UC3844, UC3845, UC2844, UC2845
V
in
= 15V
UC3845
7(12)
34V
+
−
7(11)
V
ref
UVLO
6(10)
Oscillator
1.0nF
2(3)
+
−
Error
Amplifier
+
T
0.5mA
2R
S
−
+
R
1.0V
Current Sense
Comparator
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.
Q
R
PWM
Latch
3(5)
V
O = 2.5
R2
+1
R2
R1
5(8)
1N5819
+
47
Output Load Regulation
(open loop configuration)
I
O
(mA)
0
2
9
18
36
V
O
(V)
29.9
28.8
28.3
27.4
24.4
8(14)
R
2.5V
10k
Reference
Regulator
Internal
Bias
3.6V
+
+ −
−
+
V
CC
UVLO
−
R
4(7)
15
10
+
1N5819
+
47
R2
V
O
2 (V
in
)
Connect to
Pin 2 for
closed loop
operation.
1(1)
Figure 31. Step−Up Charge Pump Converter
V
in
= 15V
UC3845
7(12)
34V
+
−
7(11)
V
ref
UVLO
6(10)
Oscillator
1.0nF
2(3)
+
−
Error
Amplifier
+
T
0.5mA
2R
S
−
+
R
1.0V
Current Sense
Comparator
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.
Q
R
PWM
Latch
3(5)
Output Load Regulation
I
O
(mA)
0
2
9
18
32
V
O
(V)
−14.4
−13.2
−12.5
−11.7
−10.6
+
5(8)
+
47
8(14)
R
2.5V
10k
Reference
Regulator
Internal
Bias
3.6V
+
+ −
−
+
V
CC
UVLO
−
R
4(7)
15
10
1N5819
1N5819
+
47
V
O
− (V
in
)
1(1)
Figure 32. Voltage−Inverting Charge Pump Converter
http://onsemi.com
13
ONSEMI [ ON SEMICONDUCTOR ]
