Noty an115fa Linear Technology
LTC3220/LTC3220-1 User’s Guide
by Marty Merchant
Application Note 115
February 2008
INTRODUCTION
This application note illustrates how to program and use
the unique features of the LTC3220/LTC3220-1 Universal
LED (ULED) Driver. These features include individually
controlling, gradually turning on and off, or blinking up to
18 LEDs. This device may also be used to provide digital
signal(s) to other devices while in shutdown using a strong
pull-down general purpose output (GPO) and an external
power source. Current limited GPO mode may also be used
to control other devices using the charge pump output
(CPO) of the device or an external supply. A programmable
shutdown feature allows the device to go into and out
of shutdown returning to its pre-shutdown state. These
features give the user vast fl exibility and control of LEDs
and other devices while saving memory space, program-
2
ming time, I
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
C traffi c, and even battery power.
Table 1. Features of LTC3220
FEATURE BENEFITS
18 Separate Outputs 18 Individually Controlled 20mA Current Sources with 64-Step Linear Dimming Control
Blink Mode Blinks One of Four Blinking Patterns
Gradation Gradually Turns On and Off LEDs
2
GPO Mode (Strong) • I
GPO Mode (Current Limited) I2C Controlled Open Drain Drivers with Adjustable Current Limit
External Reset Resets All Internal Registers and Forces Part into Shutdown
Programmable Shutdown • I
Auto Switching Charge Pump Automatically Switches to 1x, 1.5x, or 2x Modes for Better Effi ciency
Forced Charge Pump Mode May Be Programmed to Remain in 1x, 1.5x, or 2x Mode
C Controlled Open Drain Drivers
• Operates in Shutdown, Low Q Current
2
C Controlled Shutdown
• Data Registers Retain Data and Outputs Return to Previous State when Shutdown Terminates
DV
C2
2.2μF
C1P C1M
V
IN
CC
I2C
RESET
C1
2.2μF
0.1μF
V
IN
DV
CC
SCL/SDA
RST
C3
2.2μF
C2P C2M
LTC3220
LTC3220-1
ULED1-18
GND
AN115 F01
Figure 1. Typical LTC3220 Application
CPO
C4
4.7μF
18
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Application Note 115
Table 2. Write Word Protocol Used By the LTC3220/LTC3220-1
171181811
S Slave Address Wr A *Sub-Address A Data Byte A P**
S = Start Condition, Wr = Write Bit = 0, A = Acknowledge, P = Stop Condition
*The sub-address uses only the fi rst 5 bits, D0, D1, D2, D3 and D4.
**Stop can be delayed until all of the data registers have been written.
Table 3. Sub-Address Byte Assignment
MSB LSB
76543210Register Function
00000000 REG0 COMMAND
00000001 REG1 ULED1
00000010 REG2 ULED2
00000011 REG3 ULED3
00000100 REG4 ULED4
00000101 REG5 ULED5
00000110 REG6 ULED6
00000111 REG7 ULED7
00001000 REG8 ULED8
00001001 REG9 ULED9
00001010 REG10 ULED10
00001011 REG11 ULED11
00001100 REG12 ULED12
00001101 REG13 ULED13
00001110 REG14 ULED14
00001111 REG15 ULED15
00010000 REG16 ULED16
00010001 REG17 ULED17
00010010 REG18 ULED18
00010011 REG19GRAD/ BLINK
I2C Control
The LTC3220/LTC3220-1 has 20 data registers, each with
its own sub-address as shown in Table 3. The data is
loaded into the registers when the device receives a Stop
2
bit. This device is written using the standard I
C protocol
(a 7-bit slave address and write bit, followed by the 8-bit
sub-address byte and an 8-bit data byte) as illustrated
2
in Table 2. This device is a slave I
C device that can only
receive data.
The only difference between the LTC3220 and the
2
LTC3220-1 is the 7-bit I
address is 0011100 and the LTC3220-1 I
C address. The LTC3220 I2C
2
C address is
0011101.
AN115-2
DATA BYTES
Register 0 (Table 4 and Table 5) is used to enter or exit
shutdown, set the charge pump to Auto, Force 1x, Force
1.5x, or Force 2x modes, and to parallel write to the part
using the Quick Write bit. Register 1 through register 18 set
the intensity and mode for each of the eighteen individual
ULED outputs (Table 6). Register 19 is separated into three
portions as illustrated in Table 7, Table 8 and Table 9. The
blink bits, D4 and D3, are used to select the blinking ontime and period. The gradation timer bits, D2 and D1, are
used to control the gradation time while the Up bit, D0, is
used to control the gradation ramp direction.
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Application Note 115
Table 4. REG0, Command Byte
MSB LSB
D7 D6 D5 D4 D3 D2 D1 D0
Unused Unused Unused Unused Shutdown Force2x Force1p5x Quick Write
Table 5. Command Byte Bit Functions
Quick Write 01Serial Write to Each Register
Force1p5x 10Forces Charge Pump into 1.5x Mode
Force2x 10Forces Charge Pump into 2x Mode
Force1x D1 (Force1p5x) =1
Shutdown 10Shuts Down Part, While Preserving Data in Registers
Table 6. REG1 to REG18, Universal LED 6-Bit Linear DAC Data with Blink/Gradation/GPO Modes
BLINK/GRADATION/GPO MODE BITS LED CURRENT DATA
Normal
Blink Enabled
Gradation Enabled
GPO Mode*
Strong Pull-Down Mode
Current Limited Mode
High Impedance/OFF
*(Gradation/Blink/Dropout Disabled)
Parallel Write, REG1 Data Is Written to All Eighteen Universal Registers
Enables Mode Logic to Control Mode Changes Based on Dropout Signal
Enables Mode Logic to Control Mode Changes Based on Dropout Signal
Forces Charge Pump into 1x Mode
D2 (Force2x) = 1
Normal Operation
MSB LSB
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
}
0
0
1
1
1
0
0
1
0
1
1
0
D5
D5
D5
0
D5
0
D4
D4
D4
0
D4
0
D3
D3
D3
0
D3
0
D2
D2
D2
D2
D1
D1
D1
0
0
0
D1
0
D0
D0
D0
0
D0
0
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Application Note 115
Table 7. REG19, Gradation and Blinking Register
MSB LSB
D7 D6 D5 D4 D3 D2 D1 D0
Unused Unused Unused GB4 GB3 GB2 GB1 UP
Table 8. Gradation Up Bit
UP 01Gradation Counts Down
Table 9. Gradation and Blinking Register Bit Functions
D4 D3 Blink Period D2 D1 Times Period
0
0
1
1
Gradation Counts Up
BLINK TIMES AND PERIOD GRADATION TIMES AND PERIOD
0
1
0
1
0.625s
0.156s
0.625s
0.156s
1.25s
1.25s
2.5s
2.5s
0
0
1
1
0
1
0
1
Disabled
0.24s
0.48s
0.96s
Disabled
0.313
0.625
1.25
AN115-4
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