zxld1352 Zetex Semiconductors plc., zxld1352 Datasheet - Page 16

• Manufacturer Part Number: zxld1352
• Description: 350ma Led Driver With Internal Switch And Enhanced Pwm Dimming Range
• Manufacturer: Zetex Semiconductors plc.

Inductor selection
Recommended inductor values for the ZXLD1352 are in the range 47 H to 220 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 ZXLD1352 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 ( )
I
V
V
R
VD is the diode forward voltage at the required load current (V)
Issue 1 - August 2008
© Diodes Incorporated 2008
avg
Part No.
DO1608C
MSS6132ML
CD104-MC
NP04SB470M
I is the coil peak-peak ripple current (A) {Internally set to 0.3 x I
IN
LED
LX
T
T
is the supply voltage (V)
is the required LED current (A)
is the switch resistance ( )
ON
OFF
is the total LED forward voltage (V)
ONmin
OFFmin
=
=
--------------------------------------------------------------------------------------- -
V
---------------------------------------------------------------------- -
V
IN
LED
>200ns
–
>200ns
V
+
LED
VD
–
+
LΔI
I
avg
I
LΔI
avg
( H)
100
220
47
47
68
47
(
L
R
(
R
S
S
+
+
rL
rL
+
)
DCR
0.64
0.38
0.58
0.82
0.55
0.27
( )
R
LX
)
IN
pins.
0.56
0.47
0.39
0.53
0.38
I
(A)
0.5
SAT
16
Manufacturer
CoilCraft
Sumida
Taiyo Yuden
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}
ZXLD1352
www.diodes.com
www.zetex.com