DRV8704: Can i disable overcurrent protection

Battulga Ariunbolor

Part Number: DRV8704

Hello!

I have an issue with DRV8704. I designed my PCB. I made all the connections as per suggested in the DRV8704 technical document

VM = 12.6V

FET = IRF3205 (Double H bridge)

Motor = Tamiya 540 with 75:1 gearbox

Current Without Load = 1.2A

Maximum Torque = 12kg・cm (6.32A/185rpm)

Problem is OCP bit set '1', fault LED is ON and motors disabled when i change direction of motor sharply. I think voltage drop across IRF3205 is higher than 1000mV, when current is not high enough to breakdown. And now i need to disable overcurrent protection, Can i do that?

Please Help!!

over 7 years ago

0 Rick Duncan over 7 years ago

TI__Guru** 114905 points

Hi Battulga,

The overcurrent protection cannot be disabled, nor is it recommended to do so. A 1000mv drop across the IRF3205 indicates as much as 100A. This should be understood before attempting to disable the OCP.

If you are seeing an OCP fault, this could be an indication of some type of shoot-through. The DRV8704 attempts to prevent shoot-through but adding addition circuitry to slow down the rise or fall rates at the gate can affect this operation.

Using a scope to monitor the VGS and VDS of the FETs is a vital tool to determine the cause of the OCP.

Can you provide your register settings, and the sense resistor value?
Providing the schematic would also be helpful.

0 Battulga Ariunbolor over 7 years ago in reply to Rick Duncan

Prodigy 130 points

I changed that

OFF register: TOFF = 0x60

BLANK register: TBLANK = 0x00

DRIVE register: IDRIVEP = 0x00, IDRIVEN = 0x00, TDRIVEP = 0x00, TDRIVEN = 0x00, OCPDEG = 0x11, OCPTH = 0x11

other registers on default

0 Battulga Ariunbolor over 7 years ago in reply to Rick Duncan

Prodigy 130 points

Oh, And i confused that, I put 10A fuse on each power of H-bridges. Fuse is not breakdown when OCP bit set 'HIGH'

0 Rick Duncan over 7 years ago in reply to Battulga Ariunbolor

TI__Guru** 114905 points

Hi Battulga,

What is the VCC, VMA, and VMB voltages? The OCP compares the AOUTx or BOUTx against VCC.

Any difference between VCC, VMA, or VMB could cause the OCP.

0 Battulga Ariunbolor over 7 years ago in reply to Rick Duncan

Prodigy 130 points

Hi Rick Duncan,

They're all connected with fuses, and each fuses connects with Vbattery. I mean they're all the same voltage

What should i do, I need to solve this problem immediately, can you help me please

0 Rick Duncan over 7 years ago in reply to Battulga Ariunbolor

TI__Guru** 114905 points

Hi Battulga,

Please get a scope and probe the drain to source voltages 10 microseconds prior to nFAULT asserting.

Do you have the second set of FETs populated (Q1, Q3, Q5, ... , Q13, Q15)?
Do you need them for this motor? If you do not, please remove them and try again.
Also you can increase the IDRIVEx and TDRIVEx settings. A good starting point is equations 8 and 9 in the datasheet.

0 Battulga Ariunbolor over 7 years ago in reply to Rick Duncan

Prodigy 130 points

Hi Rick Duncan!

Thank you for the responses

I removed them and tried that way, but It's still not working, nFAULT LED turned on right as the motor gets to move.

I really think the problem is that OCP is not working fine, and i don't know why. I used fuses so i think it's safe, and it's seems like it'll work if OCP is disabled. Can you tell me how can i disable OCP please?

0 Rick Duncan over 7 years ago in reply to Battulga Ariunbolor

TI__Guru** 114905 points

Hi Battulga,

Sorry, I was not clear in my earlier post.

OCP cannot be disabled. OCP is intended to protect the FETs. My point was that you could have as much as 100A or 200A flowing through the FETs when the OCP threshold is set to 1V. You should understand where this current is flowing rather than disabling the protection circuits.

Do you see an OCP fault in both the AOUT and BOUT?

0 Battulga Ariunbolor over 7 years ago in reply to Rick Duncan

Prodigy 130 points

Hi Rick Duncan,

Thank you for you infomative responses

Yes, that's what i'm asking for.

Yes, OCP fault in both AOUT and BOUT

How can i make it flow 200A, you mentioned in an additional circuit in your earlier post, and i wanna ask about it please.

0 Rick Duncan over 7 years ago in reply to Battulga Ariunbolor

TI__Guru** 114905 points

Hi Battulga,

"How can i make it flow 200A"

Typically, this much current is due to some type of shoot through condition, but I cannot confirm without scope captures. The OCP circuitry is intended to protect against high currents like this. When the OCP value is set to 1V and the RDSon of the FET is 8mOhm, the OCP trip point is 1V/8mOhm = 125A per FET installed.

"you mentioned in an additional circuit in your earlier post, and i wanna ask about it please"

I mentioned additional circuitry prior to seeing the schematic. The circuitry is typically series resistors or diodes between the FET gates and AxLSBxLS/AxHS/BxHS pins.

0 Battulga Ariunbolor over 7 years ago in reply to Rick Duncan

Prodigy 130 points

Hi Rick Duncan,

I resolved this issue, the problem was fake FET, I changed FET's, its fine now

0 Rick Duncan over 7 years ago in reply to Battulga Ariunbolor

TI__Guru** 114905 points

Hi Battulga,

We are glad to hear you problem is resolved. Can you provide a little more information.

What is meant by "fake FET"?

Thank you.

0 Battulga Ariunbolor over 7 years ago in reply to Rick Duncan

Prodigy 130 points

Hi Rick Duncan,

I used 3 different package of IRF3205, i bought 1, 2 from electronic shop in my country, bought 3 from aliexpress, first one is working fine, second one is not working fine enough, 3rd one is not working on my PCB, and i think 2, 3 is the fake MOSFET from china

0 Battulga Ariunbolor over 7 years ago in reply to Rick Duncan

Prodigy 130 points

But now i'm using IRF1404 MOSFET, and I have an another issue with DRV8704

e2e.ti.com/.../663953

Help me please

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DRV8704: Can i disable overcurrent protection