UC3844, 45 UC2844, 45
Figure 14. Supply Current versus
Supply Voltage
25
20 V/DIV
I CC, SUPPLY CURRENT (mA)
20
15
10
UCX845
5
0
100 ns/DIV
0
10
20
30
VCC, SUPPLY VOLTAGE (V)
40
UCX844
RT = 10 k
CT = 3.3 nF
VFB = 0 V
ISense = 0 V
TA = 25°C
V O , OUTPUT VOLTAGE
Figure 13. Output Cross Conduction
VCC = 30 V
CL = 15 pF
TA = 25°C
I CC , SUPPLY CURRENT
PIN FUNCTION DESCRIPTION
Pin
8–Pin
1
2
3
4
5
6
7
8
–
–
14–Pin
1
3
5
7
–
10
12
14
8
11
F
i
Function
Compensation
Voltage
Feedback
Current Sense
RT/CT
Gnd
Output
VCC
Vref
Power Ground
VC
D
i i
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 (8–pin 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 one–half 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 (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.
The Output high state (VOH) is set by the voltage applied to this pin (14–pin 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 (14–pin package only) and is connected to back to
the power source ground.
No connection (14–pin package only). These pins are not internally connected.
–
–
9
2,4,6,13
Gnd
NC
6
100 mA/DIV
MOTOROLA ANALOG IC DEVICE DATA
FREESCALE [ FREESCALE SEMICONDUCTOR, INC ]
