Texas Instruments Incorporated
Dual mode switching regulator with PWM/PFM frequency control

Abstract:

A dual mode switching regulator includes a PWM/PFM control architecture with PFM frequency foldback based on extending switching cycle off time TOFF. A controller includes a PWM/PFM clock generator that, in response to assertion of a TOFF control signal, extends the nominal PWM switching cycle off-time TOFFnom for an extended off-time TOFFext (variable), so that switching cycle off-time is [TOFFnom+TOFFext]. A TOFF modulator generates the TOFF control signal based on generating a TOFF control voltage from an ITOFF control current equal to [IPWM-IPFM], generated by sourcing an IPWM reference current, and, in response to a PFM load condition, sinking an IPFM control current. The TOFF control signal is asserted when the TOFF control voltage is not substantially equal to a TOFF reference voltage at the end of TOFFnom, to cause the PWM/PFM clock generator to extend switching cycle off-time to [TOFFnom+TOFFext], with the duration of TOFFext determining PFM switching frequency.