IRS2541 International Rectifier, IRS2541 Datasheet - Page 10

• Manufacturer Part Number: IRS2541
• Description: (IRS2540 / IRS2541) LED Buck Regulator Control IC
• Manufacturer: International Rectifier

www.DataSheet4U.com
DataSheet
www.irf.com
4
operation, the IC does not enter UVLO unless the
supply voltage falls below V
Inductance Selection
To maintain tight hysteretic current regulation the
inductor and output capacitor C
the LEDs) need to be large enough to maintain the
supply to the load during t
undershooting of the load current, which in turn
causes the average current to fall below the desired
value.
First, we are going to look at the effect of the
inductor when there is no output capacitor to clearly
demonstrate the impact of the inductor. In this case,
the load current is identical to the inductor current.
Fig. 9 shows how the inductor value impacts the
frequency over a range of input voltages. As can be
seen, the input voltage has a great impact on the
frequency and the inductor value has the greatest
impact at reducing the frequency for smaller input
voltages.
Fig. 10 shows how the variation in load current
increases over a span of input voltages, as the
inductance is decreased. Fig. 11 shows the variation
of frequency over different output voltages and
different inductance values. Finally Fig. 12 shows
how the load current variation increases with lower
inductance over a range of output voltages.
The output capacitor can be used simultaneously to
achieve the target frequency and current control
accuracy.
reduces the frequency over a range of input voltage.
A small capacitance of 4.7 µF has a large effect on
reducing the frequency. Fig. 12 shows how the
current regulation is also improved with the output
capacitance. There is a point at which continuing to
U
.com
425
375
325
275
225
175
Fig.9 Frequency Response for Chosen Inductances
30
Fig. 11 shows how the capacitance
I
out
80
= 350 mA, V
Vin (V)
HO,ON
CCUV-
out
130
= 16.8 V
and avoid significant
-
.
OUT
(in parallel with
180
470uH
680uH
1mH
1.5mH
add capacitance no longer has a significant effect on
the operating frequency or current regulation, as can
be seen in Figs. 13 and 14.
Fig.11 Frequency Response for Chosen Inductances
400
390
380
370
360
350
340
330
400
380
360
340
320
300
280
260
240
220
200
345
343
341
339
337
335
333
331
329
327
325
Fig.10 Current Regulation for Chosen Inductances
Fig.12 Current Regulation for Chosen Inductances
30
13
13
18
18
I
out
I
I
out
out
80
= 350 mA, V
IRS254(0,1)(S)PbF
= 350 mA, V
= 350 mA, V
Vout (V)
Vout (V)
Vin (V)
23
23
out
130
in
in
28
28
= 16.8 V
= 50 V
= 50 V
33
33
Page 10
180
470uH
680uH
1mH
1.5mH
470uH
680uH
1mH
1.5mH
470uH
680uH
1mH
1.5mH