UC3844B, UC3845B, UC2844B, UC2845B
0
−1.0
−ꢁ2.0
Source Saturation
(Load to Ground)
V
= 15 V
80 ms Pulsed Load
CC
V
CC
V
= 15 V
C = 1.0 nF
CC
T = 25°C
A
L
90
%
120 Hz Rate
T = 25°C
A
T = −ꢁ55°C
A
3.0
2.0
1.0
0
T = −ꢁ55°C
A
T = 25°C
A
10
%
Sink Saturation
)
GND
600
(Load to V
CC
0
200
400
800
50 ns/DIV
Iꢁ , OUTPUT LOAD CURRENT (mA)
O
Figure 12. Output Saturation Voltage
versus Load Current
Figure 13. Output Waveform
25
V
= 30 V
C = 15 pF
CC
L
20
15
10
5
T = 25°C
A
R = 10 k
T
C = 3.3 nF
T
V
FB
= 0 V
I
= 0 V
Sense
T = 25°C
A
0
0
10
20
, SUPPLY VOLTAGE (V)
30
40
100 ns/DIV
V
CC
Figure 14. Output Cross Conduction
Figure 15. Supply Current versus Supply Voltage
PIN FUNCTION DESCRIPTION
Pin
8−Pin
14−Pin
Function
Description
1
2
1
3
Compensation This pin is the Error Amplifier output and is made available for loop compensation.
Voltage
This is the inverting input of the Error Amplifier. It is normally connected to the switching power
supply output through a resistor divider.
Feedback
3
4
5
7
Current Sense A voltage proportional to inductor current is connected to this input. The PWM uses this
information to terminate the output switch conduction.
R /C
The Oscillator frequency and maximum Output duty cycle are programmed by connecting resistor
R to V and capacitor C to ground. Oscillator operation to 1.0 kHz is possible.
T
T
T
ref
T
5
6
GND
This pin is the combined control circuitry and power ground.
10
Output
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 one−half the oscillator frequency.
7
8
12
14
8
V
This pin is the positive supply of the control IC.
CC
V
This is the reference output. It provides charging current for capacitor C through resistor R .
T T
ref
Power
Ground
This pin is a separate power ground return that is connected back to the power source. It is used
to reduce the effects of switching transient noise on the control circuitry.
11
V
The Output high state (V ) is set by the voltage applied to this pin. With a separate power source
C
OH
connection, it can reduce the effects of switching transient noise on the control circuitry.
This pin is the control circuitry ground return and is connected back to the powersource ground.
No connection. These pins are not internally connected.
9
GND
NC
2,4,6,13
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