AS2844 datasheet(2/20 Pages) ETC

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AS2842/3/4/5

Current Mode Controller

ASTEC Semiconductor

Functional Block Diagram

Pin Function Description

Pin Number

Function

Description

COMP

This pin is the error amplifier output. Typically used to provide loop compensation to

maintain VFB at 2.5 V.

2VFB

Inverting input of the error amplifier. The non-inverting input is a trimmed 2.5 V

bandgap reference.

3ISENSE

A voltage proportional to inductor current is connected to the input. The PWM uses

this information to terminate the gate drive of the output.

4RT/CT

Oscillator frequency and maximum output duty cycle are set by connecting a resistor

(RT) to VREG and a capacitor (CT) to ground. Pulling this pin to ground or to VREG will

accomplish a synchronization function.

GND

Circuit common ground, power ground, and IC substrate.

OUT

This output is designed to directly drive a power MOSFET switch. This output can sink

or source peak currents up to 1A. The output for the AS2844/5 switches at one-half the

oscillator frequency.

7VCC

Positive supply voltage for the IC.

8VREG

This 5 V regulated output provides charging current for the capacitor CT through the

resistor RT.

Figure 1. Block Diagram of the AS2842/3/4/5

–

OUT

ERROR AMP

GND

VCC

VREG

RT/CT

VFB

COMP

(5.0 V)

(2.5 V)

(1.0 V)

(5 V)

(3.0 V)

(1.3 V)

(0.6 V)

OSCILLATOR

PWM

COMPARATOR

OVER

TEMPERATURE

CLK ÷ 2 [3844/45]

CLK [3842/43]

5 V

REGULATOR

(5.0 V)

REF OK

(4 V)

UVLO

(4 V)

PWM LOGIC

–

ISENSE

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