UC3842B(2013) Просмотр технического описания (PDF) - ON Semiconductor

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Компоненты Описание

производитель

UC3842B
(Rev.:2013)

High Performance Current Mode Controllers

ON Semiconductor 

UC3842B, UC3843B, UC2842B, UC2843B

VCC

Vin

7(12)

5.0V Ref

8(14)

R

+

Bias

-

8(14)

R

Bias

5.0V Ref

R

+

-

7(11)

Q1

4(7)

2(3)

1.0M

R

+

-

Osc

+

1.0mA

2R

EA

R

1.0V

Osc

4(7)

+

VClamp

1.0 mA

S

Q

2(3)

EA

2R

R

R

S

R2

1.0V

Comp/Latch

Q

1(1)

R

C

R1 MPSA63

5(9)

6(10)

5(8)

3(5)

RS

1(1)

C

5(9)

tSoft-Start ≈ 3600C in mF

ǒ Ǔ VClamp  [ 

1.67

R2

R1

)

1

Where: 0 ≤ VClamp ≤ 1.0 V

ƪ ƫ tSoftStart + * In

1 *  VC

3 VClamp

R1 R2

 C R1  )  R2

Ipk(max) 

[ 

VClamp

RS

Figure 25. Soft−Start Circuit

Figure 26. Adjustable Buffered Reduction of

Clamp Level with Soft−Start

VCC

Vin

(12)

VPin 5

[

RS Ipk rDS(on)

rDM(on) ) RS

5.0V Ref

+

-

If: SENSEFET = MTP10N10M

RS = 200

Then :  VPin 5  [  0.075 Ipk

+

-

S

Q

R

(11)

G

(10)

D SENSEFET

S

K

M

(8)

Comp/Latch

(5) RS

1/4 W

Power Ground:

To Input Source

Return

Control Circuitry Ground:

To Pin (9)

Virtually lossless current sensing can be achieved with the implementation of a

SENSEFET power switch. For proper operation during over-current conditions, a

reduction of the Ipk(max) clamp level must be implemented. Refer to Figures 24 and 26.

Figure 27. Current Sensing Power MOSFET

5.0V Ref

+

-

S

Q

R

Comp/Latch

VCC

Vin

7(12)

+

-

7(11)

Q1

6(10)

5(8)

3(5)

R

C

RS

The addition of the RC filter will eliminate instability caused by the leading

edge spike on the current waveform.

Figure 28. Current Waveform Spike Suppression

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