UC3844B, UC3845B, UC2844B, UC2845B

http://onsemi.com

6

Sink Saturation

0

0

10

20

30

40

5

10

15

20

25

Figure 12. Output Saturation Voltage

versus Load Current

Figure 13. Output Waveform

80

ms Pulsed Load

120 Hz Rate

0

800

0

200

400

600

1.0

2.0

3.0

-2.0

-1.0

0

Source Saturation

(Load to Ground)

GND

50 ns/DIV

90

%

10

%

100 ns/DIV

Figure 14. Output Cross Conduction

Figure 15. Supply Current versus Supply Voltage

PIN FUNCTION DESCRIPTION

Pin

Function

Description

8−Pin

14−Pin

1

1

Compensation

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

2

3

Voltage

Feedback

This is the inverting input of the Error Amplifier. It is normally connected to the switching power

supply output through a resistor divider.

3

5

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

7

The Oscillator frequency and maximum Output duty cycle are programmed by connecting resistor

5

GND

This pin is the combined control circuitry and power ground.

6

10

Output

This output directly drives the gate of a power MOSFET. Peak currents up to 1.0 A are sourced

and sunk by this pin. The output switches at one−half the oscillator frequency.

7

12

This pin is the positive supply of the control IC.

8

14

8

Power

Ground

This pin is a separate power ground return that is connected back to the power source. It is used

to reduce the effects of switching transient noise on the control circuitry.

11

connection, it can reduce the effects of switching transient noise on the control circuitry.

9

GND

This pin is the control circuitry ground return and is connected back to the powersource ground.

2,4,6,13

NC

No connection. These pins are not internally connected.