Using DCMP and PWM Macrocell in PWM Mode

Using DCMP and PWM Macrocell in PWM Mode

Pulse-based Control Technique

This technique is for the DCMP block, available in the SLG46140, SLG46620, and SLG46621.

The DCMP/PWM block is a special macrocell used to compare two 8-bit values or generated PWM signals. There are three DCMP/PWM blocks per IC that can operate independently, and each DCMP/PWM has two 8-bit inputs (IN+, IN-) that can be used to generate a PWM signal. Inputs MTRX SEL#0 and MTRX SEL#1 are used during static PWM generation to select one of the four available registers, shared amongst the three blocks. Input SHARED PD is used to POWER ON/OFF. The PWM output duty cycle range can be configured to range from 0% to 99.61% or 0.39% to 100%.

Creating the PWM Signal

The PWM generator is similar to a digital comparator, with the exception that the data on one of the inputs is linearly cycling through a set PWM period. The other input is static at a set duty cycle or updating at a very slow rate.

So, to create a PWM signal, we need a PWM ramp source. This is an internal or external counter that counts from 255 down to 0 or vice versa. Another source of data for the DCMP/PWM block should be stable for at least 1 PWM signal period (PWM ramp counter period). It could be data from the SPI, ADC, FSM blocks, or from an internal register of DCMP/PWM. Figure 1 shows the operation of a DCMP/PWM when IN- is connected to a CNT/DLY block that counts from 255 down to 0 (PWM ramp counter) and the IN+ source is an internal register set to 250.

Figure 1 DCMP/PWM in PWM mode

The IN+ input configurability for the DCMP/PWM block is the key to the large configurability in the macrocell. Set PWM values can be made using the internal registers, PWM dynamic feedback can be made using the ADC, and an MCU-controlled PWM can be set by using the SPI interface.

The output OUT- and OUT+ has dead band time that can be from 10 to 80 ns and set in the properties pane of DCMP/PWM.

Figure 2 Deadband time OUT- and OUT+

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