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DRV411: SOIC-20 Package Immediately Hot, then shuts down

Part Number: DRV411
Other Parts Discussed in Thread: DRV401

Hi There,

I am trying to use the DRV411 in the 20-pin SOIC package on my benchtop to prototype a closed loop current sensor. Since I am using an off-the-shelf SOIC to PDIP protoyping board, there is no way to connect the thermal pad on the bottom of the package. So, I've cross checked several times, and it seems that everything is hooked up right. When I apply 5V power, though, the package get extremely hot, and after about 3-5 seconds the output goes from about 2.4V to 1.1V, which I believe may be some protective mode. So first, will this package not work at all without its thermal pad properly heatsinked? Also does the thermal pad NEED to be connected to GND, or can it be floating? I tried to use some thermal paste and a heatsink on the top of the package, but it didn't seem to help. Since the thing gets way too hot I can't safely measure the voltages on all of the pins to understand if perhaps I have connected something incorrectly.

In short, here's what I think is going on (by pin):

1 - REFSEL2 = Vss / GND (refsel 0,0 = 2.5V Voq, nominal)

2 - OVERRANGE = no connection

3 - HALL 1 

4 - HALL 2

5 - HALL 3

6 - HALL 4

7 - ERROR = no connection

8 - GSEL1 = 5V via 10k pull up resistor (high gain mode 1000 V/V open loop)

9 - GSEL2 = Vss / GND

10 - Vdd = 5V

11 - ICOMP1 = connected to pin 16 (IAIN2)

12 - ICOMP2 = (secondary) compensation coil negative

13 - Vss / GND

14 - Vss / GND 

15 - IAIN1 = (secondary) compensation coil positive and shunt resistor positive (Rs+)

16 - IAIN2 = connected to pin 11 (ICOMP1) and shunt resistor negative (Rs-)

17 - Vout = connected directly to measurement equipment, with high >1M input impedance

18 - Refin = connected via 20 ohm resistor to pin 19 (refout) 

19 - Refout = connected to pin 18, and no external connection

20 - REFSEL1 = 0, 0,0 for 2.5V Vouq

So disconnecting just about every device one at a time did not seem to allow the IC to run cool. And it didn't ever seem that the Vref pin, nor the Voq (Vout at Ip = 0A) were ever correct. What's going on?!?!

Any help is greatly appreciated. I'll upload a schematic after dinner and chores ;)

Thanks,

Dave

  • Dave,
    We'll take a look at your pin configuration and verify the power pad connection. Please allow us a few days to respond though as most of our engineers are out for the holidays.
  • Jason,

    Thanks in advance for your assistance. Here's my schematic. Note that I did not connect to OV and ERR pins, and that R4-R7 are just 0 ohm jumpers that allow the pins to be toggled high/low as I need them. FYI my shunt resistor is R1, and currently is 20 ohm.

    I am trying to monitor current 300 mA at full scale, so I calculated all the circuit parameters as follows:

    Ip = 300 mA

    Is = 25 mA

    N = 12

    Rs = 20 ohm

    Vfs' = 25mA x 20 ohm = 500 mV

    G = 4

    Vfs =  2000mV (2.5V +/- 2V)

    When I get a chance I will try to build up another chip, but this time with some sort of "thermal sink" soldered to the back of the chip. In the meantime, I would really appreciate any tips on how to use the IC, and any indication that I have set it up correctly. Thank you!

  • David,

    Please limit the current on your current supply until you determine the root cause. I suspect the magnetic feedback may be in the wrong direction. There are two ways to solve this. One is to reverse the connection of the compensation coil. Another is options is to reverse the polarity of the hall sensor. The feedback need to be in the correct direction for the DRV411 to function properly.
  • Javier,

    Thanks for the recommendation. Surprisingly, the package also got extremely hot with:
    1) Hall sensor disconnected
    2) Compensation coil disconnected

    I did try to reverse the terminals of the compensation coil, but the IC still got hot.

    As for the connection of the hall device, it goes pins 1,2,3,4 are connected to the IC 3,4,5,6, respectively?

    To current limit the IC, I would just put a small resistor in series with the 5V regulator, on the Vdd pin, yeah?

    Thanks!
    DW
  • Uhhh, Scratch that! Looking at the datasheet, it seems I've swapped all of my connections on pins 1-10 with 11-20. This means 5V Vdd was sinking current directly to ICOMP1 pin. No wonder it was getting hot. I don't know how my brain could have allowed it, but here we are. Looking at the datasheet shows my pins are not right. Anyway, I'll build the circuit correctly and we'll see where we are. I really can't wait to watch this IC run [correctly]!

  • David,
    we're glad we could help - I hope this solves your issue. If not, just come on back and let us know and we'll keep debugging.
  • Hello! I have managed to build the sensor and I have some interesting notes:

    For one, low primary:secondary turns ratio is not usable. In my previous posts I mentioned I would try n = 12. That's a non-starter. What happens is that there is a finite amount of offset error in the hall device, even at zero field. The feedback circuit of the DRV411 is used to drive the offset to zero, and requires coupling with the magnetic circuit to do this. Because it can only drive a finite amount of current (~250mA), if there are too few turns in your secondary coil, you'll never get even the hall device's offset error to be cancelled. What happens then, is that a very large error is introduced as Voq + Is x Rs. if Is = 250mA and Rs = 10 ohm, well, you've just saturated the output of the IC, at zero primary current: 2.5V + .25A x 10 = 5V. So, after failing at n =12, I tried 200, 400, and then 1000 turns. Each subsequent increase in turns reduces the secondary current required to null the hall offset, and reduced error in the quiescent offset voltage (Voq).

    Now, what I am running into is a problem with the offset, which has prevented me from being able to capture full-scale measurements of less that 25A. My goal is to make a +/-500mA sensor. As I mentioned above, there is an offset voltage in each hall device, one which causes the DRV411 to drive current in the secondary even at a zero primary current. Call this Is_0, for "quiescent offset current." Then there is a error in the quiescent output voltage (Voq), which is Voq = Vref + Is_0 x Rs x G. If everything was perfect, then Voq = Vref. My hall devices at room temperature have about 2.5mV of offset voltage on them, and could be as high 7 or 8 mV across the whole temperature range. This is a problem, because they are causing up to 6 mA to flow in the secondary (Is_0), which amount to volts on the output, depending on the shunt resistor value. This error, then, also must be removed from the measurement, which will require an external voltage reference, an op-amp buffer, and either hand-picked resistors, or a potentiometer to do the trimming (bad for thermal performance, and accuracy). If the full scale range on the sensor is 0.5 to 4.5V, using a 5V supply, that means the product of offset current (Is_0) x series resistance (Rs) x differential amp gain (G = 4) must be less than 0.5V, or the sensor will be out of range. That implies the product of Is_0 x Rs must be less than 0.5V / 4 = 125 mV. This is what's limiting my ability to create a sensor with very low full scale values (500mA, 1A, 5A, for instance), because they require large shunt resistors, which causes the Is_0 x Rs product to quickly blow up.

    I am very happy with my progress in both getting the IC and sensor to run, and achieving relatively good accuracy at current ratings down to +/-25A. Now I need to make the necessary refinements to get the current ratings I need: 500mA, 1A, and 5A. I thought that the DRV411 with its "current spinning" technique would eliminate not only the 1/f noise, but the offset error too. Unfortunately, I was mistaken. At this point I am unsure if the closed-loop w/ hall element will get me to the range and accuracy I require. I know that there is another Texas Instruments IC, DRV401, which uses a different  type of detector to form the closed-loop secondary circuit. If the DRV411 isn't the right horse, perhaps the DRV401 in the right choice to get me there. What do you think?

    Based on my account does anyone have any suggestions as to how to reduce my total offset error, and increase the sensitivity of the sensor (e.g. lower the full scale rating to <5A)? Do you think that the hall element is the problem? What would you do differently, or what might you recommend that I try?

    Thanks again for your help!

    Regards,
    David



  • David,
    Thanks for the thorough explanation and details of your application! I have to confer with my colleague on this one, and I won't be able to get back to you until early next week. I did have one question - are you using off-the-shelf hall elements, cores and coils, or do you have them custom made?
  • Hi Jason,

    I figured out a clever way to bias the hall device so that I can null the offset error out. That then allows me to use the >=100 ohm shunt resistors, and access lower current levels using my circuit. I am not completely sure about temperature stability of the hall sensor's offset voltage yet, so hopefully it doesn't hose everything. To answer your question the hall effect sensor is off the shelf, so are the cores, but I am modifying and winding them myself.

    Anyway, at this point, I'm pretty satisfied with what I have been able to do with the chip. The DRV411 is a brilliant piece, at a good price, like most of TI's ICs. Now I just wish you had a similar one for driving 4-SIP hall-elements in an open-loop configuration!

    Thanks for your help!

    D