81641 points

    Hi Zach,

    Here is a scopeshot of the TCA9511A power up sequence. The Blue waveform is Vcc, Purple/pink is EN held low, and Yellow is SDAIN where you can see the pre-charge turns on even while EN is held low.

    -Bobby