MPM3620 – SYNCHRONOUS STEP-DOWN MODULE WITH INTEGRATED INDUCTOR

MPM3620 Rev. 1.1

www.MonolithicPower.com

13

2/12/2015

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OPERATION

The

MPM3620

is

a

high-frequency,

synchronous, rectified, step-down, switch-mode

converter

with

built-in

power

MOSFETs,

inductor, and two capacitors. It offers a compact

solution that achieves a 2A continuous output

current with excellent load and line regulation

over a 4.5V to 24V input-supply range.

The MPM3620 has three working modes:

advanced asynchronous modulation (AAM),

similar to PFM mode, discontinuous conduction

mode (DCM), and continuous conduction mode

(CCM). The load current increases as the

device transitions from AAM mode to DCM to

CCM. If AAM is floated or pulled high (>2.5V),

the MPM3620 operates in CCM.

AAM Control Operation

In a light-load condition, MPM3620 operates in

AAM mode (see Figure 2). Connect a resistor

error-amplifier output, which represents the

This causes the MPM3620 to skip pulses,

achieving the light-load power save. Refer to

AN032 for additional details.

MOSFET (HS-FET) turns on and remains on

Figure 2. Simplified AAM Control Logic

DCM Control Operation

increases. When its minimum value exceeds

internal 2MHz clock initiates the PWM cycle,

the HS-FET turns on and remains on until

period of dead time), and then the low-side

MOSFET (LS-FET) turns on and remains on

until the inductor-current value decreases to

zero. The device repeats the same operation in

every clock cycle to regulate the output voltage

(see Figure 3).

Figure 3. DCM Control Operation

CCM Control Operation

The device enters CCM from DCM once the

inductor current no longer drops to zero in a

clock cycle. In CCM, the internal 2MHz clock

initiates the PWM cycle, the HS-FET turns on

then the LS-FET turns on and remains on until

the next clock cycle starts. The device repeats

the same operation in every clock cycle to

regulate the output voltage.

within 77% of one PWM period, the HS-FET will

be forced off.

A 5V internal regulator powers most of the

exceeds 5V, the output of the regulator is in full

decreases. The device integrates an internal

decoupling capacitor, so adding an external

VCC output capacitor is unnecessary.

Error Amplifier (EA)

The error amplifier compares the FB voltage to

outputs a current proportional to the difference

between the two. This output current then

charges

or

discharges

the

internal

compensation network to form the COMP

voltage; the COMP voltage controls the power

MOSFET current. The optimized, internal

compensation network minimizes the external

component count and simplifies control loop

design.