BTN8982TA strange OUT wave

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stefanozanotti
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5 sign-ins First solution authored First reply posted

I'm experiencing a strange behavior with one BTN8982TA chip.
I have other chips mounted on other identical boards and they are working fine.

The chip is a High Current PN Half Bridge.
I drive its inhibition pin INH high (to enable it), and its IN with a PWM wave.
So, the output should be a (slew-rate limited, delayed) replica of the PWM.
Instead, the faulty chip generates a strange wave which is always high during the high semiwave of the PWM, and toggles during the low semiwave of the PWM.
During this time interval, the output switches at a frequency of about 7.5kHz and a duty cycle of about 96%.
This frequency and duty cycle is completely independente of the frquency and duty cycle of the PWM applied to the IN pin.

All the oscilloscope screenshot that I'm attaching are taken in a no-load condition, but applying a ~2A load didn't change the behavior.
In the screenshots, the blue trace is the PWM input, the yellow trace is the OUT signal.
See in particular:
01: a working chip, with 18kHz 50% PWM input
02: the faulty chip, with 18kHz 50% PWM input
03: the faulty chip, with 0% PWM applied, showing the 7.5kHz 96% OUT signal
09: the faulty chip, showing the different behavior during high and low phases of the input PWM
04-05-07-08: the faulty chip, with various frequencies and duty cycles for the PWM
06: the faulty chip; at duty cycle > ~95%, it seems to work correctly (but this doesn't work equally well at all frequencies)

I'm also attaching an excerpt of my schematics. Not pictured here, there are also 330uF+330uF+10uF capacitors on VIN.
As far as I can tell, the schematics follows the guidelines and examples given in the datasheet (https://www.infineon.com/dgdl/Infineon-BTN8982TA-DS-v01_00-EN.pdf?fileId=db3a30433fa9412f013fbe32289...).

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I've captured the IS signal as you requested, without load.
As for tests with a load and with different chips on the same board, I will do them as soon as possible.

I've captured the signal on the IS pin, not CURRENT_MOT_1, because the latter is too heavily filtered to see the actual behavior of the chip.

See the attachments:
01-04: yellow=OUT, blue=IS
05: yellow=IN, blue=IS

The chip signals a fault when IN is low (~11V across a 2k21 resistor -> ~5mA, which is in line with the IS_lim value given in the datasheet).
In the screenshot you can see that when the PWM goes high, there's a delay before the fault disappears; at higher PWM frequencies, this means that the fault never disappears, since the period is less thatn the delay.

06-07: yellow=OUT, blue=IS; shows the IS signal of a working chip

07: the peak current is ~1.5V/2k21*dk_ILIS -> 1.5/2k21*19500 = ~13A
It seems high, though it's probably just the inrush current of the 220nF capacitors

In picture 04 instead (the faulty chip), the peak current is ~700mmV/2k21*dk_ILIS -> 0.7/2k21*19500 = ~6A
But then, after decreasing for a while, the fault happens.


I have 3 chips on each board, with identical configuration.
On the same board as the faulty one, the other 2 chips are working correctly.
I also have 2 other boards, and all 6 chips there are working correctly.

View solution in original post

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8 Replies
psb
Moderator
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250 sign-ins 25 solutions authored 100 replies posted

Hello @stefanozanotti ,

   Thanks for reporting this on the Infineon Community !
  
  1. Can you please let us know if only this chip is behaving with the particular board it is placed on ? Place another verified working chip on this board and confirm.

  2.  The error information is given as the output at the IS pin. Request you to capture the waveform at IS pin (CURRENT MOT 1 signal in your schematic) for the above conditions (or with the 2A output current as well) and share with us. 

Meanwhile, we'll further analyze and see what all can be the possible causes for this particular behavior idealizing the above mentioned conditions and get back to you. 

Thanks,
Sai

Best Regards,
Sai
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Attachments are accessible only for community members.

I've captured the IS signal as you requested, without load.
As for tests with a load and with different chips on the same board, I will do them as soon as possible.

I've captured the signal on the IS pin, not CURRENT_MOT_1, because the latter is too heavily filtered to see the actual behavior of the chip.

See the attachments:
01-04: yellow=OUT, blue=IS
05: yellow=IN, blue=IS

The chip signals a fault when IN is low (~11V across a 2k21 resistor -> ~5mA, which is in line with the IS_lim value given in the datasheet).
In the screenshot you can see that when the PWM goes high, there's a delay before the fault disappears; at higher PWM frequencies, this means that the fault never disappears, since the period is less thatn the delay.

06-07: yellow=OUT, blue=IS; shows the IS signal of a working chip

07: the peak current is ~1.5V/2k21*dk_ILIS -> 1.5/2k21*19500 = ~13A
It seems high, though it's probably just the inrush current of the 220nF capacitors

In picture 04 instead (the faulty chip), the peak current is ~700mmV/2k21*dk_ILIS -> 0.7/2k21*19500 = ~6A
But then, after decreasing for a while, the fault happens.


I have 3 chips on each board, with identical configuration.
On the same board as the faulty one, the other 2 chips are working correctly.
I also have 2 other boards, and all 6 chips there are working correctly.

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MMA
Moderator
Moderator
Moderator
10 replies posted 10 sign-ins 5 replies posted

Hi,

scope plots 1-4 show a fault condition which is output at pin IS. It looks like the low side switch hits the over current detection threshold and feedbacks on pin IS fault condition. When this occurs the switch is turned off and is activated again after time tcls (tzyp. 115us) expires. I propose to check if there is a short between OUT pin and VS pin, e.g. caused by solder bridges on the PCB. Please refer also to chapter 5.3.3 in datasheet.

https://www.infineon.com/cms/en/product/power/motor-control-ics/brushed-dc-motor-driver-ics/single-h...

mma

mma
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Thanks for the information, I'll do some tests.

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stefanozanotti
Level 1
Level 1
5 sign-ins First solution authored First reply posted

I've checked and there is no short between the OUT pin and VS (nor other pins of the chip). The soldering seems okay.

I've also removed the two output capacitors C43 and C44, to reduce the peak OUT current, but the problem is still there.

Do you have an idea of what else I could test, other than replacing the chip?

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MMA
Moderator
Moderator
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10 replies posted 10 sign-ins 5 replies posted

Hi, 

in case a sort can be excluded, I suggest to replace the IC with a new one / other working IC.

mma
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stefanozanotti
Level 1
Level 1
5 sign-ins First solution authored First reply posted

I've moved the faulty chip to another board, where the chip that I removed was working.
The faulty chip shows the same behavior as before, so the problem is due to the chip, not to the PCB.

Is this a known problem with some batches / some chips?
What kind of defect rate should I expect for these chips?

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MMA
Moderator
Moderator
Moderator
10 replies posted 10 sign-ins 5 replies posted

Hi,

BTN8982TA is running in high volume in automtive applications and known as a quite robust device for motor drive applications.

However operating conditions, exceeding absolute maximum ratings, can lead to electrical or thermal overstress and harm the device. Thsi could be e.g. higher voltage at VS than rated in the abs max ratings, ESD overstress, excessive current flowing when reverse polarity is applied etc..

mma
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