MP5402M – STEP-DOWN CONVERTER WITH SMART DUAL USB CHARGING PORTS

MP5402M Rev.1.0

www.MonolithicPower.com

11

10/10/2015

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OPERATION

BUCK CONVERTER

The

MP5402M

integrates

a

monolithic,

synchronous, rectified, step-down, switch-mode

converter with internal power MOSFETs and

two USB current-limit switches with charging

port auto-detection. It offers a compact solution

to achieve 5A of continuous output current over

a wide input supply range with excellent load

and line regulation.

The MP5402M operates in a fixed frequency,

peak-current-mode control to regulate the

output voltage. The internal clock initiates the

PWM cycle, which turns on the integrated high-

side power MOSFET (HS-FET). The HS-FET

remains on until its current reaches the value

set by the COMP voltage. When the power

switch is off, it remains off until the next clock

cycle begins. If the duty cycle reaches 88%

(350kHz switching frequency) in one PWM

period, the current in the power MOSFET will

not reach the COMP set current value, and the

power MOSFET will turn off.

Error Amplifier (EA)

The error amplifier (EA) compares the internal

feedback voltage against the internal 1V

reference (REF) and outputs a COMP voltage.

This COMP voltage

controls the power

MOSFET current. The optimized internal

compensation network minimizes the external

component count and simplifies the control loop

design.

Internal VCC Regulator

The 5V internal regulator powers most of the

exceeds 5.0V, the output of the regulator is in

0.22µF ceramic decoupling capacitor.

Enable Control (EN)

The MP5402M has enable control (EN). Pulling

EN high enables the IC; pulling EN low disables

automatic start-up. An internal 1MΩ resistor

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). Connect EN

through a pull-up resistor to any voltage

amplitude of the voltage source to below 10V

and the EN input current to less than 230µA to

prevent damage to the Zener diode.

(36V – 10V)/230µA = 113kΩ.

EN

Logic

1MΩ

EN

GND

12kΩ

7.6V

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 UVLO comparator monitors the input

voltage. The UVLO rising threshold is 5.7V, and

its falling threshold is 4.7V.

Internal Soft Start (SS)

The soft start (SS) prevents the converter

output voltage from overshooting during start-

up. When the chip starts up, the internal

circuitry generates an SS voltage 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 set to

1.65ms internally.

If the output of the MP5402M 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 SS

capacitor exceeds the internal feedback voltage.

Buck Over-Current Protection (OCP)

The MP5402M has a cycle-by-cycle, over-

current limit when the inductor peak current

exceeds the current-limit threshold, and FB

voltage drops below the under-voltage (UV)

threshold (70% below the reference, typically).

Once UV is triggered, the MP5402M enters

hiccup mode to restart the part periodically.

This protection mode is especially useful when

the output is dead-shorted to ground. This

greatly reduces the average short-circuit current,