IRS2541STRPBF データシートの表示（PDF） - International Rectifier

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IRS2541STRPBF

LED BUCK REGULATOR CONTROL IC

International Rectifier 

1000

100

0uF

4.7uF

10uF

22uF

33uF

47uF

10

30

50

70

90

110 130 150 170

Vin (V)

Fig. 13 Iout = 350 mA, Vout = 16.8 V, L = 470 µH

400

350

300

250

200

150

100

50

0

0

10

20

30

40

50

Capacitance (uF)

Fig. 14 I out = 350 mA, Vout = 16.8 V, L = 470 µH

40V

100V

160V

The addition of the COUT increases the amount of

energy that can be stored in the output stage, which

also means it can supply current for an increased

period of time. Therefore by slowing down the di/dt

transients in the load, the frequency is effectively

decreased.

With the COUT capacitor, the inductor current is no

longer identical to that seen in the load. The

inductor current will still have a perfectly triangular

shape, where as the load will see the same basic

trend in the current, but all sharp corners will be

rounded with all peaks significantly reduced, as can

be seen in Fig. 15

VCC Supply

Since the IRS245(0,1) is rated for 200 V (or 600 V),

VBUS can reach values of this magnitude. If only a

supply resistor to VBUS is used, it will experience

extremely high power losses. For higher voltage

applications an alternate VCC supply scheme utilizing

the micro-power start-up and a resistor feed-back

www.irf.com

IRS254(0,1)(S)PbF

from the output needs to be implemented, as seen in

Fig. 16.

Fig. 15 Iout = 350 mA, Vin = 100 V, Vout = 16.85 V, L = 470 µH,

C out = 33 µF

The resistance between VBUS and VCC supply should

be large enough to minimize the current sourced

directly from the input voltage line; value should be

on the order of hundreds of kΩ. Through the supply

resistor, a current will flow to charge the VCC

capacitor. Once the capacitor is charged up to the

VCCUV+ threshold, the IRS254(0,1) enters the micro

start-up regime and begins to operate, activating the

LO and HO outputs. After the first few cycles of

switching, the resistor connected between the output

and VCC will take over and source all necessary

current for the IC. The resistor connecting the

output to the supply should be carefully designed

according to its power rating.

RS 2 = Vout −15.6V

10mA

PRS 2 = (10mA)2 RS 2 ≤ PRS 2 _ Rated 2

Icc ≈ 10mA

VBUS

VCC

1

VB

8

COM

2

HO

7

IFB

3

VS

6

ENN

ENN

4

LO

5

COM

Fig. 16 Alternate Supply Diagram

Page 11

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