LINEAR TECHNOLOGY LTC3207, LTC3207-1 Technical data
LTC3207/LTC3207-1 User’s Guide
by Marty Merchant
Application Note 108
July 2007
INTRODUCTION
®
The LTC
3207/LTC3207-1 is a 600mA LED/Camera driver
which illuminates 12 Universal LEDs (ULEDs) and one
camera fl ash LED. The ULEDs are considered universal
because they may be individually turned on or off, set
in general purpose output (GPO) mode, set to blink at a
selected on-time and period, or gradate on and off at a
selected gradation rate. This device also has an external
enable (ENU) pin that may be used to blink, gradate, or
2
turn on/off the LEDs without using the I
C bus. This may be
useful if the microprocessor is in sleep or standby mode. If
used properly, these features may save valuable memory
2
space, programming time, and reduce the I
2
C Control
I
C traffi c.
The LTC3207/LTC3207-1 has 16 data registers, each
with its own sub-address as shown in Table 2. The data
is loaded into the registers when the device receives a
2
Stop bit. This device is written using the standard I
C
protocol. A 7-bit slave address and write bit is followed
by the 8-bit sub-address byte and an 8-bit data byte. The
only difference between the LTC3207 and LTC3207-1 is
2
C address.
the I
The LTC3207/LTC3207-1 is a slave I2C device that only
can receive data.
DATA BYTES
REG0 (Tables 3 and 4) is used to fl ash the CAM LED with
the CAMHL bit and set the charge pump to Auto, force 1x,
force 1.5x, or force 2x modes. It is also used to prepare for
a Quick write, or set the gradation UP bit. REG1 through
REG12 set the intensity and mode for the twelve individual
ULEDs (Table 5). REG13 is divided into two sub-registers
as illustrated in Table 6. The lower four bits, D3 to D0, are
the CAML register which sets the CAM LED in torch mode.
The upper four bits, D7 to D4, are the CAMH register, which
sets the CAM LED when in fl ash mode. REG14 is used to
select ULED1 to ULED8 for ENU control, as shown in Table
7. REG15 is separated into three portions as illustrated
in Tables 8 and 9. D3 to D0 are used to select ULED9 to
ULED12 for ENU control. D5 and D4 are used to control
the gradation time, while D7 and D6 are used to select the
blinking on-time and period.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Table 1. Features of LTC3207/LTC3207-1
FEATURE BENEFITS
12 Separate 27.5mA Current Sources 12 Individually Controlled LEDs
Camera LED High Current Torch Mode
Blink Mode Blinks One of Four Blinking Patterns
GPO Mode I
Gradation Gradually Turns On and Off LEDs
External Enable (ENU) Controls LEDs with Single Input
Auto Switching Charge Pump Automatically Switches to 1x, 1.5x, or 2x Modes for Better Effi ciency
Forced Charge Pump Mode Can Be Programmed to Remain in 1x, 1.5x or 2x Mode
High Current Flash
2
C Controlled Open Drain Drivers
an108f
AN108-1
Application Note 108
Table 2. Sub-Address Byte
MSB LSB
76543210 Register
XXXX0000 REG0
XXXX0001 REG1
XXXX0010 REG2
XXXX0011 REG3
XXXX0100 REG4
XXXX0101 REG5
XXXX0110 REG6
XXXX0111 REG7
XXXX1000 REG8
XXXX1001 REG9
XXXX1010 REG10
XXXX1011 REG11
XXXX1100 REG12
XXXX1101 REG13
XXXX1110 REG14
XXXX1111 REG15
X = Don’t Care
Table 3. REG0, Command Byte
MSB LSB
D7 D6 D5 D4 D3 D2 D1 D0
CAMHL Reserved Reserved Reserved Force2x Force1p5 Quickwrite UP
Table 4. Command Byte Bit Functions
UP 01Gradation Counts Down
Quickwrite 01Normal Write to Each Register
Force1p5 10Forces Charge Pump Into 1.5x Mode
Force2x 10Forces Charge Pump Into 2x Mode
Force1x
Reserved X
Reserved X
Reserved X
Camhilo 01External Control of CAM
Gradation Counts Up
Quick Write, REG1 Data is Written to All 12 Universal Registers
Enables Mode Logic to Control Mode Changes Based On Dropout Signal
Enables Mode Logic to Control Mode Changes Based On Dropout Signal
D2 (Force1p5x) = 1
D3 (Force2x) = 1
2
C Control of CAM
I
Forces Charge Pump Into 1x Mode
}
AN108-2
an108f
Application Note 108
Table 5. REG1 to REG12, Universal LED
BLINK/GRADATION/DROPOUT ENABLED LED CURRENT DATA
MSB LSB
Bits 76543210
Normal
Blink Enabled
Gradation Enabled
GPO Mode
Table 6. REG13, CAMH and CAML Registers
MSB HIGH BITS LSB MSB LOW BITS LSB
76543210
D3 D2 D1 D0 D3 D2 D1 D0
Table 7. REG14, Lower ENU Control Bits
MSB LSB
76543210
ULED8 ULED7 ULED6 ULED5 ULED4 ULED3 ULED2 ULED1
0
0
1
1
0
1
0
1
D5
D5
D5
D5
D4
D4
D4
D4
D3
D3
D3
D3
D2
D2
D2
D2
D1
D1
D1
D1
D0
D0
D0
D0
Table 8. REG15 MSB Nibble, Gradation and Blink Times
BLINK TIMES GRADATION TIMES
7 6 Blink Period 5 4 Gradation
0
0
1
1
0
1
0
1
0.625s
0.156s
0.625s
0.156s
Table 9. REG15 LSB Nibble, Upper ENU Control Bits
3210
ULED12 ULED11 ULED10 ULED9
1.25s
1.25s
2.5s
2.5s
ENU OUTPUT SELECTION
0
0
1
1
0
1
0
1
Disabled
0.24s
0.48s
0.96s
an108f
AN108-3
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