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BOOSTXL-DRV8305EVM: Current sensing limited in positive direction

Part Number: BOOSTXL-DRV8305EVM
Other Parts Discussed in Thread: DRV8305,

Test: verify the current and voltage sensing capabilities of DRV8305EVM

Setup: DRV8305EVM with Delfino F28379D Launchpad. Launchpad is powered by booster pack. A single phase inverter operation is implemented on a resistive load using Phase A and Phase B half-bridge legs of the Booster pack.

Problem: The current sense analog value available at ISENA and ISENB does not vary corresponding to the magnitude of current, when flowing out of the half-bridge. It is limited to the  DC offset value 1.67 (instead of expected 1.65). However, analog values change corresponding to the current magnitude when it flows into the half bridge. The signals are observed on oscilloscope and also read through ADC on the launchpad.

Note: VSENA, VSENB, VSENC and Vdd voltage sensing works fine

Question: Does the driver have a configuration to limit current sensing in only one direction? Or is it a hardware failure?

Do let me know if you need any further information. I would appreciate any solution/suggestion to troubleshoot the problem.

Thanks in advance

Regards
Naveen Deepak

  • Hi Naveen,

    The CSAs on the DRV8305 EVM are configured for bidirectional current flow, however, the EVM uses a low-side current sensing topology, which will only measure current flowing through the low side of each half bridge.

    As you can see in the circuit schematic on page 11 of the BOOSTXL-DRV8305EVM User's Guide, the current sense resistor is located between the low-side gate of each half bridge and the GND connection. Therefore, when the load is flowing out of the half-bridge, there is no current flowing through the low-side of that phase, and the voltage goes to the DC offset value.

    Because the DRV8305's CSAs are designed for use with a low-side current sensing topology, they do not have the common mode range for a high-side or in-line topology, and cannot be used as such.

    Does this match what you're observing, or am I not understanding your issue correctly?
  • Hello Garret,

    You have definitely answered my question.

    Thank you.