Datasheet ADM8846 Datasheet (Analog Devices)

Charge Pump Driver for LCD

Preliminary Technical Data

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 9mm
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

2

(3mm x 3mm)

FUNCTIONAL BLOCK DIAGRAM

C1 C2

White LED Backlights

ADM8846

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%.

VCC

Rset

C4

CTRL1
CTRL2

Iset

ADM8846

Control

Logic

LED Current
Control
Circuit

Charge Pump
1x/1.5x/2x mode

Osc

Vref

Current

Current

Control

Control

2

1

Current Controlled Sinks

Current
Control

GND

3

Figure 1. ADM8846 FUNCTIONAL BLOCK DIAGRAM

Rev. PrA_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.

+

-

Current
Control

Vout

C3

MAIN

FB1

FB2

FB3
FB4

FB5
FB6

Current

Current

Control

Control

5

4

6

SUB

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone]
Fax: [phone] © 2004 Analog Devices, Inc. All rights reserved.

www.analog.com

ADM8846 Preliminary Technical Data

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

REVISION HISTORY

REV. PrA 06/04

ADM8846 LED Brightness Control Using a PWM Signal
Applied to V

ADM8846 LED Brightness Control Using a DC Voltage
Applied to V

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

.......................................................................... 14

PWM

....................................................................... 14

BRIGHT

Rev. PrA 06/04 | Page 2 of 18

Preliminary Technical Data ADM8846

ADM8846—SPECIFICATIONS

(VCC = +2.6V TO 5.5V; T

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, R
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 % I
LED : I

Accuracy -1 +1 %

SET

Iset pin voltage 1.18 V
I

to I

LED

Ratio 120

SET

Min Compliance on FB pin 0.2 0.3 V I
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
Input Low 0.4 V

Input Leakage Current 1 uA
Charge Pump Power Efficiency 88 % CTRL1 = 1, CRTL2 = 1, Vcc = 3.4V, V
I
Vout Ripple 30 m V Vcc = 3.6V, I

THERMAL CHARACTERISTICS

16-Lead LFCSP Package:

θ

= 50°C/Watt

JA

= -40°C to 85°C unless otherwise noted; C1,C2 = 1.0µF; C3 = 2.2µF; C4 = 4.7µF)

A

= 20mA, VFB =0.4V

LED

= 20mA, R

I

LED

= 7.08K, VFB =0.4V, Vcc = 3.6V, TA = 25°C,

SET

Note 2

= 20mA

SET

2.6V ≤ Vcc ≤ 4.2V

2.6V ≤ Vcc ≤ 4.2V

= 20mA

FB

= 20mA, All 6 LEDs Enabled

LED

= 7.08kOhm

SET

= 0.2V,

FB

Rev. PrA 06/04| Page 3 of 18

ADM8846 Preliminary Technical Data

ABSOLUTE MAXIMUM RATINGS

Table 2. (TA = 25°C unless otherwise noted)

Parameter Rating

Supply Voltage VCC –0.3 V to +6.0 V
I

–0.3 V to +2.0 V

SET

CTRL1, CTRL2 –0.3 V to +6.0 V
V

shorted (Note 3) Indefinite

OUT

Feedback pins FB1 to FB6 –0.3 V to +6.0 V
Operating Temperature Range –40°C to +85°C
V

(Note 4) 180mA

OUT

Storage Temperature Range –65°C to +125°C
Power Dissipation 2mW
ESD Class 1

Note 1: LED Current should be derated above T

> 65C, refer to

A

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

Vcc

2.6V- 5.5V

VOUT

ADM8846

CTRL1
CTRL2

I

SET

R

SET

GND

FB1
FB2
FB3
FB4
FB5
FB6

Figure 2. ADM8846 Typical Application Diagram

Rev. PrA 06/04 | Page 4 of 18

Preliminary Technical Data ADM8846

PIN CONFIGURATION AND FUNCTION DESCRIPTION

Table 3.

Pin

ADM8846

1 VOUT

2 C2+ Flying Capacitor 2 Positive Connection

3 I

4 FB1

5 FB2

6 FB3

7 FB4

8 FB5

9 FB6

10 G N D Device Ground Pin.
11 C2− Flying Capacitor 2 Negative Connection.

12 CTRL2

13 CTRL1

14 C1− Flying Capacitor 1 Negative Connection.

15 Vcc

16 C1+ Flying Capacitor 1 Positive Connection.

- EP Expose Paddle. Connect the exposed paddle to GND.

Mnemonic Function

Charge Pump Output. A 2.2µF capacitor to ground is required on this pin. Connect Vout to the anodes
of all the LEDs.

SET

Bias current set input. The current flowing through the R
I

curent. Connect a resistor R

LED

LED1 Cathode connection and Charge Pump Feedback. The current flowing in LED1 is 120 times the
current flowing through R

LED2 Cathode connection and Charge Pump Feedback. The current flowing in LED2 is 120 times the
current flowing through R

LED3 Cathode connection and Charge Pump Feedback. The current flowing in LED3 is 120 times the
current flowing through R

LED4 Cathode connection and Charge Pump Feedback. The current flowing in LED4 is 120 times the
current flowing through R

LED5 Cathode connection and Charge Pump Feedback. The current flowing in LED5 is 120 times the
current flowing through R

LED6 Cathode connection and Charge Pump Feedback. The current flowing in LED6 is 120 times the
current flowing through R

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.

Positive Supply Voltage Input. Connect this pin to a 2.6 V to 5.5 V supply with a 4.7µF decoupling
capacitor.

resistor I

to GND to set the bias current as V

SET

, I

.

SET

SET

, I

. When using fewer than six LEDs this pin can be left unconnected.

SET

SET

, I

. When using fewer than six LEDs this pin can be left unconnected.

SET

SET

, I

. When using fewer than six LEDs this pin can be left unconnected.

SET

SET

, I

. When using fewer than six LEDs this pin can be left unconnected.

SET

SET

, I

. When using fewer than six LEDs this pin can be left unconnected.

SET

SET

SET

is gained up by 120 to give the

SET

. (Note: Vset = 1.18V)

SET/RSET

16

15

14

13

ISET

FB1

1

2

3

(NOT TO SCALE)

4

ADM8846

TOP VIEW

56

7

12

CTRL2

11

10

GND

9

FB6

8

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.

Rev. PrA 06/04| Page 5 of 18

ADM8846 Preliminary Technical Data

TYPICAL PERFORMANCE CHARACTERISTICS

35

30

25

20

15

LED Curr en t (mA)

10

5

4.75 6.75 8.75 10.75 12.75 14.75

Rset (koh m)

Figure 4. LED Current vs. R

20.35

20.3

20.25

20.2

20.15

LED current (mA)

20.1

20.05

20

2.6 3.1 3.6 4.1 4.6 5.1

-40'C

25'C

85'C

Supply Voltage (V)

Resistor

SET

Figure 6. LED Current (mA) vs. Temperature (°C), 6 LEDs enabled.

0.4

0.3

0.2

0.1

0

2.6 3 3.4 3.8 4.2 4.6 5 5.4

-0.1

Matching Error (%)

-0.2

-0.3

-0.4

Max Positive Match ing Error

Max Negative Matching Error

Supply Voltage (V)

Figure 5. LED Current Matching Error (%) vs. Supply Voltage (V),

= 25°C and I

T

A

20.24

20.22

20.2

20.18

20.16

20.14

LED Current (mA)

20.12

20.1

20.08

-40 0 40 80

Figure 7. I

(mA) Variation over Temperature (°C), with Vcc = 3.6V

LED

= 20mA

LED

Temperature ('C)

Figure 8. I

0.300

0.200

0.100

0.000

-40-200 25456585

% Error

-0.100

-0.200

-0.300

Matching (%) over Temperature (°C), with Vcc = 3.6,

LED

= 20mA , 6 LEDs enabled.

I

LED

Temperature

Rev. PrA 06/04 | Page 6 of 18

35

30

25

20

15

LED Current (mA)

10

5

2.6 3 3.4 3.8 4.2 4.6 5 5.4

Supply Voltage (V)

Figure 9. LED Current (mA) vs. Supply Voltage (V)

Preliminary Technical Data ADM8846

20

16

12

8

LED Current (mA)

4

0

0 20406080100

Duty Cycle (%)

Figure 10. LED Current (mA) vs. PWM Dimming (varying Duty Cycle),

6 LEDs enabled, Freq = 1kHz.

300

250

200

150

100

Supply Current Icc (mA)

50

20mA/LED

15mA/LED

95

90

85

80

75

Efficiency (%)

70

65

60

0 102030405060708090100

Duty Cycle (%)

Figure 11. LED Efficiency vs. Varying Duty Cycle of 1kHz PWM signal,

with 6 LEDs enabled, 20mA/LED.

0

2.6 3 3.4 3.8 4.2 4.6 5 5.4
Supply Voltage (V)

Figure 12. Input Current vs. Supply Voltage, with 6 LEDs enabled

Figure 14. 1.5x Mode Operating Waveforms

Figure 13. Softstart showing the initial in-rush current and Vout

variation with 6 LEDs @ 20mA/LED, V

2.00 V

1.00 V

160 m A 18.0 mV

= 3.6V

CC

Figure 15. 2x Mode Operating Waveforms

Rev. PrA 06/04| Page 7 of 18

ADM8846 Preliminary Technical Data

y

Power Efficiency over Li-ion Range

90
85

Figure 16. 1x Mode Operating Waveforms

80
75
70
65
60
55

Power Efficiency

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)

Vf = 4.3V

Vf = 4.0V
Vf = 3.6V
Vf = 3.8V

Vf = 3.2V

Power Efficiency over Li-ion Range

90
85
80
75
70
65
60
55

Power Efficiency

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

Vf = 4.3V

Vf = 4.0V
Vf = 3.8V
Vf = 3.6V

Vf = 3.2V

Figure 18. Power Efficiency vs. Supply Voltage over Li-ion Range

(6 LEDS @ 15mA/LED)

Power Efficiency over Li-ion Range

90
85
80
75
70
65
60
55

Power Efficiency

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

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

90
85
80
75
70
65
60

Power Efficienc

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

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

Rev. PrA 06/04 | Page 8 of 18

Preliminary Technical Data ADM8846

30mA

20mA

65°C

85°C

Figure 22. Max LED Current vs. Ambient Temperature (6 LEDs

Connected)

Rev. PrA 06/04| Page 9 of 18

ADM8846 Preliminary Technical Data

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 V

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

input voltages as low as

CC

An external resistor R

is connected between the I

SET

internally within the ADM8846 to produce the I

pin and GND, this resistor sets up a reference current I

SET

currents of up to 30mA/LED, (I

LED

LED

= I

* 120 and I

SET

SET

= 1.18V /R

SET

which is gained up by 120

). The ADM8846

SET

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.

C1 C2

VCC

C4

CTRL1
CTRL2

ADM8846

Control

Logic

Charge Pump
1x/1.5x/2x mode

Osc

Vref

+

-

Vout

FB1

FB2

FB3
FB4

FB5
FB6

C3

MAIN

SUB

Rset

Iset

LED Current
Control
Circuit

Current

Current
Control

Current

Control

Control

2

1

3

Current
Control

4

Current
Control

5

Current
Control

6

Current Controlled Sinks

GND

Figure 23. ADM8846 FUNCTIONAL BLOCK DIAGRAM

Rev. PrA 06/04 | Page 10 of 18

Preliminary Technical Data ADM8846

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 R
approximated by the following equation:

R

= 120 x (1.18V / I

SET

LED

).

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:

– V

V

OUT

is the LED forward voltage. For 20mA/LED the compliance is 0.2V typ and 0.3V max, see Table 5.

V

F

≥ Compliance

F

I

R

LED

Typ. Compliance

SET

15mA 9.44k Ohms 0.17V
20mA 7.08k Ohms 0.20V
30mA 4.72k Ohms 0.34V

Tabl e 5. I

, R

and Compliance Table

LED

SET

sets the output current,

SET

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:

= (I

+ I

I

AVG

MAX

Max Matching Error = [(I

MIN

)/2

MAX

– I

AVG

)/I

] * 100

AVG

Where I

is the largest I

MAX

current and I

LED

Min Matching Error = [(I

is the smallest I

MIN

Rev. PrA 06/04| Page 11 of 18

current.

LED

or

MIN

– I

AVG

)/I

AVG

] * 100

ADM8846 Preliminary Technical Data

C1C

2

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 R

resistor).

SET

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 I
the programmed LED current. For example, if R

being half

LED

is set to

SET

program 20mA/LED, a 50% duty cycle will result in an average

of 10mA/LED. I

I

LED

PWM Input

or

High/Low

PWM Input

or

High/Low

Iset

being half the programmed LED current.

LED

Vout

ADM8846

CTRL1

CTRL2

FB1

FB2

FB3
FB4

FB5
FB6

C3

Rset

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 R

resistor).

SET

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 (t

) allows the ADM8846 to

CP

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 (V

) or 0 (GND) must be applied.

CC

Rev. PrA 06/04 | Page 12 of 18

Preliminary Technical Data ADM8846

LED Config.

CTRL1

CTRL2

Vout

ILED

(sub)

ILED

(main)

Sub Display

Brightness

Full On

100%

sub + main 50% D.C.

50%

main + sub Off

t

cp

main 80% D.C., sub off

SHDN

80%

SHDN

Main Display

Brightness

100%

50%

37mS > tcp > 15mS

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 On / 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 Display / Main Display On 5e, 5e
PWM PWM Digital PWM Brightness Control on Su b 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 R
level (V

) is applied to CTRL1.

CC

resistor. CTRL1 = 1 means a constant logic

SET

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 R
level (V

) is applied to CTRL2.

CC

resistor. CTRL2 = 1 means a constant logic

SET

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. PrA 06/04| Page 13 of 18

ADM8846 Preliminary Technical Data

ADM8846 LED BRIGHTNESS CONTROL USING A
PWM SIGNAL APPLIED TO V

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 V
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 I
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.

I

= I

LED

SET_Voltage * 120 * (1 - Duty Cycle)

pin of the ADM8846. A 0% PWM

SET

PWM

can be

PWM

RSET * 2R 100

RSET + 2R

ADM8846

ADM8846 LED BRIGHTNESS CONTROL USING A
DC VOLTAGE APPLIED TO V

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 V
an application example of LED Brightness control using a DC
Voltage with a amplitude of 0V to 2.5V, applied to V

BRIGHT

node. Figure 28 shows

BRIGHT

BRIGHT

.

ADM8846

I

SET

V

BRIGHT

0V - 2.5V

Figure 27. ADM8846 PWM Brightness Control Using a DC

R = 15K

R

= 13.4K

SET

Voltage applied to VBRIGHT

is:

LED

+ 1/R)(V

)] – [(1/R)(V

SET

= voltage at I

SET

1.6V

7.2mA

)]

BRIGHT

pin (1.18V)

SET

0.8V

13.6mA

0V

20mA

I

SET

V

PWM

0V - 2.5V

100% = I

R = 7.5K

C5 = 1µF

0% = I

LED
LED

R = 7.5K

=0mA

= 20mA

R

SET

= 13.4K

Figure 26. ADM8846 PWM Brightness Control Using Filtered-

PWM Signal

The equation for I

= [(1/R

I

SET

I

LED

= 120*I

SET

SET

Where R = 15k Ohm, V

2.5V

V

BRIGHT

I

LED

0mA

Figure 28. ADM8846 PWM Brightness Control Application

Diagram Using a DC Voltage applied to V

BRIGHT

Rev. PrA 06/04 | Page 14 of 18

Preliminary Technical Data ADM8846

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 I
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 (I
by the R

resistor through the shorted LED.

SET

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.

per LED (I

LED

= I

LED

* 120)mA as programmed

SET

* 120). This is

SET

LCD

Vcc

R

SET

2.6V - 5.5V

CTRL1
CTRL2

I

SET

ADM8846

GND

VOUT

FB1
FB2
FB3
FB4
FB5
FB6

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.

Vcc

2.6V- 5.5V

Main Display

Sub Display

VOUT

2.6V- 5.5V

R

SET

Vcc

CTRL1
CTRL2

ADM8846

I

SET

ADM8846

CTRL1
CTRL2

VOUT

FB1
FB2
FB3
FB4
FB5
FB6

GND

Rset

4.72k

Figure 31. ADM8846 Driving three flash LEDs

GND

FB1
FB2
FB3
FB4
FB5
FB6

60mA

60mA

60mA

Figure 29. ADM8846 Driving Five White LEDs

Rev. PrA 06/04| Page 15 of 18

ADM8846 Preliminary Technical Data

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.

C1 C2

C4

Rset

9.44kΩ

VCC

CTRL1
CTRL2

Iset

ADM8845

ADM8846

Control

Logic

LED Current
Control
Circuit

Charge Pump
1x/1.5x/2xmode

Osc

Vref

Current
Control

1

Current Controlled Sinks

Current
Control

2

Current
Control

GND

Vout

C3

+

Camera

Main

Sub

-

15mA/LED

FB1

FB2
FB3
FB4

FB5
FB6

Current

Current
Control

3

4

Control

5

Current
Control

6

15mA/LED

R

Current
Control

7

15mA/LED

Figure 32. ADM8846 Driving Camera Light + Two Main + One Sub

Rev. PrA 06/04 | Page 16 of 18

Preliminary Technical Data ADM8846

ADM8846 POWER EFFICIENCY

The ADM8846 power efficiency (η) equations, are as follows:

η = P

OUT/PIN

= ((VCC * I

P

IN

P

= 6*(VF * I

OUT

* Gain) + (IQ * VCC))

LOAD

)

LED

ADM8846

: Quiescent current of the ADM8846, 2.6mA.

I

Q

V

: LED Forward Voltage

F

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 V

= 3.4V (1.5x mode), LED VF = 4.5V.

CC

P

= ((VCC * I

IN

= ((3.4 * 120mA * 1.5) + (3.4 * 2.6mA))

P

IN

= ((0.612) + (0.00884))

P

IN

P

= 0.62084

IN

* Gain) + (VCC * IQ))

LOAD

P

= 6(VF * I

OUT

= 6(4.5V * 20mA)

P

OUT

P

= 0.54

OUT

LED

)

η = P

OUT/PIN

η = 0.54/0.62084

η = 87 %

Example 2: The ADM8846 driving six white LED with 20mA/LED
at V

= 3.4 (1.5x mode), LED VF = 3.6V.

CC

P

= ((VCC * I

IN

= ((3.4 * 120mA * 1.5) + (3.4 * 2.6mA))

P

IN

P

= ((0.612) + (0.00884))

IN

= 0.62084

P

IN

* Gain) + (VCC * IQ))

LOAD

P

= 6(VF * I

OUT

P

= 6(3.6V * 20mA)

OUT

= 0.432

P

OUT

LED

)

η = P

OUT/PIN

η = 0.432/0.62084

η = 70 %

Rev. PrA 06/04| Page 17 of 18

ADM8846 Preliminary Technical Data

=

PR04974-0-6/04(PrA)

OUTLINE DIMENSIONS

16-Lead L ead Fr ame Ch ip Scal e Packag e [L FCSP]

3.00

BSC SQ

PIN 1

INDICATOR

0.90

0.85

0.80

SEATING

PLANE

128 MAX

TOP

VIEW

0.30

0.23

0.18

2.75

BSC SQ

0.20 REF

*

COMPLIANT TO JEDEC STA NDARDS MO-220-VEED-2

EXCEPT FOR EXPOSED PA D DIMENSION

Figure 34. 16-Lead Frame Chip Scale package [LFCSP] (CP-16)—Dimensions shown in millimeters

3 x 3 mm Bo dy

0.05 MAX

0.02 NOM

(CP-16-4)

0.45

0.50

BSC

0.60 MAX

1.50 REF

12

9

13

BOTTOM

8

Dimensions shown in millimeters

0.80 MAX

0.65 TYP

VIEW

0.50

0.40

0.30

16

1

4

5

PIN 1 INDICATOR

1.65

*

1.50
SQ

1.35

0.25 MIN

ORDERING GUIDE

Model Temperature Range Package Description Package Option

ADM8846ACPZ -40ºC to + 85ºC 16-Lead LFCSP
ADM8846ACPZ-REEL7 -40ºC to + 85ºC 16-Lead LF CSP

CP: Chip Scale Package
Z : Lead Free Part

CP-16
CP-16

© 2004 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.

Rev. PrA 06/04 | Page 18 of 18