Charge Pump Driver for LCD
White LED Backlights
Preliminary Technical Data
ADM8846
Rev. PrA_06/04
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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
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Tel: 781.329.4700 www.analog.com
Fax: 781.326.8703 © 2004 Analog Devices, Inc. All rights reserved.
FEATURES
ADM8846 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
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
GENERAL DESCRIPTION
The ADM8846 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%.
FUNCTIONAL BLOCK DIAGRAM
Charge Pump
1x/1.5x/2x mode
Control
Logic
VCC
C4
Osc
Vref
+
-
LED Current
Control
Circuit
Current Controlled Sinks
Iset
GND
ADM8846
Vout
FB2
FB3
FB4
FB5
FB6
FB1
C3
C1 C2
Rset
Current
Control
1
Current
Control
2
Current
Control
3
Current
Control
4
Current
Control
5
Current
Control
6
CTRL1
CTRL2
SUB
MAIN
Figure 1. ADM8846 FUNCTIONAL BLOCK DIAGRAM
ADM8846 Preliminary Technical Data
Rev. PrA 06/04 | Page 2 of 18
TABLE OF CONTENTS
General Description..................................................................... 1
ADM8846—Specifications...............................................................3
Thermal Characteristics .............................................................. 3
Absolute Maximum Ratings.............................................................4
ESD Caution.................................................................................. 4
Pin Configuration and Function Description ...............................5
Typical Performance Characteristics ..............................................6
ADM8846 Operation ..................................................................... 10
Output Current Capability........................................................ 11
Automatic Gain Control............................................................ 11
Current Matching....................................................................... 11
ADM8846 Brightness Control With a Digital PWM Signal..... 12
ADM8846 LED Brightness Control Using a PWM Signal
Applied to VPWM .......................................................................... 14
ADM8846 LED Brightness Control Using a DC Voltage
Applied to VBRIGHT ....................................................................... 14
ADM8846 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
ADM8846 Power Efficiency...........................................................17
Outline Dimensions........................................................................18
Ordering Guide .......................................................................... 18
REVISION HISTORY
REV. PrA 06/04
Preliminary Technical Data ADM8846
Rev. PrA 06/04| Page 3 of 18
ADM8846—SPECIFICATIONS
(VCC = +2.6V TO 5.5V; TA = -40°C to 85°C unless otherwise noted; C1,C2 = 1.0µF; C3 = 2.2µF; C4 = 4.7µF)
Table 1.
PARAMETER Min Typ Max Units Test Conditions
Input Voltage,VCC 2.6 5.5 V
Supply Current,ICC 2.6 4 m A All 6 LEDs Disabled, Vcc = 3.3V, RSET= 7.08kOhm
CTRL1 = 1, CRTL2 = 1
Shutdown Current 5 uA TA= 25°C
Charge-Pump Frequency 1.5 M H z
Charge Pump Mode Thresholds
1.5x to 2x 3.33 V
Accuracy 4 %
2x to 1.5x 3.36 V
Accuracy 4 %
Hysteresis 40 m V
1x to 1.5x 4.77 V
Accuracy 4 %
1.5x to 1x 4.81 V
Accuracy 4 %
Hysteresis 40 m V
Iset Pin
LED : LED Matching -1 +1 % ILED = 20mA, VFB =0.4V
LED : ISET Accuracy -1 +1 % ILED = 20mA, RSET = 7.08K, VFB =0.4V, Vcc = 3.6V, TA = 25°C,
Note 2
Iset pin voltage 1.18 V
ILED to ISET Ratio 120
Min Compliance on FB pin 0.2 0.3 V ISET = 20mA
Charge Pump Output Resistance 1.2 1.7 Ohm 1x Mode
3.5 4.5 Ohm 1.5x Mode
8.0 11 Ohm 2x Mode
LED Current 30 m A See Note 1 and Figure 22
PWM 0.1 200 KHz
Digital Inputs
Input Hi 1.6 V 2.6V ≤ Vcc ≤ 4.2V
Input Low 0.4 V 2.6V ≤ Vcc ≤ 4.2V
Input Leakage Current 1 uA
Charge Pump Power Efficiency 88 % CTRL1 = 1, CRTL2 = 1, Vcc = 3.4V, VFB = 0.2V,
I
FB = 20mA
Vout Ripple 30 m V Vcc = 3.6V, ILED = 20mA, All 6 LEDs Enabled
THERMAL CHARACTERISTICS
16-Lead LFCSP Package:
θJA = 50°C/Watt
ADM8846 Preliminary Technical Data
Rev. PrA 06/04 | Page 4 of 18
ABSOLUTE MAXIMUM RATINGS
Table 2. (TA = 25°C unless otherwise noted)
Parameter Rating
Supply Voltage VCC –0.3 V to +6.0 V
ISET –0.3 V to +2.0 V
CTRL1, CTRL2 –0.3 V to +6.0 V
VOUT shorted (Note 3) Indefinite
Feedback pins FB1 to FB6 –0.3 V to +6.0 V
Operating Temperature Range –40°C to +85°C
VOUT (Note 4) 180mA
Storage Temperature Range –65°C to +125°C
Power Dissipation 2mW
ESD Class 1
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.
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.
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
VOUT
FB1
FB2
FB3
FB4
FB5
FB6
Vcc
2.6V - 5.5V
CTRL1
CTRL2
GND
ADM8846
R
SET
I
SET
Figure 2. ADM8846 Typical Application Diagram
Preliminary Technical Data ADM8846
Rev. PrA 06/04| Page 5 of 18
PIN CONFIGURATION AND FUNCTION DESCRIPTION
Table 3.
Pin
ADM8846 Mnemonic Function
1 VOUT Charge Pump Output. A 2.2µF 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 give the
ILED curent. Connect a resistor RSET to GND to set the bias current as VSET/RSET. (Note: Vset = 1.18V)
4 FB1 LED1 Cathode connection and Charge Pump Feedback. The current flowing in LED1 is 120 times the
current flowing through RSET, ISET.
5 FB2 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.
6 FB3 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.
7 FB4 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.
8 FB5 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.
9 FB6 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.
10 G N D Device Ground Pin.
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 4.7µF decoupling
capacitor.
16 C1+ Flying Capacitor 1 Positive Connection.
- EP Expose Paddle. Connect the exposed paddle to GND.
10
11
12
9
1
2
3
4
5678
13
14
15
ADM8846
TOP VIEW
(NOT TO SCALE)
16
GND
FB6
CTRL2
ISET
FB1
Figure 3. ADM8846 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.
ADM8846 Preliminary Technical Data
Rev. PrA 06/04 | Page 6 of 18
TYPICAL PERFORMANCE CHARACTERISTICS
5
10
15
20
25
30
35
4.75 6.75 8.75 10.75 12.75 14.75
Rset (k o h m)
LED Cur r en t (mA)
Figure 4. LED Current vs. RSET Resistor
20
20.05
20.1
20.15
20.2
20.25
20.3
20.35
2.6 3.1 3.6 4.1 4.6 5.1
Supply Voltage (V)
LED current (mA)
25'C
-40'C
85'C
Figure 6. LED Current (mA) vs. Temperature (°C), 6 LEDs enabled.
-0.300
-0.200
-0.100
0.000
0.100
0.200
0.300
-40-200 25456585
Temperature
% Error
Figure 8. ILED Matching (%) over Temperature (°C), with Vcc = 3.6,
ILED = 20mA , 6 LEDs enabled.
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
2.6 3 3.4 3.8 4.2 4.6 5 5.4
Supply Voltage (V)
Matching Error (%)
Max Positive Matching Error
Max Negative Matching Error
Figure 5. LED Current Matching Error (%) vs. Supply Voltage (V),
TA = 25°C and ILED = 20mA
20.08
20.1
20.12
20.14
20.16
20.18
20.2
20.22
20.24
-40 0 40 80
Temperature ('C)
LED Current (mA)
Figure 7. ILED (mA) Variation over Temperature (°C), with Vcc = 3.6V
5
10
15
20
25
30
35
2.6 3 3.4 3.8 4.2 4.6 5 5.4
Supply Voltage (V)
LED Current ( mA)
Figure 9. LED Current (mA) vs. Supply Voltage (V)
Preliminary Technical Data ADM8846
Rev. PrA 06/04| Page 7 of 18
0
4
8
12
16
20
0 20406080100
Duty Cycle (%)
LED Current (mA)
Figure 10. LED Current (mA) vs. PWM Dimming (varying Duty Cycle),
6 LEDs enabled, Freq = 1kHz.
0
50
100
150
200
250
300
2.6 3 3.4 3.8 4.2 4.6 5 5.4
Supply Voltage (V)
Supply Current Icc (mA)
20mA/LED
15mA/LED
Figure 12. Input Current vs. Supply Voltage, with 6 LEDs enabled
Figure 14. 1.5x Mode Operating Waveforms
60
65
70
75
80
85
90
95
0 102030405060708090100
Duty Cycle (%)
Efficiency (%)
Figure 11. LED Efficiency vs. Varying Duty Cycle of 1kHz PWM signal,
with 6 LEDs enabled, 20mA/LED.
2.00 V
1.00 V 160 mA 18.0 mV
Figure 13. Softstart showing the initial in-rush current and Vout
variation with 6 LEDs @ 20mA/LED, VCC = 3.6V
Figure 15. 2x Mode Operating Waveforms
ADM8846 Preliminary Technical Data
Rev. PrA 06/04 | Page 8 of 18
Figure 16. 1x Mode Operating Waveforms
Power Efficiency over Li-ion Range
40
45
50
55
60
65
70
75
80
85
90
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
Vcc
Power Efficiency
Vf = 4.0V
Vf = 3.8V
Vf = 3.6V
Vf = 3.2V
Vf = 4.3V
Figure 18. Power Efficiency vs. Supply Voltage over Li-ion Range
(6 LEDS @ 15mA/LED)
Power Efficiency over Li-ion Range
40
45
50
55
60
65
70
75
80
85
90
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
Vcc
Power E fficiency
Vf = 4. 3V
Vf = 4.0V
Vf = 3. 8V
Vf = 3. 6V
Vf = 3. 2V
Figure 20. Power Efficiency vs. Supply Voltage over Li-ion Range
(4 LEDS @ 15mA/LED)
Power Efficiency over Li-ion Range
40
45
50
55
60
65
70
75
80
85
90
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
Vcc
Power E fficiency
Vf = 4. 3V
Vf = 4.0V
Vf = 3.8V
Vf = 3.6V
Vf = 3.2V
Figure 17. Power Efficiency vs. Supply Voltage over Li-ion Range
(6 LEDS @ 20mA/LED)
Power Efficiency over Li-ion Range
40
45
50
55
60
65
70
75
80
85
90
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
Vcc
Power Efficienc
y
Vf = 4.3V
Vf = 4.0V
Vf = 3.8V
Vf = 3.6V
Vf = 3.2V
Figure 19. Power Efficiency vs. Supply Voltage over Li-ion Range
(4 LEDS @ 20mA/LED)
Figure 21. TPC Delay
Preliminary Technical Data ADM8846
Rev. PrA 06/04| Page 9 of 18
30mA
20mA
65°C 85°C
Figure 22. Max LED Current vs. Ambient Temperature (6 LEDs
Connected)
ADM8846 Preliminary Technical Data
Rev. PrA 06/04 | Page 10 of 18
ADM8846 OPERATION
The ADM8846 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 ADM8846 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 CTRL2 LED Shutdown Operation
0 0 Sub Display Off / Main Display Off
0 1 Sub Display Off / Main Display On
1 0 Sub Display On / Main Display Off
1 1 Sub Display On / Main Display On
Table 4. ADM8846 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 ADM8846 to produce the ILED currents of up to 30mA/LED, (ILED = ISET * 120 and ISET = 1.18V /RSET). The ADM8846
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 ADM8846 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
ADM8846 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 ADM8846 is fabricated using CMOS technology for minimal power
consumption and is packaged in a 16-Lead Frame Chip Scale Package.
Charge Pump
1x/1.5x/2x mode
Control
Logic
VCC
C4
Osc
Vref
+
-
LED Current
Control
Circuit
Current Controlled Sinks
Iset
GND
ADM8846
Vout
FB2
FB3
FB4
FB5
FB6
FB1
C3
C1 C2
Rset
Current
Control
1
Current
Control
2
Current
Control
3
Current
Control
4
Current
Control
5
Current
Control
6
CTRL1
CTRL2
SUB
MAIN
Figure 23. ADM8846 FUNCTIONAL BLOCK DIAGRAM
Preliminary Technical Data ADM8846
Rev. PrA 06/04| Page 11 of 18
OUTPUT CURRENT CAPABILITY
The ADM8846 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 R
SET Typ. Compliance
15mA 9.44k Ohms 0.17V
20mA 7.08k Ohms 0.20V
30mA 4.72k Ohms 0.34V
Table 5. ILED, RSET and Compliance Table
When the ADM8846 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 Threshold
1.5x to 2x 3.33V
2x to 1.5x 3.36V
1x to 1.5x 4.77V
1.5x to 1x 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.
ADM8846 Preliminary Technical Data
Rev. PrA 06/04 | Page 12 of 18
ADM8846 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
ADM8846, 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.
ADM8846
CTRL1
CTRL2
Vout
FB2
FB3
FB4
FB5
FB6
FB1
C3
Iset
Rset
C
1
C
2
PWM Input
or
High/Low
PWM Input
or
High/Low
Figure 24. ADM8846 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 ADM8846 six white LEDs are
organized into 2 groups, Main Display (FB1-FB4) and Sub
Display (FB4 - FB6), refer to Page 10.
The ADM8846 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 ADM8846 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 ADM8846 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.
Preliminary Technical Data ADM8846
Rev. PrA 06/04| Page 13 of 18
CTRL1
CTRL2
tcp
Vout
37mS > tcp > 15mS
ILED
(sub)
ILED
(main)
Full On sub + main 50% D.C.
LED Config.
Sub Display
Brightness
main + sub Off main 80% D.C., sub off
100%
100%
50%
50% 80%
Main Display
Brightness
SHDN
SHDN
Figure 25. ADM8846 Application Timing
CTRL1 CTRL2 LED Operation Notes
0 0 Sub Display Off / Main Display Off (Full Shutdown) 5a, 5d
0 1 Sub Display Off / Main Display On 5a, 5c
1 0 Sub Display On / Main Display Off 5a, 5d
1 1 Sub Display O n / Main Display On (Full On) 5a, 5c
0 PWM Sub Display Off/ Digital PWM Brightness Control on Main Display 5b, 5e
PWM 0 Digital PWM Brightness Control on Sub Display / Main Display Off 5e, 5d
1 PWM Sub Display On/ Digital PWM Brightness Control on Main Display 5e a,5
PWM 1 Digital PWM Brightness Control on Sub Displa y / Main Displ ay On 5e, 5e
PWM PWM Digital PWM Brightness Control on Sub and Main Display 5e, 5e
Table 7. ADM8846 Digital Inputs Truth Table
The six white LED in the ADM8846 are arranged into 2 groups, sub and main. It is possible to configure the six LEDs as in Table 7,
ADM8846 Digital Inputs Truth Table, refer also to Figure 25, ADM8846 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.
ADM8846 Preliminary Technical Data
Rev. PrA 06/04 | Page 14 of 18
ADM8846 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 ADM8846. 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, ADM8846 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.
ILED = ISET_Voltage * 120 * (1 - Duty Cycle)
RSET * 2R 100
RSET + 2R
100% = ILED =0mA
0% = ILED = 20mA
ADM8846
ISET
VPWM
C5 = 1µF
R = 7.5K
R = 7.5K
RSET = 13.4K
0V - 2.5V
Figure 26. ADM8846 PWM Brightness Control Using Filtered-
PWM Signal
ADM8846 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.
ADM8846
ISET
VBRIGHT R = 15K
RSET = 13.4K
0V - 2.5V
Figure 27. ADM8846 PWM Brightness Control Using a DC
Voltage applied to VBRIGHT
The equation for ILED is:
ISET = [(1/RSET + 1/R)(VSET )] – [(1/R)(VBRIGHT)]
ILED = 120*ISET
Where R = 15k Ohm, VSET = voltage at ISET pin (1.18V)
VBRIGHT
ILED
2.5V
1.6V
0.8V
0V
0mA
7.2mA
13.6mA
20mA
Figure 28. ADM8846 PWM Brightness Control Application
Diagram Using a DC Voltage applied to VBRIGHT
Preliminary Technical Data ADM8846
Rev. PrA 06/04| Page 15 of 18
ADM8846 APPLICATIONS
LAYOUT CONSIDERATIONS AND NOISE
Because of the ADM8846 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
ADM8846.
WHITE LED SHORTING
If a LED is shorted, the ADM8846 will continue to drive the
remaining LEDs with ILED per LED (ILED = ISET * 120). This is
because the ADM8846 uses six internal currents sinks to
produce the LED current. If a LED is shorted, then the
ADM8846 will continue to sink (ISET * 120)mA as programmed
by the RSET resistor through the shorted LED.
DRIVING FEWER THAN SIX LEDS
The ADM8846 can be operated with less than 6 LEDs in
parallel, simply leave the un-used FBx pins floating or
connected to GND. For example Figure 29, shows five LEDs
being powered by the ADM8846 or Figure 30 shows three main
LEDs + one sub LED.
VOUT
FB1
FB2
FB3
FB4
FB5
FB6
Vcc
2.6V - 5.5V
CTRL1
CTRL2
GND
ADM8846
LCD
R
SET
I
SET
Figure 29. ADM8846 Driving Five White LEDs
Main Display
Sub Display
VOUT
FB1
FB2
FB3
FB4
FB5
FB6
Vcc
2.6V - 5.5V
CTRL1
CTRL2
GND
ADM8846
R
SET
I
SET
Figure 30. ADM8846 Driving 3three Main and one Sub
DRIVING FLASH LEDS
The ADM8846 can be operated with any two FBx pins operated
in parallel to double the combined LED current supplied by the
ADM8846. For example if three Flash LEDs are required to be
driven with 60mA/LED. Then the ADM8846 can be configured
as follows, see Figure 31, see also Figure 22, Max LED Current
vs. Ambient Temperature.
VOUT
FB1
FB2
FB3
FB4
FB5
FB6
Vcc
2.6V - 5.5V
CTRL1
CTRL2
GND
ADM8846
Rset
4.72k
60mA
60mA 60mA
Figure 31. ADM8846 Driving three flash LEDs
ADM8846 Preliminary Technical Data
Rev. PrA 06/04 | Page 16 of 18
DRIVING CAMERA LIGHT, MAIN AND SUB LEDS
The ADM8846 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
ADM8846 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 ADM8846 charge pump is 105mA, max load on the ADM8846 charge pump is 180mA see
Figure 22.
Charge Pump
1x/1.5x/2x mode
Control
Logic
VCC
C4
Osc
Vref
+
-
LED Current
Control
Circuit
Current Controlled Sinks
Iset
GND
ADM8845
Vout
FB2
FB3
FB4
FB5
FB6
FB1
C3
C1 C2
Rset
9.44kΩ
Current
Control
1
Current
Control
2
Current
Control
3
Current
Control
4
Current
Control
5
Current
Control
6
CTRL1
CTRL2
Main
Camera Sub
R
Current
Control
7
15mA/LED 15mA/LED 15mA/LED
Figure 32. ADM8846 Driving Camera Light + Two Main + One Sub
ADM8846
Preliminary Technical Data ADM8846
Rev. PrA 06/04| Page 17 of 18
ADM8846 POWER EFFICIENCY
The ADM8846 power efficiency (η) equations, are as follows:
η = POUT/PIN
PIN = ((VCC * ILOAD * Gain) + (IQ * VCC))
POUT = 6*(VF * ILED)
IQ : Quiescent current of the ADM8846, 2.6mA.
VF : LED Forward Voltage
Gain : Charge Pump Mode (1x, 1.5x, 2x)
Figure 33. ADM8846 Charge Pump Power Efficiency Diagram, Example 1.
Example 1: The ADM8846 driving six white LED with 20mA/LED
at VCC = 3.4V (1.5x mode), LED VF = 4.5V.
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
η = POUT/PIN
η = 0.54/0.62084
η = 87 %
Example 2: The ADM8846 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(3.6V * 20mA)
POUT = 0.432
η = POUT/PIN
η = 0.432/0.62084
η = 70 %
ADM8846
ADM8846 Preliminary Technical Data
Rev. PrA 06/04 | Page 18 of 18
OUTLINE DIMENSIONS
1
0.50
BSC
0.60 MAX PIN 1 INDICATOR
1.50 REF
0.50
0.40
0.30
0.25 MIN
0.45
2.75
BSC SQ
TOP
VIEW
128 MAX 0.80 MAX
0.65 TYP
SEATING
PLANE
PIN 1
INDICATOR
0.90
0.85
0.80
0.30
0.23
0.18
0.05 MAX
0.02 NOM
0.20 REF
3.00
BSC SQ
1.65
1.50
1.35
BOTTOM
VIEW
SQ*
16
5
13
8
9
12
4
=
16-Lead Lead Frame Chip Scale Package [LFCSP]
3 x 3 mm Body
(CP-16-4)
Dimensions shown in millimeters
*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 Temperature Range Package Description Package Option
ADM8846ACPZ -40ºC to + 85ºC 16-Lead LFCSP CP-16
ADM8846ACPZ-REEL7 -40ºC to + 85ºC 16-Lead LFCSP CP-16
CP: Chip Scale Package
Z : Lead Free Part
© 2004 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
PR04974-0-6/04(PrA)
