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Original question:

AM26C32: Output drive on logic side

AM26C32: AM26C32 Max Input current

GEORGIOS CHATZIDAKIS
Prodigy 10 points
Part Number: AM26C32


Hello,

I would like to know the maximum input current for the AM26C32. We are using the  2 channels of the AM26C32 (the other 2 channels floating) together with the MILE 512–4096 CPT encoder.

What is the expected maximum current at full speed (specific motor 6000rpm)?

 

Thanks a lot,

Georgios 

  • 0
    TI__Guru* 77791 points

    Hi Georgios,

    I'm not 100% sure I understand the question. This device's impedance is about 12k ohms. It's impact to the RS485/422 driver's current load should be minimal.

    Are you asking about the device's input pins on the RS422 side or the device's output pin on the TTL side?

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 10 points

    Hi Bobby,

    Our target is to size the supply regulator for the AM26C32.

    The worst case quiescent supply current for the device is 15mA and we are using just the 2 channels out of the 4. On the driver side we have 50K internal selection on the MCU.

    What will be the worst case total current consumption for both input and output sides?

    Thanks a lot,

    Georgios

  • 0 in reply to GEORGIOS CHATZIDAKIS
    TI__Guru* 77791 points

    Worst case on the input side (the RS422 differential pins) would be -10V as a common mode. The max is 2.5mA per pin. If there are 4 used differential pins this would be 2.5x4 = ~10mA from the input side (A/B pins). 

    The worst case for the TTL outputs (Y pins) I would say is 25mA. If we assume 2 pins are shorted to GND/Vcc then you could get 25mA per channel (likely it will saturate earlier). So 50mA from the TTL outputs.

    So total so far would be 60mA. Adding in supply current at 15mA would get us a total of 75mA. 

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 10 points

    Hi Bobby,

    Regarding the 2 unused channels, how do they contribute to the current consumption?

    Which is the best connectivity practice to minimize their consumption?

    Many thanks,

    Georgios

  • 0 in reply to GEORGIOS CHATZIDAKIS
    TI__Guru* 77791 points

    The unused channels wouldn't really do much since internally they are biased to Vcc/GND so they aren't floating. The leakage would be Vcc/12k per pin. This would be about .5mA or 2mA total. 

    You can leave those pins floating. (They are internally connected to Vcc/GND so they aren't actually floating).

    -Bobby