LINEAR TECHNOLOGY LTC3219 Technical data

Tiny Universal LED Driver Can Gradate, Blink or Turn On Nine
Individual LEDs with Minimal External Control – Design Note 422

Marty Merchant

Introduction

LEDs are the lighting workhorse of cell phones, MP3
players and diagnostic lights in telecom systems. Their
uses are many, from utilitarian backlighting to eye-catch­ing aesthetic effects such as slowly pulsing multicolor
indicators. As device designers strive to differentiate
their products on the shelf, the number and complexity of
lighting ef fects grows. It would seem that each new effect
requires signifi cant additional hardware, and/or complex
software, right? Actually, no, there is a way to apply these
effects to a number of LEDs with only a single driver IC.

®

The LTC

3219 9-output universal LED (ULED) driver
can be programmed to individually gradate, blink or
turn on nine individual LEDs using

internal

logic and
circuitry to drive nine 6-bit DAC-controlled LED current
sources. Because the gradation and blinking features
are controlled internally, effects can be realized without

2

adding ICs, extensively tying up the I

C bus or fi lling
valuable memory space with complex programming
subroutines. Any feature on any 0mA to 28mA output can
be confi gured to activate via the external enable (ENU)

2

pin or I

C interface.

The LTC3219 operates from a 2.9V to 5.5V input. The
charge pump provides up to 250 mA output current, and to
optimize effi ciency, it automatic ally changes charge pump
mode to 1x, 1.5x or 2x depending on the output current
requirement. Any of these modes can also be forced.

Blinking and Gradation Modes

Each output can be set to blink each output with a 156ms
or a 625ms on time and a 1.25s or a 2.5s period. Blink

2

mode can be initiated and ended via the I

C interface or
using the ENU pin. Once blinking has been initiated, the
LED(s) continue to blink without any interaction from the

2

C interface or the ENU pin. This allows the controlling

I
interface device to shutdown and save battery power
until needed.

The LTC3219 can gradually turn on, or gradually turn off
any number of the LED channels. The gradation ramps up

from 0mA to the programmed LED intensity with ramp
times of 240ms, 480ms or 960ms (likewise for turn off).
Like blinking mode, gradation mode can be implemented

2

via minimal I

C interaction or by the ENU pin as shown

in Figure 1.

Figure 1. The LTC3219 Gradating an LED from 0mA
to 28mA in 960ms. Prior to the Gradation Ramp, the
Gradation Timer, Up Bit and ULED Registers Are Set. A
Stop Bit on the Last I2C Write Starts the Gradation Ramp.
After the Gradation Ramp Has Finished, Gradation Is
Disabled with the LED Set at Full Intensity

Single IC Drives Cell Phone Backlight, New
Message/Missed Call/Battery Charger Indicator,
and RGB Function Select Button

The circuit in Figure 2 illustrates a fl ip cell phone lighting
circuit with four white LEDs for backlighting the keypad,
a multicolor indicator, and a function select button illumi­nated by an RGB LED. The multicolor indicator consists
of a red and a green LED. The RGB LED provides full
color gamut, including white by varying its individual
LED intensities.

When the cell phone is powered on or fl ipped open, the
keypad and the func tion select button gradually illuminate
to an intensity set by the baseband controller and CPU
using the gradation feature of the LTC3219. The Function
Select but ton may also gradually change colors using the
gradation feature. After an idle period or during power
off, the LEDs gradually turn off using the gradation fea-

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.

08/07/422

C2

1μF

C3

1μF

BACKLIGHT

FUNCTION SELECT

BUTTON RGB

DN422 F02

V

IN

BASEBAND

CONTROLLER

CPU

KEYPAD/BUTTON

INTERFACE

C1P C1M

C2P

C2M

LTC3219

GND

CPO

ULED1-4

ULED5-9

5

C4

2.2μF

MULTICOLOR

INDICATOR

V

IN

C1

2.2μF

24

SCL/SDA

I2C

ENU

Figure 2. A Single IC, Multilighting Cell Phone Application. The LTC3219 Comes in a
3mm × 3mm 20-Lead QFN Package and Only Requires Five External Components

C3

C2

2.2μF

2.2μF

BACKLIGHT VIBRATOR MOTOR

C6

0.1μF

0.1μF

C7

BASEBAND

CONTROLLER

CPU

C1P C1M

C2P

LTC3219

GND

C2M

CPO

ULED1-4

ULED5-8

ULED9

C4

2.2μF

4

5

V

BAT

DV

CC

V

BAT

C1

2.2μF

24

SCL/SDA

I2C

DV

CC

C5

0.1μF

ENU

V

CCIO

SOUND
DEVICE

DN422 F03

Figure 3. Cell Phone with Backlighting, Vibrator Motor and Sound Controller

ture. When a call is missed, the baseband controller and
CPU set the multicolor indicator to blink red to indicate
a missed call or blink green if the caller left a message.
Once the multicolor indicator is blinking, the baseband
controller hands of f control to the external enable pin and
shuts down to save battery power. The keypad and button
interface holds the ENU pin high until the cell phone user
takes action to turn off the blinking indicator.

Control for Cell Phone Backlight, Vibrator Motor
and Sound

Cell phones use various combinations of vibra tion, sound
and light to aler t the users of an incoming call or message.
Figure 3 illustrates a cell phone with four backlighting
LEDs, a vibrat or motor and a logic controlled sound device.
A single logic pin, ENU, turns on all simultaneously.

If the vibrator motor requires more than 100mA, simply
gang-up the ULED outputs to provide enough current. A

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small ceramic capacitor may be needed across the motor
terminals and between the ULED output pins and ground
to reduce inductive spikes and to prevent false dropout.

The speed and current in the motor is proportional to the
voltage across the motor, so the voltage across the motor
must be controlled in order to control the motor speed
and current. One voltage-control method is to connect
a shunt zener diode across the motor. Use a zener diode
that provides the desired voltage across the motor with
minimal zener current for maximum effi ciency.

Conclusion

The LTC3219 is a LED driver and charge pump which can
independently con trol nine outputs. Special features such
as gradation, blinking, and GPO modes require minimal

2

C communication. The LTC3219 is an ideal device for

I
many applications that use multiple lighting, logic or
other current controlled devices.

For applications help,

call [phone], Ext. 2364

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone]

●

FAX: [phone] ● www.linear.com

dn422f LT/TP 0807 305K • PRINTED IN THE USA

© LINEAR TECHNOLOGY CORPORATION 2007