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LTC3206EUF;LTC3206EUF#PBF;LTC3206EUF#TR;LTC3206EUF#TRPBF;中文规格书,Datasheet资料


LTC3206 I2C Multidisplay LED Controller

FEATURES
■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■

DESCRIPTIO

U APPLICATIO S
■ ■ ■

Step-Up/Direct-Connect Fractional Charge Pump Provides Up to 92% Efficiency Up to 400mA Continuous Output Current Independent Current and Dimming Control for 1-6 LED MAIN, 1-4 LED SUB and RGB LED Displays LED Currents Programmable Using 2-Wire I2C? Serial Interface 1% LED Current Matching Low Noise Constant Frequency Operation* Minimal Component Count Automatic Soft-Start Limits Inrush Current 16 Exponentially Spaced Dimming States Provides 128:1 Brightness Range for MAIN and SUB Displays Up to 4096 Color Combinations for RGB Display Low Operating Current: IVIN = 180?A Tiny, Low Profile 24-Lead (4mm × 4mm × 0.75mm) QFN Package

The LTC?3206 is a highly integrated multidisplay LED controller. The part contains a high efficiency, low noise fractional step-up/direct-connect charge pump to provide power for both main and sub white LED displays plus an RGB color LED display. The LTC3206 requires only four small ceramic capacitors plus two resistors to form a complete 3-display LED power supply and current controller. Maximum currents for the main/sub displays and RGB display are set independently. Current for each LED is controlled with an internal current source. Dimming and ON/OFF control for all displays is achieved via a 2-wire serial interface. Two auxiliary LED pins can be individually assigned to either the MAIN or SUB displays. 16 individual dimming states exist for both the MAIN and SUB displays. Each of the RED, GREEN and BLUE LEDs have 16 dimming states as well, resulting in up to 4096 color combinations. The LTC3206 charge pump optimizes efficiency based on VIN and LED forward voltage conditions. The part powers up in direct-connect mode and automatically switches to 1.5x step-up mode once any enabled LED current source begins to enter dropout. Internal circuitry prevents inrush current and excess input noise during start-up and mode switching. The LTC3206 is available in a 24-lead (4mm × 4mm) QFN package.

Cellular Phones Wireless PDAs Multidisplay Handheld Devices

, LTC and LT are registered trademarks of Linear Technology Corporation. I2C is a trademark of Philips Electronics N.V. * U.S. Patent 6,411,531

TYPICAL APPLICATIO
2.2?F VIN 2.7V TO 4.5V 2.2?F VIN 2.2?F LTC3206 MAIN1-4 AUX 1 SUB1-2 AUX 2 I2C SERIAL INTERFACE 2 SERIAL PORT RGB IRGB IMS 3 2 4 CPO

MAIN DISPLAY

SUB DISPLAY

RGB ILLUMINATOR EFFICIENCY (PLED/PIN) (%) 2.2?F

RED

GREEN BLUE

3206 TA01a

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5-LED Main Display Efficiency vs Input Voltage
100 90 80 70 60 50 40 30 20 10 FIVE LEDs AT 15mA/LED (TYP VF AT 15mA = 3.2V) TA = 25°C 3.3 3.6 3.9 INPUT VOLTAGE (V) 4.2
3206 TA01b

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0 3.0

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LTC3206

ABSOLUTE
(Note 1)

AXI U RATI GS

U W U PACKAGE/ORDER I FOR ATIO
TOP VIEW

VIN, DVCC, CPO to GND............................... – 0.3V to 6V SDA, SCL, ENRGB/S ................. – 0.3V to (DVCC + 0.3V) ICPO (Continuous) (Note 4) ................................ 400mA (Pulsed at 10% Duty Cycle) (Note 4) ..................... 1A IMAIN1-4, ISUB1,2, IAUX 1, 2 (Note 4) ..................... 100mA (Pulsed at 10% Duty Cycle) (Note 4) .............. 125mA IRED,GREEN,BLUE (Note 4) ..................................... 100mA (Pulsed at 10% Duty Cycle) (Note 4) .............. 125mA IMS, IRGB (Note 4) .................................................. 1mA CPO Short-Circuit Duration ............................ Indefinite Operating Temperature Range (Note 2) .. – 40°C to 85°C Storage Temperature Range ................. – 65°C to 125°C

MAIN1

MAIN2

MAIN3

24 23 22 21 20 19 SUB1 1 SUB2 2 C2– 3 C1– 4 C1+ 5 C2+ 6 7
DVCC

MAIN4

AUX2

AUX1

ENRGB/S

SDA

SCL

IRGB

IMS

The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, DVCC = 3V unless otherwise noted.
SYMBOL PARAMETER Input Power Supply VIN Operating Voltage DVCC Operating Voltage VIN Operating Current DVCC Operating Current VIN Shutdown Current DVCC Shutdown Current White LED Current (MAIN1-MAIN4, SUB1, SUB2, AUX1, AUX2) IMS Servo Voltage Full-Scale LED Current Ratio (ILED/IMS) LED Dropout Voltage LED Brightness Range LED Current Matching RGB LED Current (RED, GREEN, BLUE) IRGB Servo Voltage LED Current Ratio (ILED/IRGB) RGB LED Dropout Voltage RGB PWM (Duty Factor) Range Charge Pump (CPO) 1x Mode Output Impedance 1.5x Mode Output Impedance VIN = 3V, VCPO = 4.2V (Note 3) 0.68 1.90 ? ? 25?A < IRGB < 75?A RED, GREEN, BLUE Voltage = 1V 1.5x Mode Switch Threshold, ILED = 20mA 0/15
● ● ●

ELECTRICAL CHARACTERISTICS

CONDITIONS

ICPO = IMS = IRGB = 0?A, Direct-Connect Mode ICPO = IMS = IRGB = 0?A, 1.5x Step-Up Mode Serial Port Idle

25?A < IMS < 75?A MAIN1-MAIN4, SUB1, SUB2, AUX1, AUX2, Voltage = 1V 1.5x Mode Switch Threshold, ILED = 20mA

MAIN-MAIN, MAIN-AUX, SUB-SUB, SUB-AUX 0.585 0.582 360

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ORDER PART NUMBER
18 BLUE 17 GREEN 16 RED

LTC3206EUF

25

15 VIN 14 CPO 13 SGND

8

9 10 11 12

UF PART MARKING 3206

UF PACKAGE 24-LEAD (4mm × 4mm) PLASTIC QFN

TJMAX = 125°C, θJA = 37°C/W, θJC = 2°C/W EXPOSED PAD IS PGND (PIN 25) MUST BE SOLDERED TO PCB

Consult LTC Marketing for parts specified with wider operating temperature ranges.

MIN 2.7 1.5

TYP

MAX 4.5 5.5

UNITS V V ?A mA

180 3.9 1 7.3 10 1 0.585 0.582 368 0.78 1 0.6 0.6 400 80 15/15 0.615 0.618 440 0.6 0.6 400 80 100 0.615 0.618 432

?A ?A ?A V V mA/mA mV % % V V mA/mA mV %

● ●

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The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, DVCC = 3V unless otherwise noted.
SYMBOL PARAMETER CPO Regulation Voltage CLK Frequency SDA, SCL, ENRGB/S VIL VIH IIH IIL VOL tSCL tBUF tHD, STA tSU, STA tSU, STD tHD, DAT(OUT) tHD, DAT(IN) tSU, DAT tLOW tHIGH tf tr tSP Low Level Input Voltage High Level Input Voltage Input Current Input Current Digital Output Low (SDA) Clock Operating Frequency Bus Free Time Between Stop and Start Condition Hold Time After (Repeated) Start Condition Repeated Start Condition Setup Time Stop Condition Setup Time Data Hold Time Input Data Hold Time Data Setup Time Clock Low Period Clock High Period Clock Data Fall Time Clock Data RiseTime Spike Suppression Time 1.3 0.6 0.6 0.6 225 0 100 1.3 0.6 20 20 50 with statistical process controls. Note 3: 1.5x mode output impedance is defined as (1.5VIN – VCPO)/IOUT. Note 4: Based on long term current density limitations. Note 5: All values are referenced to VIH and VIL levels. 300 300 900 900 SDA, SCL, ENRGB/S = DVCC SDA, SCL, ENRGB/S = 0V IPULLUP = 3mA
● ● ●

ELECTRICAL CHARACTERISTICS

CONDITIONS ICPO = 20mA, 1.5x Mode

MIN 0.68

TYP 4.75 0.96

MAX 1.36 0.3 ? DVCC

UNITS V MHz V V ?A ?A V kHz ?s ?s ?s ?s ns ns ns ?s ?s ns ns ns

0.7 ? DVCC –1 –1 1 1 0.4 400

Timing Characteristics (Note 5)

Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LTC3206E is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation

TYPICAL PERFOR A CE CHARACTERISTICS
LED Pin Sink Current vs LED Pin Voltage
100% LED PIN DROPOUT VOLTAGE (mV) CPO AC COUPLED (50mV/DIV) ILED 2.5mA/DIV 50% VIN AC COUPLED (50mV/DIV)

25%

0mA 200mV/DIV VLED AT CURRENT SOURCE PIN
3206 G01

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Input and Output Charge Pump Noise
500

LED Pin Dropout Voltage vs LED Pin Current
VIN = 3.6V TA = 25°C

400

300

200

ICPO = 200mA 500ns/DIV VIN = 3.6V CIN = CCPO = 1.6?F

3206 G02

100

0 10 20 30 40 50 60 70 80 LED CURRENT (mA) 90 100
3206 GO3

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LTC3206 TYPICAL PERFOR A CE CHARACTERISTICS
1x Mode Switch Resistance vs Temperature
0.9 ICPO = 100mA

SWITCH RESISTANCE (?)

0.8 VIN = 3.3V VIN = 3.6V 0.7 VIN = 3.9V

OUTPUT RESISTANCE (?)

CPO VOLTAGE (V)

0.6

0.5 –40

–15

35 10 TEMPERATURE (°C)

Oscillator Frequency vs Supply Voltage
1100
DVCC SHUTDOWN CURRENT (?A)

1000
FREQUENCY (kHz)

TA = 25°C TA = –40°C

0.4 TA = 25°C TA = –40°C 0.2 TA = 85°C

VIN SHUTDOWN CURRENT (?A)

900

TA = 85°C

800

700 2.7 3.0 4.2 3.3 3.6 3.9 VIN SUPPLY VOLTAGE (V) 4.5
3206 G07

1x Mode No Load Supply Current vs Input Voltage
300 TA = 25°C IMS = IRGB = 0?A
SUPPLY CURRENT (mA)

SUPPLY CURRENT (?A)

250

LED CURRENT (mA)

200

150

100 2.7 3.0 3.3 3.6 3.9 INPUT VOLTAGE (V) 4.2 4.5
3206 G10

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60
3206 G04

1.5x Mode Charge Pump OpenLoop Output Resistance vs Temperature (1.5VIN – VCPO)/ICPO
2.50 VIN = 3V VCPO = 4.2V CIN = CCPO = CFLY1 = CFLY2 = 1.6?F
4.8 4.7 4.6 4.5 4.4 4.3

1.5x Mode CPO Voltage vs Load Current
CIN = CCPO = CFLY1 CFLY2 = 1.6?F TA = 25°C 3.6V 3.5V 3.4V 3.3V 3.2V

2.25

2.00

3.1V 4.2 4.1 4.0 3.9 VIN = 3V

1.75

85

1.50 –40

–15

10 35 TEMPERATURE (°C)

60

85
3206 G05

3.8

0

100

300 400 200 LOAD CURRENT (mA)

500
3206 G06

DVCC Shutdown Current vs Input Voltage
0.5 VIN = 3.6V 8 10

VIN Shutdown Current vs Input Voltage
DVCC = 3V TA = 85°C TA = 25°C

TA = –40°C 6

0.3

4

0.1

2

0

2.7

3.0

3.3 3.6 3.9 DVCC VOLTAGE (V)

4.2

4.5
3206 G08

0

2.7

3.0

3.3 3.6 3.9 INPUT VOLTAGE (V)

4.2

4.5
3206 G09

1.5x Mode Supply Current vs ICPO (IIN – 1.5ICPO)
10 VIN = 3.6V TA = 25°C 8

LED Pin Voltage for Higher LED Currents
120 100 80 IMS, IRGB = 150?A 60 40 20 0 IMS, IRGB = 100?A IMS, IRGB = 50?A VIN = 3.6V TA = 25°C IMS, IRGB = 250?A IMS, IRGB = 200?A

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4

2

0

0

50

100 150 200 LOAD CURRENT (mA)

250

300

0

0.2

0.4 0.6 0.8 LED PIN VOLTAGE (V)

1.0
3206 G12

3206 G11

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LTC3206

PI FU CTIO S
SUB1, SUB2 (Pins 1, 2): Current Source Outputs for the SUB Display White LEDs. The current for the SUB display is controlled by the resistor on the IMS pin.The LEDs on the SUB display can be set to exponentially increasing brightness levels from 0.78% to 100% of full-scale. See Table 1. C1+, C1–, C2+, C2– (Pins 5, 4, 6, 3): Charge Pump Flying Capacitor Pins. A 2.2?F X7R or X5R ceramic capacitor should be connected from C1+ to C1– and another from C2+ to C2–. DVCC (Pin 7): This pin sets the logic reference level of the SDA, SCL and ENRGB/S pins. SDA (Pin 8): Input Data for the I2C Serial Port. Serial data is shifted in one bit per clock to control the LTC3206 (see Figures 3 and 4). The logic level for SDA is referenced to DVCC. SCL (Pin 9): Clock Input for the I2C Serial Port (see Figures 3 and 4). The logic level for SCL is referenced to DVCC. ENRGB/S (Pin 10): This pin is used to enable and disable either the RED, GREEN and BLUE current sources or the SUB display depending on which is programmed to respond via the I2C port. Once ENRGB/S is brought high, the LTC3206 illuminates the RGB or SUB display with the color combination or intensity that was previously programmed via the I2C port. The logic level for ENRGB/S is referenced to DVCC. IMS (Pin 11): This pin controls the maximum amount of LED current in both the MAIN and SUB LED displays. The IMS pin servos to 0.6V when there is a resistor to ground. The full scale (100%) currents in the MAIN and SUB display LEDs will be 400 times the current at the IMS pin. IRGB (Pin 12): This pin controls the amount of LED current at the RED, GREEN and BLUE LED pins. The IRGB pin servos to 0.6V when there is a resistor to ground. The current in the RED, GREEN and BLUE LEDs will be 400 times the current at the IRGB pin when programmed to full scale. SGND (Pin 13): Ground for the control logic. This pin should be connected directly to a low impedance ground plane. CPO (Pin 14): Output of the Charge Pump. This output should be used to power white, blue and “true” green LEDs. Red LEDs can be powered from VIN or CPO. An X5R or X7R low impedance (ceramic) 2.2?F charge storage capacitor is required on CPO. VIN (Pin 15): Supply Voltage for the Charge Pump. The VIN pin should be connected directly to the battery and bypassed with a 2.2?F X5R or X7R ceramic capacitor. RED, GREEN, BLUE (Pins 16, 17, 18): Current Source Outputs for the RGB Illuminator LEDs. The currents for the RGB LEDs are controlled by the resistor on the IRGB pin. The RGB LEDs can independently be set to any duty cycle from 0/15 through 15/15 under software control giving a total of 16 shades per LED and 4096 colors for the illuminator. See Table 1. The RGB LEDs are modulated at 1/240 the speed of the charge pump oscillator (approximately 4kHz). MAIN1-MAIN4 (Pins 22, 21, 20, 19): Current Source Outputs for the Main Display White LEDs. The current for the main display is controlled by the resistor on the IMS pin. The LEDs on the MAIN display can be set to 16 exponentially increasing brightness steps from 0.78% to 100% of full scale. See Table 1. AUX1, AUX2 (Pins 23, 24): Current source outputs for the auxiliary white LEDs. The auxiliary current sources can be individually assigned to be either MAIN display or SUB display LEDs via the I2C serial port. When either AUX1 and/ or AUX2 are assigned to the MAIN display they will have the same power setting as the other MAIN LEDs. Likewise, when either AUX1 and/or AUX2 are assigned to the SUB display they will have the same power setting as the other SUB LEDs. The currents for the AUX1 and AUX2 pins are controlled by the resistor on the IMS pin. PGND (Pin 25, Exposed Pad): Power Ground for the Charge Pump. This pin should be connected directly to a low impedance ground plane.

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LTC3206

BLOCK DIAGRA

VIN 15 1x AND 1.5x CHARGE PUMP

IMS 11 23 AUX1

IRGB 12 SGND 13 2

DVCC 7 ENRGB/S 10 CONTROL LOGIC 4 4 COMMAND LATCH STOP SDA 8 SCL 9 24 I2C SERIAL PORT PWM 4 4 4 16 RED 17 GREEN 18 BLUE

U OPERATIO
Power Management To optimize efficiency, the power management section of the LTC3206 provides two methods of supplying power to the CPO pin: 1x direct connect mode or 1.5x boost mode. When any display of the LTC3206 is enabled, the power management system connects the CPO pin directly to VIN with a low impedance switch. If the voltage supplied at VIN is high enough to power all of the LEDs with the programmed current, the system will remain in this “direct connect” mode providing maximum efficiency. Internal circuits monitor all current sources for the onset of “dropout,” the point at which the current sources can no longer supply programmed current. As the battery voltage falls, the LED with the largest forward voltage will reach the dropout threshold first. When any of the LED pins reach the dropout threshold, the LTC3206 will switch to boost mode and automatically soft-start the 1.5x boost charge pump. The constant frequency charge pump is designed to minimize the amount of noise generated at the VIN supply.
3206f

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C1+ 5 C1– 4 C2+ 6 C2– 3 960kHz OSCILLATOR 25 PGND 14 CPO

– +

ENABLECP

22 MAIN1

+ –

21 MAIN2 20 MAIN3 19 MAIN4

+
2

24 AUX2



2 1 SUB1 2 SUB2

3206 BD

LTC3206
U OPERATIO
The 1.5x step-up charge pump uses a patented constant frequency architecture to combine the best efficiency with the maximum available power at the lowest noise level. The charge pump of the LTC3206 can be forced to come on even if no LEDs are programmed for current. Setting bit A3 in the I2C serial port forces the charge pump on (see Figure 3). Soft-Start To prevent excessive inrush current and supply droop when switching into step-up mode, the LTC3206 employs a soft-start feature on its charge pump. The current available to the CPO pin is increased linearly over a period of about 400?s. Charge Pump Strength When the LTC3206 operates in 1.5x boost mode, the charge pump can be modeled as a Thevenin-equivalent circuit to determine the amount of current available from the effective input voltage, 1.5VIN and the effective openloop output resistance, ROL (Figure 1). ROL is dependent on a number of factors including the switching term, 1/(2fOSC ? CFLY), internal switch resistances and the non-overlap period of the switching circuit. However, for a given ROL, the amount of current available will be directly proportional to the advantage voltage 1.5VIN – VCPO. Consider the example of driving white LEDs from a 3.1V supply. If the LED forward voltage is 3.8V and the current sources require 100mV, the advantage voltage is 3.1V ? 1.5 – 3.8V – 0.1V or 750mV. Notice that if the input voltage is raised to 3.2V, the advantage voltage jumps to 900mV—a 20% improvement in available strength. From Figure 1, the available current is given by:
IOUT 1.5VIN – VCPO = ROL
ROL

Typical values of ROL as a function of temperature are shown in Figure 2.
2.50 VIN = 3V VCPO = 4.2V CIN = CCPO = CFLY1 = CFLY2 = 1.6?F

OUTPUT RESISTANCE (?)

2.25

2.00

1.75

1.50 –40

–15

10 35 TEMPERATURE (°C)

60

85
3206 F02

Figure 2. Typical ROL vs Temperature

I2C Interface The LTC3206 communicates with a host (master) using the standard I2C 2-wire interface. The Timing Diagram (Figure 4) shows the timing relationship of the signals on the bus. The two bus lines, SDA and SCL, must be high when the bus is not in use. External pull-up resistors or current sources, such as the LTC1694 SMBus accelerator, are required on these lines. The LTC3206 is a receive-only (slave) device. Bus Speed The I2C port is designed to be operated at speeds of up to 400kHz. It has built-in timing delays to ensure correct operation when addressed from an I2C compliant master device. It also contains input filters designed to suppress glitches should the bus become corrupted. START and STOP Conditions A bus-master signals the beginning of a communication to a slave device by transmitting a START condition. A START condition is generated by transitioning SDA from high to low while SCL is high. When the master has finished communicating with the slave, it issues a STOP condition by transitioning SDA from low to high while SCL is high. The bus is then free for communication with another I2C device.
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CPO

+ –

1.5VIN


3206 F01

Figure 1. Equivalent Open-Loop Circuit

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LTC3206
U OPERATIO
Byte Format Each byte sent to the LTC3206 must be 8 bits long followed by an extra clock cycle for the Acknowledge bit to be returned by the LTC3206. The data should be sent to the LTC3206 most significant bit (MSB) first. Acknowledge The Acknowledge bit is used for handshaking between the master and the slave. An Acknowledge (active LOW) generated by the slave (LTC3206) lets the master know that the latest byte of information was received. The Acknowledge related clock pulse is generated by the master. The master releases the SDA line (HIGH) during the Acknowledge clock cycle. The slave-receiver must pull down the SDA line during the Acknowledge clock pulse so that it remains a stable LOW during the HIGH period of this clock pulse. Slave Address The LTC3206 responds to only one 7-bit address which has been factory programmed to 0011011. The eighth bit of the address byte (R/W) must be 0 for the LTC3206 to recognize the address since it is a write only device. This is equivalent to an 8-bit address where the least significant bit of the address is always 0. If the correct seven bit address is given but the R/W bit is 1, the LTC3206 will not respond. Bus Write Operation The master initiates communication with the LTC3206 with a START condition and a 7-bit address followed by the Write Bit R/W = 0. If the address matches that of the LTC3206, the LTC3206 returns an Acknowledge. The master should then deliver the most significant data byte. Again the LTC3206 acknowledges and the cycle is repeated two more times for a total of one address byte and three data bytes. Each data byte is transferred to an internal holding latch upon the return of an Acknowledge. After all three data bytes have been transferred to the LTC3206, the master may terminate the communication with a STOP condition. Alternatively, a REPEAT-START condition can be initiated by the master and another chip on the I2C bus can be addressed. This cycle can continue indefinitely and the LTC3206 will remember the last input of valid data that it received. Once all chips on the bus have been addressed and sent valid data, a STOP condition can be sent and the LTC3206 will update its command latch with the data that it had received. In certain circumstances, the data on the I2C bus may become corrupted. In these cases the LTC3206 responds appropriately by preserving only the last set of complete data that it has received. For example, assume the LTC3206 has been successfully addressed and is receiving data when a STOP condition mistakenly occurs. The LTC3206 will ignore this stop condition and will not respond until a new START condition, correct address, new set of data and STOP condition are transmitted. Likewise, if the LTC3206 was previously addressed and sent valid data but not updated with a STOP, it will respond to any STOP that appears on the bus independent of the number of REPEAT-STARTs that have occurred. An exception occurs if a REPEAT-START is given and the LTC3206 successfully acknowledges its addressed. In this case, it will not respond to a STOP after the first data byte is acknowledged. It will, however, respond after the third data byte is acknowledged.

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ENSUB_ENRGB

AUXSEL1

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1 0 C7 C6 C5 C4 C3 C2 C1 C0 STOP 1 0 ACK A7 A6 A5 A4 A3 A2 A1 A0 ACK B7 B6 B5 B4 B3 B2 B1 7 8 9 1 2 3 4 5 6 7 8 9
3206 FO3

0

0

1

1

0

1

A7 A6 A5 A4 A3 A2 A1 A0 B7 B6 B5 B4 B3 B2 B1 B0

START B0 ACK C7 C6 C5 C4 C3 C2 C1 C0 ACK

SDA

0

0

1

1

0

1

SCL

1 7 8 9 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6

2

3

4

5

6

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Figure 3. Bit Assignments

SDA tSU, DAT tLOW tHD, DAT
3206 F04

AUXSEL0

ADDRESS WR

FORCE CHARGE PUMP

RED BLUE GREEN MAIN SUB

tSU, STA tHD, STA tBUF tSU, STO

SCL tHD, STA tSP tf REPEATED START CONDITION STOP CONDITION START CONDITION START CONDITION tr tHIGH

Figure 4. Timing Parameters

Table 1. Serial Port Bit Assignments
A5 B1 B5 C5 C1 MAIN SUB AUX RED GREEN BLUE A4 B0 B4 C4 C0

RED GREEN BLUE MAIN SUB

A7 B3 B7 C7 C3

A6 B2 B6 C6 C2

Table 2. Auxilliary LED Pin Assignments
A0 0 0 1 1 A1 0 1 0 1 AUX1 MAIN MAIN SUB SUB AUX2 MAIN SUB MAIN SUB

Table 3. ENRGB/S Assignment
A2 0 1 CONTROL RGB DISPLAY SUB DISPLAY

HEX 0 1 2 3 4 5 6 7 8 9 A B C D E F 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1

4-BIT CODE 0 0 0 0 0 1 0 1 1 0 1 0 1 1 1 1 0 0 0 0 0 1 0 1 1 0 1 0 1 1 1 1

BRIGHTNESS SUB-RANGE DUTY CYCLE LEVEL NA NA OFF 1/4 3.13% 0.78% 1/4 4.42% 1.07% 1/4 6.25% 1.56% 1/4 8.80% 2.25% 1/4 12.50% 3.13% 1/4 17.70% 4.40% 1/4 25.00% 6.25% 1/4 35.35% 8.90% 1/4 50.00% 12.50% 1/4 70.70% 17.70% 1/4 100.00% 25.00% 1/2 70.70% 35.35% 1/2 100.00% 50.00% 1 70.70% 70.70% 1 100.00% 100.00% BRIGHTNESS LEVEL OFF 1/15(6.7%) 2/15(13.3%) 3/15(20.0%) 4/15(26.7%) 5/15(33.3%) 6/15(40.0%) 7/15(46.7%) 8/15(53.3%) 9/15(60.0%) 10/15(66.6%) 11/15(73.3%) 12/15(80.0%) 13/15(86.7%) 14/15(93.3%) 15/15(100.0%)

LTC3206

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LTC3206

APPLICATIO S I FOR ATIO
White LED Brightness Control

The White LED displays (MAIN, SUB and AUX) have 16 individual brightness settings. The settings are exponentially spaced to compensate for the nearly logarithmic characteristic of human vision perception. The base of the power settings is √2 . The off setting (0 power) is a special case needed for shutdown. The LTC3206 uses a subranging technique to control the LED brightness with a combination of both DC level control and pulse width modulation. Table 1 summarizes the level control operation. The DC level of the LEDs will be one of either three sub-range settings, 100%, 50% or 25% of full scale. For example, if the full scale LED current is programmed (via the IMS pin) to be 20mA, then the “on” level of the LED will be either 20mA, 10mA or 5mA respectively. The power to the LED will be the product of the subrange (DC current) and the PWM setting. For example, if an LED power of 2.25% is desired, then the LTC3206 sets the sub range to 25% and the duty cycle to 8.8%. These settings are designed to optimize the efficiency of the dual-mode LTC3206 power management system while preserving LED color accuracy at low power levels. To achieve brightness control by purely DC means, only the 100%, 50% or 25% power settings should be selected. The DC current levels of the MAIN, SUB and AUX LEDs are controlled by a precisely mirrored multiple of the current at the IMS pin. The IMS pin servos to a fixed level of 0.6V so the current is programmed simply by adding a resistor from IMS to ground. The current that flows during the “on” time will follow the relationship:

0.6V ILED = 400 ? S ? RMS
where S is the subrange for the given power setting (it will be either 25%, 50% or 100%, see Table 1) and RMS is the value of the resistor at the IMS pin. The average LED current (LED power level) will follow the relationship:

http://oneic.com/

10

U
AVG (ILED ) = 400 ?
D ? 15 0.6V ? 2 RMS

W

U U

where D is the decimal equivalent of the 4-bit digital code programmed for the given display (0 to 15). The PWM frequency is 1/1024 of the frequency of the charge pump oscillator (typically 938Hz). During PWM, the LED currents are soft-switched to minimize noise. AUX LEDs The AUX1 and AUX2 LEDs can be arbitrarily assigned to either the MAIN or SUB display. Table 2 summarizes the assignment possibilities. When an AUX pin is assigned to a display, it will follow the power level (both DC and PWM) set for that display. Unused White LED Pins The LTC3206 can power up to eight white LEDs (four for the MAIN display, two for the SUB display and the two flexible AUX pins), however, it is not necessary to use all eight in each application. Any of these LED pins can cause the LTC3206 to switch from 1x mode to 1.5x charge pump mode if they drop out. In fact, if an unused LED pin is left unconnected or grounded, it will drop out and force the LTC3206 into charge pump mode. To avoid this problem, unused MAIN, SUB or AUX LED pins can be disabled by connecting them to CPO. Power is not wasted in this configuration. When the LED pin voltage is within approximately 1V of CPO, its LED current is switched off and only a small 10?A test current remains. Figure 5 shows a block diagram of each of the MAIN, SUB and AUX LED pins.
CPO 1V

+ –
ENABLE ILED

–+

MAIN1-MAIN4 SUB1, SUB2, AUX1, AUX2

10?A

3206 F05

Figure 5. Internal MAIN, SUB and AUX LED Disable Circuit
3206f

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