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THVD1550: Fail-safe function

Shotaro Sakai
Intellectual 2950 points
Part Number: THVD1550

Hello team,

My customer has some questions related with fail-safe function.

1. When /RE=H, fail-safe in THVD1550 doesn't work, right?

2. Are pin A and B pulled up to Vcc / down to GND  in THVD1550, respectively? 

Best regards,

Shotaro

  • 0
    Guru 284570 points

    1. When /RE is high, the R output is completely disabled. If you want a high signal in this case, add a pull-up resistor.

    2. No; the fail-safe is implemented with a mechanism that works even when the differential input voltage is zero.

  • 0
    TI__Guru 60540 points
    Shotaro Sakai said:
    1. When /RE=H, fail-safe in THVD1550 doesn't work, right?

    As Clemen's pointed out, the R pin would become HI-Z and float unless you have an external resistor to keep the pin biased.

    Shotaro Sakai said:
    2. Are pin A and B pulled up to Vcc / down to GND  in THVD1550, respectively? 

    If the Driver is enabled, it will bias the A-B pins depending on the logic. If the driver is disabled, then A-B would have some leakage current but nothing strong enough to provide a strong bias. Adding external fail safe can help. The internal failsafe just places the V+threshold negative so in open, shorted, or idle situations you should see R output HIGH.

    -Bobby