DRV8256: Clarification on Reset, RθJA, and Application at 48 V/4.2 A

Part Number: DRV8256
Other Parts Discussed in Thread: DRV8262

Tool/software:

Hello,

According to this thread, the DRV8256 family does not require an nSLEEP reset pulse.

Could you clarify whether this also applies after OCP and OTSD? Specifically:

  • Does the device automatically recover from these fault conditions?

  • If not, is there a recommended low-cost auto-reset circuit that does not require a µC?

I would also like more details about the RθJA value provided in the datasheet. Was this derived from a device in free air, or from testing on a specific PCB? If the latter, could you describe the properties of that PCB?
Additionally, do the listed IVM (and therefore PQ, quiescent supply current dissipation) values include the heat generated by the DVDD regulator circuit?

My application requires a simple and inexpensive circuit to control up to 4.2 A at 48 VDC, with current limiting based on both high- and low-side current sensing. If you have alternative device or circuit recommendations for this requirement, I would be very interested.

Best regards,
Moritz

  • Hello Moritz,

    Thanks for your post.

    According to this thread, the DRV8256 family does not require an nSLEEP reset pulse.

    This refers to devices in our portfolio requiring an nSLEEP reset after power-up vs. the DRV8256. Not for fault recovery. 

    Could you clarify whether this also applies after OCP and OTSD? Specifically:

    • Does the device automatically recover from these fault conditions?

    • If not, is there a recommended low-cost auto-reset circuit that does not require a µC?

    This does not apply after latched faults - OCP and OTSD in this device. See below from its datasheet. It does not automatically recover from these two faults.

    We do not have a recommended auto-reset circuit. When a fault happens the nFAULT pin will be pulled LOW. You can use this to trigger a digital RC few ms delay circuit to create a LOW pulse output on nSLEEP.

    My application requires a simple and inexpensive circuit to control up to 4.2 A at 48 VDC, with current limiting based on both high- and low-side current sensing. If you have alternative device or circuit recommendations for this requirement, I would be very interested.

    If the 4.2 A is continuous current requirement, using 300 mΩ HS+LS FET @ 125 °C the power dissipation would be at least 4.2 x 4.2 x 0.3 = 5.3 W. This is outside the capability of this IC available packages thermal specification. The device will definitely experience a thermal shutdown. The integrated current regulation (current limiting) is based on only the internal low-side current sensing. This device does not have current sensing on high-side. None of the drivers with integrated power MOSFETs have both high-side and low-side current sensing because it is not necessary. In this device the internal current mirror senses the low-side recirculation current as well as the drive current flow in either direction of the H-bridge conduction.

      

    If your drive requirement is 4.2 A at 48 V DC you may want to consider the DRV8262 DDW package and use it in a Single H-bridge configuration. 

    I would also like more details about the RθJA value provided in the datasheet. Was this derived from a device in free air, or from testing on a specific PCB? If the latter, could you describe the properties of that PCB?

    The cited documentation in the DRV8256 datasheet provides you this information, https://www.ti.com/lit/an/slma002h/slma002h.pdf. See section A.4 Texas Instruments Example Jedec Board Design for PowerPADTm Packages

    Additionally, do the listed IVM (and therefore PQ, quiescent supply current dissipation) values include the heat generated by the DVDD regulator circuit?

    The DVDD regulator is active while nSLEEP = 1. IVM specification with nSLEEP = 1 includes the DVDD regulator IQ. See section 8.2.2.1.1 Power Dissipation and Thermal Calculation in the datasheet. This shows the PQ calculation. Thank you.

    Regards, Murugavel