ADM8845/6
REV. PrE 06/03
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reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
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Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703 Analog Devices, Inc., 2003
Charge Pump Driver for LCD
LED Backlights
Preliminary Technical Data
PRELIMINARY TECHNICAL DA TA
a
FEATURES
ADM8845 drives 6 White LEDs from a 2.6 V to 5.5 V (li-ion)
input supply
ADM8846 drives 5 White 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% LED Current Matching
Low power shutdown mode
Package footprint only 9mm2 (3mm x 3mm)
Package height only 0.9mm
Shutdown Function
Soft-start limiting inrush current
APPLICATIONS
White LED Backlighting
Micro TFT color displays
Mobile phones
DSC
PDA’s
GENERAL DESCRIPTION
The ADM8845 provides the power required to drive up to 6
white LEDs, using charge pump technology. The ADM8846
provides the power required to drive up to 5 white LEDs,
using charge pump technology. The LEDs are used for
backlighting a color LCD display. 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 correct output levels at a high 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% and LED to
ISET maximum matching of 1%.
The ADM8845/6 provides two digital input control pins,
CTRL1 and CTRL2. Which control the operation and the
brightness of the LEDs.
The ADM8845 is configured with a main and a sub display
options, the main display refers to 4 of the 6 LEDs (FB1 -
FB4) and the sub display refers to the remaining 2 LEDs
(FB5 - FB6), refer to Figure 2.
The ADM8845 provides the option to control the brightness
of the LEDs with a Digital PWM signal. The duty cycle of
the PWM signal determines the brightness of the backlight
LEDs.
Figure 1. ADM8845 FUNCTIONAL BLOCK DIAGRAM
The ADM8846 controls the operation and brightness of all
5 LEDs together. The ADM8846 provides 3 built-in
brightness levels for brightness control of the 6 LEDs.
The ADM8845/6 also allows the brightness of the LEDs to
be controlled using a DC volatage, refer to page 8, Figure
10.
The ADM8845/6 also has soft-start circuitry to limit inrush
current flow at power up.
The ADM8845/6 is fabricated using CMOS technology for
minimal power consumption. The part is packaged in a 16-
pin LFCSP package.
C2+
C2-
1␮F
C1+
C1-
1␮F
Charge Pump
1x/1.5x/2x mode
Control
Logic
VCC
C4+
C4-
C4
4.7␮F
Osc
Vref
+
-
LED Current
Control
Circuit
Current Controlled Sinks
Iset
GND
ADM8845
Vout
FB2
FB3
FB4
FB5
FB6
FB1
C3
C3+
C3-
C1 C2
Rset
Current
Control
1
Current
Control
2
Current
Control
3
Current
Control
4
Current
Control
5
Current
Control
6
2.2␮F
CTRL1
CTRL2
ADM8845/6
–2– REV. PrE 06/03
PRELIMINARY TECHNICAL DA TA
Figure 2. ADM8845 FUNCTIONAL BLOCK DIAGRAM
C2+
C2-
1␮F
C1+
C1-
1␮F
Charge Pump
1x/1.5x/2x mode
Control
Logic
Osc
Vref
+
-
LED Current
Control
Circuit
Current Controlled Sinks
Iset
GND
ADM8845
Vout
FB2
FB3
FB4
FB5
FB6
FB1
C3
C3+
C3-
C1 C2
Rset
Current
Control
1
Current
Control
2
Current
Control
3
Current
Control
4
Current
Control
5
Current
Control
6
2.2␮F
CTRL1
CTRL2
main sub
VCC
C4+
C4-
C4
4.7␮F
C2+
C2-
1␮F
C1+
C1-
1␮F
Charge Pump
1x/1.5x/2x mode
Control
Logic
Osc
Vref
+
-
LED Current
Control
Circuit
Current Controlled Sinks
Iset
GND
ADM8846
Vout
FB2
FB3
FB4
FB5
NC
FB1
C3
C3+
C3-
C1 C2
Rset
Current
Control
1
Current
Control
2
Current
Control
3
Current
Control
4
Current
Control
5
2.2␮F
CTRL1
CTRL2
VCC
C4+
C4-
C4
4.7␮F
Figure 2. ADM8846 FUNCTIONAL BLOCK DIAGRAM
–3–REV. PrE 06 /03
ADM8845/6 - SPECIFICATIONS
PRELIMINARY TECHNICAL DA TA
(VCC =2.6V to 5.5V, TA=-40°C to +85°C unless otherwise noted )
C1,C2 = 1.0␮␮
␮␮
␮F; C3 = 2.2␮␮
␮␮
␮F;
PARAMETER Min Typ Max Units Test Conditions
Input Voltage,V
CC
2.6 5.5 V
Supply Current,I
CC
2.6 mA All 6 LEDs Disconnected,
Vcc = 3.3V, R
SET
= 7.08kOhm
ADM8845: CTRL1 = 1, CRTL2 = 1,
ADM8846: CTRL1 = 0, CRTL2 = 1.
Shutdown Current 5 uA
Charge-Pump Frequency 1.5 MHz
Charge Pump Mode Thresholds
1.5x to 2x 3.33 V
Accuracy 4 %
2x to 1.5x 3.36 V
Accuracy 4 %
Hysteresis 30 mV
1x to 1.5x 4.77 V
Accuracy 4 %
1.5x to 1x 4.81 V
Accuracy 4 %
Hysteresis 40 mV
Iset Pin
LED : LED Accuracy 1 % I
LED
= 20mA, V
FB
=0.4V
LED : I
SET
Accuracy 1 % I
LED
= 20mA, V
FB
=0.4V
Iset pin voltage 1.18 V
I
LED
to I
SET
Ratio 120
Min Compliance on FB pin 0.2 0.3 V Iset = 20mA
Charge Pump Output Resistance 2.5 Ohm’s 1.5x Mode
6 Ohm’s 2x Mode
LED Current 30 mA
PWM 0.1 200 KHz
Digital Inputs
Input Hi 0.7Vcc V
Input Low 0.3Vcc V
Input Leakage Current 1 uA
Charge Pump Power Efficiency 75 % ADM8845: CTRL1 = 1, CRTL2 = 1,
ADM8846: CTRL1 = 0, CRTL2 = 1,
Vcc = 3.3V,
Iload = 120mA
Vf
LED
= 3.8V
Vout Ripple 30 mV I
LED
= 20mA
* Specifications are target values and are subject to change without notice.
THERMAL CHARACTERISTICS
16-Lead LFCSP Package:
⍜
JA
= 50°C/Watt
Note: If I
LED
= 30mA per LED and all 6 LEDs are being
used, then T
A
= -40°C to 70°C
ADM8845/6
–4– REV. PrE 06/03
PRELIMINARY TECHNICAL DA TA
PIN FUNCTION DESCRIPTION
Pin Mnemonic Function
ADM8845 ADM8846
1 4 VOUT Charge Pump Output. A 2.2µF capacitor to ground is required on
this pin.
2 2 C2+ Flying Capacitor 2 Positive Connection
33 I
SET
Bias current set input. The current flowing through the R
SET
resistor
I
SET
is gained up by 120 to give the I
LED
curent. Connect a resistor
R
SET
to GND to set the bias current as V
SET
/R
SET
. (Note: Vset =
1.18V)
4 5 FB1 LED1 Cathode connection and Charge Pump Feedback. The current
flowing in LED1 is 120 times the current flowing through R
SET
, I
SET
.
5 6 FB2 LED2 Cathode connection and Charge Pump Feedback. The current
flowing in LED2 is 120 times the current flowing through R
SET
, I
SET
.
When using fewer than six LEDs this pin can be left unconnected.
6 7 FB3 LED3 Cathode connection and Charge Pump Feedback. The current
flowing in LED3 is 120 times the current flowing through R
SET
, I
SET
.
When using fewer than six LEDs this pin can be left unconnected.
7 8 FB4 LED4 Cathode connection and Charge Pump Feedback. The current
flowing in LED4 is 120 times the current flowing through R
SET
,
I
SET
. When using fewer than six LEDs this pin can be left
unconnected.
8 9 FB5 LED5 Cathode connection and Charge Pump Feedback. The current
flowing in LED5 is 120 times the current flowing through R
SET
, I
SET
.
When using fewer than six LEDs this pin can be left unconnected.
9 11 FB6/NC LED6 Cathode connection and Charge Pump Feedback. The current
flowing in LED6 is 120 times the current flowing through R
SET
, I
SET
.
When using fewer than six LEDs this pin can be left unconnected.
This Pin is No Conect in the ADM8846.
10 10 GN D Device Ground Pin.
11 1 C2- Flying Capacitor 2 Negative Connection.
12 12 CTRL2 Digital Input. 3 V CMOS Logic. Used with CTRL1 to control the
operation of the LEDs.
13 13 CTRL1 Digital Input. 3 V CMOS Logic. Used with CTRL2 to control the
operation of the LEDs.
14 14 C1- Flying Capacitor 1 Negative Connection.
15 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 16 C1+ Flying Capacitor 1 Positive Connection.
Figure 3. ADM8845 PIN CONFIGURATION Figure 4. ADM8846 PIN CONFIGURATION
10
11
12
9
1
2
3
4
5
6
78
13
14
15
ADM8845
TOP VIEW
(NOT TO SCALE)
16
VCC
VOUT
GND
FB6
FB5
FB4
FB3
FB2
CTRL1
CTRL2
ISET
FB1
C1+
C1-
C2+ C2-
10
11
12
9
1
2
3
4
5
6
78
13
14
15
ADM8846
TOP VIEW
(NOT TO SCALE)
16
VCC
C2-
GND
FB5
FB4
FB3
FB2
FB1
CTRL1
CTRL2
ISET
VOUT
C1+
C1-
C2+ NC
ADM8845/6
–5–REV. PrE 06/03
PRELIMINARY TECHNICAL DA TA
ADM8845 LED BRIGHTNESS CONTROL WITH A
DIGITAL PWM SIGNAL
PWM brightness control provides the widest brightness
control by pulsing the LEDs on and off using the digital input
control pins, CTRL1 and CTRL2. The LEDs operate at
either zero or full current (set by the R
SET
resistor). The PWM
signal turns the current control sinks on and off. The average
current through the LEDs changes with the PWM signal duty
cycle.
Figure 4. ADM8845 Digital PWM Brightness Control Application Diagram
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 R
SET
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 allows the ADM8845 to determine
if a PWM signal is present on CTRL1 and CTRL2 or if the
user has selected a full chip shutdown.
The minimum frequency of the PWM signal is 100Hz, if a
PWM signal of frequency of less than 100Hz is used the part
shuts down. The PWM signal is applied to digital input pins,
CTRL1 and/or CTRL2. If digital PWM brightness control
of the LEDs is not required then a constant logic level 1 or
0 must be applied, refer to Page 6,
Figure 7. ADM8845
Digital Inputs Truth Table and also Page 5 Figure 4.
ADM8845 PWM Brightness Control Application Diagram.
By applying a PWM signal to the digital input control pins,
CTRL1 and/or CTRL2 you can adjust the brightness of the
sub and main displays. The ADM8845 six LEDs are organised
into 2 groups, Main Display (FB1-FB4) and Sub Display
(FB4 - FB6), refer to Figure 2, Page 2.
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 PWM 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 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 R
SET
resistor).
Vout
FB1
CTRL1
CTRL2
Voltage
Regulator
Current Control 1
Current Control 2
ADM8845/6
ILED
Figure 5. ADM8845/6 Current Control Sinks
ADM8845
CTRL1
CTRL1
Vout
FB2
FB3
FB4
FB5
FB6
FB1
C3
C3+
C3-
2.2␮F
Iset
Rset
C1
1␮F
C2
1␮F
PWM Input
or
High/Low
PWM Input
or
High/Low
ADM8845/6
–6– REV. PrE 06/03
PRELIMINARY TECHNICAL DA TA
Figure 6. ADM8845 Application Timing
Becuase the ADM8845 has its 6 LEDs arranged into 2
gropus, sub and main. It is possible to configure the 6 LEDs
as in Figure 7. ADM8845 Digital Inputs Truth Table, refer
also to Figure 6. ADM8845 Application Timing.
Note 1: Sub Display on means the display is on with the
maximum brightness set by the R
SET
resistor. CTRL1 = 1
means a constant logic level (Vcc) is applied to CTRL1.
Note 2: Sub Display off means the sub display only is off.
CTRL1 = 0 means a constant logic level (Gnd) is applied to
CTRL1.
Note 3: Main Display on means the display is on with the
maximum brightness set by the R
SET
resistor. CTRL2 = 1
means a constant logic level (Vcc) is applied to CTRL2.
Note 4: Main Display off means the main display only is off.
CTRL2 = 0 means a constant logic level (Gnd) is applied to
CTRL2.
Note 5: PWM means a Digital PWM signal is applied to the
CTRL pin with a frequency from 100Hz to 200kHz.
Figure 7. ADM8845 Digital Inputs Truth Table
CTRL1
CTRL2
tcp
Vout
37mS > tcp > 15mS
ILED
(sub)
ILED
(main)
Full On sub + main 50% D.C.
LED Config.
ILED (sub)
(Brightness)
main + sub Off main 80% D.C., sub off
ILED (main)
(Brightness)
CTRL1 CTRL2 LED Operation Notes
0 0 Sub Display Off / Main Display Off (Full SHDN) 1,4
0 1 Sub Display Off / Main Display On 1,3
1 0 Sub Display On / Main Display Off 1,4
1 1 Sub Display On / Main Display On (Full On) 1,3
0 PWM Sub Display Off / Digital PWM Brightness Control On Main Display 2,5
PWM 0 Digital PWM Control On Sub Display / Main Display Off 5,4
1 PWM Sub Display On / Digital PWM Brightness Control On Main Display 1,5
PWM 1 Digital PWM Brightness Control On Sub Display / Main Display On 5,3
PWM PWM Digital PWM Brightness Control On Sub Display and Main Display 5,5
ADM8845/6
–7–REV. PrE 06/03
PRELIMINARY TECHNICAL DA TA
AUTOMATIC GAIN CONTROL
The Automatic Gain Control block controls the operation of
the Charge Pump, by selecting the apporipate Gain for the
Charge Pump to maintain the correct outputs at a high power
efficiency. The Charge Pump Switching thresholds are:
From 1.5x to 2x : 3.33V
From 2x to 1.5x : 3.36V
From 1x to 1.5x : 4.77V
From 1.5x to 1x : 4.81V
Refer to ADM8845/6 Specification Page 3 for more details.
Figure 8. ADM8846 Digital Inputs Truth Table
ADM8846 THREE LEVELS OF BRIGHTNESS CONTROL
WITH CTRL1 AND CTRL2 PINS
The ADM8846 only allows all 5 LEDs brightness to be
controlled together. The ADM8846 has 3 levels of brightness.
By applying a constant logic CTRL1 = 0 and CTRL2 = 0 to
the digital control pins the 5 LEDs are turned off (Full
SHDN).
Applying a constant logic CTRL1 = 0 and CTRL2 = 1 to the
digital control pins all 5 LEDs are set to maximum brightness
(set by the R
SET
resistor).
A constant logic CTRL1 = 1 and CTRL2 = 0 on digital
control pins sets all 5 LEDs to one-third (1/3) the maximum
brightness.
A constant logic CTRL1 = 1 and CTRL2 = 1 on digital
control pins sets all 5 LEDs to two-thirds (2/3) the maximum
brightness.
Refer to Page 6,
Figure 8. ADM8846 Digital Inputs Truth
Table.
Figure 9. ADM8845/6 PWM Brightness Control Using
Filtered-PWM Signal
100% = ILED = 0mA
0% = ILED = 20mA
ADM8845/6
ISET
VPWM
C5 = 1µF
R = 7.5K
R = 7.5K
RSET = 13.4K
0V - 2.5V
ILED = ISET_Voltage * 120 * (1 - Duty Cycle)
RSET * 2R 100
RSET + 2R
ADM8845/6 LED BRIGHTNESS CONTROL USING A
PWM SIGNAL APPLIED TO V
PWM
By adding 2 external resistors and a capacitor as shown on
figure 9, this configuration can also be used to achieve PWM
brightness control. This PWM brightness control can be used
instead of CTRL1 and/or CTRL2 PWM brightness control.
With this configuration CTRL1 and CTRL2 digital logic
pins can be used to control the LEDs operation while VPWM
can be used to control the brightness of the LEDs. By applying
a high-frequency PWM signal (0V to 2.5V) to drive an R-C-
R filter on the ISET pin of the ADM8845/6 (See Figure 4).
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
9. ADM8845/6 PWM Brightness Control Using Filtered-
PWM Signal. The amplitude of the PWM signal must be
0 V and 2.5 V only, inorder to have 20mA flowing in each
LED.
CTRL1 CTRL2 LED Operation
0 0 Full SHDN (All 6 LEDs)
0 1 Max Brightness (1/1)
1 0 One-Third Brightness (1/3)
1 1 Two-Thirds Brightness (2/3)
ADM8846 Digital Input Control Pins
ADM8845/6
–8– REV. PrE 06/03
PRELIMINARY TECHNICAL DA TA
ADM8845/6 LED BRIGHTNESS CONTROL USING A DC
VOLTAGE APPLIED TO V
BRIGHT
By adding 1 resistor as shown in figure 10 , this configuration
can also be used to achieve brightness control of the LEDs.
Figure 11 shows an application example of LED Brightness
control using a DC Voltage applied to V
BRIGHT.
Figure 11. ADM8845/6 PWM Brightness Control Application
Diagram Using a DC Voltage applied to V
BRIGHT
ADM8845/6
ISET
VBRIGHT
R = 15K
RSET = 13.4K
0V - 2.5V
The equation for I
LED
is:
ISET = (1/RSET + 1/R)(VSET ) - (1/R)(VBRIGHT)
ILED = 120*Iset
Where R = 15k Ohm, V
SET
= voltage at Iset pin (1.18V)
Figure 10. ADM8845/6 PWM Brightness Control Using
a DC Voltage applied to V
BRIGHT
VBRIGHT
ILED
2.5V
1.6V
0.8V
0V
0mA
7.2mA
13.6mA
20mA
ADM8845/6
–9–REV. PrE 06/03
PRELIMINARY TECHNICAL DA TA
16-Lead 3mm x 3mm Chip Scale Package
(CP-16)
OUTLINE DIMENSIONS
Dimensions Shown in mm.
1
16
4
5
9
13
12
BOTTOM
VIEW
8
1.45
1.30 SQ
1.15
0.60
0.42
0.24
0.60
0.42
0.24
0.50)
0.40)
0.30)
0.30)
0.23)
0.18)
1.50
REF
0.010 (0.25)
MIN
0.5
BSC
12
o
MAX
0.20
REF
0.05
0.01
0.90 MAX
0.85 NOM
SEATING
PLANE
CONTROLLING DIMENSIONS ARE IN MILLIMETERS
PIN 1
INDICATOR
TOP
VIEW
3.0
BSC SQ
(3.0)
BSC SQ
0.00
0.80 MAX
0.65 NOM