MPM3650

– 6A, 17V, 6A, 1.2MHz, STEP-DOWN POWER MODULE WITH DCM

MPM3650 Rev. 1.1

MonolithicPower.com

13

9/17/2021

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© 2021 MPS. All Rights Reserved.

OPERATION

The MPM3650 is a fully integrated, synchronous,

rectified, step-down, switch-mode power module.

Constant-on-time (COT) control provides fast

transient response and easy loop stabilization.

Figure 2 shows the MPM3650

’s simplified ramp

compensation block.

VOUT

L

COUT

RESR

R1

R2

On

Timer

Logic

Control

VREF

SW

RAMP

VFB

Ramp

Generator

PWM

BUF

Figure 2: Simplified Ramp Compensation Block

At the beginning of each cycle, the high-side

MOSFET (HS-FET) turns on once the feedback

(FB) voltage (VFB) drops below the reference

voltage (VREF), and indicates there is an

insufficient output voltage (VOUT). The on time

(tON) is determined by both VOUT and the input

voltage (VIN) to make the switching frequency

(fSW) fairly constant across the entire VIN range.

After tON elapses, the HS-FET turns off. Once VFB

drops below VREF, it turns on again. The

converter regulates VOUT by repeating this

operation. The integrated low-side MOSFET

(LS-FET) turns on once the HS-FET turns off to

minimize conduction loss. If both the HS-FET

and LS-FET are on at the same time, a dead

short occurs between input and PGND. This is

called shoot-through. To avoid shoot-through, a

dead-time (DT) is internally generated between

the HS-FET off time (tOFF) and LS-FET tON, and

vice versa.

Internal compensation is applied during COT

control to ensure stable operation even when

ceramic capacitors are being used as the output

capacitors. This internal compensation improves

the jitter performance without affecting the line or

load regulation.

Continuous Conduction Mode (CCM)

If the output current (IOUT) is high and the inductor

current (IL) is always above 0A, the device

operates in continuous conduction mode (CCM).

If VFB+RAMP drops below the error amplifier output

(VEAO), the HS-FET turns on for a fixed interval,

which is determined by a one-shot on-timer.

Once the HS-FET turns off, the LS-FET turns on

and remains on until the next period. Figure 3

shows

CCM

under

heavy-load

conditions

Figure 3: CCM under Heavy-Load Conditions

During CCM, fSW is fairly constant. This constant

fSW during CCM is called pulse-width modulation

(PWM) mode.

VCC Regulator

The 3.5V internal regulator powers most of the

internal circuitries. This regulator takes the VIN

input and operates across the full VIN range. If VIN

exceeds 3.5V, the regulator output is in full

regulation. If VIN drops below 3.5V, the regulator

output decreases following VIN. The device

includes an internal, 1

μF decoupling ceramic

capacitor.

Enable (EN)

EN is a digital control pin that turns the converter

on and off. Drive EN above 1.23V to turn the

converter on; drive EN below 1V to turn it off.

When floating EN, pull EN down to AGND via an

internal 1.2

MΩ resistor.

EN can be connected directly to the VIN pin. It

supports a VIN range up to 17V.

Under-Voltage Lockout (UVLO) Protection

Under-voltage

lockout

(UVLO)

protection

protects the chip from operating at an insufficient

supply voltage. The UVLO comparator monitors

VOUT of the internal regulator (VCC). The VCC

UVLO rising threshold is about 2.5V, and its

falling threshold is 2.3V.

Whenever VFB+RAMP

drops below VEAO, the

HS-FET turns on

tON is constant

FB+RAMP