UC3845BD ON Semiconductor, UC3845BD Datasheet - Page 12

• Manufacturer Part Number: UC3845BD
• Description: IC CTRLR CURRENT MODE HP 14SOIC
• Manufacturer: ON Semiconductor

Specifications of UC3845BD

• Pwm Type: Current Mode
• Number Of Outputs: 1
• Frequency - Max: 275kHz
• 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: 14-SOIC (3.9mm Width), 14-SOL
• Frequency-max: 275kHz
• Duty Cycle (max): 48 %
• Output Voltage: 4.9 V to 5.1 V
• Output Current: 1000 mA
• Mounting Style: SMD/SMT
• Switching Frequency: 500 KHz
• Operating Supply Voltage: 30 V
• Maximum Operating Temperature: + 70 C
• Fall Time: 50 ns
• Minimum Operating Temperature: 0 C
• Rise Time: 50 ns
• Synchronous Pin: No
• Topology: Boost, Flyback
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: UC3845BDOS

Error Amp compensation circuit for stabilizing any current mode topology except
for boost and flyback converters operating with continuous inductor current.
From V
R
R
d
i
R
f
O
C
≥ 8.8k
f
R
1(1)
2(3)
f
2.5V
+
-
EA
5.0V Ref
+
The MCR101 SCR must be selected for a holding of < 0.5 mA @ T
simple two transistor circuit can be used in place of the SCR as shown. All
resistors are 10 k.
MCR
Comp/Latch
1.0mA
101
S
R
T
Q
Figure 29. Error Amplifier Compensation
2R
R
Figure 27. Isolated MOSFET Drive
+
-
Figure 28. Latched Shutdown
3905
5(9)
2N
7(12)
V
CC
http://onsemi.com
7(11)
6(10)
5(8)
3(5)
3903
8(14)
2N
4(7)
2(3)
1(1)
C
Boundary
Isolation
R
R
12
S
EA
R
R
N
S
Q1
+
Osc
1.0 mA
Bias
V
N
in
+
0
-
P
Error Amp compensation circuit for stabilizing current mode boost
and flyback topologies operating with continuous inductor current.
C
From V
R
p
2R
I
pk
p
R
50% DC
=
V
O
GS
R
5(9)
i
V
Waveforms
R
(Pin 1)
d
A(min)
3 R
+
0
-
C
f
- 1.4
S
. The
25% DC
R
1(1)
2(3)
f
N S
N p
2.5V
EA
+
1.0mA
2R
R
5(9)