CM9321 Datasheet, PDF (7/11 Pages) California Micro Devices Corp – Asymmetrical High Efficiency Three Channel Boost LED/OLED Driver

PRELIMINARY
CM9321
Pin Descriptions (cont’d)
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7
8
9
10
11
12
13
14
15
16
EPad
ISET3
LED3
VIN
MODE
GND
SW
VOUT
EN
NC
NC
NC
GND
PIN DESCRIPTIONS
Channel 3 LED current set pin. Between this pin and GND connect the R_SET3
resistor, calculated as follows:
R_SET3(kΩ)
=
-----------4---5---0-----------
I_LED3(mA)
where I_LED3 is the DC LED current in channel 3.
Pin to cathode of channel 3 LED string.
Input supply voltage pin. Bypass with a 10μF or larger ceramic capacitor to ground.
When MODE is HIGH (default), the circuit uses interleave mode. When MODE is
LOW (GND), the circuit uses non-interleave mode.
Ground terminal pin.
Switching node. Internally connected to the drain of the integrated switch.
Output voltage pin, which connects to the anodes of all LEDs. Bypass with a 1.0μF
or greater ceramic capacitor to ground for low output ripple voltage.
Enable pin. The circuit is ON when V_EN is above 1.0V. The circuit is OFF when V_EN
is below 0.2V. Active High (ON) by default.
Not internally connected. For better heat flow, connect to GND.
Not internally connected. For better heat flow, connect to GND.
Not internally connected. For better heat flow, connect to GND.
Ground; backside exposed pad.
Application Information
The CM9321 is a high efficiency, constant frequency
current regulating boost driver ideally suited for driving
white LEDs to backlight LCD color displays and a cam-
era flash in Li-ion powered portable devices. The
CM9321 is the perfect driver for portable applications
such as cellular phones, digital still cameras, PDAs,
and any application where small space, compact over-
all size, and low system cost, are critical.
With a maximum 140mA/19V output capability, the cir-
cuit can drive up to 10 WLEDs (5 series x 2 parallel)
allowing up to 35mA per channel. It includes a switch
and an internally compensated loop for regulating the
current into the LEDs. The CM9321 delivers a constant
current to series-connected LEDs, ensuring uniform
brightness and color purity regardless of any LED for-
ward voltage variations.
The proprietary design architecture allows asymmetri-
cal loading on each channel and maintains high effi-
ciency (typ 85%) at low V_IN resulting in longer battery
life, and cool, reliable operation when an adapter is
supplying high V_IN. The maximum LED current for
each channel is independently programmed with exter-
nal low power resistors avoiding ballast resistors.
A 1MHz constant frequency PWM scheme saves
board space using of small, low cost external compo-
nents , allowing designers to avoid sensitive IF bands
in RF applications. The circuit operates with low value
inductor and low value output ceramic capacitor keep-
ing voltage and current ripple in the 1% range.
The output over-voltage protection circuit prevents
damage in the case of a high impedance output (e.g.
faulty LED). The controlled current limit circuit limit pre-
vents large inductor current spikes, even at start-up. To
avoid possible leakage currents the EN control pin dis-
connects the LEDs from ground during shutdown.
© 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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