UC3845N ON Semiconductor, UC3845N Datasheet - Page 11

• Manufacturer Part Number: UC3845N
• Description: IC CTRLR CURRENT MODE HP 8DIP
• Manufacturer: ON Semiconductor
• Type: High Performance Current Mode Controllersr

Specifications of UC3845N

• Pwm Type: Current Mode
• Number Of Outputs: 1
• Frequency - Max: 60kHz
• Duty Cycle: 50%
• Voltage - Supply: 8.2 V ~ 25 V
• Buck: No
• Boost: Yes
• Flyback: Yes
• Inverting: Yes
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: Yes
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 8-DIP (0.300", 7.62mm)
• Frequency-max: 60kHz
• Output Voltage Range: 4.9 V to 5.1 V
• Input Voltage Range: 30 V
• Operating Temperature Range: 0 C to + 70 C
• Mounting Style: Through Hole
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: UC3845NOS

Series gate resistor R
caused by the MOSFET input capacitance and any series wiring inductance
in the gate−source circuit.
−
+
Figure 25. MOSFET Parasitic Oscillations
5.0V
−
+
+
−
Error Amp compensation circuit for stabilizing any current−mode topology except
for boost and flyback converters operating with continuous inductor current.
ref
Comp/Latch
Figure 27. Isolated MOSFET Drive
−
+
5.0V
S
R
T
Q
R
R
From V
R
−
+
d
f
+
−
i
ref
≥ 8.8 k
Comp/Latch
+
−
g
C
O
will damp any high frequency parasitic oscillations
I
S
R
T
+
Q
7(12)
−
+
−
R
2(3)
1(1)
f
V
7(11)
6(10)
5(8)
3(5)
+
CC
7(12)
−
2.5V
C
+
−
Boundary
V
Isolation
EA
CC
7(11)
6(10)
5(8)
3(5)
R
R
+
S
1.0mA
R
Figure 29. Error Amplifier Compensation
g
N
2R
S
R
Q1
Q1
R
V
5(9)
S
in
N
V
+
0
p
−
I
É É
É É É
pk
in
50% DC
http://onsemi.com
=
V
V
(pin 1)
GS
3 R
Waveforms
− 1.4
S
+
0
−
11
É
É É É
25% DC
N
N
P
S
The MCR101 SCR must be selected for a holding of less than 0.5 mA at T
The simple two transistor circuit can be used in place of the SCR as shown. All
resistors are 10 k.
Error Amp compensation circuit for stabilizing current−mode boost and flyback
topologies operating with continuous inductor current.
The totem−pole output can furnish negative base current for enhanced
transistor turn−off, with the addition of capacitor C
MCR
101
C
R
p
Figure 26. Bipolar Transistor Drive
From V
p
Figure 28. Latched Shutdown
+
0
−
R
O
R
i
I
3905
B
d
2N
C
I
6(1)
5(8)
3(5)
3903
R
2N
2(3)
1(1)
Removal
f
Charge
8(14)
Base
4(7)
2(3)
1(1)
2.5V
C
1
+
−
+
−
EA
1
.
EA
R
R
+
Q1
+
R
V
1.0mA
S
in
OSC
1.0mA
Bias
2R
2R
R
R
A(min)
5(9)
5(9)
.