Part Number: DRV8301
We used DRV8301 to design a motor driver. Up to now, we have made some PCB. But recently the same problem occurred in three different PCB: GH_A output wrong waveform while GH_B and GH_C output the correct waveform.
Here is our schematic: (V3.4)
Here is the detail. In all the test bellow, the input voltage of AH/BH/CH was 3V3, while the input voltage of AL/BL/CL was 0V. During all these tests, the nFault were always output high voltage ( No fault were reported.).
figure 1: input PWM of AH
figure 2: output of GH_A
figure 3: output of GH_A
figure 4: output of GH_A
figure 5: output of GH_A
3.In the forth V3.4 PCB, only GH_A was 1.6V. GH_B/ GH_C were 30V. (AH/BH/CH was 3V3, while AL/BL/CL was 0V.) We recorded the waveform of the forth V3.4 PCB. The waveform were recorded in the figure below.
The waveform of the forth V3.4 PCB GVDD:
The waveform of the forth V3.4 PCB GH_A
The waveform of the forth V3.4 PCB GH_B:
The waveform of the forth V3.4 PCB GH_C:
For the V3.4 PCB, I would first like to see a scope capture of PVDD1 and GVDD. It is also possible that a layout or assembly issue could be causing this, please refer to this layout best practices guide for suggestions.
We are glad that we were able to resolve this issue, and will now proceed to close this thread.
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In reply to Omar Naamani:
Thank you for your replying！
Here is the waveform of the forth V3.4 PCB. The yellow one is GVDD and the blue one is the PVDD1. ( GH_A was 1.6V. GH_B/ GH_C were 30V. AH/BH/CH was 3V3, AL/BL/CL was 0V.)
It's maybe a layout or assembly issue. But the first V3.4 PCB worked well whithout this "GH_A" problem and we haven't find any serious abnormality in its waveforms.
In reply to Leib-Niz:
I have a couple questions for you that may help me figure out what is going on here.
We have done some more test. Here is the detail.
input : AH/BH/CH 3V3 ; AL/BL/CL 0
output: We didn't change the program. So the waveforms are the same as the figures in the first post above.
Here is some more scope capture.
figure 3-1 : blue-BST_A ; yellow-SH_A
figure 3-2 : blue-BST_B ; yellow-SH_B
For some unknown reasons, we can not upload new program to The forth V3.4 PCB. So we can not change AH/BH/CH or else. We have to use The second V3.4 PCB to continue our tests.
output: GH_A/B/C around 1.6V ; GL_A/B/C 0 . The waveform of BST_A/B/C and SH_A/B/C are the same as figure 3-1.
2. Change program
input : AH/BH/CH 0 ; AL/BL/CL 3V3
output: GH_A/B 0 ; GH_C around 1.6V ; GL_A/B/C around 12V .
figure 3-3 : blue-BST_A/B/C ; yellow-GL_A/B/C( the same asGVDD)
figure 3-4 : blue-GH_C ; yellow-none
3. Change program
input : AH/BH/CH 0 ; AL/BL/CL 0
output: GH_A/B/C around 1.6V ; GL_A/B/C 0 .
figure 3-5 : blue-BST_A/B/C ; yellow-GH_A/B/C
I noticed you have 600 ohm series gate resistors, this is likely too much. A 10 ohm resistor per gate should be sufficient. As an experiment, can you retry your tests after removing all the 600 ohm resistors and replacing them with 0 ohm resistors?
Also, could you attach some pictures of the PCBs during operation?
The 600 ohm are not resistors. They are bead inductance.
We only used 10 ohm per gate in V3.2. But the waveform oscillated(figure 4-1). So we add 600R bead inductance in order to eliminate gate oscillations. And it is proved that the beads are effective in eliminate gete oscillations.
figure 4-1 : The third V3.2 PCB GL_A
By the way, in the fifth V3.2 PCB without 600R bead, we also meet the "GH_A" problem (GH_A around 1.6V).
Here is our V3.4 PCB(four layers):
Regarding the V3.2 gate oscillation:
For more information about choosing the gate drive current and sizing the gate resistance, please take a look at this FAQ.
I am so sorry for I didn't reply for such a long time.
We have made some more V3.4PCB, and we have tried to fix the PCBs with GH 1.6V problem.
What puzzled us most is that while the GH is 1.6V, the SH is also 1.6V. We think the SH act as a independent wire. When high-MOS open, the SH will be 24V. When low-MOS open, the SH will be 0V. When high-MOS and low-MOS close, the SH should not be same as GH. We suspected there was a short circuit between GH-SH in drv8301. So we measured the resistance between GH-SH-GL. The GH-SH in A/B/C were all about 1MΩ in 3rdPCB and were all about 4MΩ in 5th and 6th PCB. The GL-SH in A/B/C were all about 11MΩ in 3rdPCB and were all about 16MΩ in 5th and 6th PCB. These proved that there were no short circuit in drv8301.
Are there any possibility that the GH1.6V problem were all caused by drv8301 because drv8301 were broken down?
For your information, we're getting close to a national holiday in the US so I ask for your patience as response times might be delayed, as people (like Omar) will be taking time off.
For the gate ringing:
I just want to reiterate Omar's advice, please make sure you test the lower gate drive current. This should help reduce the gate ringing oscillations. Less current means less energy coupling through parasitic capacitances and weaker electric fields radiated by the gate trace (which could couple into other circuits).
Adding the ferrite beads in the path add inductance in the path which is not recommended design as inductance will cause ringing and oscillations as the L interact with the C of the FETs and gate traces. Replace with them with low resistances, as Omar suggested, to help with these.
SH act as a independent wire [from GH]:
This is mostly true. We know that the voltage on the gate of the MOSFET needs to be higher than the source voltage in order to turn on. This satisfices V_GS > V_th. But we know the MOSFET has to be off if V_G - V_S = 0V, or V_G = V_S. This is why R41 - R43 exist on your board correct? To allow current to flow out of the gate and to the source node until I = 0A between the two nodes (which means V_G and V_S would be at the same voltage).
In addition, pulling the ENABLE pin to an off state will enable pull down within the GHx pin of the DRV8301 and start to pull current out of the gate and push it to the SHx pin. This is represented by the R_gate_off spec in the datasheet
Guessing by the M ohm measurements, you probably measured it when the device was enabled but no pulling of the gates high. This would at least mean there isn't a short from gate to GND, but did you compare against a known good board and device to see if they were similar?
Soldering (or welding) and Debug:
Based on everything I've read, you still haven't figured out if the problems are caused by the boards or the device, correct? You've replaced devices but have put "bad" devices on "good" boards to see if the problem follows the device or the board? Please, correct me if I'm wrong.
There is a problem with this, it sounds like the soldering (or welding) is not being done by manufacturer when replacing the DRV. If the re-weld process is not using solder paste, a heat gun, and a board warmer; or a specialized solder reflow machine, then we cannot be sure the welding work is up to the quality of a manufacturer. This means, there's a chance for a good part to fail, regardless of good or bad boards, because the device isn't connected to the board properly. Be sure to factor this into the debug.
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