MAX15118 Datasheet, PDF(12/23 Page) Maxim Integrated Products – High-Efficiency, 18A, Current-Mode Synchronous Step-Down Regulator with Integrated Switches

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MAX15118

High-Efficiency, 18A, Current-Mode Synchronous

Step-Down Regulator with Integrated Switches

Detailed Description

The MAX15118 high-efficiency, current-mode switching

regulator delivers up to 18A of output current. The regu-

lator provides output voltages from 0.6V up to 0.94 x VIN

from 2.7V to 5.5V input supplies, making the device ideal

for on-board point-of-load applications.

The MAX15118 delivers current-mode control architecÂ

ture using a high-gain transconductance error amplifier.

The current-mode control architecture facilitates easy

compensation design and ensures cycle-by-cycle curÂ

rent limit with fast response to line and load transients.

The regulator features a 1MHz fixed switching frequencÂ y,

allowing for all-ceramic capacitor designs and fast tran-

sient responses. The high operating frequency minimÂ izes

the size of external components.

The regulator offers a selectable skip-mode functionalÂity

to reduce current consumption and achieve a higher

efficiency at light output loads. IntegratÂed switches

ensure high efficiency at heavy loads while minimizing

critical inductances.

The MAX15118 features PWM current-mode control,

allowing for an all-ceramic capacitor solution. The regu-

lator offers capacitor-programmable soft-start to reduce

input inrush current. The device safely starts up into a

prebiased output. The MAX15118 includes an enable

input and open-drain PGOOD output for sequencing with

other devices.

Controller FunctionâPWM Logic

The controller logic block is the central processor that

determines the duty cycle of the high-side MOSFET

under different line, load, and temperature conditions.

Under normal operation, where the current-limit and

temperature protection are not triggered, the controller

logic block takes the output from the PWM comparator

and generates the driver signals for both high-side and

low-side MOSFETs. The control logic block controls the

break-before-make logic and all the necessary timing.

The high-side MOSFET turns on at the beginning of the

oscillator cycle and turns off when the COMP voltÂage

crosses the internal current-mode ramp waveform. The

internal ramp is the sum of the compensation ramp and

the current-mode ramp derived from the inductor current

(current-sense block). The high-side MOSFET also turns

off if either the maximum duty cycle (94%, typ) or the cur-

rent limit is reached. The low-side MOSFET turns on for

the remainÂder of the oscillation cycle.

Starting into a Prebiased Output

The MAX15118 can soft-start into a prebiased output

without discharging the output capacitor. In safe pre-

biased startup, both low-side and high-side MOSFETs

remain off to avoid discharging the prebiased output.

PWM operation starts when the voltage on SS/REFIN

crosses the voltage on FB.

The MAX15118 can start into a prebiased voltage higher

than the nominal set point without abruptly discharg-

ing the output. Forced PWM operation starts when the

SS/REFIN voltage reaches 0.58V (typ), forcing the con-

verter to start. The low-side current limit is increased over

350Âµs to the maximum from the first LX pulse. When the

low-side sink current-limit threshold of 30A is reached,

the low-side switch turns off before the end of the clock

period and the high-side switch turns on until one of the

following conditions is satisfied:

U High-side source current hits the reduced high-side

current limit (30A, typ); in this case, the high-side

switch is turned off for the remaining time of the clock

period.

U The clock period ends.

Reduced high-side current limit is activated to recirculate

the current into the high-side power switch rather than

into the internal high-side body diode

Low-side sink current limit is provided to protect the

low-side switch from excessive reverse current durÂing

prebiased operation.

Enable Input and Power-Good

(PGOOD) Output

The MAX15118 features independent enable control and a

power-good signal that allows for flexible power sequenc-

ing. Drive the enable input (EN) high to enable the regula-

tor, or connect EN to IN for always-on operation.

Power-good (PGOOD) is an open-drain outÂput that

asserts when VFB is above 555mV (typ) and deasserts

low if VFB is below 530mV (typ).

Programmable Soft-Start (SS/REFIN)

The MAX15118 utilizes a soft-start feature to slowly

ramp up the regulated output voltage to reduce input

inrush current during startup. Connect a capacitor from

SS/REFIN to GND to set the startup time (see the Setting

the Soft-Start Time section for capacitor selection details).

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