Charge Pump Driver for LCD
White LED Backlights
ADM8845
Data Sheet
FEATURES
GENERAL DESCRIPTION
Drives 6 LEDs from 2.6 V to 5.5 V (Li-Ion) input supply
1×/1.5×/2× fractional charge pump to maximize power
efficiency
1% maximum LED current matching
Up to 88% power efficiency over Li-Ion range
Powers main and sub display LEDs with individual shutdown
Package footprint only 9 mm2 (3 mm × 3 mm)
Package height only 0.75 mm
Low power shutdown mode
Shutdown function
Soft-start limiting in-rush current
The ADM8845 uses charge pump technology to provide the
power required to drive up to six LEDs. The LEDs are used for
backlighting a color LCD display, having regulated constant
current for uniform brightness intensity. The main display can
have up to four LEDs, and the sub display can have one or two
LEDs. The digital CTRL1 and CTRL2 input control pins control
the shutdown operation and the brightness of the main and sub
displays.
To maximize power efficiency, the charge pump can operate in
a 1×, 1.5×, or 2× mode. The charge pump automatically
switches between 1×/1.5×/2× modes, based on the input voltage,
to maintain sufficient drive for the LED anodes at the highest
power efficiency.
APPLICATIONS
Cellular phones with main and sub displays
White LED backlighting
Camera flash/strobes and movie lights
Micro TFT color displays
DSC
PDAs
Improved brightness matching of the LEDs is achieved by a
feedback pin to sense individual LED current with a maximum
matching accuracy of 1%.
FUNCTIONAL BLOCK DIAGRAM
C1
1F
VCC
C2
1F
ADM8845
VOUT
CHARGE PUMP
1/1.5/2 MODE
C4
4.7F
C3
2.2F
MAIN
SUB
OSC
CTRL1
CTRL2
CONTROL
LOGIC
VREF
04867-0-001
CURRENT
CONTROL 6
CURRENT
CONTROL 5
CURRENT
CONTROL 4
CURRENT
CONTROL 3
RSET
LED
CURRENT
CONTROL
CIRCUIT
CURRENT
CONTROL 2
ISET
CURRENT
CONTROL 1
FB1
FB2
FB3
FB4
FB5
FB6
CURRENT CONTROLLED SINKS
GND
Figure 1.
Rev. D
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ADM8845
Data Sheet
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications ....................................................................................... 1
General Description ......................................................................... 1
Functional Block Diagram .............................................................. 1
Revision History ............................................................................... 2
Specifications..................................................................................... 3
Absolute Maximum Ratings............................................................ 4
Thermal Resistance ...................................................................... 4
ESD Caution .................................................................................. 4
Pin Configuration and Function Descriptions ............................. 5
Typical Performance Characteristics ............................................. 6
Theory of Operation ...................................................................... 10
Output Current Capability ........................................................ 11
Automatic Gain Control ............................................................ 11
LED Brightness Control Using a PWM Signal Applied to
VPWM ............................................................................................. 13
LED Brightness Control Using a DC Voltage Applied to
VBRIGHT .......................................................................................... 13
Applications Information .............................................................. 14
Layout Considerations and Noise ............................................ 14
White LED Shorting .................................................................. 14
Driving Fewer than Six LEDs ................................................... 14
Driving Flash LEDs .................................................................... 15
Driving Camera Light, Main, and Sub LEDs.......................... 15
Driving Four Backlight White LEDs and Flash LEDs ........... 16
Power Efficiency ......................................................................... 17
Outline Dimensions ....................................................................... 18
Ordering Guide .......................................................................... 18
Current Matching ....................................................................... 11
Brightness Control with a Digital PWM Signal ..................... 11
REVISION HISTORY
5/2018—Rev. C to Rev. D
Changes to Features Section............................................................ 1
Add Thermal Resistance Section .................................................... 4
Changes to Figure 2 .......................................................................... 5
Updated Outline Dimensions ....................................................... 18
Changes to Ordering Guide .......................................................... 18
Changes to Figure 16 to Figure 19...................................................8
Changes to Brightness Control with a Digital PWM Signal
Section.............................................................................................. 11
Added Exposed Pad Notation to Outline Dimensions ............. 18
Changes to Ordering Guide .......................................................... 18
1/2011—Rev. B to Rev. C
Changes to Figure 18 and Figure 19 ............................................... 8
Changes to Ordering Guide .......................................................... 18
7/2005—Rev. 0 to Rev. A
Changes to Table 3.............................................................................5
Changes to Table 7.......................................................................... 12
Updated Outline Dimensions ....................................................... 18
Changes to Ordering Guide .......................................................... 18
4/2010—Rev. A to Rev. B
Changes to Figure 2 .......................................................................... 5
Changes to Figure 4 .......................................................................... 6
10/2004—Revision 0: Initial Version
Rev. D | Page 2 of 18
Data Sheet
ADM8845
SPECIFICATIONS
VCC = 2.6 V to 5.5 V, TA = −40°C to +85°C, unless otherwise noted. C1, C2 = 1.0 µF, C3 = 2.2 µF, and C4 = 4.7 µF.
Table 1.
Parameter
INPUT VOLTAGE, VCC
SUPPLY CURRENT, ICC
SHUTDOWN CURRENT
CHARGE PUMP FREQUENCY
CHARGE PUMP MODE THRESHOLDS
1.5× to 2×
Accuracy
2× to 1.5×
Accuracy
Hysteresis
1× to 1.5×
Accuracy
1.5× to 1×
Accuracy
Hysteresis
ISET PIN
LED
LED Matching
ISET Accuracy
ISET Pin Voltage
ILED to ISET Ratio
MIN COMPLIANCE ON FBx PIN
Charge Pump Output Resistance
LED Current
PWM
DIGITAL INPUTS
Input High
Input Low
Input Leakage Current
CHARGE PUMP POWER EFFICIENCY
VOUT RIPPLE
Min
2.6
Typ
2.6
Max
5.5
5
Unit
V
mA
5
µA
MHz
1.5
3.33
3.36
4
40
4.77
4
4.81
4
40
1.18
120
0.2
1.2
3.5
8.0
0.1
+1
+1
%
%
V
ILED = 20 mA, VFB =0.4 V
ILED = 20 mA, RSET = 7.08 kΩ, VFB = 0.4 V, VCC = 3.6 V, TA = 25°C
0.3
1.8
5.1
14
30
200
V
Ω
Ω
Ω
mA
kHz
ISET = 20 mA
1× mode
1.5× mode
2× mode
Guaranteed by design. Not 100% production tested. See Figure 21.
0.5 VCC
0.3 VCC
1
88
30
All six LEDs disabled, VCC = 3.3 V, RSET = 7.08 kΩ, CTRL1 = 1, CRTL2 =
1
V
%
V
%
mV
V
%
V
%
mV
4
−1
−1
Test Conditions
V
V
µA
%
mV
CTRL1 = 1, CRTL2 = 1, VCC = 3.4 V, VFB = 0.2 V, IFB = 20 mA
VCC = 3.6 V, ILED = 20 mA, all six LEDs enabled
Rev. D | Page 3 of 18
ADM8845
Data Sheet
ABSOLUTE MAXIMUM RATINGS
TA = 25°C, unless otherwise noted.
Table 2.
Parameter
Supply Voltage, VCC
ISET
CTRL1, CTRL2
VOUT Shorted 1
Feedback Pins FB1 to FB6
Operating Temperature Range
Six LEDs Enabled with 30 mA/LED 2
Six LEDs Enabled with 20 mA/LED2
VOUT 3
Storage Temperature Range
Power Dissipation
Electrostatic Discharge (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 +65°C
−40°C to +85°C
180 mA
−65°C to +125°C
2 mW
1
Stresses at or above those listed under Absolute Maximum
Ratings may cause permanent damage to the product. This is a
stress rating only; functional operation of the product at these
or any other conditions above those indicated in the operational
section of this specification is not implied. Operation beyond
the maximum operating conditions for extended periods may
affect product reliability.
THERMAL RESISTANCE
Thermal resistance values specified in Table 3 are simulated
based on JEDEC specifications, unless specified otherwise, and
must be used in compliance with JESD51-12.
Table 3. Thermal Resistance
Package Type
CP-16-222
1
Short through LED.
2
LED current should be derated above TA > 65°C, refer to Figure 21.
3
Based on long-term current density limitations.
1
2
θJA
39.25
θJC1
7.5
θJB
17.4
ΨJT
0.8
ΨJB
12.4
Unit
°C/W
For θJC, 100 µm thermal interface material is used. Thermal interface material
is assumed to have 3.6 W/mK.
Using enhanced heat removal (printed circuit board (PCB), heat sink, and
airflow) techniques improves thermal resistance values.
ESD CAUTION
Rev. D | Page 4 of 18
Data Sheet
ADM8845
13 CTRL1
14 C1–
16 C1+
15 VCC
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
12 CTRL2
VOUT 1
C2+ 2
ADM8845
11 C2–
ISET 3
TOP VIEW
(Not to Scale)
10 GND
9
FB6
NOTES
1. CONNECT EXPOSED PADDLE TO GND.
04867-0-003
FB5 8
FB4 7
FB3 6
FB2 5
FB1 4
Figure 2. Pin Configuration
Table 4. Pin Function Descriptions
Pin No.
1
Mnemonic
VOUT
2
3
C2+
ISET
4 to 9
FB1 to FB6
10
11
12
13
14
15
16
GND
C2−
CTRL2
CTRL1
C1−
VCC
C1+
EP
Function
Charge Pump Output. A 2.2 μF 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, ISET, flowing through the resistor, RSET, is gained up by 120 to give the ILED
current. Connect RSET to GND to set the bias current as VSET/RSET. Note that VSET = 1.18 V.
LED1 to LED6 Cathode Connection and Charge Pump Feedback. The current, ISET, flowing in these LEDs is 120 times
the current flowing through resistor, RSET. When using fewer than six LEDs, this pin can be left unconnected or
connected to GND.
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 4.7 μF decoupling capacitor.
Flying Capacitor 1 Positive Connection.
Exposed Paddle. Connect the exposed paddle to GND.
Rev. D | Page 5 of 18
ADM8845
Data Sheet
TYPICAL PERFORMANCE CHARACTERISTICS
35
0.4
0.3
30
MAX POSITIVE MATCHING ERROR
25
20
15
0.1
0
–0.1
–0.2
10
MAX NEGATIVE MATCHING ERROR
5
4.75
10.75
8.75
RSET (k)
6.75
12.75
14.75
04867-0-004
–0.3
–0.4
2.6
5.0
5.4
20.22
20.30
–40C
20.20
20.25
LED CURRENT (mA)
20.20
25C
20.15
85C
20.10
20.18
20.16
20.14
20.12
20.05
3.1
4.1
3.6
4.6
SUPPLY VOLTAGE (V)
5.1
5.6
20.08
–40
Figure 4. LED Current vs. Supply Voltage Over Various Temperatures,
Six LEDs Enabled
0
40
TEMPERATURE (C)
80
04867-0-008
20.00
2.6
04867-0-005
20.10
Figure 7. LED Current Variation over Temperature, VCC = 3.6 V
35
0.2
30
LED CURRENT (mA)
0.3
0.1
0
–0.1
–0.2
25
20
15
–40
–20
25
0
45
TEMPERATURE (C)
65
85
04867-0-006
10
Figure 5. LED Current Matching over Temperature, VCC = 3.6 V, ILED = 20 mA,
Six LEDs Enabled
Rev. D | Page 6 of 18
5
2.6
3.0
3.4
4.2
4.6
3.8
SUPPLY VOLTAGE (V)
5.0
Figure 8. Lead Current vs. Supply Voltage
5.4
04867-0-009
LED CURRENT (mA)
3.8
4.2
4.6
SUPPLY VOLTAGE (V)
20.24
20.35
% ERROR
3.4
Figure 6. ILED Matching Error vs. Supply Voltage,
TA = 25°C and ILED = 20 mA
Figure 3. LED Current vs. RSET
–0.3
3.0
04867-0-007
MATCHING ERROR (%)
LED CURRENT (mA)
0.2
Data Sheet
ADM8845
95
20
90
85
EFFICIENCY (%)
LED CURRENT (mA)
16
12
8
80
75
70
4
0
20
40
60
DUTY CYCLE (%)
80
100
60
Figure 9. LED Current vs. PWM Dimming (Varying Duty Cycle),
Six LEDs Enabled, Frequency = 1 kHz
0
10
20
30
40
50
60
DUTY CYCLE (%)
70
80
90
100
04867-0-013
0
04867-0-010
65
Figure 12. LED Efficiency vs. Varying Duty Cycle of 1 kHz PWM Signal,
Six LEDs Enabled, 20 mA/LED
300
CTRL1/2
200
20mA/LED
1
CURRENT
150
15mA/LED
2
100
VOUT
50
3.0
3.4
3.8
4.2
4.6
SUPPLY VOLTAGE (V)
5.0
5.4
3
04867-0-011
0
2.6
Figure 10. Supply Current ICC vs. Supply Voltage,
Six LEDs Enabled
CH1 2.00V
CH3 1.00V
B
CH2 160mA
W
B
W
M 5.00s CH2
180mV
Figure 13. Soft Start Showing the Initial In-Rush Current and VOUT Variation,
Six LEDs at 20 mA/LED, VCC = 3.6 V
VCC 1
2
VCC
1
VOUT
2
CH1 20.0mV
B
W
CH2 20.0mV
B
W
M 400ns CH1
04867-0-015
04867-0-012
VOUT
04867-0-014
SUPPLY CURRENT ICC (mA)
250
220mV
CH1 20.0mV
Figure 11. 1.5× Mode Operating Waveforms
B
W
CH2 20.0mV
B
W
M 400ns CH1
Figure 14 .2× Mode Operating Waveform
Rev. D | Page 7 of 18
220mV
ADM8845
Data Sheet
90
VF = 3.8V
85
VF = 4.0V
1
2
70
65
60
55
VF = 3.6V
04867-0-016
50
CH1 20.0mV
B
W
CH2 20.0mV
B
W
M 400ns CH1
VF = 3.2V
45
40
2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2
220mV
VCC (V)
Figure 18. Power Efficiency vs. VCC over Li-Ion Range,
Six LEDS at 20 mA/LED
Figure 15. 1× Mode Operating Waveforms
90
90
VF = 3.8V
85
POWER EFFICIENCY (%)
70
65
60
VF = 3.6V
VF = 4.3V
75
70
65
60
55
VF = 3.6V
50
VF = 3.2V
VF = 3.2V
45
45
40
2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2
40
2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2
VCC (V)
04867-0-017
POWER EFFICIENCY (%)
VF = 4.0V
80
VF = 4.3V
75
50
VF = 3.8V
85
VF = 4.0V
80
55
04867-0-019
VOUT
VF = 4.3V
75
VCC (V)
04867-0-020
VCC
POWER EFFICIENCY (%)
80
Figure 19. Power Efficiency vs. VCC over Li-Ion Range
Four LEDS at 20 mA/LED
Figure 16. Power Efficiency vs. VCC over Li-Ion Range,
Six LEDS at 15 mA/LED
85
VF = 3.8V
80
VF = 4.0V
75
VF = 4.3V
C2 FALL
: 44.0ms
@: –44.4ms 200s
LOW SIGNAL
AMPLITUDE
CTRL1/2
1
70
65
VOUT
60
55
45
VF = 3.6V
VF = 3.2V
40
2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2
VCC (V)
2
Figure 17. Power Efficiency vs. VCC over Li-Ion Range,
Four LEDS at 15 mA/LED
04867-0-021
50
04867-0-018
POWER EFFICIENCY (%)
90
CH1 2.00V
CH2 2.00V
M10.0ms
Figure 20. TPC Delay
Rev. D | Page 8 of 18
CH2
4.36V
Data Sheet
ADM8845
30mA
65°C
85°C
04867-0-022
20mA
Figure 21. Maximum ILED vs. Ambient Temperature,
Six LEDs Connected
Rev. D | Page 9 of 18
ADM8845
Data Sheet
THEORY OF OPERATION
An external resistor, RSET, is connected between the ISET pin and
GND. This resistor sets up a reference current, ISET, which is
internally gained up by 120 within the ADM8845 to produce
the ILED currents of up to 30 mA/LED (ILED = ISET × 120 and
ISET = 1.18 V/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 charge pump driver for LCD white LED backlights implements a multiple gain charge pump (1×, 1.5×, 2×) to
maintain the correct voltage on the anodes of the LEDs over a
2.6 V to 5.5 V (Li-Ion) input supply voltage. The charge pump
automatically switches between 1×/1.5×/2× modes, based on
the input voltage, to maintain sufficient drive for the LED anodes,
with VCC input voltages as low as 2.6 V. It also includes regulation of the charge pump output voltage for supply voltages up to
5.5 V. The six LEDs of the ADM8845 are arranged into two
groups, main and sub. The main display can have up to four
LEDs, FB1 to FB4, and the sub display can have one or 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 5).
The ADM8845 lets the user 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 (see Figure 22). Softstart circuitry limits the in-rush current flow at power-up. The
ADM8845 is fabricated using CMOS technology for minimal
power consumption and is packaged in a 16-lead lead frame
chip scale package.
Table 5. Shutdown Truth Table
CTRL2
0
1
0
1
LED Shutdown Operation
Sub display off/main display off
Sub display off/main display on
Sub display on/main display off
Sub display on/main display on
ADM8845
ISET
R = 15k
RSET = 13.4k
04867-0-027
VBRIGHT
0V–2.5V
Figure 22. PWM Brightness Control Using a DC Voltage Applied to VBRIGHT
C1
1F
VCC
C2
1F
ADM8845
VOUT
CHARGE PUMP
1/1.5/2 MODE
C4
4.7F
C3
2.2F
MAIN
SUB
OSC
CTRL1
CTRL2
CONTROL
LOGIC
VREF
CURRENT CONTROLLED SINKS
GND
Figure 23. Functional Block Diagram
Rev. D | Page 10 of 18
04867-0-001
CURRENT
CONTROL 6
CURRENT
CONTROL 5
CURRENT
CONTROL 4
RSET
LED
CURRENT
CONTROL
CIRCUIT
CURRENT
CONTROL 3
ISET
CURRENT
CONTROL 2
FB1
FB2
FB3
FB4
FB5
FB6
CURRENT
CONTROL 1
CTRL1
0
0
1
1
Data Sheet
ADM8845
OUTPUT CURRENT CAPABILITY
CURRENT MATCHING
The ADM8845 can drive up to 30 mA of current to each of the
six LEDs given an input voltage of 2.6 V to 5.5 V. The LED
currents have a maximum current matching of 1% between any
two LED currents. An external resistor, RSET, sets the output
current, approximated by the following equation:
The 1% maximum current matching performance is defined by
the following equations:
VOUT − VF ≥ Compliance
where VF is the LED forward voltage. For 20 mA/LED, the
compliance is 0.20 V typical and 0.30 V maximum (see Table 6).
Table 6. ILED, RSET, and Compliance Table
Typical Compliance (V)
0.17
0.20
0.34
When the ADM8845 charge pump is loaded with 180 mA
(six LEDs at 30 mA/LED), the ambient operating temperature
is reduced (see Figure 21).
AUTOMATIC GAIN CONTROL
The automatic gain control block controls the operation of the
charge pump by selecting the appropriate gain for the charge
pump. This maintains sufficient drive for the LED anodes at
the highest power efficiency over a 2.6 V to 5.5 V input supply
range. The charge pump switching thresholds are described in
Table 7.
Table 7. Charge Pump Switching Thresholds
Gain
1.5× to 2×
2× to 1.5×
1× to 1.5×
1.5× to 1×
Threshold (V)
3.33
3.36
4.77
4.81
Minimum Matching Error = [(IMIN − IAVG)/IAVG] × 100
where:
IMAX is the largest ILED current.
IMIN is the smallest ILED current.
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, because the LEDs operate
either at zero current or full current (set by RSET).
The digital PWM signal applied with a frequency of 100 Hz to
200 kHz 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 100 Hz, flicker could be seen in the LEDs. For the
ADM8845, zero duty cycle turns off the LEDs, and a 50% duty
cycle results in an average LED current ILED being half the programmed LED current. For example, if RSET is set to program
20 mA/LED, a 50% duty cycle results in an average ILED of
10 mA/LED, ILED being half the programmed LED current.
C1
1F
C2
1F
VOUT
ADM8845
PWM INPUT
OR HIGH/LOW
CTRL1
PWM INPUT
OR HIGH/LOW
CTRL2
ISET
C3
2.2F
FB1
FB2
FB3
FB4
FB5
FB6
RSET
04867-0-024
To regulate the LED currents 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 to ensure that the desired current and
matching performance can be realized. To ensure that the
desired current is obtained, use the following equation to find
the minimum input voltage required:
RSET (kΩ)
9.44
7.08
4.72
Maximum Matching Error = [(IMAX − IAVG)/IAVG] × 100
or
RSET = 120 × (1.18 V/ILED)
ILED (mA)
15
20
30
IAVG = (IMAX + IMIN)/2
Figure 24. Digital PWM Brightness Control Application Diagram
By applying a digital PWM signal to the digital input control
pins, CTRL1 and/or CTRL2 can adjust the brightness of the sub
and/or main displays. The six white LEDs of the ADM8845 are
organized into two groups: main display, FB1 to FB4, and sub
display, FB5 and FB6. For more information, refer to the Theory
of Operation section.
Rev. D | Page 11 of 18
ADM8845
Data Sheet
The main and sub display brightness of the ADM8845 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. Varying the duty cycle of the
applied PWM signal also varies the brightness of the main and
sub displays from 0% to 100%.
duty cycle of the applied digital PWM signal. The brightness of
the main display is set to the maximum, which is set by RSET.
By holding CTRL1 low and applying a digital PWM signal to
CTRL2, the sub display is turned off and the main display is
turned on. The brightness of the main display is then determined
by the duty cycle of the applied digital PWM signal.
When CTRL1 and CTRL2 go low, the LED current control
sinks shutdown. Shutdown of the charge pump is delayed by
15 ms. 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).
By applying a digital PWM signal to CTRL1 and holding CTRL2
low, the sub display is turned on and the main display is turned
off. Then the brightness of the sub display is determined by the
duty cycle of the applied digital PWM signal.
By applying a digital PWM signal to CTRL1 and holding CTRL2
high, the sub display is turned on and the main display is turned
on. Then the brightness of the sub display is determined by the
By holding CTRL1 high and applying a digital PWM signal to
CTRL2, the sub display is turned on and the main display is
turned on. Then the brightness of the main display is determined
by the duty cycle of the applied digital PWM signal. The brightness of the sub display is set to the maximum, which is set by RSET.
If digital PWM brightness control of the LEDs is not required, a
constant logic level 1 (VCC) or 0 (GND) must be applied.
The six white LEDs in the ADM8845 are arranged in two groups,
sub and main. It is possible to configure the six LEDs as in
Table 8. For more information, also refer to Figure 25.
Table 8. Digital Inputs Truth Table
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) 1, 2
Sub display off/main display on1, 3
Sub display on/main display off 4, 2
Sub display on/main display on (full on)4, 3
Sub display off/digital PWM brightness control on main display1, 5
Digital PWM brightness control on sub display/main display off5, 2
Sub display on/ digital PWM brightness control on main display4, 5
Digital PWM brightness control on sub display/main display on5
Digital PWM brightness control on sub and main display5
Sub display off means the sub display LEDs only is off. CTRL1 = 0 means a constant logic level (GND) is applied to CTRL1.
Main display off means the main display only is off. CTRL2 = 0 means a constant logic level (GND) is applied to CTRL2.
Main display on means the display is on with the maximum brightness set by the RSET resistor. CTRL2 = 1 means a constant logic level (VCC) is applied to CTRL2.
4
Sub display 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.
5
PWM means a digital PWM signal is applied to the CTRL1 and/or the CTRL2 pin with a frequency from 100 Hz to 200 kHz.
1
2
3
Rev. D | Page 12 of 18
Data Sheet
ADM8845
LED CONFIG.
FULL ON
SUB AND MAIN 50%
DUTY CYCLE
MAIN AND SUB OFF
MAIN 80% DUTY CYCLE,
SUB OFF
tCP
CTRL1
CTRL2
VOUT
ILED
(SUB)
ILED
(MAIN)
100%
SUB DISPLAY
BRIGHTNESS
50%
SHDN
100%
MAIN DISPLAY
BRIGHTNESS
80%
50%
04867-0-025
SHDN
37ms > tCP > 15ms
Figure 25. Application Timing
LED BRIGHTNESS CONTROL USING A
PWM SIGNAL APPLIED TO VPWM
LED BRIGHTNESS CONTROL USING A
DC VOLTAGE APPLIED TO VBRIGHT
Adding two external resistors and a capacitor, as shown in
Figure 26, can also be used to control PWM brightness. This
PWM brightness control method can be used instead of CTRL1
and/or CTRL2 digital PWM brightness control. With this configuration, the 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 0 V to 2.5 V) to drive
an R-C-R filter on the ISET pin of the ADM8845. A 0% PWM
duty cycle corresponds to 20 mA/LED, while a 100% PWM
duty cycle corresponds to a 0 mA/LED. At PWM frequencies
above 5 kHz, C5 may be reduced (see Figure 26). To have 20 mA
flowing in each LED, the amplitude of the PWM signal must be
0 V and 2.5 V only.
By adding one resistor, as in Figure 22, this configuration can
control the brightness of the white LEDs using a dc voltage
applied to the VBRIGHT node. Figure 27 shows an application
example of LED brightness control using a dc voltage with a
amplitude of 0 V to 2.5 V, applied to VBRIGHT.
ISET = [(1/RSET + 1/R)(VSET)] − [(1/R)(VBRIGHT)]
ILED = 120 × ISET
where:
R = 15 kΩ.
VSET the voltage at ISET pin (1.18 V).
2.5V
VBRIGHT
1.6V
0.8V
0V
R SET 2R
20mA
13.6mA
100% = ILED = 0mA
0% = ILED = 20mA
ADM8845
7.2mA
ILED
0mA
ISET
Figure 27. PWM Brightness Control Application Diagram Using a
DC Voltage Applied to VBRIGHT
R = 7.5k R = 7.5k
C5 = 1F
RSET = 13.4k
04867-0-026
VPWM0V–2.5V
Figure 26. PWM Brightness Control Using Filtered PWM Signal
Rev. D | Page 13 of 18
04867-0-028
I LED
(1 Duty Cycle)
I
_ Voltage
SET
120
R SET 2R
100
The equation for ILED is
ADM8845
Data Sheet
APPLICATIONS INFORMATION
LCD
LAYOUT CONSIDERATIONS AND NOISE
Because of the s switching behavior of the ADM8845, PCB
trace layout is an important consideration. To ensure optimum
performance, a ground plane should be used, and all capacitors
(C1, C2, C3, C4) must be located with minimal track lengths to
the pins of the ADM8845.
WHITE LED SHORTING
VCC
2.6V–5.5V
VOUT
ADM8845
FB1
FB2
FB3
FB4
FB5
FB6
CTRL1
CTRL2
DRIVING FEWER THAN SIX LEDs
GND
The ADM8845 can be operated with fewer than six LEDs in
parallel by simply leaving the unused FBx pins floating or
connected to GND. For example, Figure 28 shows five LEDs
being powered by the ADM8845, and Figure 29 shows three
main LEDs and one sub LED.
04867-0-029
If an LED is shorted, the ADM8845 continues to drive the
remaining LEDs with ILED per LED (ILED = ISET × 120 mA). This
is because the ADM8845 uses six internal currents sinks to
produce the LED current. If an LED is shorted, the ADM8845
continues to sink (ISET × 120 mA) as programmed by RSET
through the shorted LED.
Figure 28. Driving Five White LEDs
MAIN DISPLAY
SUB DISPLAY
VCC
2.6V–5.5V
VOUT
ADM8845
ISET
GND
FB1
FB2
FB3
FB4
FB5
FB6
04867-0-030
CTRL1
CTRL2
RSET
Figure 29. Driving Three Main LEDs and One Sub LED
MAIN DISPLAY
SUB DISPLAY
VCC
2.6V–5.5V
VOUT
ADM8845
ISET
GND
FB1
FB2
FB3
FB4
FB5
FB6
04867-0-002
CTRL1
CTRL2
RSET
Figure 30. Typical Application Diagram
Rev. D | Page 14 of 18
Data Sheet
ADM8845
DRIVING FLASH LEDS
DRIVING CAMERA LIGHT, MAIN, AND SUB LEDs
The ADM8845 can be operated with any two FBx pins used in
parallel to double the combined LED current supplied by the
ADM8845. For example, if three flash LEDs need to be driven
with 60 mA/LED, the ADM8845 can be configured as in
Figure 31 (see also Figure 21).
The ADM8845 can be configured to power a camera light that
is composed of four white LEDs in parallel, along with the main
and sub display bundled into one package. FB1 to FB4 now
power the camera light, and FB5 and FB6 power the main
display. 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
15 mA/LED. Total load on the ADM8845 charge pump is
therefore 105 mA, and the maximum load on the ADM8845
charge pump is 180 mA (see Figure 21).
VCC
2.6V–5.5V
VOUT
ADM8845
GND
RSET
4.27k
60mA
60mA
60mA
FB1
FB2
FB3
FB4
FB5
FB6
04867-0-031
CTRL1
CTRL2
Figure 31. Driving Three Flash LEDs
C1
1F
VCC
C2
1F
ADM8845
VOUT
CHARGE PUMP
1/1.5/2 MODE
C4
4.7F
C3
2.2F
CAMERA
OSC
CTRL1
CTRL2
CONTROL
LOGIC
15mA/LED
15mA/LED
15mA/LED
R
04867-0-032
CURRENT CONTROLLED SINKS
CURRENT
CONTROL7
CURRENT
CONTROL 6
CURRENT
CONTROL 5
CURRENT
CONTROL 4
CURRENT
CONTROL 3
CURRENT
CONTROL 2
LED
CURRENT
CONTROL
CIRCUIT
CURRENT
CONTROL 1
ISET
SUB
VREF
FB1
FB2
FB3
FB4
FB5
FB6
RSET
9.44k
MAIN
GND
Figure 32. Driving Camera Light, Two Main LEDs, and One Sub LED
Rev. D | Page 15 of 18
ADM8845
Data Sheet
CTRL1 controls the flash on/off, and CTRL2 controls the backlight on/off and brightness control. Because the RSET resistor sets
the current that each of the six current control blocks can sink,
a PWM signal is used to change the current in the backlight
from 20 mA to 5 mA/LED. The CTRL2 duty cycle is 15/20 to
give 15 mA/backlight LED.
DRIVING FOUR BACKLIGHT WHITE LEDS AND
FLASH LEDS
The ADM8845 can be configured to power four backlight white
LEDs and a camera flash, bundled into one package. FB1 to FB4
power the backlight light, FB5 and FB6 power two of the flash
LEDs, while the third is powered by an external current mirror
to control the current flowing through the third flash LED (see
Figure 33). All the backlight white LEDs have 15 mA/LED, and
the flash current is 20 mA/LED. The total load on the
ADM8845 charge pump is 120 mA; the maximum load on
the ADM8845 charge pump is 180 mA (see Figure 21).
C1
1F
ADM8845
VOUT
CHARGE PUMP
1×/1.5×/2× MODE
C4
4.7F
C3
2.2F
OSC
CTRL1
CONTROL
LOGIC
15mA/LED
20mA/LED
R
CURRENT
CONTROL 7
CURRENT
CONTROL 6
CURRENT
CONTROL 5
CURRENT
CONTROL 4
CURRENT
CONTROL 3
CURRENT
CONTROL 2
LED
CURRENT
CONTROL
CIRCUIT
CURRENT
CONTROL 1
FB1
FB2
FB3
FB4
FB5
FB6
RSET
7.32k
FLASH
VREF
CTRL2
ISET
BACKLIGHT
CURRENT CONTROLLED SINKS
GND
Figure 33. Driving Four Backlight LEDs and Flash LED
Rev. D | Page 16 of 18
04867-0-034
VCC
C2
1F
Data Sheet
ADM8845
POWER EFFICIENCY
Example 1
The ADM8845 power efficiency (η) equations are the following:
The ADM8845 driving six white LEDs with a 20 mA/LED at
VCC = 3.4 V (1.5× mode) and LED VF = 4.5 V.
η = POUT/PIN
PIN = ((VCC × ILOAD × Gain) + (IQ × VCC))
POUT = 6 × (VF × ILED)
PIN = ((VCC × ILOAD × Gain) + (VCC × IQ))
PIN = ((3.4 × 120 mA × 1.5) + (3.4 × 2.6 mA))
PIN = ((0.612) + (0.00884))
PIN = 0.62084
where:
Gain is equal to the charge pump mode (1×, 1.5×, 2×).
IQ is the quiescent current of the ADM8845, 2.6 mA.
VF is the LED forward voltage.
3.4V I
IN
POUT = 6 × (VF × ILED)
POUT = 6 × (4.5 V × 20 mA)
POUT = 0.54
ILOAD
η = POUT/PIN
η = 0.54/0.62084
η = 87%
VOUT
VCC
ADM8845
VCC
Example 2
CTRL1
ISET
RSET
GND
FB1
FB2
FB3
FB4
FB5
FB6
The ADM8845 driving six white LEDs with a 20 mA/LED at
VCC = 3.4 (1.5× mode) and LED VF = 3.6 V.
04867-0-033
CTRL2
Figure 34. Charge Pump Power Efficiency Diagram
Example 1 and Example 2 show calculations of the ADM8845
power efficiency. See Figure 34 as well.
PIN = ((VCC × ILOAD × Gain) + (VCC × IQ))
PIN = ((3.4 × 120 mA × 1.5) + (3.4 × 2.6 mA))
PIN = ((0.612) + (0.00884))
PIN = 0.62084
POUT = 6 × (VF × ILED)
POUT = 6 × (3.6 V × 20 mA)
POUT = 0.432
η = POUT/PIN
η = 0.432/0.62084
η = 70%
Rev. D | Page 17 of 18
ADM8845
Data Sheet
OUTLINE DIMENSIONS
PIN 1
INDICATOR
DETAIL A
(JEDEC 95)
0.30
0.23
0.18
0.50
BSC
13
PIN 1
INDICATOR AREA OPTIONS
16
12
1
1.75
1.60 SQ
1.45
EXPOSED
PAD
9
TOP VIEW
0.80
0.75
0.70
SIDE VIEW
PKG-005138
SEATING
PLANE
0.50
0.40
0.30
(SEE DETAIL A)
4
8
5
BOTTOM VIEW
0.05 MAX
0.02 NOM
COPLANARITY
0.08
0.20 REF
0.20 MIN
FOR PROPER CONNECTION OF
THE EXPOSED PAD, REFER TO
THE PIN CONFIGURATION AND
FUNCTION DESCRIPTIONS
SECTION OF THIS DATA SHEET.
COMPLIANT TO JEDEC STANDARDS MO-220-WEED-6.
02-23-2017-E
3.10
3.00 SQ
2.90
Figure 35. 16-Lead Lead Frame Chip Scale Package [LFCSP]
3 mm × 3 mm Body and 0.75 mm Package Height
(CP-16-22)
Dimensions shown in millimeters
ORDERING GUIDE
Model1
ADM8845ACPZ-REEL7
ADM8845EB-EVALZ
1
Temperature Range
−40°C to + 85°C
Package Description
16-Lead Lead Frame Chip Scale Package [LFCSP]
Evaluation Board
Z = RoHS Compliant Part.
©2004–2018 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D04867-0-5/18(D)
Rev. D | Page 18 of 18
Package Option
CP-16-22
Marking Code
M5G
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