DRV8812: Power supply VMA and GND are shorted

Part Number: DRV8812

We are evaluating mobile printers.
After about 10 sheets of printing, 2 units have occurred.

No.1: 2 Ω between VM and GND
No. 2: 15 Ω between VM and BOUT 2

VM = 15.5 V
Motor current: 290 mA or 400 mA

Overvoltage can not be confirmed

We are controlling as follows.

① Start the VM power supply
② AENBL and BENBL are set to "H" simultaneously nSLEEP and nRESET are set to "H"
③ Signal input to APHASE and BPHASE for back feed
④ Back feed stop
Set AENBL and BENBL to "L"
Set AENBL and BENBL to "L" at the same time nSLEEP and nRESET to "L"
In case
⑤ AENBL and BENBL are set to "H" simultaneously nSLEEP and nRESET are set to "H"
⑥ Signal input to APHASE and BPHASE to feed forward
⑦Stop the normal feed
Set AENBL and BENBL to "L" at the same time nSLEEP and nRESET to "L"

Is there a possibility that through current etc. flow when switching frequently, such as the nRESET signal?

Hello user1116846,

I want to understand the failure you see better. Here are my follow-up questions:

• How many units do you see fail like this?
• Do they always fail after 10 sheets, or does this number change across trials?
• Is this a complete device failure, or are you able to use the device again after you power cycle your board?

Thank you for your reply

• How many units do you see fail like this?

  →Two out of 30 units have occurred.

  　The test is stopped because there is a possibility that the device will be damaged.

  　It may occur more.

• Do they always fail after 10 sheets, or does this number change across trials?

  →There are about 10 defects. Some products do not occur

• Is this a complete device failure, or are you able to use the device again after you power cycle your board?

　　　→Since the device is damaged, it will not recover even if it is restarted.

There was a mistake in the description.
Please correct me.

Do they always fail after 10 sheets, or does this number change across trials?
　→Two troubles occurred.
　　A problem occurred when about 10 sheets were printed at 15 ℃ environment.

Part Number: DRV8812

Trouble has occurred that the BACK FEED can not be performed due to the initial phase input pattern of the motor.

Drive from the following phase pattern

NG pattern
Pattern 1: APHASE = L BPHASE = H
Pattern 2: APHASE = H BPHASE = H

OK pattern
Pattern 1: APHASE = L BPHASE = L
Pattern 2: APHASE = H BPHASE = L

It occurs frequently when it is 15 ℃ environment.
However, there is no problem as long as it is in the 30 ° C or 0 ° C environment.

I warmed the DRV 8812 with a hand blower in a 15 ° C environment.
This also improves.

This was also improved when nSLEEP signal is fixed to "H" level.

What is the cause of trouble easily in 15 ℃ environment?

Regards Aoki

Please let me supplement

Up to now, two DRV 8812 have failed.

The failure mode of the DRV 8812 is a shortage between VMA and GND / BOUT 2.

Each DRV 8812 was able to print normally at more than 3000 sheets at -10 ° C or 23 ° C.

However, when tested at 15 ° C for both of the two, it was damaged after printing about 10 sheets.

Hello Aoki-san,

Thanks for the additional information. Let me speak with my team to see if anyone has seen this issue in the past.

Hello James Lockridge san

The problem of BACKFEED and the problem of short circuit are different.

One BACKFEED NG has occurred.
Two problems occurred in short circuit.

I have included backfeed consultation for consultation on short problems.

Regards Aoki

Aoki-san,

I combined your posts to help me stay organized while troubleshooting these issues.

Here is a summary of my understanding. Please correct me if I misunderstand or if I miss any details.

3 devices out of 30 have failed

• 2 devices fail with shorts - both devices are damaged and do not recover.
  • No.1: 2 Ω between VM and GND
  • No. 2: 15 Ω between VM and BOUT 2
  • Both devices function correctly at -10 °C and 23 °C for printing 3000 sheets.
  • Both devices failed after printing ~10 sheets at 15 °C
• 1 device fails functionally at 15 °C, but can recover (BACKFEED fail)
  • When device is at 15 °C
    • Device operates correctly for APHASE = don't care, BPHASE = L
    • Device fails for APHASE = don't care, BPHASE = H
    • Device improves when warmed or nSLEEP is fixed to H level.
  • When device is tested at 30 °C or 0 °C, this issue does not occur.

I have a couple follow-up questions.

Q1) In a post about the BACKFEED issue, you said "This was also improved when nSLEEP signal is fixed to "H" level." What was the condition of nSLEEP when you saw failures?

Q2) When you see improvement for the BACKFEED issue, does the device not fail at all, or does it fail less frequently?

Dear James san

Answer of Q1
It is restored from SLEEP 30ms after VM is started up.
(nSLEEP="L"→"H")
And after 10 ms we are switching PHASE.

However, there are OK and NG under the conditions of APHASE and BPHASE.
Improvement at 0 ° C and 30 ° C and NG at 15 ° C

Improvement by fixing nSLEEP to "H" or replacing the device.


Answer of Q2
Even if backfeed improves, device short-circuit has not occurred.


■Short problem
　I asked the agent to check the No. 1 device.
　When the distributor confirmed between the terminals, it was short- circuited between 7, 11, 12, 13, 14 pin and GND.
　Mainly B phase is damaged.
　
　I am carrying out the reproduction test, but it does not occur.

Regards
Aoki

Dear James san

Another phenomenon occurred today another one.

This also occurred at 15 ℃ environment.

I will attach the findings.

■phenomenon
Motor current larger than set current flowed

When FEED was performed at 20 second intervals, abnormal motor current flowed after 20 sheets.
When printing 100 sheets, only 2 pieces of motor current abnormality occurred.
There is no problem in 30 ℃ environment.

■Device seal
I bought a new device from another trading company and tested it
NG:「DRV8812 TI 72I C1V1 G4 」　←　Backfeed NG, short NG, motor current abnormality occurrence
No problem:「DRV8812 TI 3BI C63K G4 」　←　Purchased from another trading company

Various problems occur when testing in the 15 ° C environment.
Backfeed error, device short, motor current abnormality

Please comment on what is affecting.

Regards AokiMotor electric current abnormality inspection.pdf

Dear James san

I changed the control of the motor driver IC where the motor current abnormality occurred.

Change point
nSLEEP is fixed at "H" level.

Result
It was improved and there was no problem.

I attach a sequence table.
Attached "Operation sequence at high speed FEED.pdf"

Please point out where there are problems.
Should all input signals be set before the VM starts up?

Regards Aoki

Operation sequence at high speed FEED.pdf

Dear James san

I saw a post about the previous DRV 8812.

Is it necessary to set nSLEEP to "H" level when turning on the power supply(VMA and VMB)?
Is there a possibility of malfunctioning if the power supply is turned on with nSLEEP kept at "L" level?

Regards

Aoki

Dear James san

I sent from a private message.
Please contact me if the message has not arrived.

Regards　Aoki

Hi user,

If Mr. James' suggestion or internal discussions with you resolved your question, please close this post by accepting the post is resolved in James' highlighted in yellow answer above me.

Thanks!