Tool/software:
I'm having issues with the some DRV8262DDW chips and the current limit functionality. Most boards are working correctly. I've found 2 of the last 10 where the DRV8262 seems to be ignoring the current limit setting on half of the chip. With a good board, the start up current is limited to 5A and then ramps down to 1A. On the problem boards, the startup current is higher than 5A and are different for the forward and reverse directions. The input signals have been verified to look good. nSleep is always high. At rest IN1 and IN2 are both low. When operating the motor, IN1,IN2 are either high,low or low,high.
As a test, I lowered the current limit on OUT1 to 4A by changing IPROPI1 to 3.9K. That had no effect on the currents seen.
On both bad boards, it was verified that the chip was soldered correctly and the current limit resistors are the correct values.
On the first board, the issue was with OUT1 and OUT2. The DRV8262 was replaced and the problem went away.
On the second board, The issue is also with OUT1 and OUT2. OUT3 and OUT4 are working correctly. I'm holding off on replacing the chip in case further testing is necessary.
I'm looking for some help in tracking down the root cause.
The DRV8262 is setup as:
Dual output
PWM mode (MODE1 is low, MODE2 is high)
nSleep is high
IPROPI1= 3.09K (5A setting)
IPROPI2= 3.09K
TOFF is high
DECAY is low
OCPM is low
IN1, IN2 are driven from a 3.3V output.
The outputs drive a 28VDC brushed motor.
At full torque the motor is rated at 4A.
With no load the motor is rated at 1A.
The circuit looks like this:
For the scope pictures:
Channel 1 - + lead of motor (out2)
Channel 2 - Current Probe (into + lead of motor)
Channel 3 - if present, is nfault
Channel 4 - - lead of motor (out1)
This is what OUT3, OUT4 (good output) look like driving the motor with no load:
This is what OUT1, OUT2 (bad output) look like driving the same motor with no load:
In the above picture, the current is more than the 5A limit setting, but no faults were generated.
Driving in the opposite direction. What is interesting in this picture, is that nFault is pulsing every 5.4ms. That doesn't correspond to any of the possible TOFF settings.
Any suggestions as to what is the issue?
