UC3842A Просмотр технического описания (PDF) - Motorola => Freescale

Номер в каталоге

Компоненты Описание

производитель

UC3842A

HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER

Motorola => Freescale 

UC3842A, 43A UC2842A, 43A

Figure 20. External Clock Synchronization

Vref

8(14)

RT

R

Bias

R

External

Sync

0.01

CT

4(7)

Input

47

2(3)

1(1)

Osc

+

+

–

EA

2R

R

5(9)

The diode clamp is required if the Sync amplitude is large enough to

cause the bottom side of CT to go more than 300 mV below ground.

Figure 21. External Duty Cycle Clamp and

Multi Unit Synchronization

RA

8

4

RB

6

5.0k

+

–

R

5

Q

3

2

+

–

S

7

C

5.0k MC1455

1

f=

1.44

(RA + 2RB)C

Dmax =

RB

RA + 2RB

8(14)

R

Bias

R

Osc

4(7)

+

+

–

2(3)

EA

2R

R

1(1)

To Additional

5(9)

UCX84XA’s

Figure 22. Adjustable Reduction of Clamp Level

VCC

7(12)

Vin

8(14)

4(7)

R2

2(3)

1(1)

R1

R

Bias

R

Osc

+

+

–

EA

1.0mA

2R

R

5.0Vref

+ +–

–

+

–+

–

VClamp

–+

1.0V

S

RQ

Comp/Latch

5(9)

7(11)

Q1

6(10)

5(8)

3(5)

RS

VClamp =

1.67

R2 + 1

R1

+ 0.33 x 10 – 3

R1 R2

R1 + R2

Ipk(max) =

VClamp

RS

Where: 0 ≤ VClamp ≤ 1.0 V

Figure 23. Soft–Start Circuit

8(14)

R

Bias

R

5.0Vref

+ +–

–

Osc

4(7)

+

2(3)

1.0M

C

1(1)

+

–

EA

1.0mA

2R

R

S

–+

RQ

1.0V

 tSoft–Start 3600C in µF

5(9)

Figure 24. Adjustable Buffered Reduction of

Clamp Level with Soft–Start

VCC

7(12)

Vin

8(14)

R

5.0Vref

+– +

Bias

R

+ +–

–

7(11)

–

Q1

Osc

4(7)

2(3)

R2

1(1)

+

+

1.0mA

–

EA

2R

R

VClamp

–+

1.0V

S

RQ

Comp/Latch

6(10)

5(8)

3(5)

RS

C

MPSA63

R1

1.67

VClamp =

R2 + 1

R1

5(9)

Ipk(max) =

VClamp

RS

tSoftstart = – In

Where: 0 ≤ VClamp ≤ 1.0 V

1–

VC

3VClamp

C

R1 R2

R1 + R2

Figure 25. Current Sensing Power MOSFET

5.0Vref

+ +–

–

VCC

(12)

+– +

–

(11)

Vin

VPin 5

=

RS Ipk rDS(on)

rDM(on) + RS

If: SENSEFET = MTP10N10M

RS = 200

Then: Vpin 5 = 0.075 Ipk

D SENSEFET

S

S

–+ R Q

Comp/Latch

Control CIrcuitry

Ground:

To Pin (9)

(10) G M

(8)

(5) RS

1/4 W

K

Power Ground

To Input Source

Return

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 22 and 24.

MOTOROLA ANALOG IC DEVICE DATA

11

Share Link: