MP2317 – 26V, 1A, SYNCHRONOUS, STEP-DOWN CONVERTER

MP2317 Rev. 1.0

www.MonolithicPower.com

10

3/24/2016

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OPERATION

The MP2317 is a high-frequency, synchronous,

rectified, step-down, switch-mode converter

with built-in, internal power MOSFETs. It offers

a very compact solution that achieves 1A of

continuous output current with excellent load

and line regulation over a wide input supply

range.

The MP2317 operates in a fixed-frequency,

peak-current-control mode to regulate the

output voltage. A pulse width modulation

(PWM) cycle is initiated by the internal clock.

The integrated high-side power MOSFET (HS-

FET) turns on and remains on until its current

reaches the value set by the COMP voltage

remains off until the next clock cycle begins. If

the current in the power MOSFET does not

reach the current value set by COMP within

93% of one PWM period, the power MOSFET is

forced off.

Internal VCC Regulator

Most of the internal circuitries are powered by

the internal VCC regulator. This regulator takes

threshold, the output of the regulator is in full

falling threshold, the internal VCC regulator

shuts off. A 0.1µF ceramic capacitor is required

for decoupling.

Error Amplifier (EA)

The error amplifier compares the FB voltage

with the internal 0.791V reference (REF) and

outputs a COMP voltage, which is used to

control the power MOSFET current. The

optimized

internal

compensation

network

minimizes the external component counts and

simplifies the control loop design.

AAM Operation

The MP2317 uses advanced asynchronous

modulation (AAM) power-save mode for light

loads. The AAM voltage is set at 0.4V internally.

blocked, and the MP2317 skips some pulses for

pulse frequency modulation (PFM) mode and

achieves light-load power save.

Figure 2: Simplified AAM Control Logic

Under-Voltage Lockout (UVLO)

Under-voltage lockout (UVLO) is implemented

to protect the chip from operating at an

insufficient

supply

voltage.

The

UVLO

comparator monitors the input voltage. When

the input voltage is higher than the UVLO rising

threshold, the MP2317 powers up and shuts off

when the input voltage is lower than the UVLO

falling threshold. It has non-latch protection.

Internal Soft Start (SS)

The soft start (SS) is implemented to prevent

the converter output voltage 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 0.791V reference voltage. At this

point, the reference voltage takes over. The

soft-start time is set to be around 1.5ms

Over-Current Protection (OCP) and Hiccup

The MP2317 employs a cycle-by-cycle over-

current limit when the inductor current peak

value exceeds the set current-limit threshold.

Meanwhile, the output voltage starts to drop

until FB is below the under-voltage (UV)

threshold, typically 50% below the reference.

Once UV is triggered, the MP2317 enters

hiccup mode to restart the part periodically.

This protection mode is especially useful when

the output is dead-shorted to ground. The

average short-circuit current is greatly reduced

to alleviate thermal issues and to protect the

regulator. The MP2317 exits hiccup mode once

the over-current condition is removed.