MC33025 View Datasheet(PDF) - Motorola => Freescale

Part Name

Description

MFG CO.

MC33025

High speed double-ended PWM controller

Motorola => Freescale 

MC34025 MC33025

Figure 28A. Slope Compensation (Noise Sensitive)

4

5

6

CT

C1

Current Sense

R1 7

Information

R2

3

Oscillator

1.25 V

This method of slope compensation is easy to implement, however, it is noise sensitive. Capacitor C1 provides AC coupling. The oscillator signal is added to the

current signal by a voltage divider consisting of resistors R1 and R2.

Figure 28B. Slope Compensation (Noise Immune)

Output

Current Sense

Transformer

Rw

Rf

RM

Cf

CM

Ramp

Input

7

3

Figure 28. Keeps Fig numbering sequence correct Output

1.25 V

Current Sense

Resistor

RM

CM

Rf

Cf

Ramp

Input

7

3

1.25 V

When only one output is used, this method of slope compensation can be used and it is relatively noise immune. Resistor RM and capacitor CM provide the added

slope necessary. By choosing RM and CM with a larger time constant than the switching frequency, you can assume that its charge is linear. First choose CM, then RM

can be adjusted to achieve the required slope. The diode provides a reset pulse at the ramp input at the end of every cycle. The charge current IM can be calculated

by IM = CMSe. Then RM can be calculated by RM = VCC/IM.

Figure 29. Current Mode Master/Slave Operation Over Short Distances

Oscillator

4

4

5

Vref 5

6

6

CT RT

Oscillator

12

MOTOROLA ANALOG IC DEVICE DATA

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