UC3844B, UC3845B, UC2844B, UC2845B
Output Load Regulation
(Open Loop Configuration)
V
in
= 15V
7(12)
I
O
(mA)
V (V)
O
UC3845B
+
47
0
2
9
18
36
29.9
28.8
28.3
27.4
24.4
34V
Reference
Regulator
8(14)
10k
+
−
V
R
R
CC
1N5819
2.5V
7(11)
6(10)
Internal
Bias
UVLO
+
−
V
ref
UVLO
3.6V
15 10
1N5819
Osc
V ≈ 2 (V )
O in
+
4(7)
2(3)
1.0nF
T
+
+
Connect to
Pin 2 for
closed loop
operation.
47
S
R
0.5mA
5(8)
3(5)
R2
R1
2R
Q
PWM
Latch
1.0V
R
Error
Amplifier
Current Sense
Comparator
1(1)
R2
R1
ǒ
) 1Ǔ
V
O
= 2.5
5(9)
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
V
in
= 15V
Output Load Regulation
UC3845B
7(12)
I
O
(mA)
V (V)
O
+
47
0
2
9
18
32
−14.4
−13.2
−12.5
−11.7
−10.6
34V
Reference
Regulator
8(14)
R
R
+
−
V
CC
UVLO
2.5V
7(11)
6(10)
Internal
Bias
10k
+
−
V
ref
UVLO
3.6V
15 10
1N5819
V
O
≈ −V
in
Osc
4(7)
2(3)
1.0nF
T
+
1N5819
+
47
S
R
0.5mA
5(8)
3(5)
2R
Q
PWM
Latch
1.0V
R
Error
Amplifier
Current Sense
Comparator
1(1)
5(9)
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
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