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DRV8835: Question for logic input current in datasheet

Lee, Sam
Expert 6035 points
Part Number: DRV8835

Hi team,

 

For customer's question, I’d like to double check the meaning of max. IIH(Input high current=50uA) in datasheet.

-. The current from external host device to DRV8835(logic input) should not be exceeded over 50uA? And is it okay even for small current?

-. Otherwise, does DRV8835 need the current about 50uA?

Best Regards,

Sam Lee

  • 0
    TI__Guru** 114905 points
    Hi Sam,

    The current for the IIH condition indicates the minimum pulldown resistance (3.3V/50ua = 66k). This value can be used to calculate the maximum current consumed by the pulldown resistor at other VIN voltages.

    This resistance value is important if an input is to be connected directly to a pullup resistor.
  • 0 in reply to Rick Duncan
    TI__Expert 6035 points
    Hi Rick,

    Thank you for your support. The customer asks more detailed questions about the IIH condition because their circuit is unusual.

    Configuration: SoC -> H-Bridge circuits (for control signals) -> DRV8835

    So, the output from H-Bridge circuits is 5V(High) and 0V(Low) and it will be inputted to the AIN1/AIN2 pins of IN/IN mode of DRV8835. Also, the output current of H-Bridge is supported up to 200mA.


    Question 1. Is it possible to use this configuration (output from H-Bridge) for the AIN1/2 input of DRV8835 when considering max. 50uA of IIH?

    Question 2. We’re now confused about the meaning of 50uA, so can you let us know which one is correct in the following statements?
    2-1 From current flow point of view,
    a. External host is to give the specific current (fixed by external host) to AIN1/2 of DRV8835?
    b. DRV8835 is to draw the specific current (required by AIN1/2) from external host?

    2-2 a. AIN1/2 in DRV8835 need less than 50uA to drive motors?
    : In this case, is there any limitation of min. current to make AIN1/AIN2 work normally?
    b. AIN1/2 in DRV8835 need more than 50uA to drive motors?

    Best Regards,
    Sam Lee
  • 0 in reply to Lee, Sam
    TI__Guru** 114905 points

    Hi Sam,

    Lee, Sam said:
    Question 1. Is it possible to use this configuration (output from H-Bridge) for the AIN1/2 input of DRV8835 when considering max. 50uA of IIH?

    Yes, this configuration is possible. The output of the H-Bridge will provide the current required to the input of the DRV8835. The input is high impedance and does not require more the 50uA.

    Lee, Sam said:
    Question 2. We’re now confused about the meaning of 50uA, so can you let us know which one is correct in the following statements?
    2-1 From current flow point of view,
    a. External host is to give the specific current (fixed by external host) to AIN1/2 of DRV8835?
    b. DRV8835 is to draw the specific current (required by AIN1/2) from external host?

    b -- an example is using a 1A power supply to connect to AIN1. The current used by AIN1 is specified by the input circuit.

    Lee, Sam said:
    2-2 a. AIN1/2 in DRV8835 need less than 50uA to drive motors?
    : In this case, is there any limitation of min. current to make AIN1/AIN2 work normally?
    b. AIN1/2 in DRV8835 need more than 50uA to drive motors?

    2-2 a. Yes, the limitation is based on the minimum current to create a logic high at the input and the input voltage. Assuming the worst case internal 66kOhm pulldown, you will need a minimum of 30uA to achieve a logic high.

    2-2 b. Yes, it could use more than 50uA across temperature. The values in the datasheet are at 25C.

    In general, use a circuit that can provide at least 1mA to the pin. A 3.3kOhm pullup or a GPIO can do this easily. The input will consume the current needed to operate properly.