how to set up PWM dead time at the end of period

Question

Hello, 
 I use nrf52840 hardware FallingEdge polarity PWM (NRF_PWM0) , to generate 2 signals ~50% each (inverted). I do manage to set dead time between pulses in same period, but I cant set up dead at the end of each period (and i do fully undestand that it is impossible, acoording to PWM Specification Figure 2. PWM counter in up mode example - FallingEdge polarity). 
 But is there a way to set up a dead time around 120ns using Hardware PWM (NRF_PWMx)? 
 On figure below is what i want to achive. 
 
 Wasky

hmolesworth · Answer

Yes; using Count Up Mode you require 2 x 4-word entries for each period, assuming you want a variable cycle length and up to 3 outputs. However if you switch to Dual Ramp Mode you only require a single 4-word entry for each period with Dead band between every pulse. 
 // DECODER.LOAD = Repeat
// =====================
// +----------------------------------> COMP0 OUT[0] Compare 0
// | +------------------------> COMP1 OUT[1] Compare 1
// | | +--------------> COMP2 OUT[2] Compare 2
// | | | (COMP3 OUT[3] Compare 3 not used)
// | | | 
// +---------+---------+---------+---------+
// | Compare | Compare | Compare | Top | Cycle N
// +---------+---------+---------+---------+
// | Compare | Compare | Compare | Top | Cycle N+1
// +---------+---------+---------+---------+
// |
// +----> COUNTERTOP Cycle Period 4 steps, 1MHz clocks. Range 3-32767

#define MAX_TOP 16096 // 4096 is 500uSec dual-ramp PWM at Prescaler div 1 - base clock frequency /1 -> 16MHz
#define DEAD_BAND 8 // 8 is 1uSec dead band either side at Prescaler div 2 - base clock frequency /2 ->8MHz
#define PHASE_HIGH (DEAD_BAND+(MAX_TOP/2))

// This table is designed to use the Loops mode
nrf_pwm_values_wave_form_t PWM_LoopTable[] = {
 // Index PWM-1 PWM-2 Other Top Value
 // ===== ====================== ============== =========== ============
 { /* - */ 0x8000 | (PHASE_HIGH), (PHASE_HIGH), (0), (MAX_TOP) }
};
 . 
 This is a sample, hope it helps

how to set up PWM dead time at the end of period

Top Replies