DRV8703-Q1: DRV8703-Q1

Hi Christian,

I could not duplicate your findings on the EVM.

I ran a test on the EVM @ VM=12V.

When the device is awake and outputs are Hi-Z, I measured the following voltages at the SO header. The voltage at the header is reduced to 57% of the DRV8703-Q1 SO voltage.

Av     SO_Header (mV)      SO_DRV8703pin (mV)      VIO(mV) calculated 
10     27.3                           47.0                                   4.7
20     52.3                           90.6                                   4.53
40     102.5                        177.8                                  4.44
80     200.2                        350                                     4.375

If you did something different please let me know.

Hi Rick,

Thanks for your reply.

We have simply (in relation to the Eval board) powered it up. And changed the Av to 78 and set the Vso max limit to 3V6 via the registers.

At that point with no current flowing with Av=78 we measure 0V at Vso.

Yes, I do know there is a voltage division on the eval board

What can we do to solve this? Is there a register setting that can cause this? Or what can cause this? Can we have you help us dig a little into this?

Again, we have confirmed that the Vso pin responds when current is flowing in the sense resistor (motor is spinning).

Is there a point, points or settings where the Vso pin is not valid? You seem to have the four gate outputs all high impedance (off). So do we when we test. 

Thanks!

Best, Christian

Hi Christian,

Please measure and report the following voltages on the DRV8703-Q1 EVM when you are monitoring the SO output.

nSLEEP -- Must be 3.3V, need GUI to set this 
AVDD -- Must be ~5V
DVDD -- Must be ~3.3V
VCP -- Must be ~VM + 10V if VM >13.5
MODE
IN1
IN2

This will  assist in duplicating your issue. 

Hi Rick,

As mentioned the motor can spin just fine and we can read the output from the Vso. That means when the motor is not spinning (confirmed by measurements):

nSLEEP -3V3
AVDD -- ~5V
DVDD -- ~3.3V
VCP -- ~VM + 10V
MODE: PWM
IN1: Low 
IN2: Low

If you like you can put it this way: Should Vso even be able to be <~350mV? If so, when? Sleep pin is high. Motor has just been spinning. Motor was stopped by only setting IN1 and IN2 low. Then measure Vso.

Thanks.

Best, Christian

Hi Christian,

How are you measuring the Vso?

I am using a DMM at the SO header and changing the gain. The output at SO header is the divided value.

I cannot explain why you are seeing 0V when the device is awake and the outputs are not enabled. With the outputs enabled or disabled, I measured the same voltages listed in my original reply with no current flowing through the sense resistor.

Please measure using a DMM so we are comparing with similar equipment. The voltage range setting of the DMM is 2V.

Hi Rick,

Ok. Somehow we need to solve this however. 

And yes again we know it is the divided value. We have measured both.

Do you have a load (motor) connected when measuring?

What is the signals on the two PWM inputs? High, low or with a duty cycle, when you measure?

Best, Christian

Hi Christian,

I agree we need to solve this. I will be in the lab again tomorrow so I should have an update by Thursday.

Can you confirm that you made the measurements on SO header with a multimeter?

All of my experiments were with no load.
I used PH/EN mode with device awake

EN at 100%
PH at 0% and 100% 

Since I was using a multimeter I did not want to add a duty cycle variable in the equation, but will try tomorrow.

Hi Christian,

I tried two more EVMs today. Both operate as expected.

Using a multimeter to read the voltage at the SO header, I found similar voltages as described above.

I then tried all three operating modes, and combinations of duty cycles.

All of the above were without a load.

Next a load was added, and I observed the same voltages when there was no current flowing.

As I loaded the motor I could see the SO voltage increase at the header.