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Preliminary Technical Data
FEATURES
ADM8845 drives 6 LEDs from a 2.6 V to 5.5 V (li-ion) input supply 1x/1.5x/2x Fractional Charge Pump to maximise power efficiency 1% Max LED Current Matching Up to 88% Power Efficiency over Li-ion Range Powers Main and Sub Display LEDs with individual shutdown Package footprint only 9mm2 (3mm x 3mm) Package height only 0.9mm Low power shutdown mode Shutdown Function Soft-start limiting inrush current
Charge Pump Driver for LCD White LED Backlights ADM8845
GENERAL DESCRIPTION
The ADM8845 provides the power required to drive up to six LEDs, using charge pump technology. The LEDs are used for backlighting a color LCD display, with up to four LEDs in the main display and up to two LEDs in the sub display, with regulated constant current for uniform brightness intensity. Two digital input control pins, CTRL1 and CTRL2 control the shutdown operation and the brightness of the main and sub displays. To maximize power efficiency, a charge pump that can operate in either of a 1x, 1.5x or 2x mode is used. The charge pump automatically switches between 1x/1.5x/2x 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 the use of a feedback pin to sense individual LED current with a maximum matching accuracy of 1%.
APPLICATIONS
Mobile phones with Main and Sub Displays White LED Backlighting Camera Flash/Strobes and Movie Light Applications Micro TFT color displays DSC PDA's
FUNCTIONAL BLOCK DIAGRAM
C1 C2
VCC
ADM8845
Charge Pump 1x/1.5x/2x mode
Vout
C4
C3
MAIN SUB
Osc
CTRL1 CTRL2
+ -
Control Logic Vref
FB1 FB2 FB3 FB4 FB5 FB6
Iset
Rset
LED Current Control Circuit
Current Control 1
Current Control 2
Current Control 3
Current Control 4
Current Control 5
Current Control 6
Current Controlled Sinks
GND
Figure 1. ADM8845 FUNCTIONAL BLOCK DIAGRAM
Rev. PrJ_06/04
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. Trademarks and registered trademarks are the property of their respective companies.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. www.analog.com Tel: 781.329.4700 Fax: 781.326.8703 (c) 2004 Analog Devices, Inc. All rights reserved.
ADM8845 TABLE OF CONTENTS
General Description..................................................................... 1 ADM8845--Specifications ...............................................................3 Thermal Characteristics .............................................................. 3 Absolute Maximum Ratings.............................................................4 ESD Caution.................................................................................. 4 Pin Configuration and Function Description ...............................5 Typical Performance Characteristics ..............................................6 ADM8845 Operation ..................................................................... 10 Output Current Capability ........................................................ 11 Automatic Gain Control............................................................ 11 Current Matching ....................................................................... 11 ADM8845 Brightness Control With a Digital PWM Signal..... 12
Preliminary Technical Data
ADM8845 LED Brightness Control Using a PWM Signal Applied to VPWM .......................................................................... 14 ADM8845 LED Brightness Control Using a DC Voltage Applied to VBRIGHT....................................................................... 14 ADM8845 Applications ..................................................................15 Layout considerations and noise .............................................. 15 White LED Shorting .................................................................. 15 Driving Fewer than six LEDs.................................................... 15 Driving Flash LEDs.................................................................... 15 Driving Camera Light, Main and sub leds .............................. 16 ADM8845 Power Efficiency...........................................................17 Outline Dimensions ........................................................................18 Ordering Guide .......................................................................... 18
REVISION HISTORY
REV. PrJ 06/04
Rev. PrJ 06/04 | Page 2 of 18
Preliminary Technical Data ADM8845--SPECIFICATIONS
(VCC = +2.6V TO 5.5V; TA = -40C to 85C unless otherwise noted; C1,C2 = 1.0F; C3 = 2.2F; C4 = 4.7F)
Table 1.
PARAMETER Input Voltage,VCC Supply Current,ICC Shutdown Current Charge-Pump Frequency Charge Pump Mode Thresholds 1.5x to 2x Accuracy 2x to 1.5x Accuracy Hysteresis 1x to 1.5x Accuracy 1.5x to 1x Accuracy Hysteresis Iset Pin LED : LED Matching LED : ISET Accuracy Iset pin voltage ILED to ISET Ratio Min Compliance on FB pin Charge Pump Output Resistance Min 2.6 Typ 2.6 Max 5.5 5 5 1.5 3.33 4 3.36 4 40 4.77 4 4.81 4 40 -1 -1 1.18 120 0.2 1.2 3.5 8.0 0.1 0.5VCC 0.3VCC 1 88 30 +1 +1 Units V mA uA MHz V % V % mV V % V % mV % % V 0.3 1.7 4.5 11 30 200 V Ohm Ohm Ohm mA KHz V V uA % mV ISET = 20mA 1x Mode 1.5x Mode 2x Mode See Note 1 and Figure 22 Test Conditions
ADM8845
All 6 LEDs Disabled, Vcc = 3.3V, RSET= 7.08kOhm CTRL1 = 1, CRTL2 = 1 TA= 25C
ILED = 20mA, VFB =0.4V ILED = 20mA, RSET = 7.08K, VFB =0.4V, Vcc = 3.6V, TA = 25C, Note 2
LED Current PWM Digital Inputs Input Hi Input Low Input Leakage Current Charge Pump Power Efficiency Vout Ripple
CTRL1 = 1, CRTL2 = 1, Vcc = 3.4V, VFB = 0.2V, IFB = 20mA Vcc = 3.6V, ILED = 20mA, All 6 LEDs Enabled
THERMAL CHARACTERISTICS
16-Lead LFCSP Package: JA = 50C/Watt
Rev. PrJ 06/04| Page 3 of 18
ADM8845 ABSOLUTE MAXIMUM RATINGS
Table 2. (TA = 25C unless otherwise noted)
Parameter Supply Voltage VCC ISET CTRL1, CTRL2 VOUT shorted (Note 3) Feedback pins FB1 to FB6 Operating Temperature Range VOUT (Note 4) Storage Temperature Range Power Dissipation ESD Class Rating -0.3 V to +6.0 V -0.3 V to +2.0 V -0.3 V to +6.0 V Indefinite -0.3 V to +6.0 V -40C to +85C 180mA -65C to +125C 2mW 1
Preliminary Technical Data
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
Note 1: LED Current should be derated above TA > 65C, refer to Figure 22. Note 2: Guaranteed by design. Not 100% production tested. Note 3: Short through LED. Note 4: Based on long term current density limitations.
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
Main Display
Sub Display
Vcc 2. 6V - 5.5V VO UT
ADM8845
CTRL1 CTRL2 FB1 FB2 FB3 FB4 I SET R SET GND FB5 FB6
Figure 2. ADM8845 Typical Application Diagram
Rev. PrJ 06/04 | Page 4 of 18
Preliminary Technical Data PIN CONFIGURATION AND FUNCTION DESCRIPTION
Table 3.
Pin ADM8845 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Mnemonic VOUT C2+ ISET FB1 FB2 FB3 FB4 FB5 FB6 GND C2- CTRL2 CTRL1 C1- Vcc C1+ EP
ADM8845
Function Charge Pump Output. A 2.2F capacitor to ground is required on this pin. Connect Vout to the anodes of all the LEDs. Flying Capacitor 2 Positive Connection Bias current set input. The current flowing through the RSET resistor ISET is gained up by 120 to give the ILED curent. Connect a resistor RSET to GND to set the bias current as VSET/RSET. (Note: Vset = 1.18V) LED1 Cathode connection and Charge Pump Feedback. The current flowing in LED1 is 120 times the current flowing through RSET, ISET. LED2 Cathode connection and Charge Pump Feedback. The current flowing in LED2 is 120 times the current flowing through RSET, ISET. When using fewer than six LEDs this pin can be left unconnected. LED3 Cathode connection and Charge Pump Feedback. The current flowing in LED3 is 120 times the current flowing through RSET, ISET. When using fewer than six LEDs this pin can be left unconnected. LED4 Cathode connection and Charge Pump Feedback. The current flowing in LED4 is 120 times the current flowing through RSET, ISET. When using fewer than six LEDs this pin can be left unconnected. LED5 Cathode connection and Charge Pump Feedback. The current flowing in LED5 is 120 times the current flowing through RSET, ISET. When using fewer than six LEDs this pin can be left unconnected. LED6 Cathode connection and Charge Pump Feedback. The current flowing in LED6 is 120 times the current flowing through RSET, ISET. When using fewer than six LEDs this pin can be left unconnected. Device Ground Pin. Flying Capacitor 2 Negative Connection. Digital Input. 3 V CMOS Logic. Used with CTRL1 to control the shutdown operation of the main and sub LEDs. Digital Input. 3 V CMOS Logic. Used with CTRL2 to control the shutdown operation of the main and sub LEDs. Flying Capacitor 1 Negative Connection. Positive Supply Voltage Input. Connect this pin to a 2.6 V to 5.5 V supply with a 4.7F decoupling capacitor. Flying Capacitor 1 Positive Connection. Expose Paddle. Connect the exposed paddle to GND.
CTRL1
13
VCC
C1+
VOUT C2+ ISET FB1
16 15
C114
1 2
ADM8845 TOP VIEW
12
CTRL2 C2GND FB6
11
10
3
4
(NOT TO SCALE)
9
5
6
7
8
FB3
FB5
Figure 3. ADM8845 Pin Configuration
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
Rev. PrJ 06/04| Page 5 of 18
FB2
FB4
ADM8845 TYPICAL PERFORMANCE CHARACTERISTICS
35 30 LED Current (mA) 25
0.2 0.4 0.3
Preliminary Technical Data
Max Positive Matching Error
20 15 10 5 4.75
Matching Error (%)
0.1 0 2.6 -0.1 -0.2 -0.3 Max Negative Matching Error 3 3.4 3.8 4.2 4.6 5 5.4
6.75
8.75
10.75
12.75
14.75
-0.4 Supply Voltage (V)
Rset (kohm)
Figure 4. LED Current vs. RSET Resistor
Figure 5. LED Current Matching Error (%) vs. Supply Voltage (V), TA = 25C and ILED = 20mA
20.35 20.3 -40'C 20.25 LED current (mA)
20.24 20.22 20.2 LED Current (mA)
3.6 4.1 Supply Voltage (V) 4.6 5.1
20.2 25'C 20.15 20.1 20.05 85'C
20.18 20.16 20.14 20.12 20.1
20 2.6 3.1
20.08 -40 0 Temperature ('C) 40 80
Figure 6. LED Current (mA) vs. Temperature (C), 6 LEDs enabled.
Figure 7. ILED (mA) Variation over Temperature (C), with Vcc = 3.6V
0.300
35
0.200
30
0.100 % Error
LED Current (mA)
25
20
0.000 -40 -0.100 -20 0 25 45 65 85
15
10
-0.200
5 2.6 3 3.4 3.8 4.2 4.6 5 5.4 Supply Voltage (V)
Temperature
-0.300
Figure 9. LED Current (mA) vs. Supply Voltage (V) Figure 8. ILED Matching (%) over Temperature (C), with Vcc = 3.6, ILED = 20mA , 6 LEDs enabled.
Rev. PrJ 06/04 | Page 6 of 18
Preliminary Technical Data
20 16 12 8 4 0 0 20 40 60 80 100
60 0 10 20 30 40 50 60 70 80 95 90 85 Efficiency (%) 80 75 70 65
ADM8845
LED Current (mA)
Duty Cycle (%)
90
100
Duty Cycle (%)
Figure 10. LED Current (mA) vs. PWM Dimming (varying Duty Cycle), 6 LEDs enabled, Freq = 1kHz.
Figure 11. LED Efficiency vs. Varying Duty Cycle of 1kHz PWM signal, with 6 LEDs enabled, 20mA/LED.
300
250 Supply Current Icc (mA)
20mA/LED
200
150
15mA/LED
100
50
0 2.6 3 3.4 3.8 4.2 4.6 5 5.4 Supply Voltage (V)
2.00 V 1.00 V 160 mA 18.0 mV
Figure 12. Input Current vs. Supply Voltage, with 6 LEDs enabled
Figure 13. Softstart showing the initial in-rush current and Vout variation with 6 LEDs @ 20mA/LED, VCC = 3.6V
Figure 14. 1.5x Mode Operating Waveforms
Figure 15. 2x Mode Operating Waveforms
Rev. PrJ 06/04| Page 7 of 18
ADM8845
90 85 80 Power Efficiency 75 70 65 60 55 50 45 40 2.8 2.9 3 3.1
Preliminary Technical Data
Power Efficiency over Li-ion Range
Vf = 4.3V
Vf = 4.0V Vf = 3.6V Vf = 3.8V Vf = 3.2V
3.2
3.3
3.4
3.5 Vcc
3.6
3.7
3.8
3.9
4
4.1
4.2
Figure 17. Power Efficiency vs. Supply Voltage over Li-ion Range (6 LEDS @ 20mA/LED)
Figure 16. 1x Mode Operating Waveforms
Power Efficiency over Li-ion Range
Power Efficiency over Li-ion Range
90 85 80 Power Efficiency 75 70 65 60 55 50 45 40 2.8 2.9 3 3.1 3.2 3.3 3.4 3.5 Vcc 3.6 3.7 3.8 3.9 4 4.1 4.2
Vf = 4.0V Vf = 3.8V Vf = 3.6V Vf = 3.2V
90 85 80
Vf = 4.3V
Power Efficiency
Vf = 4.3V
75 70 65 60 55 50 45 40 2.8 2.9 3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4 4.1 4.2
Vf = 3.2V Vf = 4.0V Vf = 3.8V Vf = 3.6V
Vcc
Figure 18. Power Efficiency vs. Supply Voltage over Li-ion Range (6 LEDS @ 15mA/LED)
Figure 19. Power Efficiency vs. Supply Voltage over Li-ion Range (4 LEDS @ 20mA/LED)
Power Efficiency over Li-ion Range
90 85 80 Power Efficiency 75 70 65 60 55 50 45 40 2.8 2.9 3 3.1 3.2 3.3 3.4 3.5 Vcc 3.6 3.7 3.8 3.9 4 4.1 4.2
Vf = 4.0V Vf = 3.8V Vf = 3.6V Vf = 3.2V Vf = 4.3V
Figure 20. Power Efficiency vs. Supply Voltage over Li-ion Range (4 LEDS @ 15mA/LED)
Figure 21. TPC Delay
Rev. PrJ 06/04 | Page 8 of 18
Preliminary Technical Data
ADM8845
30mA
20mA
65C
85C
Figure 22. Max LED Current vs. Ambient Temperature (6 LEDs Connected)
Rev. PrJ 06/04| Page 9 of 18
ADM8845 ADM8845 OPERATION
Preliminary Technical Data
The ADM8845 charge pump driver for LCD white LED backlights implements a multiple gain charge pump (1x, 1.5x, 2x)to maintain the correct voltage on the anodes of the LEDs over a 2.6V to 5.5V (li-ion) input supply voltage. The charge pump automatically switches between 1x/1.5x/2x modes based on the input voltage, to maintain sufficient drive for the LED anodes, with VCC input voltages as low as 2.6V. It also includes regulation of the charge pump output voltage for supply voltages up to 5.5V. The ADM8845 six LEDs are arranged into two groups; main and sub. The main display can be up to four LEDs (FB1 to FB4) and the sub display can be up to two LEDs (FB5 and FB6), see Figure 23. Two digital input control pins, CTRL1 and CTRL2, control the shutdown operation and the brightness of the main and sub displays, see Table 4.
CTRL1 0 0 1 1
CTRL2 LED Shutdown Operation 0 Sub Display Off / Main Display Off 1 Sub Display Off / Main Display On 0 Sub Display On / Main Display Off 1 Sub Display On / Main Display On Table 4. ADM8845 Digital Inputs Truth Table
An external resistor RSET is connected between the ISET pin and GND, this resistor sets up a reference current ISET which is gained up by 120 internally within the ADM8845 to produce the ILED currents of up to 30mA/LED, (ILED = ISET * 120 and ISET = 1.18V /RSET). The ADM8845 uses six individual current sinks to individually sense each LED current with a maximum matching performance of 1%. This current matching performance ensures uniform brightness across a color display. The ADM8845 provides the option to control the brightness of the white LEDs with a digital PWM signal applied to CTRL1 and/or CTRL2. The duty cycle of the applied PWM signal determines the brightness of the main and/or sub display backlight white LEDs. The ADM8845 also allows the brightness of the white LEDs to be controlled using a DC voltage, refer to page 14, Figure 27Figure . Soft-start circuitry limits the inrush current flow at power up. The ADM8845 is fabricated using CMOS technology for minimal power consumption and is packaged in a 16-Lead Frame Chip Scale Package.
C1
C2
VCC
ADM8845
Charge Pump 1x/1.5x/2x mode
Vout
C4
C3
MAIN SUB
Osc
CTRL1 CTRL2
+ -
Control Logic Vref
FB1 FB2 FB3 FB4 FB5 FB6
Iset
Rset
LED Current Control Circuit
Current Control 1
Current Control 2
Current Control 3
Current Control 4
Current Control 5
Current Control 6
Current Controlled Sinks
GND
Figure 23. ADM8845 FUNCTIONAL BLOCK DIAGRAM
Rev. PrJ 06/04 | Page 10 of 18
Preliminary Technical Data
OUTPUT CURRENT CAPABILITY
ADM8845
The ADM8845 is capable of driving up to 30mA of current to each of the six LEDs given an input voltage of 2.6V to 5.5V. The LED currents have a max current matching of 1% between any two LED currents. An external resistor RSET sets the output current, approximated by the following equation: RSET = 120 x (1.18V / ILED). In order for the LED currents to be regulated properly, sufficient headroom voltage (compliance) must be present. The compliance refers to the minimum amount of voltage that must be present across the internal current sinks in order to ensure the desired current and matching performance is realizable. To ensure the desired current is obtained, apply the following equations to find the minimum input voltage required: VOUT - VF Compliance VF is the LED forward voltage. For 20mA/LED the compliance is 0.2V typ and 0.3V max, see Table 5.
ILED 15mA 20mA 30mA
RSET 9.44k Ohms 7.08k Ohms 4.72k Ohms
Typ. Compliance 0.17V 0.20V 0.34V
Table 5. ILED, RSET and Compliance Table When the ADM8845 charge pump is loaded with 180mA (six LEDs at 30mA/LED) the ambient operating temperature is reduced, see Figure 22.
AUTOMATIC GAIN CONTROL
The Automatic Gain Control block controls the operation of the charge pump by selecting the appropriate gain for the charge pump, to maintain sufficient drive for the LED anodes at the highest power efficiency over a 2.6V to 5.5V input supply range. The charge pump switching thresholds are:
Gain 1.5x to 2x 2x to 1.5x 1x to 1.5x 1.5x to 1x Threshold 3.33V 3.36V 4.77V 4.81V
Table 6. Charge Pump Switching Thresholds
CURRENT MATCHING
The 1% max current matching performance is defined by the following two equations: IAVG = (IMAX + IMIN)/2
Max Matching Error = [(IMAX - IAVG)/IAVG] * 100 or Min Matching Error = [(IMIN - IAVG)/IAVG] * 100 Where IMAX is the largest ILED current and IMIN is the smallest ILED current.
Rev. PrJ 06/04| Page 11 of 18
ADM8845
Preliminary Technical Data
ADM8845 BRIGHTNESS CONTROL WITH A DIGITAL PWM SIGNAL
PWM brightness control provides the widest brightness control method by pulsing the white LEDs on and off using the digital input control pins, CTRL1 and/or CTRL2. PWM brightness control also removes any chromaticity shifts associated with changing the white LED current, as the LEDs operate at either zero current or full current (set by the RSET resistor). The digital PWM signal applied with a frequency of 100Hz to 200kHz turns the current control sinks on and off using CTRL1 and/or CTRL2. The average current through the LEDs changes with the PWM signal duty cycle. If the PWM frequency is much less than 100Hz, flicker may be seen in the LEDs. For the ADM8845, zero duty cycle will turn off the LEDs and a 50% duty cycle will result in an average LED current ILED being half the programmed LED current. For example, if RSET is set to program 20mA/LED, a 50% duty cycle will result in an average ILED of 10mA/LED. ILED being half the programmed LED current.
C1 C2
The ADM8845 main and sub display brightness can be controlled together or separately. By applying a digital PWM signal to both CTRL1 and CTRL2 pins. The duty cycle of the applied digital PWM signal determines the brightness of the main and sub displays together. By varying the duty cycle of the applied PWM signal you vary the brightness of the main and sub displays from 0% to 100%. By holding CTRL1 low and applying a digital PWM signal to CTRL2, the sub display is turned off and the main display is on, the brightness of the main display is determined by the duty cycle off the applied digital PWM signal. Also applying a digital PWM signal to CTRL1 and holding CTRL2 low, the sub display is turned on and the main display is off, the brightness of the sub display is determined by the duty cycle off the applied digital PWM signal. Also applying a digital PWM signal to CTRL1 and holding CTRL2 high, the sub display is turned on and the main display is turned on, the brightness of the sub display is determined by the duty cycle off the applied digital PWM signal. The brightness of the main display is set to the maximum (maximum is set by the RSET resistor). By holding CTRL1 high and applying a digital PWM signal to CTRL2, the sub display is turned on and the main display is on, the brightness of the main display is determined by the duty cycle off the applied digital PWM signal. The brightness of the sub display is set to the maximum (maximum is set by the RSET resistor) When CTRL1 and CTRL2 go low the LED Current Control Sinks shutdown. Shutdown of the Charge Pump is delayed by 15mS. This timeout period (tCP) allows the ADM8845 to determine if a digital PWM signal is present on CTRL1 and CTRL2 or if the user has selected a full chip shutdown, see Figure 25 ADM8845 Application Timing. If digital PWM brightness control of the LEDs is not required then a constant logic level 1 (VCC) or 0 (GND) must be applied.
ADM8845
PWM Input or High/Low PW M Input or High/Low
Vo ut
C3
CT RL1 CT RL2
FB1 FB2 FB3
Iset
FB4 FB5 FB6
Rset
Figure 24. ADM8845 Digital PWM Brightness Control Application Diagram By applying a digital PWM signal to the digital input control pins, CTRL1 and/or CTRL2 you can adjust the brightness of the sub and/or main displays. The ADM8845 six white LEDs are organized into 2 groups, Main Display (FB1-FB4) and Sub Display (FB4 - FB6), refer to Page 10.
Rev. PrJ 06/04 | Page 12 of 18
Preliminary Technical Data
LED Config. Full On sub + main 50% D.C. tcp CTRL1 CTRL2 Vout ILED (sub) ILED (main) Sub Display Brightness main + sub Off main 80% D.C., sub off
ADM8845
100% 50% 100% 50% SHDN SHDN 80%
Main Display Brightness
37mS > tcp > 15mS
Figure 25. ADM8845 Application Timing
CTRL1 0 0 1 1 0 PWM 1 PWM PWM
CTRL2 0 1 0 1 PWM 0 PWM 1 PWM
LED Operation Sub Display Off / Main Display Off (Full Shutdown) Sub Display Off / Main Display On Sub Display On / Main Display Off Sub Display On / Main Display On (Full On) Sub Display Off/ Digital PWM Brightness Control on Main Display Digital PWM Brightness Control on Sub Display / Main Display Off Sub Display On/ Digital PWM Brightness Control on Main Display Digital PWM Brightness Control on Sub Display / Main Display On Digital PWM Brightness Control on Sub and Main Display
Notes 5a, 5d 5a, 5c 5a, 5d 5a, 5c 5b, 5e 5e, 5d 5e a,5 5e, 5e 5e, 5e
Table 7. ADM8845 Digital Inputs Truth Table The six white LED in the ADM8845 are arranged into 2 groups, sub and main. It is possible to configure the six LEDs as in Table 7, ADM8845 Digital Inputs Truth Table, refer also to Figure 25, ADM8845 Application Timing. Note 5a: 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. Note 5b: Sub Display off means the sub display LEDs only is off. CTRL1 = 0 means a constant logic level (GND) is applied to CTRL1. Note 5c: 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. Note 5d: Main Display off means the main display only is off. CTRL2 = 0 means a constant logic level (GND) is applied to CTRL2. Note 5e: PWM means a digital PWM signal is applied to the CTRL1 and/or CTRL2 pin with a frequency from 100Hz to 200kHz.
Rev. PrJ 06/04| Page 13 of 18
ADM8845
ADM8845 LED BRIGHTNESS CONTROL USING A PWM SIGNAL APPLIED TO VPWM
Adding two external resistors and a capacitor as shown on Figure 26, can also be used to achieve PWM brightness control. This PWM brightness control method can be used instead of CTRL1 and/or CTRL2 digital PWM brightness control. With this configuration, CTRL1 and CTRL2 digital logic pins can be used to control shutdown of the white LEDs, while VPWM can be used to control the brightness of all the white LEDs. By applying a high-frequency PWM signal (Amplitude 0V to 2.5V) to drive an R-C-R filter on the ISET pin of the ADM8845. A 0% PWM duty cycle corresponds to 20mA/LED, while a 100% PWM duty cycle corresponds to a 0mA/LED. At PWM frequencies above 5kHz, C5 may be reduced. Refer to Figure 26, ADM8845 PWM Brightness Control Using Filtered-PWM Signal. The amplitude of the PWM signal must be 0 V and 2.5 V only, in order to have 20mA flowing in each LED.
Preliminary Technical Data
ADM8845 LED BRIGHTNESS CONTROL USING A DC VOLTAGE APPLIED TO VBRIGHT
Adding one resistor as shown in figure 27 , this configuration can also be used to achieve brightness control of the white LEDs using a DC voltage applied to the VBRIGHT node. Figure 28 shows an application example of LED Brightness control using a DC Voltage with a amplitude of 0V to 2.5V, applied to VBRIGHT.
ADM8845
ISET
ILED =
ISET_Voltage * 120 * (1 - Duty Cycle) RSET * 2R 100 RSET + 2R
VBRIGHT 0V - 2.5V
R = 15K RSET = 13.4K
100% = ILED = 0mA 0% = ILED = 20mA
ADM8845
Figure 27. ADM8845 PWM Brightness Control Using a DC Voltage applied to VBRIGHT
ISET VPWM
R = 7.5K C5 = 1F R = 7.5K
The equation for ILED is: ISET = [(1/RSET + 1/R)(VSET )] - [(1/R)(VBRIGHT)]
0V - 2.5V
RSET = 13.4K
ILED = 120*ISET Where R = 15k Ohm, VSET = voltage at ISET pin (1.18V)
Figure 26. ADM8845 PWM Brightness Control Using FilteredPWM Signal
2.5V VBRIGHT 1.6V 0.8V 0V 20mA 13.6mA ILED 0mA 7.2mA
Figure 28. ADM8845 PWM Brightness Control Application Diagram Using a DC Voltage applied to VBRIGHT
Rev. PrJ 06/04 | Page 14 of 18
Preliminary Technical Data ADM8845 APPLICATIONS
LAYOUT CONSIDERATIONS AND NOISE
Because of the ADM8845 switching behavior, PCB trace layout is an important consideration. To ensure optimum performance a ground plane should be used, all capacitors (C1,C2,C3,C4) should be located with minimal track lengths to the pins of the ADM8845.
Main Display
ADM8845
Sub Display
WHITE LED SHORTING
If a LED is shorted, the ADM8845 will continue to drive the remaining LEDs with ILED per LED (ILED = ISET * 120). This is because the ADM8845 uses six internal currents sinks to produce the LED current. If a LED is shorted, then the ADM8845 will continue to sink (ISET * 120)mA as programmed by the RSET resistor through the shorted LED.
Vcc 2.6V - 5.5V VOUT
ADM8845
CTRL1 CTRL2 FB1 FB2 FB3 FB4 ISET RSET GND FB5 FB6
Figure 30. ADM8845 Driving 3three Main and one Sub
DRIVING FEWER THAN SIX LEDS
The ADM8845 can be operated with less than 6 LEDs in parallel, simply leave the un-used FBx pins floating. For example Figure 29, shows five LEDs being powered by the ADM8845 or Figure 30 shows three main LEDs + one sub LED.
DRIVING FLASH LEDS
The ADM8845 can be operated with any two FBx pins operated in parallel to double the combined LED current supplied by the ADM8845. For example if three Flash LEDs are required to be driven with 60mA/LED. Then the ADM8845 can be configured as follows, see Figure 31, see also Figure 22, Max LED Current vs. Ambient Temperature.
Vcc 2.6V - 5.5V VOUT
LCD
ADM8845
CTRL1
Vcc 2.6V - 5.5V VOUT
60mA FB1 FB2 FB3 FB4 FB5
60mA
60mA
CTRL2
ADM8845
CTRL1 CTRL2 FB1 FB2 FB3 FB4 FB5 GND FB6
Rset 4.72k
GND
FB6
Figure 31. ADM8845 Driving three flash LEDs Figure 29. ADM8845 Driving Five White LEDs
Rev. PrJ 06/04| Page 15 of 18
ADM8845
DRIVING CAMERA LIGHT, MAIN AND SUB LEDS
Preliminary Technical Data
The ADM8845 can also be configured to power a camera light which is composed of four white LEDs in parallel, packaged into one package. FB1 to FB4 now power the camera light and FB5 and FB6 powers the main display and the sub display LED is powered from the ADM8845 by using an external current mirror to control the current flowing through the sub white LED, see Figure 32. All white LEDs have 15mA/LED, therefore total load on the ADM8845 charge pump is 105mA, max load on the ADM8845 charge pump is 180mA see Figure 22.
C1 C2
VCC
ADM8845
Charge Pump 1x/1.5x/2x mode
Vout
C4
C3
Osc
CTRL1 CTRL2
+ -
Camera
Main
Sub
Control Logic Vref
15mA/LED
15mA/LED
15mA/LED
FB1 FB2 FB3 FB4 FB5 FB6
R
Current Control 7
Iset
Rset 9.44k
LED Current Control Circuit
Current Control 1
Current Control 2
Current Control 3
Current Control 4
Current Control 5
Current Control 6
Current Controlled Sinks
GND
Figure 32. ADM8845 Driving Camera Light + Two Main + One Sub
Rev. PrJ 06/04 | Page 16 of 18
Preliminary Technical Data ADM8845 POWER EFFICIENCY
The ADM8845 power efficiency () equations, are as follows: = POUT/PIN PIN = ((VCC * ILOAD * Gain) + (IQ * VCC)) POUT = 6*(VF * ILED) IQ VF Gain
ADM8845
: Quiescent current of the ADM8845, 2.6mA. : LED Forward Voltage : Charge Pump Mode (1x, 1.5x, 2x)
Figure 33. ADM8845 Charge Pump Power Efficiency Diagram, Example 1.
Example 1: The ADM8845 driving six white LED with 20mA/LED at VCC = 3.4V (1.5x mode), LED VF = 4.5V. Example 2: The ADM8845 driving six white LED with 20mA/LED at VCC = 3.4 (1.5x mode), LED VF = 3.6V.
PIN = ((VCC * ILOAD * Gain) + (VCC * IQ)) PIN = ((3.4 * 120mA * 1.5) + (3.4 * 2.6mA)) PIN = ((0.612) + (0.00884)) PIN = 0.62084 POUT = 6(VF * ILED) POUT = 6(4.5V * 20mA) POUT = 0.54 = POUT/PIN = 0.54/0.62084 = 87 %
PIN = ((VCC * ILOAD * Gain) + (VCC * IQ)) PIN = ((3.4 * 120mA * 1.5) + (3.4 * 2.6mA)) PIN = ((0.612) + (0.00884)) PIN = 0.62084 POUT = 6(VF * ILED) POUT = 6(3.6V * 20mA) POUT = 0.432 = POUT/PIN = 0.432/0.62084 = 70 %
Rev. PrJ 06/04| Page 17 of 18
ADM8845 OUTLINE DIMENSIONS
=
16-Lead Lead Frame Chip Scale Package [LFCSP] 3 x 3 mm Body (CP-16-4) Dimensions shown in millimeters 0.50 0.40 0.30
Preliminary Technical Data
3.00 BSC SQ 0. 5 4 PIN 1 INDICATOR
TOP VIEW
0.60 MAX
13 12 BOTT OM VIEW 16
PIN 1 INDICATOR 1.65 1.50 SQ* 1.35
1
2.75 BSC SQ 0. 0 5 BSC
9 8
5
4
0. 5 MIN 2
128MAX 0.90 0.85 0.80 SEATING PLANE 0.30 0.23 0.18
0.80 MAX 0.65 TYP 0.05 MAX 0.02 NOM 0.20 REF
1.50 REF
*COMPLIANT TO JEDEC STANDARDS MO-220-VEED-2 EXCEPT FOR EXPOSED PAD DIMENSION
Figure 34. 16-Lead Frame Chip Scale package [LFCSP] (CP-16)--Dimensions shown in millimeters
ORDERING GUIDE
Model ADM8845ACP ADM8845ACP-REEL7 ADM8845ACPZ ADM8845ACPZ-REEL7 CP: Chip Scale Package Z : Lead Free Part Temperature Range -40C to + 85C -40C to + 85C -40C to + 85C -40C to + 85C Package Description 16-Lead LFCSP 16-Lead LFCSP 16-Lead LFCSP 16-Lead LFCSP Package Option CP-16 CP-16 CP-16 CP-16
(c) 2004 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners.
PR04867-0-6/04(PrJ)
Rev. PrJ 06/04 | Page 18 of 18

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