Hi, i am designing a motor driver, and i met a problem when it comes to verify the high side mosfets Vgs output, i gave a square wave with 50% duty cycle and 25khz signal, and this is the waveform of Vgs looks like, i could not figure what the issue is, i tried to measure the voltage between bootstrap caps, and the voltage is 14V which is close to the VCC for gate driver i gave, it is fine, however for the low side mosfets the vgs ouput results is right, so i am not sure what is the problem is, anyone could help, thank you in advance,

 

This is totally meaningless without a schematic and an explanation of how you are measuring this Vgs.

 

and this is the HO ouputs from gate driver, this is not what i want at all, is it the problem of driver it self?

 

Show us the waveforms of all the INH and INL signals.

 

Show us the waveforms of all the INH and INL signals.

Hi, thanks for reolying, this is the signal

 

Look at the example in the data sheet. There must be a capacitor from VB to Vs. There must be capacitors from Vcc to Vss and Vs0. These caps need to be right at the pins of the IC.

Where are the caps? Why D5?

 

Look at the example in the data sheet. There must be a capacitor from VB to Vs. There must be capacitors from Vcc to Vss and Vs0. These caps need to be right at the pins of the IC.
View attachment 336965
Where are the caps? Why D5?
View attachment 336967

Hi, Thank you for replying, for the three bootstrap caps, it shows here:

and the Vcc to Vss is the bypass cap shows here:

the diode is beacsue this:

And yeah i don't have Vcc to Vso cap

 

Also…..did you measure the high side waveforms with a differential probe or not??

Those waveforms ride on top of a line that is swinging up and down. A normal probe tied to a common rail won’t be able to display them correctly.

 

Also…..did you measure the high side waveforms with a differential probe or not??

Those waveforms ride on top of a line that is swinging up and down. A normal probe tied to a common rail won’t be able to display them correctly.

H, thanks for replying, i meausred with both regular and voltage differential probe, they have the same waveforms,

 

Is the "Fault" pin indicating a problem?
---edit----
It looks like current limit.

 

The Post #5 scope shots aren't labelled to identify which input signals are shown.
If the low-side FET isn't being switched (I don't see a INL pulse anywhere in those shots) then the bootstrap arrangement won't work.

 

Is the "Fault" pin indicating a problem?

i didn't connect the

Is the "Fault" pin indicating a problem?
---edit----
It looks like current limit.

I didn't gave fault any signal, it might be current limitaion, thank you for replying and helping

 

The Post #5 scope shots aren't labelled to identify which input signals are shown.
If the low-side FET isn't being switched (I don't see a INL pulse anywhere in those shots) then the bootstrap arrangement won't work.

That is the input signal for all inputs, and i always turn on low side mosfet first then turn on high side, the bootstrap might be too small, and also current limitation, thank you for helping

 

i didn't connect the

I think the Fault pin is an output.
It looks like the IC is turning off as soon as it can. That is why I am concerned about CA-, IRIP, FAULT.

 

That is the input signal for all inputs

If you are switching high-side and low-side FETs on simultaneously you will get shoot-through, Perhaps the driver IC is detecting that and shutting down?

 

If you are switching high-side and low-side FETs on simultaneously you will get shoot-through, Perhaps the driver IC is detecting that and shutting down?

The IC has logic to detect both inputs =on. You may be right. If H=1 and L=1 then all MOFETS=off.

 

If you are switching high-side and low-side FETs on simultaneously you will get shoot-through, Perhaps the driver IC is detecting that and shutting down?

I replace the bootstrap and used a bjt buffer to amplify the current,

now from the HO ouputs of driver i can get right waveform like this
but when i measured the Vgs of mosfet, the voltage level is droped to 100 to 200mV

 

The IC has logic to detect both inputs =on. You may be right. If H=1 and L=1 then all MOFETS=off.
View attachment 337027

I replace the bootstrap and used a bjt buffer to amplify the current,

now from the HO ouputs of driver i can get right waveform like this

but when i measured the Vgs of mosfet, the voltage level is droped to 100 to 200mV

 

The purpose of the bootstrap is to ensure the hi-side gate voltage can go about 10V above the high-side source voltage, even when the hi-side FET is switched on and its drain and source are at similar voltages. So why have you removed the bootstrap?

 

The purpose of the bootstrap is to ensure the hi-side gate voltage can go about 10V above the high-side source voltage, even when the hi-side FET is switched on and its drain and source are at similar voltages. So why have you removed the bootstrap?

I didn't remove, i replaced it with a 3.3uF, before it was 0.03uF