IRS25411PBF View Datasheet(PDF) - International Rectifier

Part Name

Description

MFG CO.

IRS25411PBF

LED BUCK REGULATOR CONTROL IC

International Rectifier 

IRS254(0,1)(S)PbF

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 IRS254(01,11) is rated for 200 V (or 600 V),

VBUS can reach values of this magnitude. If a supply

resistor to VBUS is used, it can experience high power

losses. For higher voltage applications if the output

voltage is above VCCUV+ plus one diode drop an

alternate VCC supply scheme utilizing the micro-power

start-up and a resistor feed-back from the output can 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(01,11) 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

Fig. 16 Alternate Supply Diagram

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© 2010 International Rectifier

16

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