UC3844B, UC3845B, UC2844B, UC2845B

http://onsemi.com

14

Osc

+

-

Reference

Regulator

+

-

34V

S

R

Q

Internal

Bias

+

0.5mA

Osc

R

R

R

2R

Error

Amplifier

1.0V

7(12)

7(11)

6(10)

5(8)

3(5)

R1

1(1)

2(3)

4(7)

8(14)

10k

1.0nF

The capacitor's equivalent series resistance must limit the Drive Output current to 1.0 A. An additional series resistor

may be required when using tantalum or other low ESR capacitors. The converter's output can provide excellent line

and load regulation by connecting the R2/R1 resistor divider as shown.

Figure 31. Step−Up Charge Pump Converter

5(9)

PWM

T

Latch

Current Sense

Comparator

2.5V

3.6V

UVLO

UVLO

UC3845B

+

47

1N5819

15

10

1N5819

+

47

R2

Connect to

Pin 2 for

closed loop

operation.

R2

R1

) 1

Output Load Regulation

(Open Loop Configuration)

0

2

9

18

36

29.9

28.8

28.3

27.4

24.4

+

-

+

-

S

R

+

R

R

R

2R

5(9)

PWM

T

Latch

Current Sense

Comparator

+

47

15

10

1N5819

+

47

Reference

Regulator

34V

Q

Internal

Bias

0.5mA

Error

Amplifier

1.0V

7(12)

7(11)

6(10)

5(8)

3(5)

1(1)

2(3)

4(7)

8(14)

10k

1.0nF

The capacitor's equivalent series resistance must limit the Drive Output current to 1.0 A.

An additional series resistor may be required when using tantalum or other low ESR capacitors.

Figure 32. Voltage−Inverting Charge Pump Converter

2.5V

3.6V

UVLO

UVLO

UC3845B

Output Load Regulation

0

2

9

18

32

−14.4

−13.2

−12.5

−11.7

−10.6

1N5819

+