MP2235S –3 A, 16 V, 800 kHz SYNCHRONOUS STEP-DOWN CONVERTER

MP2235S Rev.1.0

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12

4/15/2015

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voltage, which controls the power MOSFET

current. The optimized internal compensation

network minimizes the external component

count and simplifies the control loop design.

Enable/SYNC Control

EN/SYNC is a digital control pin that turns the

regulator on and off. Drive EN high to turn on

the regulator, drive EN low to turn off the

regulator. An internal 1 MΩ resistor from

EN/SYNC to GND allows EN/SYNC to be

floated to shut down the chip. EN/SYNC is

clamped internally using a 6.5 V Zener diode

(see Figure 4). Connecting the EN input pin

through a pull-up resistor to the voltage on IN

limits the EN input current to less than 100 µA.

For example, with 12 V connected to IN,

Connecting EN directly to a voltage source

without a pull-up resistor requires limiting the

amplitude of the voltage source to ≤6 V to

prevent damage to the Zener diode (see Figure

4).

1M

Figure 4—6.5 V Zener diode connection

For external clock synchronization, connect a

clock with a frequency range between 300 kHz

and 2 MHz 2 ms after the output voltage is set:

The internal clock rising edge synchronizes with

the external clock rising edge. Select an

external clock signal with a pulse width less

than 1 μs.

Under-Voltage Lockout (UVLO)

The MP2235S has under-voltage lockout

protection (UVLO). When the VCC voltage

exceeds the UVLO rising threshold voltage, the

device begins to power-up. It shuts off when

the VCC voltage drops below the UVLO falling

threshold voltage. This is non-latch protection.

The MP2235S is disabled when the input

voltage falls below 3.2 V, typically. If an

application requires a higher under-voltage

lockout (UVLO) threshold, use EN to adjust the

input voltage UVLO by using two external

resistors (see Figure 5). For best results, set

the UVLO falling threshold (VSTOP) above

4.5 V using the enable resistors. Set the rising

threshold

(VSTART)

to

provide

enough

hysteresis to allow for input-supply variations.

Figure 5

Soft-Start (SS)

Adjust the soft-start time by connecting a

capacitor from SS to ground. When the soft-

start begins, an internal 11 µA current source

charges the external capacitor. The soft-start

capacitor connects to the non-inverting input of

the error amplifier. The soft-start period

continues until the voltage on the soft-start

capacitor exceeds the 0.804 V reference. Then

the non-inverting amplifier takes the reference

voltage as the input. Use Equation (1) to

calculate the soft-start time:

SS

0.804V Css(nF)

t(ms)

11 A

×

=

μ

(1)

Over-Current-Protection (OCP) and Hiccup

The MP2235S has a cycle-by-cycle over-

current limit when the inductor current peak

value exceeds the set current limit threshold.

below the under-voltage (UV) threshold (50

percent below the reference, typically). Once

UV is triggered, the MP2235S enters hiccup

mode to re-start the part periodically. This

protection mode is useful when the output is

dead shorted to ground, greatly reducing the

average short-circuit current to alleviate thermal

issues and protect the regulator. The MP2235S

exits hiccup mode once the over-current

condition is removed.