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DRV8873-Q1: IPROP1 & IPROP2 Resistor Selection

Manny Salazar
Prodigy 290 points
Part Number: DRV8873-Q1

I’m trying to choose my current sense resistors but I am having difficulty understanding exactly what is being output by the IPROP1 and IPROP2 pins. The datasheet says 1.5k Ohm for a typical application and the EVM schematic shows 330 Ohm resistors. It also gives an equation, but I don’t know what ‘k’ is. Can you give a better explanation?

  • 0
    TI__Guru** 114905 points
    Hi Manny,

    Please see section 7.3.1.3 of the datasheet for a detailed explaination.

    k is the current mirror scaling factor (typically 1100). For each 1.1 Amps through the high side FET, the current mirror provides 1mA at the IPROPI output.

    A 1.5kOhm IPROPI resistor will max out at ~3.6A. By lowering the resistor to 330 Ohms reduces the maximum IPROPI voltage to work with a 3.3V mcu and provides more range of current (up to 11A at 3.3V and 16A at 5V). Both 11 and 16A are above the overcurrent protection value of 10A.
  • 0 in reply to Rick Duncan
    TI__Prodigy 290 points
    Rick,

    What does is mean by ‘typically’? Is there a tolerance or deviation?

    Also, where is the 5V or 3.3V coming from that you mentioned? I see that there are internal regulators but I’m not seeing what that is used for.
  • 0 in reply to Manny Salazar
    TI__Guru** 114905 points
    Hi Manny,

    The tolerance is based on the load current. If the current is >= 1A, the tolerance is +/-5%. Below 1A, the tolerance is +/- 50mA. These values are listed as Kerr.

    The 5V is based on the maximum voltage of the DVDD regulator.

    The 3.3V is attempting to keep the IPROPI voltage below a 3.3V mcu voltage requirements. This would allow the IPROPI voltage to be directly connected to a 3.3V mcu ADC input.