SNOU216 February   2025

 

  1.   1
  2.   Description
  3.   Applications
  4.   Features
  5.   5
  6. 1Evaluation Module Overview
    1. 1.1 Introduction
    2. 1.2 Kit Contents
    3. 1.3 Specification
    4. 1.4 Device Information
  7. 2Hardware
    1. 2.1 BOOSTXL-LMG2100-MD PCB Overview
    2. 2.2 Heatsink
    3. 2.3 Jumper Information
    4. 2.4 Header Information
    5. 2.5 Setup
  8. 3Software
    1. 3.1 Software Description
    2. 3.2 Opening Project Inside CCS
    3. 3.3 Modification on Universal Motor Control Lab Example
    4. 3.4 Change PWM Frequency and Deadtime
    5. 3.5 Software Guide
  9. 4Hardware Design Files
    1. 4.1 Design Files
  10. 5Additional Information
    1. 5.1 Trademarks
  11. 6Related Documentation

3.4 Change PWM Frequency and Deadtime

The default PWM switching frequency is 15kHz. This section describes how to change the PWM frequency and deadtime to further evaluate the GaN device.

BOOSTXL-LMG2100-MD Files Containing the Key Variables to Vary PWM Frequency and Deadtime Figure 3-7 Files Containing the Key Variables to Vary PWM Frequency and Deadtime
  • To change PWM frequency, open “src_board\user_mtr1.h”, change the MACRO definition “USER_M1_PWM_FREQ_kHz” to desired PWM frequency (Line 834).

CAUTION:

Please be aware that with the increase in PWM frequency, control loop frequency might need to vary accordingly, this can be set through MACRO definition USER_M1_NUM_TICKS_PER_ISK_TICK (Line 811) the default value is 1, meaning control computation cycle is the same as PWM cycle.

Under sensorless FOC method with FAST as the speed estimator, the below combinations have been verified at TI lab.

PWM Switching Frequency (kHz) Control Loop Frequency (USER_M1_NUM_TICKS_PER_ISK_TICK value) Deadtime (ns)
40 40kHz (1) 50
60 30kHz (2) 50
80 40kHz (2) 50
120 40kHz (3) 50

The deadtime can be changed through MACRO MTR1_PWM_DBFED_CNT and MTR1_PWM_DBRED_CNT in “src_board/hal.h” (Line 1479 and Line 1482). The default value is 5, which is equivalent to 50ns by default. Without any changes on ePWM configuration, PWM timebase clock TBCLK = EPWMCLK = 100MHz, and the deadtime is calculated as:

Equation 1. F a l l i n g   e d g e   d e l a y :   M T R 1 _ P W M _ D B F E D _ C N T × T T B C L K = 5 × ( 1 / 100 M ) = 50 n s
Equation 2. R i s i n g   e d g e   d e l a y :   M T R 1 _ P W M _ D B R E D _ C N T × T T B C L K = 5 × ( 1 / 100 M ) = 50 n s