Charge Pump Driver for LCD
White LED Backlights
ADM8845
Preliminary Technical Data
FEATURES
GENERAL DESCRIPTION
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
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.
APPLICATIONS
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%.
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.
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
VCC
C2
ADM8845
Charge Pump
1x/1.5x/2x mode
C4
Vout
C3
MAIN
Osc
CTRL1
CTRL2
SUB
+
-
Control
Logic
FB1
FB2
Vref
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
© 2004 Analog Devices, Inc. All rights reserved.
ADM8845
Preliminary Technical Data
TABLE OF CONTENTS
General Description..................................................................... 1
ADM8845—Specifications ...............................................................3
ADM8845 LED Brightness Control Using a PWM Signal
Applied to VPWM .......................................................................... 14
Thermal Characteristics .............................................................. 3
ADM8845 LED Brightness Control Using a DC Voltage
Applied to VBRIGHT ....................................................................... 14
Absolute Maximum Ratings.............................................................4
ADM8845 Applications ..................................................................15
ESD Caution.................................................................................. 4
Layout considerations and noise .............................................. 15
Pin Configuration and Function Description ...............................5
White LED Shorting .................................................................. 15
Typical Performance Characteristics ..............................................6
Driving Fewer than six LEDs.................................................... 15
ADM8845 Operation ..................................................................... 10
Driving Flash LEDs.................................................................... 15
Output Current Capability ........................................................ 11
Driving Camera Light, Main and sub leds .............................. 16
Automatic Gain Control............................................................ 11
ADM8845 Power Efficiency...........................................................17
Current Matching ....................................................................... 11
Outline Dimensions ........................................................................18
ADM8845 Brightness Control With a Digital PWM Signal..... 12
Ordering Guide .......................................................................... 18
REVISION HISTORY
REV. PrJ 06/04
Rev. PrJ 06/04 | Page 2 of 18
Preliminary Technical Data
ADM8845
ADM8845—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
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
Min
2.6
2.6
Vout Ripple
Max
5.5
5
Units
V
mA
5
uA
MHz
1.5
3.33
4
4
40
4.77
4
4.81
4
40
-1
-1
+1
+1
1.18
120
0.2
1.2
3.5
8.0
%
%
All 6 LEDs Disabled, Vcc = 3.3V, RSET= 7.08kOhm
CTRL1 = 1, CRTL2 = 1
TA= 25°C
ILED = 20mA, VFB =0.4V
ILED = 20mA, RSET = 7.08K, VFB =0.4V, Vcc = 3.6V, TA = 25°C,
Note 2
V
0.3
1.7
4.5
11
30
200
V
Ohm
Ohm
Ohm
mA
KHz
0.3VCC
1
88
V
V
uA
%
30
mV
0.1
Test Conditions
V
%
V
%
mV
V
%
V
%
mV
3.36
Iset pin voltage
ILED to ISET Ratio
Min Compliance on FB pin
Charge Pump Output Resistance
LED Current
PWM
Digital Inputs
Input Hi
Input Low
Input Leakage Current
Charge Pump Power Efficiency
Typ
0.5VCC
THERMAL CHARACTERISTICS
16-Lead LFCSP Package:
θJA = 50°C/Watt
Rev. PrJ 06/04| Page 3 of 18
ISET = 20mA
1x Mode
1.5x Mode
2x Mode
See Note 1 and Figure 22
CTRL1 = 1, CRTL2 = 1, Vcc = 3.4V, VFB = 0.2V,
IFB = 20mA
Vcc = 3.6V, ILED = 20mA, All 6 LEDs Enabled
ADM8845
Preliminary Technical Data
ABSOLUTE MAXIMUM RATINGS
Table 2. (TA = 25°C 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
–40°C to +85°C
180mA
–65°C to +125°C
2mW
1
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
FB1
CTRL2
FB2
FB3
FB4
I SET
GND
FB5
FB6
R SET
Figure 2. ADM8845 Typical Application Diagram
Rev. PrJ 06/04 | Page 4 of 18
Preliminary Technical Data
ADM8845
PIN CONFIGURATION AND FUNCTION DESCRIPTION
Table 3.
2
C2+
3
ISET
4
FB1
5
FB2
6
FB3
7
FB4
8
FB5
9
FB6
10
11
GND
C2−
12
CTRL2
13
CTRL1
14
C1−
15
Vcc
16
-
C1+
EP
16 15
VOUT
1
C2+
2
ISET
3
FB1
4
C1-
VOUT
C1+
1
Function
Charge Pump Output. A 2.2µF 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 4.7µF decoupling
capacitor.
Flying Capacitor 1 Positive Connection.
Expose Paddle. Connect the exposed paddle to GND.
CTRL1
Mnemonic
VCC
Pin
ADM8845
14
13
12
ADM8845
TOP VIEW
(NOT TO SCALE)
FB2
FB3
7
8
FB4
6
FB5
5
CTRL2
11
C2-
10
GND
9
FB6
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
ADM8845
Preliminary Technical Data
TYPICAL PERFORMANCE CHARACTERISTICS
35
0.4
0.3
Max Positive Matching Error
25
0.2
Matching Error (%)
LED Current (mA)
30
20
15
0.1
0
2.6
3
3.4
3.8
4.2
4.6
5
5.4
-0.1
-0.2
10
Max Negative Matching Error
-0.3
5
4.75
6.75
8.75
10.75
12.75
-0.4
14.75
Supply Voltage (V)
Rset (kohm)
Figure 5. LED Current Matching Error (%) vs. Supply Voltage (V),
Figure 4. LED Current vs. RSET Resistor
TA = 25°C and ILED = 20mA
20.35
20.24
20.22
20.3
-40'C
20.2
LED Current (mA)
LED current (mA)
20.25
20.2
25'C
20.15
85'C
20.1
20.18
20.16
20.14
20.12
20.05
20.1
20
2.6
3.1
3.6
4.1
4.6
20.08
5.1
-40
Supply Voltage (V)
0
40
80
Temperature ('C)
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
30
LED Current (mA)
0.200
% Error
0.100
0.000
-40
-20
0
25
45
65
85
-0.100
25
20
15
10
-0.200
5
2.6
3
3.4
3.8
4.2
4.6
5
5.4
Supply Voltage (V)
-0.300
Temperature
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
ADM8845
95
90
16
85
12
Efficiency (%)
LED Current (mA)
20
8
4
80
75
70
65
0
0
20
40
60
80
100
60
Duty Cycle (%)
0
10
20
30
40
50
60
70
80
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
Supply Current Icc (mA)
250
20mA/LED
200
150
15mA/LED
100
50
0
2.6
3
3.4
3.8
4.2
4.6
5
5.4
2.00 V
1.00 V
Supply Voltage (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
Preliminary Technical Data
Power Efficiency over Li-ion Range
90
85
Power Efficiency
80
Vf = 4.3V
75
Vf = 4.0V
70
Vf = 3.6V
65
Vf = 3.8V
60
Vf = 3.2V
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
Vcc
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
90
80
Power Efficiency
80
Power Efficiency
85
Vf = 4.3V
75
Vf = 4.0V
70
Vf = 3.8V
65
Vf = 3.6V
60
Vf = 3.2V
55
Vf = 4.3V
75
70
Vf = 4.0V
Vf = 3.8V
65
Vf = 3.6V
60
Vf = 3.2V
55
50
50
45
45
40
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
2.8
2.9
3
3.1
3.2
3.3
3.4
3.5
3.6
3.7
Figure 18. Power Efficiency vs. Supply Voltage over Li-ion Range
(6 LEDS @ 15mA/LED)
Power Efficiency over Li-ion Range
85
Power Efficiency
80
Vf = 4.3V
75
Vf = 4.0V
70
Vf = 3.8V
65
Vf = 3.6V
60
Vf = 3.2V
55
50
45
40
2.9
3
3.1
3.2
3.3
3.4
3.5
3.9
4
4.1
4.2
Figure 19. Power Efficiency vs. Supply Voltage over Li-ion Range
(4 LEDS @ 20mA/LED)
90
2.8
3.8
Vcc
Vcc
3.6
3.7
3.8
3.9
4
4.1
4.2
Vcc
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
65°C
85°C
Figure 22. Max LED Current vs. Ambient Temperature (6 LEDs
Connected)
Rev. PrJ 06/04| Page 9 of 18
ADM8845
Preliminary Technical Data
ADM8845 OPERATION
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
VCC
C2
ADM8845
Charge Pump
1x/1.5x/2x mode
C4
Vout
C3
MAIN
+
-
Osc
CTRL1
CTRL2
Control
Logic
FB1
FB2
Vref
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
SUB
Preliminary Technical Data
ADM8845
OUTPUT CURRENT CAPABILITY
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
Vo ut
ADM8845
PWM Input
or
High/Low
PW M Input
or
High/Low
C3
CT RL1
CT RL2
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)
FB1
FB2
FB3
Iset
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%.
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.
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.
Rev. PrJ 06/04 | Page 12 of 18
Preliminary Technical Data
LED Config.
Full On
ADM8845
sub + main 50% D.C.
main + sub Off
main 80% D.C., sub off
tcp
CTRL1
CTRL2
Vout
ILED
(sub)
ILED
(main)
Sub Display
Brightness
Main Display
Brightness
100%
50%
SHDN
100%
80%
50%
SHDN
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
Preliminary Technical Data
ADM8845 LED BRIGHTNESS CONTROL USING A
PWM SIGNAL APPLIED TO VPWM
ADM8845 LED BRIGHTNESS CONTROL USING A
DC VOLTAGE APPLIED TO VBRIGHT
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.
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
0V - 2.5V
C5 = 1µF
0V - 2.5V
RSET = 13.4K
Figure 27. ADM8845 PWM Brightness Control Using a DC
Voltage applied to VBRIGHT
ISET
R = 7.5K
R = 15K
ADM8845
100% = ILED = 0mA
0% = ILED = 20mA
VPWM
VBRIGHT
The equation for ILED is:
R = 7.5K
ISET = [(1/RSET + 1/R)(VSET )] – [(1/R)(VBRIGHT)]
ILED = 120*ISET
RSET = 13.4K
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
7.2mA
0mA
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
ADM8845 APPLICATIONS
Main Display
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.
Sub Display
Vcc
2.6V - 5.5V
WHITE LED SHORTING
VOUT
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.
ADM8845
FB1
CTRL1
FB2
CTRL2
FB3
FB4
FB5
ISET
GND
RSET
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.
LCD
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
ADM8845
Vcc
2.6V - 5.5V
60mA
CTRL1
FB1
CTRL2
FB2
60mA
FB3
FB4
VOUT
ADM8845
FB5
CTRL1
FB1
CTRL2
FB2
FB3
FB4
Rset
4.72k
GND
FB6
FB5
GND
FB6
Figure 31. ADM8845 Driving three flash LEDs
Figure 29. ADM8845 Driving Five White LEDs
Rev. PrJ 06/04| Page 15 of 18
60mA
ADM8845
Preliminary Technical Data
DRIVING CAMERA LIGHT, MAIN AND SUB LEDS
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
VCC
C2
ADM8845
Charge Pump
1x/1.5x/2x mode
C4
C3
Camera
+
-
Osc
CTRL1
CTRL2
Vout
15mA/LED
Control
Logic
Sub
Main
15mA/LED
FB1
FB2
Vref
FB3
FB4
FB5
FB6
Iset
Rset
9.44kΩ
LED Current
Control
Circuit
15mA/LED
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
R
Current
Control
7
Preliminary Technical Data
ADM8845
ADM8845 POWER EFFICIENCY
The ADM8845 power efficiency (η) equations, are as follows:
η = POUT/PIN
IQ
VF
Gain
PIN = ((VCC * ILOAD * Gain) + (IQ * VCC))
POUT = 6*(VF * ILED)
: 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
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 = 6(VF * ILED)
POUT = 6(3.6V * 20mA)
POUT = 0.432
η = POUT/PIN
η = POUT/PIN
η = 0.54/0.62084
η = 0.432/0.62084
η = 87 %
η = 70 %
Rev. PrJ 06/04| Page 17 of 18
ADM8845
Preliminary Technical Data
OUTLINE DIMENSIONS
=
16-Lead Lead Frame Chip Scale Package [LFCSP]
3 x 3 mm Body
(CP-16-4)
Dimensions shown in millimeters
3.00
BSC SQ
0.60 MAX
0.45
PIN 1
INDICATOR
13
12
2.75
BSC SQ
TOP
VIEW
0.80 MAX
0.65 TYP
128MAX
0.90
0.85
0.80
16
1
BOTTOM
VIEW
0.50
BSC
SEATING
PLANE
0.50
0.40
0.30
9
8
5
PIN 1 INDICATOR
1.65
1.50 SQ*
1.35
4
0.25 MIN
1.50 REF
0.05 MAX
0.02 NOM
0.30
0.23
0.18
0.20 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
Temperature Range
-40ºC to + 85ºC
-40ºC to + 85ºC
-40ºC to + 85ºC
-40ºC to + 85ºC
Package Description
16-Lead LFCSP
16-Lead LFCSP
16-Lead LFCSP
16-Lead LFCSP
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.
PR04867-0-6/04(PrJ)
Rev. PrJ 06/04 | Page 18 of 18
Package Option
CP-16
CP-16
CP-16
CP-16