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TPS61194: Ground connection for unused outputs

Dallas Clow
Intellectual 360 points
Part Number: TPS61194

The TPS61194 datasheet states:  "TPS61194 detects LED output configuration during start-up. Any current sink output connected to ground is disabled and excluded from the adaptive voltage control of the DC-DC and fault detections."

Can this connection to ground be made with a pull-down resistor instead of a direct connection?  We would like the same HW design to support backlights with both 3 and 4 strings. 

We've considered using a FET to short the 4th output to ground in 3 string cases, but don't want to have the potential for a ground short in the 4 string case present in the design.

  • 0
    TI__Mastermind 22745 points
    Hi Clow,
    I'm not very clear about your application. Can you provide a simple circuit of your application. I will check whethwer your configuration is ok or not. Thanks.
    Sean
  • 0 in reply to Sean Zhou
    Intellectual 360 points
    Thanks for the quick response. Another way to state my questions is:

    If a 10 kOhm resistor is connected from the OUT4 pin to ground and OUT4 has no other connections, will the TPS61194 detect that the OUT4 string is not present and disable it or will it report a failure due to an open?

    The datasheet says a direct connection to ground will result in no failure being reported and will instead disable that string output. My question is whether that same behavior (disable the 4th output) will occur if the connection to ground is through a 10 kOhm resistor instead of direct.
  • 0 in reply to Dallas Clow
    TI__Mastermind 22745 points
    Hi Clow,

    When it power on, the OUTx pin will output a small source current to detect the voltage on OUTx pin. When it detects a low volatge , it means this pin has connect to GND and disable this current sink. 10k is too large, I will check with the system and designer to know the source current and Vth and tell you later.

    Sean
  • 0 in reply to Dallas Clow
    TI__Mastermind 22745 points
    Hi Clow,
    I have get the detail information form our designer, When TPS61194 is power on, it will source about 160uA to OUTx pin, then it will detect the voltage on OUTx pin. And compare with a internal 500mV reference, when the detect voltage is less than 500mV, it means this channel is connect to GND. So the maximum resistance of OUTx pin is 500mV/160uA=3.1k. If you want to use external FET to disable channel 4, Make sure the impedence of OUT4 is less than about 3k. Please be careful with this kind of application.
    Sean