Unable to generate a PWM pulse

[samruddhi_daithankar]

I am using the ST discovery board, which has STM8S003K3. I have written a code that generates a PWM pulse when ADC senses that the input voltage is higher than a threshold value. I have tested this program with a Potentiometer and verified the waveform using an Oscilloscope. However, when I try to run the program integrating my custom PCB, it does not give any output at all. I have made the following connections: 
MCU VDD - 5V on PCB 

MCU GND - PCB GND 

MCU pin B0 - voltage follower OPAMP on PCB

MCU pin D4 - MOSFET driver on PCB 
I have verified that the MCU is getting 5V. 
am I missing any connections? What could be the possible reason for this behaviour? Thanks for your help!