CM9321 Datasheet, PDF (9/11 Pages) California Micro Devices Corp – Asymmetrical High Efficiency Three Channel Boost LED/OLED Driver

PRELIMINARY
CM9321
Application Information (cont’d)
should be chosen well above the steady state peak
inductor current. At minimum Vin and full duty cycle
(worse case), this is approximately:
I_P
E
A
K
≅
-V----^I--^N----⁽--^M----^I--^N----⁾---^×-----t-^O----^N--
L
≅
3----V------×_{----0--4-.--9.--7-5--μ--}×_{--H---1--------M------1-----H---------z--}
≅
0.7
A
Diode Selection
The low forward voltage and fast switching time make
Schottky diodes the choice for high efficiency opera-
tion. Make sure the diode has a reverse voltage rating
greater than the maximum output voltage. The diode
conducts only when the power switch is on, so a peak
current rating above 1A should be sufficient for a typi-
cal design.
Capacitor Selection
For proper performance, use surface-mount, low ESR
ceramic capacitors for C_IN and C_OUT. X7R or X5R
ceramic dielectric provides good stability over the oper-
ating temperature and voltage range.
In most LED applications, high frequency output ripple
is not a concern because it will not cause intensity vari-
ations that are visible to the human eye.
For such applications, when low ripple is needed, a
22μF input capacitor and/or 2.2 μF output capacitor are
recommended.
REF
DES
C_IN
C_OUT
L₁
D₁
DESCRIPTION
Capacitor, 10μF,
10V, Ceramic, 1206
Capacitor, 1μF, 16V,
Ceramic, 0805
Inductor, 4.7μH, 1A,
Low DCR
Schottky Diode, 1A,
20V, SMD
SOURCE
Murata, GRM319R61A106KE19D
Vishay, VJ1206G106KXQ
Murata, GRM188R61C105KA93D
TDK, C2012X5R1C105K
Coilcraft, LP06013-472ML
TMP Electronics Co., SPC-03802-4R7
CHILISIN, SCD03015-4R7
SUMIDA, CDH3D13/S4R7
IR, MBRS120
CHENMKO, SSM5817S
Input Filter
If CM9321 is more than 4" from main power supply
point, use an input RC filter to avoid high ripple and
input transients to the circuit input pin (see Figure 2).
In this case, because of small input ripple, the effi-
ciency is about 2% higher.
to ^V_IN
CM9321 _{GND 10}
MODE ^{9 interlv (by default)}
non-interlv
7
8
R_F
100
C_F
0.1 uF/10V
Figure 2. Input Filter Solution
Mode Selection
Two working modes are available for CM9321: inter-
leave mode (output voltage is periodically adjusted
depending on each channel load) and non-interleave
mode (same output voltage level for all channels). For
interleave option, keep MODE pin floating (HIGH by
default) and for non-interleave option, connect MODE
pin to GND.
Layout Guide
Components should be placed as close as practical to
the IC to assure good performance. The input and out-
put capacitors should be close, with minimum trace
resistance and inductance. Reflected input ripple
depends on the impedance of the VIN source, such as
the PCB traces and the Li-ion battery, which has ele-
vated impedance at higher frequencies. The input
capacitor located near the converter input reduces this
source impedance and ripple. Any ESR from the
capacitor will result in steps and spikes in the ripple
waveform, and possibly produce EMI.
Route any noise sensitive traces away from the switch-
ing power components. Place the inductor and diode
as close as possible to the SW pin to prevent noise
emissions.
The ground connections for RSET(1,21,22,3) resistors
should be kept separate from the high power grounds
and connect directly to the ground pin to assure accu-
rate current and voltage settings. For better heat flow,
connect all NC pins to GND plane. Also connect the
© 2006 California Micro Devices Corp. All rights reserved.
04/26/06 490 N. McCarthy Blvd., Milpitas, CA 95035-5112 l Tel: [phone] l Fax: [phone] l www.cmd.com
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