DRV8873: can DRV8873H detect brake current over 11 [A]?

Hello Ryan,

many thanks for your answer.

We now have a problem with a customer. He didn't use our control box properly, so the IC is short-circuited and has a temperature of up to 200 °C. I'm now investigating why it might be happening. All we know is that he runs 2 motors in parallel (with a Y adapter cable), so the starting and braking currents are very high. On start the IC switches to PWM mode, but on braking it doesn't, so I suspect that's shorting it out. I'm still of the opinion that if current > Iocp, the IC shuts down no matter it's in driving or braking phase. Is that correct?

Other question: How can the IC be short circuited? If you have any idea how the IC shorts out, please let me know.

Best regards, 

Oat

PS. Here you can see the motor current when I run 2 motors in parallel. The motors are not loaded yet, when the motors are loaded, the starting and braking currents are much higher. 

Oat,

Can you post schematic please and how load is connected?

Regards,

Ryan

Hi Ryan,

here is it

Normally there should only be one motor per channel (as in the schematic), but the customer runs it with 2 motors per channel, although we have a datasheet with all the technical info.

Regards

Oat

PS. Customer schematic. There are two power-supply for 1 controlbox and every channel with two motor in parallel

There are no connection between U1 and U4. U1 must controll two motor at the same time, there for I_Start and I_Brake very large. Is it the reason, why the ICs "shoot-thru"?

Picture 3

Oat,

It is really difficult for me to read that attachment.  Are the DRV8873 outputs (U1 and U4) connected in any way?  It looks like maybe they are, but I can't tell.  This is NOT recommended as the internal timing can be different between U1 and U4 and cause a short between supply and GND due to one FET turning on before the other.

Regards,

Ryan

Hi Ryan,

I can not upload better attachment. Can you give me your mailadress? How can i upload better attachments?

thanks

Regards,

Oat

Oat,

Actually, I can read it better now!  Not sure what happened.  So, it appears that U1 drives one motor and U4 drives the other motor.  There should be no issue with that configuration as attached.  

If somehow in their connection the outputs of U1 and U4 are connected together, that is when you can have a "shoot-thru" condition between the two drivers.

Regards,

Ryan

Hi Ryan,

there should be no connections between U1 and U4, you can see at the Picture 3 how our customer uses the motor controllers, each driver controls 2 motors at the same time, so the I_Start and I_Brake are very high. At start the driver limits the current by I_Trip = 6.5A, but at braking I_Brake can be over 15A. My question: does the driver have no protection mechanism during the braking phase? Is it the reason, why drivers "shoot-thru"?

Thanks

Regards

Oat

Oat,

Current regulation is only active during a "drive" state.  So, makes sense that during high-side braking the current can exceed and will not be regulated.  As long as EN = 1 (drive state), the current should be regulated.

OCP is ALWAYS active.  I think they are just not hitting a level where OCP will trip.  So, they are in a state where temperature will rise, but OCP will not trip.

Regards,

Ryan

Hi Ryan,

ok. that means, there ist not regulation by braking, that is true . But OCP must be there.

But it doesn't work. You can see on the picture, I_brake is up to 12 A (lila linier), but driver is always enable.

- Lila: motor current 

- yellow: supply voltage (+29V) 

Tomorrow, I'll try more load to get higher I_brake and let you know. Which current do you expect that the driver will be disable? actually 10A, isn't it?

Regards,

Oat