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UC2845N View Datasheet(PDF) - ON Semiconductor

Part Name
Description
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UC2845N Datasheet PDF : 16 Pages
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UC3844, UC3845, UC2844, UC2845
VCC = 30 V
CL = 15 pF
TA = 255C
100 ns/DIV
Figure 14. Output Cross Conduction
25
20
15
10
RT = 10 k
CT = 3.3 nF
VFB = 0 V
5
ISense = 0 V
TA = 255C
0
0
10
20
30
40
VCC, SUPPLY VOLTAGE (V)
Figure 15. Supply Current versus
Supply Voltage
PIN FUNCTION DESCRIPTION
Pin
8Pin 14Pin
Function
1
1
Compensation
2
3
Voltage
Feedback
3
5
Current Sense
4
7
5
6
10
RT/CT
GND
Output
7
12
VCC
8
14
Vref
8
Power Ground
11
9
2,4,6,13
VC
GND
NC
Description
This pin is Error Amplifier output and is made available for loop compensation.
This is the inverting input of the Error Amplifier. It is normally connected to the switching
power supply output through a resistor divider.
A voltage proportional to inductor current is connected to this input. The PWM uses this
information to terminate the output switch conduction.
The Oscillator frequency and maximum Output duty cycle are programmed by connecting
resistor RT to Vref and capacitor CT to ground. Operation to 1.0 MHz is possible.
This pin is combined control circuitry and power ground (8pin package only).
This output directly drives the gate of a power MOSFET. Peak currents up to 1.0 A are
sourced and sunk by this pin. The output switches at onehalf the oscillator frequency.
This pin is the positive supply of the control IC.
This is the reference output. It provides charging current for capacitor CT through resistor RT.
This pin is a separate power ground return (14pin package only) that is connected back to
the power source. It is used to reduce the effects of switching transient noise on the control
circuitry.
The Output high state (VOH) is set by the voltage applied to this pin (14pin package only).
With a separate power source connection, it can reduce the effects of switching transient
noise on the control circuitry.
This pin is the control circuitry ground return (14pin package only) and is connected to back
to the power source ground.
No connection (14pin package only). These pins are not internally connected.
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