UC3845BVD ON Semiconductor, UC3845BVD Datasheet - Page 11

• Manufacturer Part Number: UC3845BVD
• Description: IC CTRLR CURRENT MODE HP 14SOIC
• Manufacturer: ON Semiconductor

Specifications of UC3845BVD

• 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: -40°C ~ 105°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: UC3845BVDOS

Figure 25. MOSFET Parasitic Oscillations
Series gate resistor R
parasitic oscillations caused by the MOSFET input
capacitance and any series wiring inductance in the
gate-source circuit.
+
-
5.0V Ref
Comp/Latch
S
R
T
Q
-
+
g
will damp any high frequency
5.0V Ref
+
-
7(12)
Comp/Latch
Figure 24. Current Waveform Spike Suppression
V
CC
R
S
7(11)
6(10)
5(8)
3(5)
T
Q
R
g
+
-
7(12)
Q1
R
V
V
in
S
CC
7(11)
6(10)
5(8)
3(5)
http://onsemi.com
C
R
11
Q1
R
V
S
in
The addition of the RC filter will eliminate
instability caused by the leading edge spike
on the current waveform.
+
0
-
The totem pole output can furnish negative base current
for enhanced transistor turn-off, with the addition of
capacitor C
Figure 26. Bipolar Transistor Drive
I
B
1
.
Base Charge
Removal
6(10)
5(8)
3(5)
C1
Q1
V
R
in
S