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PDF ADM8843 Data sheet ( Hoja de datos )
| Número de pieza | ADM8843 | |
| Descripción | Four White LED Backlight Driver | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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Four White LED Backlight Driver
ADM8843
FEATURES
Drives 4 LEDs from a 2.6 V to 5.5 V (Li-Ion) input supply
1×/1.5×/2× fractional charge pump to maximize
power efficiency
0.3% typical LED current matching
Up to 88% power efficiency over Li-Ion range
Powers main and sub display LEDs with individual shutdown
Package footprint only 9 mm2 (3 mm × 3 mm)
Package height only 0.55 mm
Low power shutdown mode
Shutdown function
Soft start limiting in-rush current
APPLICATIONS
Cellular phones with main and sub displays
White LED backlighting
Camera flash/strobes and movie light applications
Micro TFT color displays
DSC
PDAs
GENERAL DESCRIPTION
The ADM8843 uses charge pump technology to provide the
power to drive up to four LEDs. The LEDs are used for back-
lighting a color LCD display that has regulated constant current
for uniform brightness intensity. The main display can use up to
three LEDs, and the sub display uses one LED. The CTRL1 and
CTRL2 digital input control pins control the shutdown opera-
tion and the brightness of the main and sub displays.
To maximize power efficiency, the charge pump can operate in
1×, 1.5×, or 2× mode. The charge pump automatically switches
among 1×/1.5×/2× modes, based on the input voltage, to
maintain sufficient drive for the LED anodes at the highest
power efficiency.
Improved brightness matching of the LEDs is achieved by a
feedback pin that senses individual LED current with a typical
matching accuracy of 0.3%.
FUNCTIONAL BLOCK DIAGRAM
C1 C2
1μF 1μF
VCC ADM8843
C4
4.7μF
CHARGE PUMP
1×/1.5×/2× MODE
CTRL1
CTRL2
CONTROL
LOGIC
OSC
VREF
VOUT
C3
2.2μF
MAIN
SUB
FB1
FB2
FB3
FB4
ISET
RSET
LED
CURRENT
CONTROL
CIRCUIT
CURRENT CONTROLLED SINKS
GND
Figure 1.
Rev. C
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113 ©2004–201 Analog Devices, Inc. All rights reserved.
1 page  
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
ADM8843
VOUT 1
C2+ 2
ISET 3
GND 4
PIN 1
INDICATOR
ADM8843
TOP VIEW
(Not to Scale)
12 CTRL2
11 C2–
10 GND
9 GND
NOTES
1. CONNECT THE EXPOSED PADDLE TO GND.
Figure 2. Pin Configuration
Table 3. Pin Function Descriptions
Pin No. Mnemonic Description
1 VOUT
Charge Pump Output. A 2.2 μF capacitor to ground is required on this pin. Connect VOUT to the anodes of all the LEDs.
2 C2+
Flying Capacitor 2 Positive Connection.
3 ISET
Bias Current Set Input. The current flowing through the RSET resistor, ISET, is gained up by 120 to provide the ILED
current. Connect a resistor, RSET, to GND to set the bias current as VSET/RSET. Note that VSET = 1.18 V.
4, 9, 10 GND
Device Ground Pins.
5 to 8 FB1 to FB4
LED1 to LED4 Cathode Connection and Charge Pump Feedback. The current flowing in these LEDs is 120 times
the current flowing through RSET, ISET. When using fewer than four LEDs, this pin can be left unconnected or
connected to GND.
11 C2−
Flying Capacitor 2 Negative Connection.
12 CTRL2
Digital Input. 3 V CMOS Logic. Used with CTRL1 to control the shutdown operation of the main and sub LEDs.
13 CTRL1
Digital Input. 3 V CMOS Logic. Used with CTRL2 to control the shutdown operation of the main and sub LEDs.
14 C1−
Flying Capacitor 1 Negative Connection.
15 VCC
Positive Supply Voltage Input. Connect this pin to a 2.6 V to 5.5 V supply with a 4.7 μF decoupling capacitor.
16 C1+
Flying Capacitor 1 Positive Connection.
– EP
Expose Paddle. Connect the exposed paddle to GND.
Rev. C | Page 5 of 16
5 Page 
ADM8843
Table 6. Digital Inputs Truth Table
CTRL1
CTRL2
LED Operation
0 0 Sub display off/main display off (full shutdown)1, 2
0 1 Sub display off/main display on1, 3
1 0 Sub display on/main display off1, 2
1 1 Sub display on/main display on (full on)1, 3
0
PWM
Sub display off/digital PWM brightness control on main display4, 5
PWM
0
Digital PWM brightness control on sub display/main display off2, 4
1
PWM
Sub display on/digital PWM brightness control on main display1, 5
PWM
1
Digital PWM brightness control on sub display/main display on5
PWM
PWM
Digital PWM brightness control on sub and main display5
1 Sub display on means the display is on with the maximum brightness set by the RSET resistor. CTRL1 = 1 means a constant logic level (VCC) is applied to CTRL1.
2 Main display off means only the main display is off. CTRL2 = 0 means a constant logic level (GND) is applied to CTRL2.
3 Main display on means the display is on with the maximum brightness set by the RSET resistor. CTRL2 = 1 means a constant logic level (VCC) is applied to CTRL2.
4 Sub display off means only the sub display LEDs is off. CTRL1 = 0 means a constant logic level (GND) is applied to CTRL1.
5 PWM means a digital PWM signal is applied to the CTRL1 and/or the CTRL2 pin with a frequency from 100 Hz to 200 kHz.
LED CONFIG.
FULL ON
CTRL1
CTRL2
VOUT
ILED
(SUB)
ILED
(MAIN)
SUB DISPLAY
BRIGHTNESS
MAIN DISPLAY
BRIGHTNESS
100%
100%
SUB AND MAIN 50%
DUTY CYCLE
MAIN AND SUB OFF
tCP
50%
50%
SHDN
SHDN
37ms > tCP > 15ms
Figure 20. Application Timing
MAIN 80% DUTY CYCLE,
SUB OFF
80%
Rev. C | Page 11 of 16
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet ADM8843.PDF ] | |
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