EC3293A

3A, 18V, 500KHz,

Synchronous Step Down DC/DC Converter

E-CMOS Corp. (www.ecmos.com.tw)

5G01N-Rev. F002

7/11

Application Information

Overview

The EC3293A is a synchronous rectified, current-mode, step-down regulator. It regulates input voltages from

4.7V to 18V down to an output voltage as low as 0.8V, and supplies up to 3A of load current.

The EC3293A uses current-mode control to regulate the output voltage. The output voltage is measured

at FB through a resistive

voltage divider and amplified through the internal trans-conductance error

amplifier.

The converter uses internal N-Channel MOSFET switches to step-down the input voltage to the regulated output

voltage. Since the high side MOSFET

requires a gate voltage greater than the input voltage, a boost

capacitor connected between SW and BOOT is needed to drive the high side gate. The boost capacitor is

charged from the internal 5V rail when SW is low.

When

the

EC3293A

FB

pin

exceeds

10%

of

the nominal regulation voltage of 0.8V, the over

voltage comparator is tripped forcing the high-side switch off.

Pins Description

BOOT: High-Side Gate Drive Boost Input. BOOT supplies the drive for the high-side N-Channel MOSFET

switch. Connect

a 0.1μF or greater capacitor from SW to BOOT to power the high side switch.

IN: Power Input. IN supplies the power to the IC, as well as the step-down converter switches. Drive IN with

a 4.7V to 18V power source. Bypass IN to GND with a suitably large capacitor to eliminate noise on the

input to the IC.

SW: Power Switching Output. SW is the switching node that supplies power to the output. Connect the output

LC

filter

from

SW

to

the

output

load.

Note

that

a capacitor is required from SW to BOOT to

power the high-side switch.

GND: Ground.

FB: Feedback Input. FB senses the output voltage to regulate that voltage. Drive FB with a resistive

voltage divider from the output voltage. The feedback threshold is 0.8V.

EN: Enable Input. EN is a digital input that turns the regulator

on

or

off.

Drive

EN

high

to

turn

on the regulator, drive it low to turn it off. Pull up with 100kΩ resistor for automatic startup.

Setting the Output Voltage

The external resistor divider sets output voltage. The feedback resistor R1 also sets the feedback loop

bandwidth through the internal compensation capacitor.

(see the typical application circuit). Choose the R1 around 10KΩ,and R2 by R2=R1/(Vout/0.8V-1)

Use T-type network for when Vout is low.

Figure 1：T-type network