High-Efficiency, 2A, Current-Mode

Synchronous, Step-Down Switching Regulator

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Detailed Description

The MAX15053 high-efficiency, current-mode switching

regulator can deliver up to 2A of output current. The

MAX15053 provides output voltages from 0.6V to 0.94 x

ideal for on-board point-of-load applications.

The MAX15053 delivers current-mode control architec-

ture using a high gain transconductance error amplifier.

The current-mode control architecture facilitates easy

compensation design and ensures cycle-by-cycle cur-

rent limit with fast response to line and load transients.

The MAX15053 features a 1MHz fixed switching frequen-

cy, allowing for all-ceramic capacitor designs and fast

transient responses. The high operating frequency mini-

mizes the size of external components. The MAX15053

is available in a 1.5mm x 1.5mm (3 x 3 array) x 0.5mm

pitch WLP package.

The MAX15053 offers a selectable skip-mode functional-

ity to reduce current consumption and achieve a higher

ed switches (30mI high-side and 18mI low-side, typ)

ensure high efficiency at heavy loads while minimizing

critical inductances, making the layout design a much

simpler task with respect to discrete solutions. Utilizing

a simple layout and footprint assures first-pass success

in new designs.

The MAX15053 features 1MHz Q15%, factory-trimmed,

fixed-frequency PWM mode operation. The MAX15053 also

offers capacitor-programmable, soft-start reducing inrush

current, startup into PREBIAS operation, and a PGOOD

open-drain output for sequencing with other devices.

Controller Function–PWM 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 volt-

age crosses the internal current-mode ramp waveform,

which is the sum of the slope compensation ramp and

the current-mode ramp derived from inductor current

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

off if the maximum duty cycle is 94%, or when the current

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

remainder of the oscillation cycle.

Starting into a Prebiased Output

The MAX15053 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 MAX15053 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

converter to start. In case of prebiased output, below

or above the output nominal set point, if low-side sink

current-limit threshold (set to the reduced value of -0.4A

(typ) for the first 32 clock cycles and then set to -4A typ)

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:

• High-sidesourcecurrenthitsthereducedhigh-side

current limit (0.4A, typ); in this case, the high-side

switch is turned off for the remaining time of the clock

period.

• 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, which could be damaged.

Low-side sink current limit is provided to protect the

low-side switch from excessive reverse current dur-

ing prebiased operation.

In skip mode operation, the prebias output needs to be

lower than the set point.

Enable Input

The MAX15053 features independent device enable

control and power-good signal that allow for flexible

power sequencing. Drive the enable input (EN) high to

enable the regulator, or connect EN to IN for always-on

operation. Power-good (PGOOD) is an open-drain out-

Programmable Soft-Start (SS/REFIN)

The MAX15053 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).