Datasheet ADM8845 Datasheet (Analog Devices)

Charge Pump Driver for LCD

FEATURES

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% 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 9 mm
Package height only 0.9 mm
Low power shutdown mode
Shutdown function
Soft-start limiting in-rush current

APPLICATIONS

Cellular phones with main and sub displays
White LED backlighting
Camera flash/strobes and movie lights
Micro TFT color displays
DSC
PDAs

2

(3 mm × 3 mm)

C1

1µF

FUNCTIONAL BLOCK DIAGRAM

C2

1µF

White LED Backlights

ADM8845

GENERAL DESCRIPTION

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
either 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.

Improved brightness matching of the LEDs is achieved by a
feedback pin to sense individual LED current with a maximum
matching accuracy of 1%.

V

ADM8845

CC

C4

4.7µF

CTRL1

CTRL2

R

SET

Rev. 0

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 owners.

I

SET

CONTROL

LOGIC

LED
CURRENT
CONTROL

CIRCUIT

CHARGE PUMP

1×/1.5×/2× MODE

OSC

V

REF

CURRENT

CURRENT

CURRENT

CONTROL 1

CONTROL 2

CURRENT CONTROLLED SINKS

GND

CONTROL 3

CURRENT

CONTROL 4

CURRENT

CONTROL 5

Figure 1.

V

OUT

CURRENT

CONTROL 6

FB1
FB2
FB3
FB4
FB5
FB6

C3

2.2µF

MAIN SUB

04867-0-001

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

ADM8845

TABLE OF CONTENTS

Specifications......................................................................................3

Absolute Maximum Ratings.............................................................4

Thermal Characteristics .............................................................. 4

ESD Caution.................................................................................. 4

Pin Configuration and Function Description ...............................5

Typical Performance Characteristics ..............................................6

Theory of Operation ...................................................................... 10

Output Current Capability........................................................ 11

Automatic Gain Control ............................................................ 11

Current Matching ....................................................................... 11

Brightness Control with a Digital PWM Signal..................... 11

LED Brightness Control Using a PWM Signal Applied to

............................................................................................. 13

V

PWM

REVISION HISTORY

LED Brightness Control Using a DC Voltage Applied to

.......................................................................................... 13

V

BRIGHT

Applications......................................................................................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

10/04—Revision 0: Initial Version

Rev. 0 | Page 2 of 20

ADM8845

SPECIFICATIONS

VCC = 2.6 V to 5.5 V; T

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

A

Table 1.

Parameter Min Typ Max Unit Test Conditions

INPUT VOLTAGE, VCC 2.6 5.5 V
SUPPLY CURRENT, ICC 2.6 5 mA

All six LEDs disabled, V

= 3.3 V, R

CC

= 7.08 kΩ

SET

CTRL1 = 1, CRTL2 = 1
SHUTDOWN CURRENT 5 µA
CHARGE PUMP FREQUENCY 1.5 MHz
CHARGE PUMP MODE THRESHOLDS

1.5× to 2× 3.33 V
Accuracy 4 %

2× to 1.5× 3.36 V

Accuracy 4 %
Hysteresis 40 mV

1× to 1.5× 4.77 V

Accuracy 4 %

1.5× to 1× 4.81 V
Accuracy 4 %
Hysteresis 40 mV

I

PIN

SET

LED : LED Matching −1 +1 % I
LED : I

I
I

Accuracy −1 +1 %

SET

Pin Voltage 1.18 V

SET

to I

LED

Ratio 120

SET

MIN COMPLIANCE ON FBx PIN 0.2 0.3 V I

= 20 mA, VFB =0.4 V

LED

= 20 mA, R

I

LED

T

= 25°C

A

= 20 mA

SET

SET

= 7.08 kΩ, VFB = 0.4 V, VCC = 3.6 V,

Charge Pump Output Resistance 1.2 1.8 Ω 1× mode

3.5 5.1 Ω 1.5× mode

8.0 14 Ω 2× mode

LED Current 30 mA See Note 1 and Figure 21
PWM 0.1 200 kHz
DIGITAL INPUTS

Input High 0.5 VCC V

Input Low 0.3 VCC V

Input Leakage Current 1 µA
CHARGE PUMP POWER EFFICIENCY 88 % CTRL1 = 1, CRTL2 = 1, VCC = 3.4 V, VFB = 0.2 V, IFB = 20 mA
V

RIPPLE 30 m V VCC = 3.6 V, I

OUT

= 20 mA, all six LEDs enabled

LED

_______________________

1

Guaranteed by design. Not 100% production tested.

Rev. 0 | Page 3 of 20

ADM8845

ABSOLUTE MAXIMUM RATINGS

TA = 25°C, unless otherwise noted.

Table 2.

Parameter Rating

Supply Voltage, V
I

–0.3 V to +2.0 V

SET

CC

–0.3 V to +6.0 V

CTRL1, CTRL2 –0.3 V to +6.0 V
V

Shorted1 Indefinite

OUT

Feedback pins FB1 to FB6 –0.3 V to +6.0 V
Operating Temperature Range

Six LEDs Enabled with 30 mA/LED2 –40°C to +65°C
Six LEDs Enabled with 20 mA/LED2 –40°C to +85°C

3

V

180 mA

OUT

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

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.

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.

THERMAL CHARACTERISTICS

16-Lead LFCSP Package:

θ

= 50°C/W

JA

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.

Rev. 0 | Page 4 of 20

ADM8845

V

PIN CONFIGURATION AND FUNCTION DESCRIPTION

1
L
R

+

C

–

1

1

T

C

V

C

C

C

4

3

5

6

1

1

1

1

PIN 1
INDICATOR

1

OUT

2C2+

ADM8845

3I
4FB1

TOP VIEW

(Not to Scale)

5

6

2

3

B

B

F

F

SET

Figure 2. Pin Configuration

Table 3. Pin Function Descriptions

Pin No. Mnemonic Function

1 V

OUT

Charge Pump Output. A 2.2 µF capacitor to ground is required on this pin. Connect V

the LEDs.
2 C2+ Flying Capacitor 2 Positive Connection.
3 I

4–9 FB1–FB6

SET

Bias Current Set Input. The current flowing through R

Connect R

to GND to set the bias current as V

SET

LED1–LED6 Cathode Connection and Charge Pump Feedback. The current flowing in these LEDs is 120 times

the current flowing through R

, I

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

SET

SET

connected to GND.
10 GND Device Ground Pin.
11

C2−

Flying Capacitor 2 Negative Connection.
12 CTRL2 Digital Input. 3 V CMOS Logic. Used with CTRL1 to control the shutdown operation of the main and sub LEDs.
13 CTRL1 Digital Input. 3 V CMOS Logic. Used with CTRL2 to control the shutdown operation of the main and sub LEDs.
14 C1− Flying Capacitor 1 Negative Connection.
15 VCC Positive Supply Voltage Input. Connect this pin to a 2.6 V to 5.5 V supply with a 4.7 µF decoupling capacitor.
16 C1+ Flying Capacitor 1 Positive Connection.

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

12 CTRL2
11 C2–
10 GND
9 FB6

8

7

5

4

B

B

F

F

04867-0-003

to the anodes of all

OUT

, I

SET/RSET

, is gained up by 120 to give the I

SET

SET

. Note that V

= 1.18 V.

SET

current.

LED

Rev. 0 | Page 5 of 20

ADM8845

TYPICAL PERFORMANCE CHARACTERISTICS

35

0.4

30

25

20

15

LED CURRENT (mA)

10

5

4.75 6.75 12.75 14.758.75

Figure 3. I

10.75

R

(kΩ)

SET

(mA) Current vs. R

LED

20.35

20.30

20.25

20.20

20.15

LED CURRENT (mA)

20.10

20.05

20.00

2.6 3.1 4.6 5.63.6 5.1

Figure 4. I

SUPPLY VOLTAGE (kΩ)

(mA) vs. Temperature (°C), Six LEDs Enabled

LED

4.1

0.3

–40°C

25°C

85°C

0.3

0.2

0.1

0

–0.1

MATCHING ERROR (%)

–0.2

–0.3

–0.4

04867-0-004

2.6 4.2 5.03.4 4.6

SET

Figure 6. I

MAX POSITIVE MATCHING ERROR

MAX NEGATIVE MATCHING ERROR

3.0 5.4

(mA) Matching Error (%) vs. Supply Voltage (V),

LED

3.8

SUPPLY VOLTAGE (V)

T

= 25°C and I

A

= 20 mA

LED

04867-0-007

20.24

20.22

20.20

20.18

20.16

20.14

LED CURRENT (mA)

20.12

20.10

20.08

04867-0-005

–40 0 8040

Figure 7. I

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

LED

TEMPERATURE (°C)

04867-0-008

35

0.2

0.1

0

% ERROR

–0.1

–0.2

–0.3

–40 –20 45 850 65

Figure 5. I

Matching (%) over Temperature (°C), VCC = 3.6 V, I

LED

TEMPERATURE (°C)

Six LEDs Enabled

30

25

20

15

LED CURRENT (mA)

10

25

= 20 mA,

LED

04867-0-006

5

2.6 3.0 4.6 5.43.4 5.04.2

Figure 8. I

3.8

SUPPLY VOLTAGE (V)

(mA) vs. Supply Voltage (V)

LED

04867-0-009

Rev. 0 | Page 6 of 20

ADM8845

V

20

16

12

8

LED CURRENT (mA)

4

0

0 20 60 1008040

Figure 9. I

LED

Six LEDs Enabled, Frequency = 1 kHz

300

250

(mA)

200

CC

150

100

SUPPLY CURRENT I

50

DUTY CYCLE (%)

(mA) vs. PWM Dimming ( Varying Duty Cycle),

20mA/LED

15mA/LED

04867-0-010

95

90

85

80

75

EFFICIENCY (%)

70

65

60

10 20

04060807050

30

DUTY CYCLE (%)

90 100

Figure 12. LED Efficiency vs. Varying Duty Cycle of 1 kHz PWM Signal,

Six LEDs Enabled, 20 mA/LED

CTRL1/2

1

CURRENT

2

V

OUT

04867-0-013

0

2.6 3.0 3.8 4.64.23.4

V

1

CC

2

V

OUT

SUPPLY VOLTAGE (V)

5.0 5.4

Figure 10. Input Current vs. Supply Voltage,

Six LEDs Enabled

B

CH2 20.0mVCH1 20.0mV M 400ns CH1 220mV

W

B

W

Figure 11. 1.5× Mode Operating Waveforms

04867-0-011

04867-0-012

3

CH3 1.00V

B

CH2 160mACH1 2.00V M 5.00µs CH2 180mV

W

B

W

Figure 13. Soft Start Showing the Initial In-Rush Current and V

Six LEDs @ 20 mA/LED, V

= 3.6 V

CC

1

V

CC

2

OUT

B

CH2 20.0mVCH1 20.0mV M 400ns CH1 220mV

W

B

W

Figure 14 .2× Mode Operating Waveform

Varia tion,

OUT

04867-0-014

04867-0-015

Rev. 0 | Page 7 of 20

ADM8845

1

V

CC

2

V

OUT

B

CH2 20.0mVCH1 20.0mV M 400ns CH1 220mV

W

B

W

Figure 15. 1× Mode Operating Waveforms

90

85

80

75

70

65

60

55

POWER EFFICIENCY

50

45

40

2.8 3.0 3.4 3.83.63.2 4.0 4.22.9 3.1 3.3 3.5 3.7 3.9 4.1

V

= 3.6V

F

VF = 3.2V

V

CC

Figure 16. Power Efficiency vs. Supply Voltage over Li-ion Range,

Six LEDS @ 15 mA/LED

90

85

80

75

70

65

60

55

POWER EFFICIENCY

50

45

40

2.8 3.0 3.4 3.83.63.2 4.0 4.22.9 3.1 3.3 3.5 3.7 3.9 4.1

V

= 3.6V

F

VF = 3.2V

V

CC

Figure 17. Power Efficiency vs. Supply Voltage over Li-Ion Range,

Four LEDS @ 15 mA/LED

V

= 3.8V

F

VF = 4.0V

= 4.3V

V

F

V

= 3.8V

F

VF = 4.0V

= 4.3V

V

F

04867-0-016

04867-0-017

04867-0-018

90

85

80

75

70

65

60

55

POWER EFFICIENCY

50

45

40

2.8 3.0 3.4 3.83.63.2 4.0 4.22.9 3.1 3.3 3.5 3.7 3.9 4.1

V

= 3.8V

F

VF = 3.2V

V

CC

V

= 3.6V

F

VF = 4.0V

= 4.3V

V

F

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

Six LEDS @ 20 mA/LED

90

85

80

75

70

65

60

55

POWER EFFICIENCY

50

45

40

2.9 3.1 3.3 3.5 3.7 3.9 4.1

2.8 3.0 3.4 3.83.63.2

= 3.6V

V

F

VF = 3.2V

V

CC

= 4.3V

V

F

VF = 4.0V

= 3.8V

V

F

4.0 4.2

Figure 19. Power Efficiency vs. Supply Voltage over Li-Ion Range

Four LEDS @ 20 mA/LED

CTRL1/2

1

V

OUT

2

CH1 2.00V CH2 2.00V M10.0ms CH2 4.36V

∆: 44.0ms
@: –44.4ms

C2 FALL
200µs
LOW SIGNAL
AMPLITUDE

Figure 20. TPC Delay

04867-0-019

04867-0-020

04867-0-021

Rev. 0 | Page 8 of 20

ADM8845

30mA

20mA

Figure 21. Maximum I

65°C 85°C

(mA) vs. Ambient Temperature,

LED

04867-0-022

Six LEDs Connected

Rev. 0 | Page 9 of 20

ADM8845

THEORY OF OPERATION

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 V
tion of the charge pump output voltage for supply voltages up to

5.5 V. The ADM8845’s six LEDs 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 4).

Table 4. Shutdown Truth Table

input voltages as low as 2.6 V. It also includes regula-

CC

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

C1

C2

1

µ

F

1

µ

F

An external resistor, R
GND. This resistor sets up a reference current, I

, is connected between the I

SET

SET

, which is

SET

pin and

internally gained up by 120 within the ADM8845 to produce

currents of up to 30 mA/LED (I

the I

LED

= 1.18 V/R

). The ADM8845 uses six individual current sinks

SET

LED

= I

SET

× 120 and I

SET

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 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.

ADM8845

I

SET

BRIGHT

R = 15kΩ

R

SET

= 13.4kΩ

04867-0-027

BRIGHT

V
0V–2.5V

Figure 22. PWM Brightness Control Using a DC Voltage Applied to V

V

ADM8845

CC

C4

4.7

µ

F

CTRL1

CTRL2

R

SET

I

SET

CONTROL

LOGIC

LED
CURRENT
CONTROL

CIRCUIT

CHARGE PUMP

1

×

/1.5×/2× MODE

OSC

V

REF

CURRENT

CURRENT

CURRENT

CONTROL 1

CONTROL 2

CURRENT CONTROLLED SINKS

GND

CURRENT

CONTROL 3

Figure 23. Functional Block Diagram

CURRENT

CONTROL 4

CONTROL 5

CURRENT

CONTROL 6

V

OUT

FB1
FB2
FB3
FB4
FB5
FB6

C3

2.2

MAIN SUB

µ

F

04867-0-001

Rev. 0 | Page 10 of 20

ADM8845

OUTPUT CURRENT CAPABILITY

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, R

, sets the output

SET

current, approximated by the following equation:

R

= 120 × (1.18 V/I

SET

LED

)

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 is realizable. To ensure that the desired
current is obtained, use the following equation to find the
minimum input voltage required:

– VF ≥ Compliance

V

OUT

where V

is the LED forward voltage. For 20 mA/LED, the

F

compliance is 0.20 V typ and 0.30 V max (see Table 5).

, R

Table 5. I

I

R

LED

15 mA

20 mA

30 mA

LED

, and Compliance Table

SET

SET

9.44 kΩ

7.08 kΩ

4.72 kΩ

Typ. Compliance

0.17 V

0.20 V

0.34 V

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
Tabl e 6.

Table 6. Charge Pump Switching Thresholds

Gain Threshold

1.5× to 2× 3.33 V
2× to 1.5× 3.36 V
1× to 1.5× 4.77 V

1.5× to 1× 4.81 V

CURRENT MATCHING

The 1% maximum current matching performance is defined by
the following equations:

= (I

+ I

I

AVG

MAX

Max Matching Error = [(I

MIN

)/2

MAX

– I

AVG

)/I

] × 100

AVG

or

– I

)/I

Min Matching Error = [(I

where I

is the largest I

MAX

MIN

current, and I

LED

AVG

] × 100

AVG

is the smallest I

MIN

LED

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 R

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 I
grammed LED current. For example, if R
20 mA/LED, a 50% duty cycle results in an average I
10 mA/LED, I

PWM INPUT

OR HIGH/LOW

PWM INPUT

OR HIGH/LOW

R

Figure 24. Digital PWM Brightness Control Application Diagram

being half the programmed LED current.

LED

C1

C2

1µF

1µF

V

FB1
FB2
FB3
FB4
FB5
FB6

OUT

SET

ADM8845

CTRL1

CTRL2

I

SET

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 ADM8845’s six white LEDs are
organized into two groups, main display (FB1 to FB4) and sub
display (FB4 to FB6); refer to the Theory of Operation section.

).

SET

being half the pro-

LED

is set to program

SET

LED

of

C3

2.2µF

04867-0-024

Rev. 0 | Page 11 of 20

ADM8845

The ADM8845’s 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. Varying the duty cycle of the
applied PWM signal also varies 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
turned on. Then the brightness of the main display is determined
by the duty cycle of the applied digital PWM signal.

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
duty cycle of the applied digital PWM signal. The brightness of
the main display is set to the maximum (maximum is set by R

SET

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 (maximum is set
by R

).

SET

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 (t

) allows the ADM8845 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).

If digital PWM brightness control of the LEDs is not required, a
constant Logic Level 1 (V

) or 0 (GND) must be applied.

CC

The six white LED in the ADM8845 are arranged in two groups,
sub and main. It is possible to configure the six LEDs as in
Table 7; refer also to Figure 25.

).

Table 7. Digital Inputs Truth Table

CTRL1 CTRL2 LED Operation

0 0 Sub Display Off / Main Display Off (Full Shutdown)
0 1 Sub Display Off / Main Display On
1 0 Sub Display On / Main Display Off

1, 3

1, 2

1 1 Sub Display On / Main Display On (Full On)
0 PWM Sub Display Off/ Digital PWM Brightness Control on Main Display
PWM 0 Digital PWM Brightness Control on Sub Display / Main Display Off
1 PWM Sub Display On/ Digital PWM Brightness Control on Main Display
PWM 1 Digital PWM Brightness Control on Sub Display / Main Display On

1, 2

1, 3

4, 5

2, 4

1, 5

5

PWM PWM Digital PWM Brightness Control on Sub and Main Display5

1

Sub Display On means the display is on with the maximum brightness set by the R

2

Main Display Off means the main display only is off. CTRL2 = 0 means a constant logic level (GND) is applied to CTRL2.

3

Main Display On means the display is on with the maximum brightness set by the R

4

Sub Display Off means the sub display LEDs only is off. CTRL1 = 0 means a constant logic level (GND) 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.

resistor. CTRL1 = 1 means a constant logic level (VCC) is applied to CTRL1.

SET

resistor. CTRL2 = 1 means a constant logic level (VCC) is applied to CTRL2.

SET

Rev. 0 | Page 12 of 20

ADM8845

V

LED CONFIG.

CTRL1

CTRL2

V

(SUB)

(MAIN)

SUB DISPLAY

BRIGHTNESS

MAIN DISPLAY

BRIGHTNESS

I

I

OUT

LED

LED

FULL ON MAIN AND SUB OFF

100%

100%

SUB AND MAIN 50%

DUTY CYCLE

50%

50%

37ms >

t

CP

SHDN

SHDN

t

> 15ms

CP

MAIN 80% DUTY CYCLE,

SUB OFF

80%

04867-0-025

Figure 25. Application Timing

LED BRIGHTNESS CONTROL USING A
PWM SIGNAL APPLIED TO V

Adding two external resistors and a capacitor, as shown on
Figure 26, also can 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 V
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 I
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.

SET

=

I

LED

Figure 26. PWM Brightness Control Using Filtered-PWM Signal

PWM

SET

SET

0V–2.5V

pin of the ADM8845. A 0% PWM

SET

_

VoltageI

2

RR

×

2

RR

+

100% = I

LED

= 20mA

0% = I

LED

R = 7.5kΩ

C5 = 1µF

120

= 0mA

R = 7.5kΩ

××

PWM

−

100

ADM8845

I

SET

R

CycleDuty

SET

)1(

= 13.4kΩ

can be

PWM

04867-0-026

LED BRIGHTNESS CONTROL USING A
DC VOLTAGE APPLIED TO V

Adding one resistor, as shown in Figure 22, this configuration
can also be used to control brightness the white LEDs by using
a dc voltage applied to the V
application example of LED brightness control using a dc
voltage with a amplitude of 0 V to 2.5 V, applied to V

The equation for I

= [(1/R

I

SET

= 120 × I

I

LED

where R = 15 kΩ and V

2.5V

V

BRIGHT

I

LED

0mA

Figure 27. PWM Brightness Control Application Diagram Using a

is

LED

+ 1/R)(V

SET

SET

= voltage at I

SET

1.6V

7.2mA

DC Voltage Applied to V

BRIGHT

node. Figure 27 shows an

BRIGHT

)] – [(1/R)(V

SET

BRIGHT

pin (1.18 V).

SET

0.8V

13.6mA

BRIGHT

)]

BRIGHT

0V

20mA

.

04867-0-028

Rev. 0 | Page 13 of 20

ADM8845

APPLICATIONS

LAYOUT CONSIDERATIONS AND NOISE

Because of the ADM8845’s switching behavior, 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

If an LED is shorted, the ADM8845 continues to drive the
remaining LEDs with I

per LED (I

LED

is because the ADM8845 uses six internal currents sinks to
produce the LED current. If an LED is shorted, the ADM8845
continues to sink (I

× 120 mA) as programmed by R

SET

through the shorted LED.

LED

= I

× 120 mA). This

SET

LCD

SET

DRIVING FEWER THAN SIX LEDS

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.

MAIN DISPLAY

V

2.6V–5.5V

CTRL1
CTRL2

SUB DISPLAY

CC

V

OUT

ADM8845

FB1
FB2
FB3
FB4
FB5

GND

FB6

Figure 28. Driving Five White LEDs

V

CC

2.6V–5.5V

ADM8845

CTRL1
CTRL2

GND

I

R

SET

SET

V

OUT

FB1
FB2
FB3
FB4
FB5
FB6

04867-0-029

Figure 30. Typical Application Diagram

V

2.6V–5.5V

R

SET

MAIN DISPLAY

CC

V

OUT

CTRL1
CTRL2

I

SET

ADM8845

GND

FB1
FB2
FB3
FB4
FB5
FB6

Figure 29. Driving Three Main LEDs and One Sub LED

SUB DISPLAY

04867-0-030

04867-0-002

Rev. 0 | Page 14 of 20

ADM8845

4

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 need to be driven
with 60 mA/LED, the ADM8845 can be configured as in
Figure 31 (see also Figure 21).

V

CC

2.6V–5.5V

V

OUT

R

SET

.27kΩ

CTRL1
CTRL2

ADM8845

GND

FB1
FB2
FB3
FB4
FB5
FB6

60mA 60mA

Figure 31. Driving Three Flash LEDs

C1

C2

1µF

1µF

60mA

04867-0-031

DRIVING CAMERA LIGHT, MAIN, AND SUB LEDS

The ADM8845 can also be configured to power a camera light
that is composed of four white LEDs in parallel, packaged 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
load on the ADM8845 charge pump is 105 mA, and the maxi­mum load on the ADM8845 charge pump is 180 mA (see
Figure 21).

). All white LEDs have 15 mA/LED, therefore total

VCC

4.7µF

CTRL1

CTRL2

R

SET

9.44kΩ

ADM8845

C4

CONTROL

LOGIC

I

SET

LED
CURRENT
CONTROL

CIRCUIT

CHARGE PUMP

1×/1.5×/2× MODE

OSC

V

REF

CURRENT

CURRENT

CURRENT

CONTROL 1

CONTROL 2

CURRENT CONTROLLED SINKS



GND

CURRENT

CONTROL 3

CURRENT

CONTROL 4

CONTROL 5

CURRENT

CONTROL 6

V

OUT

FB1
FB2
FB3
FB4
FB5
FB6

C3

2.2µF

CAMERA MAIN SUB

CURRENT
CONTROL7

R

15mA/LED

15mA/LED

15mA/LED

04867-0-032

Figure 32. Driving Camera Light, Two Main LEDs, and One Sub LED

Rev. 0 | Page 15 of 20

ADM8845

DRIVING FOUR BACKLIGHT WHITE LEDS AND FLASH LEDS

The ADM8845 also can be configured to power four backlight
white LEDs and a camera flash, packaged into one package. FB1
to FB4 power the backlight light, FB5 and FB6 powers the two
of the flash LEDs, and the third is powered 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

C2

1µF

1µF

ADM8845

V

CC

CHARGE PUMP

4.7µF

C4

CTRL1

CTRL2

CONTROL

LOGIC

1×/1.5×/2× MODE

OSC

V

REF

CTRL1 controls the flash on/off, and CTRL2 controls the back­light on/off and brightness control. Because the R

resistor sets

SET

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.

V

OUT

C3

FB1
FB2
FB3
FB4
FB5
FB6

2.2µF
BACK-

LIGHT

15mA/LED

FLASH

20mA/LED

CURRENT
CONTROL 7

R

LED
CURRENT
CONTROL

CIRCUIT

CURRENT

CURRENT

CURRENT

CONTROL 1

CONTROL 2

CURRENT CONTROLLED SINKS

CONTROL 3

GND

CURRENT

CURRENT

CONTROL 4

CONTROL 5

CURRENT

CONTROL 6

04867-0-034

R

SET

7.32kΩ

I

SET

Figure 33. Driving Four Backlight LEDs and Flash LED

Rev. 0 | Page 16 of 20

ADM8845

POWER EFFICIENCY

The ADM8845 power efficiency (η) equations are

η = P

OUT/PIN

PIN = ((VCC × I
P

= 6×(VF × I

OUT

× Gain) + (IQ × VCC))

LOAD

)

LED

where:

I

is the quiescent current of the ADM8845, 2.6 mA.

Q

is the LED forward voltage.

V

F

I

LOAD

×, 1.5×, 2×).

Gain is equal to charge pump mode (1

3.4V

I

IN

GND

V

OUT

FB1
FB2
FB3
FB4
FB5
FB6

V

CC

V

CC

R

SET

ADM8845

CTRL1
CTRL2

I

SET

Figure 34. Charge Pump Power Efficiency Diagram

Examples 1 and 2 show calculations of the ADM8845 power
efficiency; also see Figure 34.

04867-0-033

Example 1

The ADM8845 driving six white LED with 20 mA/LED at
V

= 3.4 V (1.5× mode), LED VF = 4.5 V.

CC

P

= ((VCC × I

IN

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

P

IN

P

= ((0.612) + (0.00884))

IN

P

= 0.62084

IN

= 6(VF × I

P

OUT

= 6(4.5V × 20 mA)

P

OUT

= 0.54

P

OUT

η = P

OUT/PIN

× Gain) + (VCC × IQ))

LOAD

)

LED

η = 0.54/0.62084
η = 87 %

Example 2

The ADM8845 driving six white LED with 20 mA/LED at

= 3.4 (1.5× mode), LED VF = 3.6 V.

V

CC

P

= ((VCC × I

IN

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

P

IN

= ((0.612) + (0.00884))

P

IN

P

= 0.62084

IN

× Gain) + (VCC × IQ))

LOAD

= 6(VF × I

P

OUT

= 6(3.6 V × 20 mA)

P

OUT

P

= 0.432

OUT

η = P

OUT/PIN

LED

)

η = 0.432/0.62084
η = 70 %

Rev. 0 | Page 17 of 20

ADM8845

R

OUTLINE DIMENSIONS

PIN 1

INDICATOR

0.90

0.85

0.80

SEATING

PLANE

12° MAX

3.00

BSC SQ

TOP

VIEW

0.30

0.23

0.18
*

COMPLIANT TO JEDEC STANDARDS MO-220-VEED-2
EXCEPT FOR EXPOSED PAD DIMENSION

2.75

BSC SQ

0.80 MAX

0.65 TYP

0.20 REF

0.05 MAX

0.02 NOM

0.45

0.50

BSC

1.50 REF

0.60 MAX

Figure 35. 16-Lead Lead Frame Chip Scale Package [LFCSP]

(CP-16)

Dimensions shown in millimeters

13

12

EXPOSED

PAD

(BOTTOM VIEW)

9

8

0.50

0.40

0.30

16

1

4

5

PIN 1 INDICATO

1.45
*

1.30 SQ

1.15

0.25 MIN

ORDERING GUIDE

Model Temperature Range Package Description Package Option Branding

ADM8845ACP-REEL

ADM8845ACP-REEL7

ADM8845ACPZ-REEL

ADM8845ACPZ-REEL7

ADM8845ACPZ-WP

1, 2

1

1

−40ºC to + 85ºC

−40ºC to + 85ºC

−40ºC to + 85ºC

−40ºC to + 85ºC

−40ºC to + 85ºC

EVAL-ADM8845EB Evaluation Board

1

Z = Pb-free part.

2

WP = waffle pack.

16-Lead LFCSP CP-16 M0P

16-Lead LFCSP CP-16 M0P

16-Lead LFCSP CP-16 M0P

16-Lead LFCSP CP-16 M0P

16-Lead LFCSP CP-16 M0P

Rev. 0 | Page 18 of 20

ADM8845

NOTES

Rev. 0 | Page 19 of 20

ADM8845

NOTES

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

D04867–0–10/04(0)

Rev. 0 | Page 20 of 20