UC2844B 查看數據表（PDF） - ON Semiconductor

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UC2844B

High Performance Current Mode Controllers

ON Semiconductor 

UC3844B, UC3845B, UC2844B, UC2845B

0

ÄÄÄÄÄÄÄÄÄÄÄÄÄ −1.0

VCC

Source Saturation VCC = 15 V

(Load to Ground)

TA = 25°C

80 ms Pulsed Load

120 Hz Rate

ÄÄÄÄÄÄÄÄÄÄÄ − 2.0

ÄÄÄÄ TA = − 55°C

ÄÄÄÄ 3.0

ÄÄÄÄ TA = − 55°C

ÄÄÄÄ ÄÄÄÄ 2.0

TA = 25°C

ÄÄÄÄÄÄÄÄÄ 1.0

Sink Saturation

ÄÄÄÄÄÄÄ (Load to VCC)

GND

0

0

200

400

600

800

I O, OUTPUT LOAD CURRENT (mA)

Figure 12. Output Saturation Voltage

versus Load Current

VCC = 30 V

CL = 15 pF

TA = 25°C

100 ns/DIV

Figure 14. Output Cross Conduction

VCC = 15 V

90

%

CL = 1.0 nF

TA = 25°C

10

%

50 ns/DIV

Figure 13. Output Waveform

25

20

15

10

5

0

ÄÄÄÄ RT = 10 k

CT = 3.3 nF

ÄÄÄÄ VFB = 0 V

ÄÄÄÄ ISense = 0 V

ÄÄÄÄ TA = 25°C

0

10

20

30

40

VCC, SUPPLY VOLTAGE (V)

Figure 15. Supply Current versus Supply Voltage

PIN FUNCTION DESCRIPTION

Pin

8−Pin 14−Pin Function

Description

1

1

Compensation This pin is the Error Amplifier output and is made available for loop compensation.

2

3

Voltage

This is the inverting input of the Error Amplifier. It is normally connected to the switching power

Feedback supply output through a resistor divider.

3

5

Current Sense A voltage proportional to inductor current is connected to this input. The PWM uses this

information to terminate the output switch conduction.

4

7

5

RT/CT

GND

The Oscillator frequency and maximum Output duty cycle are programmed by connecting resistor

RT to Vref and capacitor CT to ground. Oscillator operation to 1.0 kHz is possible.

This pin is the combined control circuitry and power ground.

6

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

12

VCC

This pin is the positive supply of the control IC.

8

14

Vref

This is the reference output. It provides charging current for capacitor CT through resistor RT.

8

Power

This pin is a separate power ground return that is connected back to the power source. It is used

Ground

to reduce the effects of switching transient noise on the control circuitry.

11

VC

The Output high state (VOH) 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.

9

GND

This pin is the control circuitry ground return and is connected back to the powersource ground.

2,4,6,13

NC

No connection. These pins are not internally connected.

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6

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