MPQ4487 – STEP-DOWN CONVERTER WITH DUAL USB CHARGING PORTS, AEC-Q100

MPQ4487 Rev.1.0

www.MonolithicPower.com

13

10/17/2017

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OPERATION

BUCK CONVERTER SECTION

The

MPQ4487

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. The MPQ4487 offers a

compact

solution

that

achieves

6A

of

continuous output current with excellent load

and line regulation over a wide input supply

range.

The MPQ4487 operates in a fixed-frequency,

peak-current-mode control to regulate the

output voltage. The internal clock initiates the

pulse-width modulation (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

is off, it remains off until the next clock cycle

begins. If the duty cycle reaches 95% (450kHz

switching frequency) in one PWM period, the

current in the power MOSFET does not reach

the COMP-set current value, and the power

MOSFET turns off.

Error Amplifier (EA)

The error amplifier (EA) compares the internal

feedback voltage against the internal reference

the power MOSFET current. The optimized,

internal compensation network minimizes the

external component count and simplifies the

control loop design.

Internal VCC Regulator

The 4.6V internal regulator powers most of the

exceeds 4.6V, the output of the regulator is in

1µF ceramic decoupling capacitor.

After the buck output starts up, the internal VCC

LDO output is biased by the buck output

through a Schottky diode.

Enable (EN) Control

The MPQ4487 has an enable control pin (EN).

Pull EN high to enable the IC. Pull EN low or

float EN to disable the IC. Once EN is pulled

high, the buck output is enabled regardless of

the status of EN1, EN2, or CC1 through CC4.

This requires limiting the amplitude of the EN

voltage source below 10V or limiting the EN

input current below 500μA if the EN pull-up

voltage is larger than 10V.

Figure 2: Zener Diode between EN and GND

Setting the Frequency

Connect a resistor from FREQ to ground to set

the switching frequency (see Table 1). The

value of the frequency can be calculated

approximately with Equation (1):





Ω

FREQ

1000000

FREQ(kHz)

42.5 R

(K ) 53.7

(1)

200

700

1200

1700

2200

0

20

40

60

80 100 120