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DRV8251: Vs ABS (max) (V) with high resistance loads.

ENG
Prodigy 20 points
Part Number: DRV8251

Tool/software:

Hello,

we are working on a design with DRV8251 to drive piezo loads with parallel 1 k resistance. A prototype (1 k load only, no piezo) showed nice operation at Vs 10 V and Vs 30 V. However, with 45 V Vs the DRV8251 was destroyed and the output bridge has permanent low resistance now. The datasheet shows 48 V recommended Vs and a maximum of 50 V Vs.

Are there any limitations to Vs if relatively high resistive loads like 1k (or even capacitive load like piezos) are used? There is nothing in the datasheet about this.

Thanks for your advice.

Regards
Michael

  • 0
    TI__Mastermind 23180 points

    Hey Michael,

    It is likely that at 45V there was a voltage transient spike of >50V that destroyed the device.  I recommend putting a scope on the VM input of the device and letting it trigger at 50V to verify this. Though I am a little surprised that this could happen with a resistive/capacitive load with minimum inductance, as typically this spike is from the Back EMF which is caused by the inductive load.   But typically you want a 20% margin on voltage rating for your system - so for 45V Vs  you'd want a 54V rated part

    How much bulk capacitance do you have?  Is this on your own board or the EVM?  

    ENG said:
    Are there any limitations to Vs if relatively high resistive loads like 1k (or even capacitive load like piezos) are used? There is nothing in the datasheet about this.

    Hmm not that I know of.  Maybe if the inductance of the system is very low, it could result in the current spiking above the OCP threshold faster than the device could protect itself from.  More inductance would reduce the slew rate of the spike, allowing the device to protect itself. 

    Have you checked out TI's line of Piezo speaker drivers / receivers? I think a LM48560 might suit you better 

    Best,

    Jacob

  • 0 in reply to Jacob Thompson
    Prodigy 20 points

    Hello Jacob,

    thanks for you fast and qualified answer! We use a boost converter to create the supply voltage. The scope shows 7 % overshoot at startup. At 45 V Vs, this brings the supply voltage temporarely very close to the maximum rating. I was not expecting this as we put a bulk capacitance 4.7 uF at the DRV8251 and another 20 uF at the output of the boost converter. BTW, we use two DRV8251 with the same supply. The other one is still working fine. Lessons learned, we will implement a higher margin to keep away from maximum Vs. Thanks for your help!

    Regards
    Michael