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DRV8305-Q1: Current Sense Amplifiers Drive Capability

Genius 14360 points
Part Number: DRV8305-Q1
Other Parts Discussed in Thread: TIDA-00643, TIDA-00771, BOOSTXL-DRV8305EVM

Hi all

My customer has this question for the DRV8305-Q1:

What is the output drive capability of the current sense amplifiers ?

Please find the customer inputs posted below. They find long settling time while driving an RC from the SO2 output.

Best regards

Ueli

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Yellow : coil current ; Green : shunt voltage ; Purple : SO2 driver pin ; Pink : I_sense (see schematic below)

Comments

 

  • 5 * Constant time of the RC filter (99.3% of the final value) = 2.7 us
  • Max current sink by the filter = 3.3/36000 = 10 uA

 

Why there is still a voltage difference between the purple curve (output of the driver) and the pink curve (I_sense)

  • Hi Ueli,

    DRV8305-Q1 SOx pins have a short-circuit current limitation of 20mA (typical value). We normally recommend operating at 5mA peak or lower. Since the purple line (sense amplifier output) is immediately hitting the target value it does not look like the SOx output is being current limited.

    R205 in the circuit will be limiting the rise time, and additional capacitance on I_sense (added components, parasitic board capacitance, or ADC input) will influence the actual RC time constant of this circuit. To achieve the effect seen, only an additional 15pF is needed on the trace (twice the expected rise time is observed).

    We recommend series resistors in the range of 10~1k. For example on BOOSTXL-DRV8305EVM and TIDA-00643 we use 56 ohms and 2200pF. TIDA-00771 uses 100 ohms and 3300pF.

    Thanks,

    Matt

  • Hi Matt

    Thank you for the quick reply and understood, your feedback is helpful and appreciated.

    Best regards

    Ueli