zxld1360 Zetex Semiconductors plc., zxld1360 Datasheet - Page 19

• Manufacturer Part Number: zxld1360
• Description: 1a Led Driver With Internal Switch
• Manufacturer: Zetex Semiconductors plc.

Inductor selection
Recommended inductor values for the ZXLD1360 are in the range 33 H to 100 H.
Higher values of inductance are recommended at higher supply voltages in order to minimize
errors due to switching delays, which result in increased ripple and lower efficiency. Higher
values of inductance also result in a smaller change in output current over the supply voltage
range. (See graphs). The inductor should be mounted as close to the device as possible with low
resistance connections to the LX and V
The chosen coil should have a saturation current higher than the peak output current and a
continuous current rating above the required mean output current.
Suitable coils for use with the ZXLD1360 are listed in the table below:
The inductor value should be chosen to maintain operating duty cycle and switch 'on'/'off' times
within the specified limits over the supply voltage and load current range.
The following equations can be used as a guide, with reference to Figure 1 - Operating
waveforms.
LX Switch 'On' time
Note: T
LX Switch 'Off' time
Note: T
Where:
L is the coil inductance (H)
rL is the coil resistance ( )
R
I
V
V
R
V
Issue 1 - March 2007
© Zetex Semiconductors plc 2007
avg
Part no.
MSS1038-333
MSS1038-683
NPIS64D330MTRF
S
I is the coil peak-peak ripple current (A) {Internally set to 0.3 x Iavg}
IN
LED
LX
D
is the current sense resistance
T
T
is the diode forward voltage at the required load current (V)
is the supply voltage (V)
is the required LED current (A)
is the switch resistance ( ) {=0.5
ON
OFF
is the total LED forward voltage (V)
ONmin
OFFmin
=
=
------------------------------------------------------------------------------------- -
V
--------------------------------------------------------------------- -
V
>240ns
>200ns
IN
LED
–
V
+
LED
VD
( H)
33
68
33
–
L
+
L I
I
avg
I
L I
avg
(
(
R
0.093
0.213
0.124
R
DCR
S
( )
S
+
+
rL
nominal}
IN
rL
+
pins.
)
R
I
(A)
2.3
1.5
1.1
SAT
LX
19
)
Manufacturer
CoilCraft www.coilcraft.com
NIC www.niccomp.com
ZXLD1360
www.zetex.com