LM3842A Ver la hoja de datos (PDF) - HTC Korea

Número de pieza

componentes Descripción

Fabricante

LM3842A

CURRENT MODE PWM CONTROLLER

HTC Korea 

CURRENT MODE PWM CONTROLLER

LM3842A/3A/4A/5A

A fraction of the oscillator ramp can be resistively summed with the current sense signal to

provide slope compensation for converters requiring duty cycles over 50%.

Note that capacitor, C, forms a filter with R2 to suppress the leading edge switch spikes.

Fig.1 Output Dead Time

80

50

CT=10nF

20

8.0

CT=200pF

CT=5.0nF CT=2.0nF

CT=1.0nF

CT=100pF

CT=500pF

5.0

2.0

0.8

10k 20k

50k100k 200k

500k

1.0M

fosc, Frequency (kHz)

Fig.2 Timing Resistor vs Frequency

100

CT=100nF

CT=47nF

30

CT=22nF

CT=10nF

CT=4.7nF

10

CT=2.2nF

CT=10nF

3

100 1k

10k 100k 1M

fosc, Frequency(Hz)

Fig.3 Output Saturation Characteristics

Fig.4 Error Amplifier Open Loop

Gain and Phase Frequency

4

VCC=15V

TA=25℃

3

2

80

Gain

60

40

0

-45

Phase

-90

20

1 SOURCE (VCC-VOH)

SINK (VOL)

0

0 10-3 2

4

6 8 10-1 2

4 68

-135

-180

Io, Output Load Current (A)

10 100

1K

10K 100K 1M 10M

Fosc, Frequency (Hz)

PIN FUNCTION DESCRIPTION

Pin No. Function

Description

1

Compensation This pin is the Error Amplifier output and is made available for loop

compensation.

2

Voltage

This is the inverting input of the Error Amplitier. It is normally connected

Feedback to the switching power supply output through a resister divider.

3

Current Sense A voltage proportional to inductor current is connected to this input.

The PWM uses this information to terminate the output switch conduction.

4

RT/CT

The Oscillator frequency and maximum Output duty cycle are

programmed by connecting resistor RT to VREF and capacitor CT

to ground. Operation to 500kHz is possible.

5

GND

This pin is the combined control circuitry and power ground.

6

Output This output directly drives the gate of a power MOSFET. Peak currents

up to 1.0A are sourced and sunk by this pin.

7

Vcc

This pin is the positive supply of the control IC.

8

VREF

This is the reference output. It provides charging current for capacitor

CT through resistor RT.

−6−

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