MP23701 – 24V, 2A, 1.5MHZ, SYNCHRONOUS, STEP-DOWN, LED DRIVER

MP23701 Rev. 1.0

www.MonolithicPower.com

10

3/22/2019

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© 2019 MPS. All Rights Reserved.

OPERATION

The MP23701 is a high-frequency, synchronous,

rectified, step-down, switch-mode LED driver

with a built-in, internal power MOSFET and

synchronous rectifier switch. The MP23701

offers a very high-performance solution that

achieves up to 2A of continuous output LED

current with excellent load and line regulation

over a wide input supply range.

The MP23701 operates with a fixed 1.5MHz

frequency and uses peak-current control mode

to regulate the output current. A new switching

cycle is initiated by the internal clock at the

beginning of every switching cycle.

The integrated high-side power MOSFET (HS-

FET) is turned on, and the inductor current rises

linearly to provide energy to the load. The HS-

FET remains on until its current reaches the

value of the COMP level, which is the output of

the internal error amplifier. The output voltage

of the error amplifier depends on the difference

of the output feedback and the internal, high-

precision reference.

The HS-FET remains off until the next clock

cycle begins. After the HS-FET turns off, the

low-side sync switch (LS-FET) turns on, and the

inductor current flows through the LS-FET. To

prevent

shoot-through,

a

dead

time

is

implemented to prevent the HS-FET and LS-

FET from turning on at the same time.

If the duty cycle reaches 94% in one switching

period, the current in the HS-FET cannot reach

the COMP-set current value, and the HS-FET is

forced to turn off.

Under-Voltage Lockout (UVLO) and IC Start-

Up/Shutdown Procedure

Under-voltage lockout (UVLO) is implemented

to prevent the chip from operating at an

insufficient supply voltage. The MP23701 UVLO

comparator monitors the output voltage of the

internal regulator, which is supplied from VIN.

If both VIN and EN/DIM are higher than their

appropriate thresholds, the chip starts up. The

reference block starts first to generate a stable

reference voltage and current. The internal

regulator is then enabled. The regulator

provides a stable supply for the remaining

circuitries.

Three events can shut down the chip: EN/DIM

dropping low for longer than tOFF_DELAY, VIN

dropping below UVLO, and thermal shutdown.

During the shutdown procedure, the signaling

path is blocked first to prevent any fault

triggering. The COMP voltage (VCOMP) and the

internal supply rail are then pulled down.

Error Amplifier (EA)

The

internal,

low,

offset

error

amplifier

compares the FB voltage with the internal

100mV reference and outputs a VCOMP value in

the chip internally. This VCOMP value is used to

control the HS-FET peak current and regulate

the output current.

Internal Soft Start (SS)

Soft start (SS) is implemented to prevent the

converter output current from overshooting

during start-up. When the chip starts up, the

internal circuitry generates a soft-start voltage

that ramps up from 0V. The soft-start period

lasts until the voltage on the soft-start capacitor

exceeds the 0.1V reference voltage. At this

point, the reference voltage takes over.

Floating Driver and Bootstrap Charging

The high-side, floating, power MOSFET driver

is powered by an external bootstrap capacitor.

The bootstrap capacitor voltage is regulated

internally. During normal operation, a 5.1V

bootstrap voltage is maintained between BST

and SW.

Enable and Dimming Control (EN/DIM)

EN/DIM is a control pin that turns the regulator

on and off and dims the output LED current

through a DC signal. Leave EN/DIM floating or

drive it high to turn on the MP23701. After

EN/DIM is pulled low for tOFF_DELAY (typically

22ms), the MP23701 is turned off. Figure 2

shows the control logic of EN/DIM.

Figure 2: EN/DIM Time Sequence