DRV8704: DRV8704 - OCP register values are set to '1' and fault triggered when I apply PWM to the inputs

Hi Husnain,

Is this the DRV8704EVM? If not, have you tried a second board?
Do you have FETs installed? If not, please install the FETs.
What are the settings of the DRIVE register?
Is the motor/load connected? If yes, please disconnect the motor and determine if the fault is still present.

Please measure the VDS voltage of the FETs. The OCP fault is an indication of too much current based on the VDS of the FETs.

Hi Rick,

Thanks for the quick response.

Here are the few details.

Its is not a DRV8704EVM and we are developing a new one a fresh.

Yes the FETs are installed and the once installed are IRF540N.(http://www.infineon.com/dgdl/irf540n.pdf?fileId=5546d462533600a4015355e396cb199f).

The settings for Driver Register were tested in two parts 

Default Values

Status Register
UVLO = 0
BPDF = 0
APDF = 0
BOCP = 0
AOCP = 1
OTS = 0
1000111110100101
Drive Register
IDRIVEP = 11
IDRIVEN = 11
TDRIVEP = 10
TDRIVEN = 10
OCPDEG = 1
OCPTH = 1

 and non default values set as below 

Status Register
UVLO = 0
BPDF = 0
APDF = 0
BOCP = 0
AOCP = 1
OTS = 0
1000111110101111
Drive Register
IDRIVEP = 11
IDRIVEN = 11
TDRIVEP = 10
TDRIVEN = 10
OCPDEG = 11
OCPTH = 11

 In either  cases when PWM is applied the OCP register is set as above.

The motor/load is not connected in any case.

The  VDS of the high side FETS  measured as 10.9 V  and corresponding VM as 11.6 V 

Please let me know where i am going wrong.

Hi Husnain,

Thank you for the information.

With the settings in the DRIVE register, an OCP fault will occur if the VDS (VM - A/BOUT1/2) is greater than 0.5V

Assuming the VDS is really 0.7V when the high side is enabled, please determine the reason for this. What is the charge pump voltage?

Hi Rick,

Thanks for the response.

One of the reason for  VDS as 0.7V can be  the IRF540N  FET  which has has a  ("RDS(on) Static Drain-to-Source On-Resistance ––– ––– 44 mΩ  )

The Charge pump voltage measured( for VM - 11.6V) 

VCP = 21.2 V

CP1 = 0.4V

CP2 = 11.4V

Also I tried with setting the DRIVE REGISTER's  to

OCPTH  - 11  :1000mV

OCPDEG - 11 : 8.4uS

But still see the same fault of OCP.

Please let me know any changes.

 

 

 

Hi Husnain,

If the motor is not connected, the drain to source voltage of the enabled FET should be close to 0V.

Please place a resistor divider at an output. A 20k to VM and 10k to GND is used to determine if the output is enabled. The midpoint of the resistor is connected to the output.

Please capture the voltages at VM, and the drain, gate, and source of a high side FET when the FET is being enabled. This should be done with no load. Prior to the fault disabling the output, you should see:
drain voltage = VM
gate voltage = VM + ~11V
source voltage = ~VM

For low side FETs, you should see:
drain voltage = ~0V
gate voltage = ~11V
source voltage = 0V

Repeat with the other three outputs.

If you do not see these voltages, then you should determine the reason for this.