M62281P Просмотр технического описания (PDF) - Renesas Electronics

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M62281P

General Purpose Current Mode PWM Control IC

Renesas Electronics 

M62281P/FP

In the case that feed forward system by photo-coupler is applied, following two methods are available.

One is the method by error amp. as in figure 3-1, the other is by the direct connection to photo-coupler as in figure

3-2.

When photo-coupler is directly connected to EA OUT terminal, input terminal of error amp. is connected to GND,

photo-coupler is connected directly to EA OUT terminal.

VCC

R1

Reference voltage (2.5 V)

RIN

R2

+

−

EA IN

RF

EA

OUT

Figure 3-1 Method to Use Photo-Coupler (1)

Reference voltage (2.5 V)

+

−

EA IN

EA OUT

Figure 3-2 Method to Use Photo-Coupler (2)

In figure 3-1, AC gain is represented as :

AV =  RF / RIN 

Proper gain setting is about 40 dB.

RF should be 52 kΩ or more due to the current source capability of error amp.

R1, R2 should meet the condition as below so that the voltage of EA IN terminal should not be over 5 V.

R2 • VCC / (R1 + R2) ≤ 5 V

Due to the input impedance of EA IN terminal, the current in R1, R2 should be less than several mA.

CT (OVP) Terminal

Timer type latch circuit works as follows.

Constant charge current flows out from CT terminal to the external capacitor when CLM is operative.

When the voltage of CT terminal rises up to over 4.0 V (Typ.), the latch circuit operates to make functions of this IC

inoperative. Inoperative status is sustained until supply voltage becomes less than stop voltage. The value for start-up

register has to be set so that the current over 1.8 mA (Typ.) can flow the resistor because the stop status has to be kept

by the current in start-up resistor R1 shown in application circuit.

When timer latch circuit is operative, supply current increases at high voltage as shown in figure 4 to avoid the damage

caused by unnecessarily in creased supply voltage.

Inoperative status goes back to operation by forcibly decreasing the voltage of CT terminal to less then 0.7 V.

REJ03D0840-0201 Rev.2.01 Nov 14, 2007

Page 6 of 12

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