MAX1579 Maxim Integrated Products, MAX1579 Datasheet - Page 11

• Manufacturer Part Number: MAX1579
• Description: Complete Bias and White LED Power Supplies for Small TFT Displays
• Manufacturer: Maxim Integrated Products

Use only ceramic capacitors with an X5R, X7R, or bet-
ter dielectric. See Table 1 for a list of recommended
components.
Use low-ESR ceramic capacitors. Recommended val-
ues for the capacitors are shown in Table 1. To ensure
stability over a wide temperature range, ceramic
capacitors with an X5R or X7R dielectric are recom-
mended. Place these capacitors as close to the IC as
possible.
Recommended inductor values range from 10µH to
47µH. A 22µH inductor optimizes the efficiency for most
applications while maintaining low 15mV
With input voltages near 5V, a larger value of inductance
can be more efficient. To prevent core saturation, ensure
that the inductor-saturation current rating exceeds the
peak inductor current for the application. Calculate the
peak inductor current with the following formula:
The MAX1578/MAX1579 require a high-speed rectifica-
tion diode (D1) for optimum performance. A Schottky
diode is recommended due to its fast recovery time
and low forward-voltage drop. Ensure that the diode’s
average and peak current ratings exceed the average
output current and the peak inductor current, respec-
tively. In addition, the diode’s reverse breakdown volt-
age must exceed V
calculated as:
Due to fast switching waveforms, careful PC board lay-
out is required. An evaluation kit (MAX1578EVKIT) is
available to speed design. When laying out a board,
minimize trace lengths between the IC and R1, the
I
PEAK
Complete Bias and White LED Power Supplies
=
V
I
OUT MAX
DIODE RMS
0 8
(
.
PC Board Layout and Routing
______________________________________________________________________________________
(
×
V
)
OUT
IN MIN
×
)
I
(
LED MAX
=
. The RMS diode current is
I
Component Selection
(
)
OUT
Schottky Diode Selection
)
×
I
+
Capacitor Selection
PEAK
Inductor Selection
V
IN MIN
(
P-P
2
)
×
input ripple.
×
L
0 8
.
µ
s
inductor, the diode, the input capacitor, and the output
capacitor. Keep traces short, direct, and wide. Keep
noisy traces, such as the LX node trace, away from CS.
The IN bypass capacitor (C
close to the IC as possible. The transfer capacitors for
the charge pumps should be located as close as possi-
ble to the IC. PGND and GND should be connected
directly to the exposed paddle underneath the IC. The
ground connections of C
close together as possible. The traces from IN to the
inductor and from the Schottky diode to the LEDs may
be longer. The MAX1579 evaluation kit contains a sam-
ple layout to speed designs.
TRANSISTOR COUNT: 3801
PROCESS: BiCMOS
for Small TFT Displays
IN
Chip Information
IN
and C
) should be placed as
www.DataSheet4U.com
OUT
should be as
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