Programmable Limits PWM

This project describes how to design PWM with programmable limits using GreenPAK IC. 

This application note describes three PWM design variants using GreenPAK IC:

1. “0-100% PWM” is PWM signal generator with the possibility to control the signal’s duty cycle from 0 to 100% full range, controlled by external or internal signal (for instance: signal from external pin, I2C signal, from a comparator, etc.).

2. “Programmable Limits PWM” is modification of “0-100% PWM” with settable maximum and minimum limits of the PWM’s duty cycle. The limits can be changed by I2C.

3. “Sawtooth modulated” is a PWM generator with settable maximum and minimum limits of PWM’s duty cycle and generates a sawtooth PWM modulation.

Below we described steps needed to understand how the solution has been programmed to design an ultrasonic humidifier using SLG47105. However, if you just want to get the result of programming, download GreenPAK Designer Software, a part of the Go Configure™ Software Hub, to view the already completed GreenPAK Design File.

Let’s start from a simplified design. The following design is just a PWM generator that controls the PWM duty cycle with UP and DOWN buttons.

The PWM’s duty cycle is determined by the shift between CNT3 and CNT5 output pulses. CNT3 counter data should equal CNT5 counter data. DFF3 is set by the rising edge of CNT5 pulse and reset by the low pulse of CNT3. CNT3 output is inverted, so active signal is LOW (see Figure 2).