MP2496M – STEP-DOWN CONVERTER WITH SINGLE USB CHARGING PORT

MP2496M Rev.1.0

www.MonolithicPower.com

11

10/10/2015

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OPERATION

BUCK CONVERTER SECTION:

The

MP2496M

integrates

a

monolithic,

synchronous, rectified, step-down, switch-mode

converter with internal power MOSFETs and a

USB current-limit switch with charging port auto-

detection. It offers a very compact solution that

achieves 2.5A of continuous output current with

excellent load and line regulation over a wide

input supply range.

The MP2496M operates in a fixed-frequency,

peak current-mode control to regulate the output

voltage. The internal clock initiates the PWM

cycle, turning on the integrated high-side power

MOSFET (HS-FET). The HS-FET remains on

the power switch is off, it remains off until the

next clock cycle starts. If the duty cycle reaches

88% (350kHz switching frequency) in one PWM

period, the current in the power MOSFET does

Error Amplifier (EA)

The error amplifier compares the internal

feedback voltage against the internal 1V

reference (REF) and outputs the COMP voltage,

which controls the power MOSFET current. The

optimized

internal

compensation

network

minimizes the external component count and

simplifies the control loop design.

VCC Regulator

The 5V internal regulator powers most of the

is greater than 5.0V, the output of the regulator is

0.22µF

ceramic

capacitor

is

required

for

decoupling.

Enable Control (EN)

The MP2496M has an enable control (EN).

Pulling EN high enables the IC; pulling EN low

resistor for automatic start-up. An internal 1MΩ

resistor connected from EN to GND allows EN to

float to shut down the IC.

EN is clamped internally using a 7.6V series

Zener diode (see Figure 2). Connecting the EN

input through a pull-up resistor to the voltage on

and the amplitude of the voltage source below

10V, preventing damage to the Zener diode.

– 10V)/230µA = 113kΩ.

Figure 2: Zener Diode between EN and GND

Under-Voltage Lockout (UVLO)

Under-voltage lockout (UVLO) protects the chip

from operating at an insufficient supply voltage.

The MP2496M’s UVLO comparator monitors the

input voltage. The UVLO rising threshold is 5.7V

while its falling threshold is 4.7V.

Internal Soft Start (SS)

The soft start prevents the converter output

voltage from overshooting during start-up. When

the chip starts, the internal circuitry generates a

soft-start voltage (SS) that ramps up from 0V to

5V. When SS is lower than REF, the error

amplifier uses SS as the reference. When SS is

higher than REF, the error amplifier uses REF as

the reference. The SS time is internally set to

1.65ms.

If the output of the MP2496M is pre-biased to a

certain voltage during start-up, the IC disables

the switching of both the high-side and low-side

switches until the voltage on the internal soft-start

capacitor exceeds the internal feedback voltage.

Buck Over-Current Protection (OCP)

The MP2496M has a cycle-by-cycle, over-current

limit for when the inductor peak current exceeds

the current limit threshold and FB voltage drops

below the under-voltage (UV) threshold, typically

70% below the reference. Once UV is triggered,

the MP2496M 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

protect the regulator. The MP2496M exits hiccup

mode once the over-current condition is removed.