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DRV5032: DRV5032FCDBZR strange startup behavior

k ch
Prodigy 80 points
Part Number: DRV5032

Hi Team

We are using DRV5032FCDBZR.

The Datasheet states that the time between points when the supply voltage reaches 1.65V and valid data on output pin is max. 100us.

But in our application the valid output data appears only after the second sample (~47ms after start up).

2 channel - VCC (+3.3V), 4 channel - Data Out

This problem was not present in the previous batch of devices

2 channel - VCC (+3.3V), 4 channel - Data Out

Is this normal IC behavior if the first sample is not valid?

For what reason may the behavior of the IC differ between batches?

  • 0
    TI__Mastermind 23045 points

    Hello k ch,

    Thanks for posting the sensors forum!

    We have noticed this issue can happen when using a lab based power supply with a slow Vcc ramp rate to power on the device. Lab based power supplies have a pretty slow ramp rate compared to other supplies you would normally use on your end application like an LDO, buck, or in some cases GPIO. But they also contain various safety features which could contribute to the problem as well.

    What happens internally is that the digital logic can power up faster than the analog portion of the circuit. If the digital portion is enabled first it will try to sample the magnetic field but since the analog portion of the circuit is not ready it cannot output any information, so the device will wait until the next sample period to update the output. The DRV5032FC is a 20Hz device which equates to approximately 50ms, so this is the amount of time you must wait until the next update and you are seeing approximately ~47ms so that lines up pretty well. Some devices have a closer power on time for the digital and the analog part of the circuitry hence why you may not see this behavior on some units.

    I have two work arounds for this power supply issue, the first one was to increase the current limit on the power supply. Increasing the current limit allows the voltage to ramp faster and will update the output as specified by the datasheet (~55us to 100us after voltage reaches 1.65V) The other workaround was to power the device the way it would be powered on in an application so using an LDO or other device.

    This image was captured using an Agilent power supply with a low current. I used a different DRV5032 variant with a 5Hz update hence why the timeline is longer.

    This is the same agilent supply but when I increased the current on the power supply the on time was as defined in the datasheet ~50us

    When I use an LDO to power up I also get the appropriate behavior defined in the datasheet.

    I hope this helps, let me know if there are any other questions!

    Best,

    Isaac

  • 0 in reply to Isaac Lara
    Prodigy 80 points

    Thanks for your reply.

    Could you specify maximum and minimum power supply ramp for this device?

  • 0 in reply to k ch
    TI__Mastermind 23045 points

    Hello k ch,

    I am out of the office today I will review your response tomorrow. Thanks for your patience!

    Best,

    Isaac

  • 0 in reply to Isaac Lara
    TI__Mastermind 23045 points

    Hello k Ch,

    We will have to check this in lab, we are on holiday tomorrow in the U.S., I will try to provide results by Monday. Let me know if there are any other questions I may be able to help with. 

    Best,

    Isaac

  • 0 in reply to Isaac Lara
    Prodigy 80 points

    Hi

    Do you have any updates for me?

  • 0 in reply to k ch
    TI__Mastermind 23045 points

    Hello k Ch,

    I have not had a chance to look at this yet, but I should have some time tomorrow to look at this.

    Best,

    Isaac

  • 0 in reply to Isaac Lara
    TI__Mastermind 23045 points

    Hello  k Ch,

    I tested this in the lab and noticed I was not seeing an issue when I used a slew rate higher than 3.3V/10us. This was with a 0.1uF bypass cap so if you are using different values this may be a little bit different.

    As far as a max I tried using a function generator with square waves and had not issues there. As mentioned the issue happens when the slew rate is just too slow.

    Best,

    Isaac

  • 0 in reply to Isaac Lara
    Prodigy 80 points

    Many thanks for the information!