MP1475S – HIGH-EFFICIENCY, 3A, 16V, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER

MP1475S Rev. 1.0

www.MonolithicPower.com

11

1/8/2015

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OPERATION

The

MP1475S

is

a

high-frequency,

synchronous, rectified, step-down, switch-mode

converter with built-in power MOSFETs. It

offers a compact solution that achieves a 3A

continuous output current with excellent load

and line regulation over 4.5V to 16V input-

supply range.

The MP1475S has three working modes:

advanced asynchronous modulation (AAM)

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.

AAM Control Operation

In a light-load condition, MP1475S works in

advanced asynchronous modulation (AAM)

fixed voltage when input and output voltages

(which represents the peak inductor-current

the internal clock is blocked. This causes the

MP1475S to skip pulses, achieving the light-

load power save. Refer to AN032 for additional

details.

side MOSFET (HS-FET) turns on and remains

The light-load feature in this device is optimized

for 12V input applications.

Figure 2. Simplified AAM Control Logic

DCM Control Operation

current increases. When its minimum value

conduction mode (DCM). In DCM, the internal

clock initiates the PWM cycle, the HS-FET turns

and 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 continuous conduction mode

(CCM) from DCM once the inductor current no

longer drops to zero in a clock cycle. In CCM,

the internal clock initiates the PWM cycle, the

of dead time), and the LS-FET turns on and

remains on until the next clock cycle begins.

The device repeats the same operation in every

clock cycle to regulate the output voltage.

within 95% of one PWM period, the HS-FET is

forced off.

Internal Regulator

A 5V internal regulator powers most of the

internal circuitries. This regulator is supplied by

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

decreases, and the device requires a 0.1µF

ceramic decoupling capacitor.

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, which controls the power MOSFET