UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV
Vsat, OUTPUT SATURATION VOLTAGE (V)
0
−1.0
− 2.0
3.0
2.0
1.0
0
0
V O , OUTPUT VOLTAGE
I CC , SUPPLY CURRENT (mA)
20 V/DIV
I CC , SUPPLY CURRENT
10
UCX843B
5
0
UCX842B
0
10
20
100 ns/DIV
V
CC
, SUPPLY VOLTAGE (V)
Figure 16. Output Cross Conduction
Figure 17. Supply Current versus Supply Voltage
PIN FUNCTION DESCRIPTION
8−Pin
1
2
3
4
5
6
7
8
10
12
14
8
11
9
2,4,6,1
3
14−Pin
1
3
5
7
Function
Compensation
Voltage
Feedback
Current
Sense
R
T
/C
T
GND
Output
V
CC
V
ref
Power
Ground
V
C
GND
NC
Description
This pin is the 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
R
T
to V
ref
and capacitor C
T
to ground. Operation to 500 kHz is possible.
This pin is the combined control circuitry and power ground.
This output directly drives the gate of a power MOSFET. Peak currents up to 1.0 A are sourced
and sunk by this pin.
This pin is the positive supply of the control IC.
This is the reference output. It provides charging current for capacitor C
T
through resistor R
T
.
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.
The Output high state (V
OH
) is set by the voltage applied to this pin. 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 and is connected back to the power source ground.
No connection. These pins are not internally connected.
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100 mA/DIV
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V
CC
T
A
= 25°C
Source Saturation
(Load to Ground)
V
CC
= 15 V
80
ms
Pulsed Load
120 Hz Rate
T
A
= − 55°C
T
A
= − 55°C
T
A
= 25°C
Sink Saturation
(Load to V
CC
)
400
GND
600
200
I
O
, OUTPUT LOAD CURRENT (mA)
90%
V
CC
= 15 V
C
L
= 1.0 nF
T
A
= 25°C
10%
800
50 ns/DIV
Figure 14. Output Saturation Voltage
versus Load Current
25
V
CC
= 30 V
C
L
= 15 pF
T
A
= 25°C
20
15
Figure 15. Output Waveform
R
T
= 10 k
C
T
= 3.3 nF
V
FB
= 0 V
I
Sense
= 0 V
T
A
= 25°C
30
40
ONSEMI [ ON SEMICONDUCTOR ]
