MAX15109 Datasheet, PDF(10/19 Page) Maxim Integrated Products – High-Efficiency, 8A, Current-Mode Synchronous Step-Down Switching Regulator

◁

High-Efficiency, 8A, Current-Mode Synchronous

Step-Down Switching Regulator with VID Control

Detailed Description

The MAX15109 high-efficiency, current-mode switch-

ing regulator delivers up to 8A of output current. The

regulator operates from 2.7V to 5.5V and provides a VID

selectable output.

The IC current-mode control architecture uses a high

gain transconductance error amplifier that facilitates an

easy compensation design and ensures cycle-by-cycle

current limit with fast response to line and load transients.

The regulator features a 1MHz fixed switching fre-

quency, allowing for all-ceramic capacitor designs with

fast transient responses. The high operating frequency

minimizes the size of external components. The IC is

available in a 2.5mm x 2mm (4 x 5 array), 0.5mm pitch

WLP package.

The regulator offers skip-mode functionality to reduce

current consumption and achieve a high efficiency at

light output loads. The low RDS(ON) integrated switches

ensure high efficiency at heavy loads while minimizing

critical inductance, making the layout design a much

simpler task than that of discrete solutions. The ICâs

simple layout and footprint assure first-pass success in

new designs.

The IC has output voltages of 0.9V, 0.8V, 0.725V, and

0.625V by configuring the VID inputs. The regulator

offers capacitor-programmable soft-start to reduce input

inrush current. The device safely starts up into a prebi-

ased output. The IC includes an enable input and open-

drain PGOOD output for sequencing with other devices.

Controller FunctionâPWM Logic

The controller logic block 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 trig-

gered, the controller logic block takes the output from

the PWM comparator to generate 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 voltage

crosses the internal current-mode ramp waveform. The

internal ramp is the sum of the compensation ramp and

the current-mode ramp. The high-side MOSFET also

turns off if the maximum duty cycle exceeds 95%, or

when the current limit is reached. The low-side MOSFET

turns on for the remainder of the switching cycle.

Starting into a Prebiased Output

The IC can soft-start into a prebiased output with-

out discharging the output capacitor. In safe prebi-

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

remain off to avoid discharging the prebiased out-

put. PWM operation starts when the voltage on

SS crosses the voltage on FB.

The IC can start into a prebiased voltage higher than the

nominal set point without abruptly discharging the out-

put. Forced PWM operation starts when the SS voltage

reaches 0.58V, forcing the converter to start. When the

low-side sink current-limit threshold of 14A is reached,

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

period. The low-side sink current limit is 14A. The high-

side switch turns on until one of the following conditions

is satisfied:

â¢ High-side source current hits the reduced high-side

current limit (14A). The high-side switch turns off for

the remaining time of clock period.

â¢ The clock period ends.

Reduced high-side current limit is activated in order to

recirculate the current into the high-side power switch

rather than into the internal high-side body diode, which

can cause damage to the devices. The high-side current

limit is set to 14A.

Low-side sink current limit protects the low-side switch

from excessive reverse current during prebiased

operation.

Enable Input

The IC features independent device enable control and

power-good signal that allow for flexible power sequenc-

ing. 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 output that goes

high when VFB is above the PGOOD threshold, and goes

low if VFB is below the PGOOD threshold.

▷