AP2014/A

SYNCHRONOUS PWM DC-DC BUCK CONTROLLER

DS30883 Rev. 1 - 0

5 of 13

AP2014/A

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Introduction

The AP2014 is a fixed frequency, voltage mode synchronous

controller and consists of a precision reference voltage, an error

amplifier, an internal oscillator, a PWM comparator, 0.5A peak

gate driver, soft-start and shutdown circuits (see Block Diagram).

The output voltage of the synchronous converter is set and

controlled by the output of the error amplifier; this is the amplified

error signal from the sensed output voltage and the reference

voltage.

This voltage is compared to a fixed frequency linear sawtooth

ramp and generates fixed frequency pulses of variable duty-cycle,

which drives the two N-channel external MOSFETs.The timing of

the IC is provided through an internal oscillator circuit which uses

on-chip capacitor to set the oscillation frequency to 200 KHz (400

KHz for “A” version).

Soft-Start

The AP2014 has a programmable soft-start to control the output

voltage rise and limit the current surge at the start-up. To ensure

generates the Power On Reset (POR) signal. Soft-start function

operates by sourcing an internal current to charge an external

capacitor to about 3V. Initially, the soft-start function clamps the

E/A’s output of the PWM converter. As the charging voltage of

the external capacitor ramps up, the PWM signals increase from

zero to the point the feedback loop takes control.

The outputs are protected against the short circuit. The AP2014

protects the circuit for shorted output by sensing the output

voltage (through the external resistor divider). The AP2014 shuts

down the PWM signals, when the output voltage drops below

0.6V (0.4V for AP2014A).

The AP2014 also protects the output from over-voltaging when

the control FET is shorted. This is done by turning on the sync

FET with the maximum duty cycle.

Under-Voltage Lockout

The under-voltage lockout circuit assures that the MOSFET

driver outputs remain in the off state whenever the supply voltage

below 3.3V and 4.2V respectively. Normal operation resumes

IC Quiescent Power Dissipation

Power dissipation for PWM DC-DC controller IC is a function of

applied voltage, gate driver loads and switching frequency. The

IC's maximum power dissipation occurs when the IC operating

with single 12V supply voltage (Vcc=12V and Vc

≅24V) at 400KHz

switching frequency and maximum gate loads. Page 8 show

voltage vs. current, when the gate drivers loaded with 1500pF

capacitors. The IC's power dissipation results to an excessive

temperature rise. This should be considered when using

AP2014A for such application.

Typical Application Circuit