UC3842BVN Просмотр технического описания (PDF) - Motorola => Freescale

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производитель

UC3842BVN

HIGH PERFORMANCE CURRENT MODE CONTROLLERS

Motorola => Freescale 

UC3842B, 43B UC2842B, 43B

Figure 24. Adjustable Buffered Reduction of

Clamp Level with Soft–Start

VCC

7(12)

8(14)

R

Bias

R

5.0V Ref

+

–

+

–

7(11)

Osc

4(7)

+

VClamp

6(10)

1.0 mA

S

Q

2(3)

EA

R2

2R

R

1.0V

R

Comp/Latch

5(8)

1(1)

3(5)

C

R1 MPSA63

5(9)

[ VClamp

+ *ǒ ƪ )* Ǔ ƫ ) [ tSoft-Start

1.67

R2 1

R1

Where: 0 ≤ VClamp ≤ 1.0 V

In 1

VC

3 VClamp

C

R1

R1

R2

R2

Ipk(max)

VClamp

RS

Figure 25. Current Sensing Power MOSFET

Vin

+

Q1 –

RS

5.0V Ref

S

Q

R

Comp/Latch

VCC

(12)

+

–

(11)

G

(10)

Vin

[ ) VPin 5

RS Ipk rDS(on)

rDM(on) RS

If: SENSEFET = MTP10N10M

RS = 200

[ Then : VPin 5 0.075 Ipk

D SENSEFET

S

K

M

(8)

(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 22 and 24.

Figure 26. Current Waveform Spike Suppression

VCC

Vin

7(12)

5.0V Ref

+

–

S

Q

R

Comp/Latch

+

–

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 27. MOSFET Parasitic Oscillations

VCC

Vin

7(12)

5.0V Ref

+

–

S

Q

R

Comp/Latch

+

–

7(11)

Rg

Q1

6(10)

5(8)

3(5)

RS

Series gate resistor Rg will damp any high frequency parasitic oscillations

caused by the MOSFET input capacitance and any series wiring inductance in

the gate–source circuit.

12

MOTOROLA ANALOG IC DEVICE DATA

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