UC3844, 45 UC2844, 45
Figure 30. Step–Up Charge Pump Converter
Vin = 15V
UC3845
7(12)
34V
+
–
7(11)
Vref
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)
VO = 2.5 R2 + 1
R2
R1
5(8)
1N5819
+
47
Output Load Regulation
(open loop configuration)
IO (mA)
0
2
9
18
36
VO (V)
29.9
28.8
28.3
27.4
24.4
8(14)
R
2.5V
10k
4(7)
R
3.6V
Internal
Bias
Reference
Regulator
+
+ –
–
+
VCC
UVLO
–
15
10
+
1N5819
+
47
R2
VO
2 (Vin)
Connect to
Pin 2 for
closed loop
operation.
1(1)
Figure 31. Voltage–Inverting Charge Pump Converter
Vin = 15V
UC3845
7(12)
34V
+
–
7(11)
Vref
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
IO (mA)
0
2
9
18
32
VO (V)
–14.4
–13.2
–12.5
–11.7
–10.6
+
5(8)
+
47
8(14)
R
2.5V
10k
4(7)
R
3.6V
Internal
Bias
Reference
Regulator
+
+ –
–
+
VCC
UVLO
–
15
10
1N5819
1N5819
+
47
VO
– (Vin)
1(1)
MOTOROLA ANALOG IC DEVICE DATA
13
FREESCALE [ FREESCALE SEMICONDUCTOR, INC ]
