MP2229 – 21V, 6A SYNCHRONOUS STEP-DOWN CONVERTER

MP2229 Rev. 1.0

www.MonolithicPower.com

12

2/12/2015

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OPERATION

The MP2229 is a high-frequency, synchronous,

rectified, step-down, switch-mode converter

with internal power MOSFETs. It offers a

compact solution to achieve a 6A continuous

output current over a wide input-supply range

with excellent load and line regulation.

When MP2229 works in fixed-frequency peak

current-mode control to regulate the output

voltage, the internal clock initiates the PWM

cycle and 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 starts. If the current in the power

MOSFET does not reach the value set by the

COMP value within 95% of one PWM period,

then the HS-FET is forced off.

Error Amplifier (EA)

The error amplifier compares the FB voltage

outputs a current proportional to the difference

between the two. This output current charges or

discharges the internal compensation network

to form the COMP voltage, which controls the

power MOSFET current. The optimized internal

compensation network minimizes the external

component count and simplifies control loop

design.

Internal Regulator

The 5V internal regulator powers most of the

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

ceramic decoupling capacitor.

Enable Control (EN)

The MP2229 has a dedicated enable control pin

(EN). Pull EN high, or float, to enable the IC;

pull EN low to disable the IC.

The EN voltage is clamped to around 5.6V by

an internal Zener diode (see Figure 2). A pull-

up resistor is not needed to pull up the EN

voltage. If EN is connected to a voltage source

higher than 5V, a resistor is needed from the

voltage source to EN in order to limit the EN

input current to less than 100µA. This helps

prevent damage to the internal Zener diode.

For example, connecting 12V to EN through a

64kΩ.

Connecting EN directly to a voltage source

without a pull-up resistor requires limiting the

amplitude of the voltage source to below 5V to

prevent damage to the internal Zener diode.

FIGURE 2. Zener Diode between EN and GND

Setting the Frequency and Synchronizing

Connect a resistor from FREQ/SYNC to ground

to set the switching frequency. The value of the

frequency can be calculated approximately from:

S

FREQ

16000

F(kHz)

R(k ) 2.3

=

Ω+

Also, the MP2229 can be synchronized to an

external clock with a range from 300kHz to

2MHz

through

FREQ/SYNC.

The