Hello TI experts-
We have seen some strange behavior from the DRV120APWR with our solenoid valves. With the programming resistor set at either 0 Ohm or 200K Ohm, we got an audible ~6.7KHz PWM frequency where 20KHz was expected. We could hear the coils whining and this audible sound was not desirable.
It seems like our solenoids are causing the PWM oscillator to detune (doesn’t seem like this should be happening based on block diagram on sheet 3 of the data sheet). One thing we notice is that the data sheet indicates solenoids with 1 H coil are typical (seems like a typo since very large inductance). Our coils are ~50mH when measured with LCR meter at 10KHz. They also have ~150 to 200 Ohm coil resistance.
We tried using 50K Ohm to set frequency to 60KHz. We found the PWM frequency did not always start up at 60KHz, but we could kick start it by brushing the OSC pin with my finger. We started playing with resistor value and found better operation above 70K Ohm.
We seems to have solved the unstable startup and audible noise issue by changing to 80K Ohm frequency setting resistor. However, we would like an explanation for the frequency shift and instability using a 50K Ohm resistor.
We should add that we can duplicated our findings on the DRV120EVM, so it is not a layout issue with our PCB.
Thanks and best,
-Tim Starr on behalf of JY@IN
