MPQ9842GL datasheet(21/37 Pages) MPSIND

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MPQ9842

– 36V, 2A, LOW IQ, SYNCHRONOUS STEP-DOWN CONVERTER

MPQ9842 Rev. 1.1

www.MonolithicPower.com

7/29/2022

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

OPERATION

The MPQ9842 is a synchronous, step-down,

switching regulator with integrated, internal,

high-side and low-side power MOSFETs. The

MPQ9842 provides 2A of highly efficient output

current

with

current

mode

control.

The

MPQ9842 features a wide input voltage range,

switching

frequency

programmable

from

350kHz to 2.5MHz, external soft start, and

precision current limit. Its very low operational

quiescent current makes it suitable for battery-

powered applications.

Pulse-Width Modulation (PWM) Control

moderate-to-high

output

currents,

the

MPQ9842 operates in a fixed-frequency, peak-

current-control mode to regulate the output

voltage. An internal clock initiates a PWM cycle.

At the rising edge of the clock, the high-side

power MOSFET (HS-FET) is turned on and

remains on until its current reaches the value

set by the COMP voltage (VCOMP).

If the current in the HS-FET does not reach

VCOMP in one PWM period, the HS-FET remains

on, saving a turn-off operation.

When the high-side power switch is off, the low-

side MOSFET (LS-FET) turns on immediately

and remains on until the next cycle begins.

For each turn-on and -off in a switching cycle,

the HS-FET turns on and off with a minimum on

and off time limit.

Advanced Asynchronous Mode (AAM)

The

MPQ9842

employs

advanced

asynchronous mode (AAM) functionality to

optimize efficiency during light-load or no-load

conditions. AAM can be enabled by connecting

SYNC to a low level (<0.4V) before start-up;

CCM can be able when connecting SYNC to a

high level (>1.8V) before start-up. SYNC can be

used to synchronize switching again after start-

up.

continuous

conduction

mode

(CCM)

enabled, the MPQ9842 is forced to work with a

fixed frequency regardless of the output load

current.

The

advantage

CCM

the

controllable frequency and smaller output ripple,

but it also has low efficiency at light load (see

Figure 2).

If AAM is enabled, the MPQ9842 first enters

non-synchronous operation for as long as the

inductor current is approaching zero at light

load. If the load is further decreased or is at no

load, VCOMP drops below the AAM voltage

(VAAM). The MPQ9842 enters power-save mode

(PSM), putting the chip into sleep mode, which

consumes very low quiescent current to further

improve light-load efficiency.

In PSM, the internal clock is reset whenever

VCOMP crosses over VAAM, and the crossover

time is taken as the benchmark of the next

clock. When the load increases, and the DC

value of VCOMP is higher than VAAM, the

operation mode is discontinuous conduction

mode (DCM) or CCM, which have a constant

switching frequency.

AAM

(SYNC = Low)

Inductor

Current

Load

Decreased

Forced CCM

(SYNC = High)

Inductor

Current

Load

Decreased

Figure 2 : AAM and Forced CCM

Error Amplifier (EA)

The error amplifier (EA) compares the FB

voltage with the internal reference (0.8V) and

outputs a current proportional to the difference

between the two. This output current is then

used to charge or discharge the internal

compensation network to form VCOMP, which is

used to control the power MOSFET current.

The optimized internal compensation network

minimizes the external component count and

simplifies the control loop design.

Bootstrap Charging

The bootstrap capacitor (0.1µF to 1µF) is

charged and regulated to about 5V by the

dedicated internal bootstrap regulator. When

the voltage between the BST and SW nodes is

lower

than

its

regulation,

PMOS

pass

transistor connected from VIN to BST is turned

on. The charging current path is from VIN to

BST to SW. The external circuit should provide

enough voltage headroom to facilitate charging.

When the HS-FET is on, VIN is about equal to

SW, so the bootstrap capacitor cannot be

charged.

MPQ9842GL Datasheet(PDF) 21 Page - MPS Industries, Inc.

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