AS3843NT 查看數據表（PDF） - Astec Semiconductor => Silicon Link

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AS3843NT

Current Mode Controller

Astec Semiconductor => Silicon Link 

AS384x

Current Mode Controller

Functional Block Diagram

1

COMP

2

VFB

+

Ð

ERROR AMP

(5.0 V)

(2.5 V)

2R

(1.0 V)

R

5V

(5.0 V)

REGULATOR

8

VREG

REF OK

7

(4 V)

VCC

UVLO

(6 V)

PWM

Ð

COMPARATOR

+

3

CURRENT

SENSE

(3.0 V)

(5 V)

Ð

+

Ð

4

RT/CT

(1.3 V)

+

Ð

(0.6 V)

+

FF

S

PWM LOGIC

R

FF

S

R

OSCILLATOR

CLK ÷ 2 [3844/45]

CLK [3842/43]

FF

T

OVER

TEMPERATURE

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

6

OUTPUT

5

GND

Pin Function Description

Pin Number Function

Description

1

COMP

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

maintain VFB at 2.5 V.

2

VFB

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

RT/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.

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

VCC

Positive supply voltage for the IC.

8

VREG

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

resistor RT.

ASTEC Semiconductor

2

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