MP2319

– 18V, 3A, SYNCHRONOUS, STEP-DOWN CONVERTER

MP2319 Rev. 1.0

www.MonolithicPower.com

12

6/29/2016

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© 2016 MPS. All Rights Reserved.

OPERATION

The MP2319 is fully integrated, synchronous,

rectified, step-down, switch-mode converter.

Constant-on-time (COT) control is employed to

provide a fast transient response and ease loop

stabilization. Figure 2 shows the simplified ramp

compensation block in the MP2319.

At the beginning of each cycle, the high-side

MOSFET (HS-FET) is turned on when the

voltage

indicates

insufficient

output voltage. The on period is determined by

both the output voltage and input voltage to

make the switching frequency fairly constant

over the input voltage range.

After the on period elapses, the HS-FET is

turned off or enters an off state. It is turned on

this operation, the converter regulates the

output

voltage.

The

integrated

low-side

MOSFET (LS-FET) is turned on when the HS-

FET is in its off state to minimize conduction

loss. There is a dead short between the input

and GND if both the HS-FET and LS-FET are

turned on at the same time. This is called a

shoot-through. To prevent a shoot-through, a

dead time (DT) is generated internally between

HS-FET off and LS-FET on, or LS-FET off and

HS-FET on.

Internal compensation is applied for COT

control to provide a more stable operation, even

when ceramic capacitors are used as output

capacitors.

This

internal

compensation

improves jitter performance without affecting

the line or load regulation.

VOUT

L

Cout

R1

R2

On

Timer

Logic

Control

REF

SW

RAMP

FB

RAMP

GENERATOR

PWM

Figure 2: Simplified Ramp Compensation Block

Heavy-Load Operation

Continuous conduction mode (CCM) occurs

when the output current is high, and the

inductor current is always above zero amps

HS-FET is turned on for a fixed interval

determined by the one-shot on-timer. When the

HS-FET is turned off, the LS-FET is turned on

until the next period.

Figure 3: Heavy-Load Operation

In CCM operation, the switching frequency is

fairly

constant.

This

is

called

pulse-width

modulation (PWM) mode.

Light-Load Operation

When the MP2319 works in pulse-frequency

modulation (PFM) and light-load operation, the

MP2319

reduces

the

switching

frequency

automatically to maintain high efficiency, and

the inductor current drops almost to zero. When

the inductor current reaches zero, the LS-FET

driver goes into tri-state (Hi-Z) (see Figure 4).

Therefore, the output capacitors discharge

slowly to GND through R1 and R2. This

operation improves the device efficiency greatly

when the output current is low.

Figure 4: Light-Load Operation