2

ASTEC Semiconductor

AS384x

Current Mode Controller

Functional Block Diagram

Figure 1. Block Diagram of the AS3842/3/4/5

Pin Function Description

Pin Number Function

Description

1

COMP

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

maintain V

2

V

FB

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

bandgap reference.

3

Current

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

Sense

this information to terminate the gate drive of the output.

4

R

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

(R

accomplish a synchronization function.

5

GND

Circuit common ground, power ground, and IC substrate.

6

Output

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 AS3844/5 switches at one-half

the oscillator frequency.

7

V

CC

Positive supply voltage for the IC.

8

V

REG

This 5 V regulated output provides charging current for the capacitor C

resistor R

Ð

+

6

OUTPUT

2

ERROR AMP

1

4

5

7

8

GND

CURRENT

SENSE

COMP

S

R

FF

S

R

FF

(5.0 V)

(2.5 V)

(1.0 V)

2R

R

(5 V)

(3.0 V)

(1.3 V)

(0.6 V)

OSCILLATOR

PWM

COMPARATOR

OVER

TEMPERATURE

T

FF

CLK

÷ 2 [3844/45]

CLK [3842/43]

5 V

REGULATOR

(5.0 V)

REF OK

(4 V)

UVLO

(6 V)

PWM LOGIC

3

+

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