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THVD1400: Bus input current

FZ
Prodigy 60 points

Part Number: THVD1400

Hello, I am interested in using the THVD1400 in a system with multiple modules The application is a bit specific and requires a very low bus input current when the transceiver is not used.

The datasheet specifies the maximum bus input current as 100µA when the driver is disabled.

grafik.png

These numbers relate to the case when the input voltage is 12V. In my use case there are several transceivers powered by 3.3V within a closed system. Therefore, the input voltage is limited to much lower levels by design.

Additionally, the low bus input current is only needed for the case when the transceiver is not used (both, driver and receiver disabled). I assume the numbers from the datasheet show the case when the receiver is enabled.

Is it possible to get the maximum bus input current for my use case when:

  • driver is disabled,
  • receiver is disabled, and
  • the bus input voltage is <3.3V

Thank you in advance for your assistance

  • 0
    TI__Guru* 79981 points

    Hello,

    FZ said:
    These numbers relate to the case when the input voltage is 12V. In my use case there are several transceivers powered by 3.3V within a closed system. Therefore, the input voltage is limited to much lower levels by design.

    The 12V voltage in this spec doesn't assume the transceivers are using 12V Vcc, it assumes that they operate at 5V and there is a 7V GND shift. You could still apply the same logic with a 3.3V system, GND shift of 9V occurs and a drive to 3.3V rail could generate a 12.3V signal as a worst case scenario. GND shift typically occur when there is a long cable distance and the two GND potentials between the two nodes are not the same. 

    That being said, the receiver circuit is the same regardless of the Vcc and whether it is disabled or enable. 

    So you could estimate the input impedance by taking the VI (12V) and the bias current (100uA) to get the input resistance (12V/100uA = 120k ohms). 

    This resistance should be flat across voltages so at 3.3V you would get a worst case current of 27.5uA.

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 60 points

    Hello Bobby, thank you for your reply.

    Does it make a difference if the receiver is disabled by the \RE pin?

  • +1 in reply to FZ
    TI__Guru* 79981 points

    From a bus loading point of view, no. The 120k ohm impedance is still present when RE# is disabled. 

    From supply current (Icc) point of view, this will lower the supply current since the digital receiver block is disabled. 

    -Bobby