UC3844, 45 UC2844, 45
Figure 14. Supply Current versus
Supply Voltage
Figure 13. Output Cross Conduction
25
20
15
10
5
V
= 30 V
= 15 pF
= 25°C
CC
L
C
T
A
R
C
= 10 k
= 3.3 nF
= 0 V
= 0 V
T
T
V
I
T
FB
Sense
= 25°C
A
0
0
10
20
30
40
100 ns/DIV
V
, SUPPLY VOLTAGE (V)
CC
PIN FUNCTION DESCRIPTION
Pin
8–Pin
14–Pin
Function
Description
This pin is Error Amplifier output and is made available for loop compensation.
1
2
1
3
Compensation
Voltage
Feedback
This is the inverting input of the Error Amplifier. It is normally connected to the switching power
supply output through a resistor divider.
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
T
The Oscillator frequency and maximum Output duty cycle are programmed by connecting
T
resistor R to V and capacitor C to ground. Operation to 1.0 MHz is possible.
T
ref
T
5
6
–
Gnd
This pin is combined control circuitry and power ground (8–pin package only).
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
ref
This is the reference output. It provides charging current for capacitor C through resistor R .
T T
Power Ground
This pin is a separate power ground return (14–pin 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.
–
11
V
C
The Output high state (V
a separate power source connection, it can reduce the effects of switching transient noise on the
control circuitry.
) is set by the voltage applied to this pin (14–pin package only). With
OH
–
–
9
Gnd
NC
This pin is the control circuitry ground return (14–pin package only) and is connected to back to
the power source ground.
2,4,6,13
No connection (14–pin package only). These pins are not internally connected.
6
MOTOROLA ANALOG IC DEVICE DATA
MOTOROLA [ MOTOROLA ]
