drv8301

Hi Shashank,

The current shunt amplifier is not used to determine overcurrent. Please see section 7.3.4.1 of the datasheet (OCP) for details.

Then why my IC is not working in OCP current limit mode??????????????????????????????

It works only when i disable the OCP mode.

Hi Shashank,

Does the device work in report only mode also? Have you looked for 64us pulses on nOCTW?

For current limit mode or latched mode, please provide scope captures of the following signals with respect to the input changing:

BST_x
GH_x
SH_x
GL_x
SL_x
n_OCTW
n_FAULT

my device work in report only mode with nOCTW remains low.

In current limit mode whenever input PWM signal changes state nOCTW goes low for a very short time(I think 64us).Otherwise it stay high.

One more thing, my device work in current limit mode for HIGHER Vds threshold value such as 2.131V and 2.400V (set by SPI).So I think my device encounter overcurrent event in the lower Vds threshold values.But i don't know WHY?

Hi Shashank,

The device appear to encounter an overcurrent threshold. Depending on which FET you enabled, the VDS monitor is comparing PVDD1 to SH_x or SH_x to SL_x. I suggest you monitor the two pins looking for the Vds when switching. This will help you determine why.

Also please refer to www.ti.com/.../slva552.pdf for layout recommendations regarding overcurrent monitoring.

When I put four 0.1uF capacitor across the drain and source of the lower MOSFET or across the SHx and SLx pins then the lower MOSFET starts working properly in the lower Vds threshold values also.
1st thing is it okay to put capacitor over there (across the SHx and SLx pins)??
2nd thing my higher MOSFET still DON'T work.
I have already read slva552.but that thing didn't solve my problem.

While adding the capacitors may work, this is probably masking the root cause.

I suggest you carefully examine the SHx signal, the SLx signal and GLx signal. Ideally a differential probe to measure the difference across the SHx and SLx pins of the DRV8301 would help. You should also examine the rise and fall time of both GHx and GLx to make sure the high side FET is off before the low side FET is turned on.

I solved the problem by removing the gate resistance of the MOSFETs.Gate resistance reduces the switching speed of MOSFETs.

Due to gate resistance Vds sensing starts before completely TURNING ON the MOSFETs.So,before turning ON the MOSFETs Vds was 1.32V.So, Thats why my device work for higher threshold values such as 2.400V.

But, When i attache motor with the 3-phase bridge, device again encounter an overcurrent event like before.If i attache resistors with the 3-phase bridge than my device works properly.It means at the starting moment may be motor takes large amount current.

one more thing i wanted to know........

In OCP current limit mode, after enabling the MOSFETs how much time does DRV8301 takes to start Vds sensing???
If i know this than i can select proper gate resistances and MOSFETs for my project.