DFE252012F-R47M datasheet(40/122 Pages) AD

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master and slave phases are activated and always switch in sequence during steady-state operation. The phases do not

add or shed.

Buck Operating Modes

The buck converters have three operating modes shown in Figure 5. Transitions between the modes are determined

by operating conditions and mode control settings. The operating mode setting can be changed any time while the I2C

communication is available. Toggling between skip and FPWM modes is also controlled by the MFIOx pins (when the

FPWM_Mx function is selected). Pull the FPWM_Mx (MFIOx) pin high to operate the corresponding buck in forced-PWM

mode. When the FPWM_Mx (MFIOx) pin is held low, the operating mode is controlled by the Mx_LPM and the Mx_FPWM

bits.

DCM OPERATION

REGULATED BY

ERROR AMPLIFIER

CCM OPERATION

REGULATED BY

ERROR AMPLIFIER

ZX DETECTED AND

AND

Mx_FPWM = 0 AND

AND

FPWM_Mx = 0

ZX NOT DETECTED OR

Mx_FPWM = 1 OR

FPWM_Mx = 1

DCM OPERATION

IN LOW

IN LOW-POWER MODE

-POWER MODE

REGULATED BY UV

COMPARATOR

8 TIMES OF < 4µs LX

THREE-STATE

DECTECTED OR

OR Mx_LPM

= 0

ZX NOT DETECTED OR

Mx_FPWM = 1 OR

FPWM_Mx = 1

2 TIMES OF > 8µs LX

THREE-STATE

DECTECTED AND

AND

Mx_LPM = 1

Figure 5. Buck Operating Modes

Detail mode control settings are described below:

Skip Mode

In skip mode (Mx_LPM = LPM_Mx = Mx_FPWM = FPWM_Mx = 0), the buck converter operates either in discontinuous

conduction mode (DCM) or continuous conduction mode (CCM) depending on loading. If the averaged output current

is lower than a half of inductor peak-to-peak ripple current under light load condition, the low-side MOSFET turns off as

soon as the inductor current drops to near zero ampere (zero-crossing). Then, the switching node (LX) remains in three-

state (high impedance) until the next on-time is triggered. In this way, the buck prevents a negative inductor current which

results in improving light-load efficiency by reducing the total number of switching cycles needed to regulate the output

voltage.

When no zero crossing (ZX) is detected (under heavier load), the buck controller goes into CCM where the averaged

MAX77542

16VIN/16A, Quad-Phase High-Efficiency Buck

Converter

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