Specifications

Section 43. High-Speed PWM

High-Speed PWM

43.15 EXTERNAL CONTROL OF INDIVIDUAL TIME BASE(S)

(CURRENT RESET MODE)

External signals can reset the primary dedicated time bases, if the XPRES bit (PWMCONx<1>)

is set. This mode of operation is called Current Reset PWM mode. If the user-assigned

application sets the Independent Time Base Mode bit, ITB (PWMCONx<9>), a PWM generator

operates in Independent Time Base mode. If the user-assigned application sets the XPRES bit

and operates the PWM generator in Master Time Base mode, the results can be unpredictable.

The current-limit source signal specified by the CLSRC<4:0> bits (FCLCONx<14:10>) causes

the independent time base to reset. The active edge of the selected current-limit signal is

specified by the CLPOL bit (FCLCONx<9>).

In Primary Independent Time Base mode, and Hysteresis and Critical Conduction mode, PFC

applications must maintain the inductor current value above minimum desired current level.

These applications use the external Reset feature. If the inductor current falls below the desired

value, the PWM cycle is terminated early so that the PWM output can be asserted to increase

the inductor current. The PWM period varies according to the application need. This type of

application is a variable frequency PWM mode.

43.16 APPLICATION INFORMATION

Typical applications that use different PWM operating modes and features are as follows:

• Complementary PWM Output Mode

• Push-Pull PWM Output Mode

• Multi-Phase PWM

• Variable Phase PWM

• Current Reset PWM

• Constant Off-Time PWM

• Current-Limit PWM

Each application is described in the following sections.

43.16.1 Complementary PWM Output Mode

The Complementary PWM Output mode illustrated in Figure 43-46, is generated in a manner that

is similar to Standard Edge-Aligned mode. This mode provides a second PWM output signal on

the PWMxL pin that is the complement of the primary PWM signal (PWMxH).

Note: With XPRES = 1 and SWAP = 1, the PWM generator will still require the signal

arriving at the PWMxH pin to be inactive to Reset the PWM counter.