DRV8320: VDRAIN and VM

Hi Hamamoto-san,

Revised my answer after speaking with the team.

It is not recommended that the Vm and Vdrain be separated. The device is designed to operate with these supply lines being only one supply line, as the Vds monitors and Vgs can be negatively affected.

When Vm is above Vdrain, you need to have enough voltage on the gate and drain of the high side to still switch the FET. Therefore, calculating the bridge operation with voltages on Vdrain and GHx will net you the answer. No issue here

When Vdrain goes below Vm, you have to be careful about the Zener clamp diode on the high side, basically, the diode will not function correctly if the delta (Vdrain - Vm) is not large enough.

Hi Hamamoto-san,

See replies below this sentence:

>When Vm is above Vdrain, you need to have enough voltage on the gate and drain of the high side to still switch the FET. Therefore, calculating the bridge operation with voltages on Vdrain and GHx will net you the answer. No issue here

 Does this mean VM is under Vdrain?

>> Vm > Vdraiin

>When Vdrain goes below Vm, you have to be careful about the Zener clamp diode on the high side, basically, the diode will not function correctly if the delta (Vdrain - Vm) is not large enough.

I think it is not "Vdain goes below Vm". It is "Vdain goes up over VM" . Is this correct? (Because "Vdain goes below VM" is same as above #1 answer(VM is above Vdrain).

Also as you mentioned,Vdain and VM should be same. So that, delta(Vdrain-VM) should be zero. Is this correct?

>> Vm < Vdrain. It is suggested that they stay the same, due to the case when Vm < Vdrain. You can separate them, but you have to watch out for the clamp diode operation. Recommended the difference between when Vm < Vdrain be 4 V or less.

And I have one more question.

On the datasheet, it is mentioned about the separation of VM and VDRAIN and the filter.

If we would like to add a filter on VM,how can we add the filter? and how can we configure the VM and Vdrain line?

>> Separate the Vm and Vdrain lines if you wish to operate with them separately. The filter can similar to the one found on our DRV8305-Q1EVM User's Guide (Rev. A)'s User's Guide. Filter found on Page 14 as Optional PI Filter. Please note that EVM is designed for up to 45 V. While the DRV832x device works up to 60 V. 

Hi Koji-san,

- In the customer case, VM is supplied by the battery and VDRAIN is connected to the drain of high side FET of the bridge.

- Could you let me summarize your answer?
If VM > VDRAIN, we should care about the voltage of Vdrain and GHx. (We need to check it can drive the external MOSFET or not.)
But It may be no issue. 

>>> Correct :)

If VM< VDRAIN, we need the voltage difference of between VM and VDRAIN should be less than 4V. Because of the internal clamp diode.
Is my understanding correct?

- If the difference voltage between VM and VDRAIN is larger than 4V, what happens?

>>>You potentially violate the Vds protection based on the minimum clamp diode voltage of 15 V.

>> Separate the VM and Vdrain lines if you wish to operate with them separately. The filter can similar to the one found on our DRV8305-Q1EVM User's Guide (Rev. A)'s User's Guide. Filter found on Page 14 as Optional PI Filter. Please note that EVM is designed for up to 45 V. While the DRV832x device works up to 60 V. 

- Thank you for the information. I will suggest the customer refer the EVM above.

>>> Okey-dokey.