el1848 Intersil Corporation, el1848 Datasheet - Page 10

• Manufacturer Part Number: el1848
• Description: White Led Step-up Regulator
• Manufacturer: Intersil Corporation

For the same inductance, higher overall efficiency can be
obtained by using lower DCR inductor.
The diode should be Schottky type with minimum reverse
voltage of 20V. The diode's peak current is the same as
inductor's peak current, the average current is I
current is:
Ensure the diode's ratings exceed these current
requirements.
White LED Connections
One leg of LEDs connected in series will ensure the
uniformity of the brightness. 14V maximum voltage enables
3 LEDs can be placed in series.
I
DRMS
FIGURE 20. EFFICIENCY OF DIFFERENT INDUCTANCE
=
85
83
81
79
77
I
5
LAVG
EFFICIENCY vs I
V
DIFFERENT L
(4 LEDs IN A SERIES)
IN
=3.3V FOR
L=33µH
u
I
10
O
O
15
10
I
O
(mA)
L=22µH
L=Coilcraft
LPO1704 SERIES
1mm HEIGHT
20
L=15µH
L=10µH
25
O
, and RMS
30
EL1848
However, placing LEDs into series/parallel connection can
give higher efficiency as shown in the efficiency curves. One
of the ways to ensure the brightness uniformity is to pre-
screen the LEDs.
PCB Layout Considerations
The layout is very important for the converter to function
properly. Power Ground ( ) and Signal Ground (
be separated to ensure the high pulse current in the power
ground does not interference with the sensitive signals
connected to Signal Ground. Both grounds should only be
connected at one point right at the chip. The heavy current
paths (V
be as short as possible.
The trace connected to the CS pin is most important. The
current sense resister R
When the trace is long, use a small filter capacitor close to
the CS pin.
The heat of the IC is mainly dissipated through the PGND
pin. Maximizing the copper area around the plane is
preferable. In addition, a solid ground plane is always helpful
for the EMI performance.
The demo board is a good example of layout based on the
principle. Please refer to the EL1848 Application Brief for the
layout.
IN
-L-L
X
pin-PGND, and V
1
should be very close to the pin
IN
-L-D-C
2
-PGND) should
) should