Hi,
I have a DRV10983 application (ventilation fan) where there is already a separate buck regulator on the PCB, so there is no need to use the onboard buck regulator of the DRV10983 (it couldn't supply enough current for the rest of the board, anyway). I could have used the "linear regulator" option as described in the datasheet to power the internal circuitry of the DRV10983, but that would have been inefficient and this application has a strict power budget. So, instead I just left the SW pin floating and fed power to the VREG pin (with a 10u cap to ground), from the separate regulator.
On a trial batch, around 50% of the boards run perfectly normally and the other half do not - the DRV10983 does not seem to make any attempt to align or accelerate the motor. All I2C comms behave normally and all registers read back correctly, but nothing happens.
Temporarily breaking the connection from the power supply to VREG and fitting a 39R resistor to SW allows the device to work normally and the motor runs, so there is clearly nothing 'wrong' with it as such.
The power supply voltage is nominally 3.4V and they measure around 3.36V on both "working" and "non-working" boards. However, I found that if I slightly raise the power supply voltage, to about 3.5V, then suddenly the DRV10983 will work.
Any idea what's going on here? Is there a lockout feature that stops the device running if the internal 3.3V and 1.8V LDO's are not in regulation? That's what it looks like, but then I would think that the on-board buck/linear regulator is not that accurate anyway?
Can you throw any light on this? It would be really good NOT to use the onboard regulator
TIA :-)
