Hi Support team,
I have an issue with the RDY pin on the UCC21750DW.
The LED connected to RDY will turn on when RDY pin is pulled to GND due to Undervoltage condition. The LED Anode is connect to 5V rail with 4.99k Resistor, and the Cathode connected to the RDY pin
Firstly, the VDD pin of the UCC21750DW was not getting any voltage because the 16V regulator IC was not enable. The RDY LED was steady. It was sorted. But the LED went from steady to blinking.
Secondly, I noticed that the RST/EN pin was not getting enough voltage to Enable the UCC21750DW IC because LED was connected to the RST/EN without zero Ohm resistor. The LED was removed so that the RST/EN pin enough voltage to power the UCC21750DW IC. The RDY LED stopped blinking and was turned OFF. It was sorted.
The RDY LED was turned OFF, because the Undervoltage condition was sorted.
The UCC21750DW IC worked fine But the following day, I mistakenly powered the PCB while it was on top of a bench digital multimeter, the RDY pin was pulling LOW and Open drain causing the RDY LED to blink at a frequency continuously. I figured that it may have damaged the IC. So, I replace the UCC21750DW with a new one. But the RDY LED was still blinking continuously. Before it starts blinking, upon power on, the RDY LED will be OFF and starts blinking after 10 seconds of powering ON.
The following measurement was taken at the different pins:
VDD 14.7V
VEE -4.5V
VCC 4.9V
RST/EN 4.45
RDY 2.9V (This is normally open drain and should pull to GND only if there is Undervoltage condition). I have checked the block diagram of the UCC21750DW, it appears that the MOSFET at the RDY pin is turning ON and OFF at a frequency, causing the RDY LED to blink.
I used Arduino Nano to provide the PWM signal to the Non-inverting pin of the IC, the inverting pin of the IC is tied to GND.
The question then is; what is triggering the RDY MOSFET to turn ON/OFF at a frequency?
Kind regards,
Bright
