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Original question:

DRV594: Using DRV593/DRV594 as a Peltier Driver

DRV594: DRV594 no activity on PWM and H/C outputs

Bojan Jovanovic
Prodigy 145 points
Part Number: DRV594

Dear Sirs,

I am using the DRV594 Evaluation kit to test the possibility of driving a Peltier Module (2.7Ohms resistance). DRV594 is supplied with 3.3V and driven the following way:

VIN- is kept to VDD/2 and VIN+ is set by the output of the 10-bit DAC module (controlled by the host MCU). According to the formulas given in DRV594 datasheet:

Vload = D x VDD;

D = A (Vin+ - Vin-) / VDD;

A = 14.5V/V in the case of DRV594
A = 2.3V/V in the case of DRV593

The difference of about 200mV between VIN+ and VIN- inputs should lead to a 100% duty cycle, i.e. Vload = VDD.

By using a logic analyzer, I can confirm that the VIN+/VIN- inputs of the DRV594 are driven properly (at some point, there is a difference of ~200mV between VIN+ and VIN-):

However, the output pins of DRV594 (PWM and H/C) remain at 0% duty cycle):

Do you have any idea about what I am doing wrong here?

Thanks in advance for your time and efforts. Looking forward to hearing from you.

Sincerely,

Bojan.

  • 0
    Prodigy 145 points

    Hey guys...

    It seems the issue I experience has something with the power supply quality. When I connected bypass capacitors across VDD and GND, waveforms became slightly better.

    However, I am still experiencing unexpected voltage drop on VIN- input that should always be constant and equal to VDD/2:

    Given the fact that VIN- comes from the voltage divider, the voltage drop on VIN- implies that there is a drop on VDD during the runtime of the system. The power supply used is KORAD KA3005SP.

    Do you have any advice on how to improve the behavior of the system? Perhaps the long wires that interconnect the boards have an unacceptably negative effect?

    In our final design, when we design a custom PCB and put everything on it, we plan to use a DC-DC converter of Buck type to generate +5V for supplying DRV594. Any suggestion for DC-DC converter that will play well with DRV594?

    Thanks once again!

    Cheers, Beers

    Bojan.

  • +1 in reply to Bojan Jovanovic
    TI__Genius 9790 points

    Bojan,

    I didn't played with the EVM yet.  But from what i see in 2nd waveform, seems like there is a voltage drop at VDD, which result in IN- drop, will you monitor VDD also? As it is lab power supply, usually this voltage drop is not expected. But if there is long wire, there could be some drop when large current happen. That probably could explain why add extra cap helps this problem.

    About DCDC, there is no suggestions from my side. i would suggest you ask help from DCDC forum.

    Dylan

  • 0 in reply to Dylan Yao
    Prodigy 145 points

    Makes sense what you say, . I am indeed using long wires. Let me give it a try with shorter wires and report the results back to you.

    Regards,

    Bojan.

  • 0 in reply to Dylan Yao
    Prodigy 145 points

    With short wires, the signals look pretty stable and as expected, . There is NO voltage drop on the IN- input.

    Thanks for your assistance, . I will close this thread.

    Cheers!