LTC3208

FEATURES ■ ■ ■ LTC3208 High Current Software Configurable Multidisplay LED Controller DESCRIPTIO The LTC®3208 is a highly integrated multidisplay LED controller. The part contains a 1A high efficiency, low noise charge pump to provide power to the MAIN, SUB, RGB, CAM and AUX LED displays. The LTC3208 requires only small ceramic capacitors and one current set resistor to form a complete LED power supply and current controller. The maximum display currents are set by a single external resistor. Current for each LED is controlled by a precision internal current source. Dimming and On/Off for all displays is achieved via the I2C serial interface. 256 brightness levels are available for the MAIN and SUB displays. 16 levels are available for the RGB and CAM displays. Four AUX current sources can be independently assigned via the I2C port to the CAM, SUB, MAIN or AUX DAC controlled displays. The LTC3208 charge pump optimizes efficiency based on the voltage across the LED current sources. The part powers up in 1x mode and will automatically switch to boost mode whenever any enabled LED current source begins to enter dropout. The first dropout switches the part into 1.5x mode and a subsequent dropout switches the LTC3208 into 2x mode. The part is available in a small 5mm × 5mm 32-lead QFN package. ■ ■ ■ ■ ■ ■ ■ ■ ■ 1x/1.5x/2x Charge Pump Provides Up to 95% Efficiency Up to 1A Total Output Current 17 Current Sources Available as MAIN, SUB, RGB, CAM and AUX LED Drivers LED ON/OFF, Brightness Level and Display Configuration Programmable Using 2-Wire I2C™ Interface Low Noise Constant Frequency Operation with Flying Capacitor Edge Rate Control Automatic Charge Pump Mode Switching Internal Soft-Start Limits Inrush Current During Startup and Mode Switching Open/Shorted LED Protection Short-Circuit/Thermal Protection 256 Brightness States for MAIN and SUB Displays 4096 Color Combinations for the RGB Display 5mm × 5mm 32-Lead QFN Plastic Package APPLICATIO S ■ Video/Camera Phones with QVGA + Displays , LTC and LT are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 6411531. TYPICAL APPLICATIO C2 2.2mF C3 2.2mF VBAT C1 4.7mF EFFICIENCY (PLED/PIN) (%) C1P C1M C2P C2M VBAT1,2,3 CPO C4 4.7mF 4 2 4 3 4 MAIN SUB CAMERA RGB AUX LTC3208 MAIN1-4 I2C ENABLE DISABLE LOW HI SCL/SDA ENRGBS CAMHL RREF 24.3k 1% SUB1-2 CAM1-4 RGB AUX1-4 GND U U U 4-LED MAIN Display Efficiency vs Input Voltage 100 90 80 70 60 50 40 30 20 4 LEDs AT 15mA/LED 10 (TYP VF AT 15mA = 3.2V) TA = 25°C 0 3.0 3.2 3.4 3.6 3.8 VBAT (V) 4.0 4.2 4.4 3208 TA01a 3208 TA01b 3208fa 1 LTC3208 ABSOLUTE (Note 1) AXI U RATI GS PACKAGE/ORDER I FOR ATIO TOP VIEW ENRGBS VBAT1 C1M C2M GND CPO C1P C2P VBAT, DVCC, CPO to GND ................................– 0.3 to 6V SDA, SCL, ENRGBS, CAMHL .....– 0.3V to (DVCC + 0.3V) ICPO (Note 2) ............................................................1.3A IMAIN1-4, ISUB1-2 (Note 3) .......................................33mA IRED, IGRN, IBLUE (Note 3) .......................................33mA ICAM1-4, IAUX1-4 (Note 3) ......................................120mA CPO, RREF Short-Circuit Duration .................... Indefinite Operating Temperature Range (Note 4) .. – 40°C to 85°C Storage Temperature Range.................. – 65°C to 125°C 32 31 30 29 28 27 26 25 CAM1 1 CAM2 2 CAM3 3 CAM4 4 AUX1 5 AUX2 6 AUX3 7 AUX4 8 9 10 11 12 13 14 15 16 MAIN1 CAMHL MAIN2 SDA SCL VBAT3 DVCC RREF 33 24 VBAT2 23 RED 22 GRN 21 BLUE 20 SUB1 19 SUB2 18 MAIN4 17 MAIN3 UH PACKAGE 32-LEAD (5mm × 5mm) QFN EXPOSED PAD IS GND (PIN 33) MUST BE SOLDERED TO PCB TJMAX = 125°C, θJA = 34°C/W ORDER PART NUMBER LTC3208EUH UH PART MARKING 3208 Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for parts specified with wider operating temperature ranges. The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VBAT = 3.6V, DVCC = 3V, ENRGBS = Hi, RREF = 24k, C2 = C3 = 2.2µF, C1 = C4 = 4.7µF, unless otherwise noted. PARAMETERS VBAT Operating Voltage IVBAT Operating Current CONDITIONS ● ELECTRICAL CHARACTERISTICS MIN 2.9 TYP 280 4.7 7 MAX 4.5 UNITS V µA mA mA V µA V V µA V k mA µA % mV 3208fa ICPO = 0, 1x Mode, LEDs Disabled ICPO = 0, 1.5x Mode ICPO = 0, 2x Mode ● DVCC Operating Voltage DVCC Operating Current VBAT UVLO Threshold DVCC UVLO Threshold VBAT Shutdown Current RREF VRREF RRREF White LED Current (MAIN1-4, SUB1-2), 8-Bit Linear DACs Full-Scale LED Current Minimum (1LSB) LED Current LED Current Matching LED Dropout Voltage 1.5 1.5 1 3.2 DVCC = 1.8V, Serial Port Idle ● 5.5 1 DVCC = 1.8V ● Reference Resistor Range MAIN, SUB = 1V MAIN, SUB = 1V Any Two MAIN or SUB Outputs, 50% FS ILED = FS ● ● 1.195 22 25.3 1.215 1.235 30 29.7 27.5 108 1 180 2 U W U U WW W LTC3208 ELECTRICAL CHARACTERISTICS PARAMETERS CONDITIONS ● The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VBAT = 3.6V, DVCC = 3V, ENRGBS = Hi, RREF = 24k, C2 = C3 = 2.2µF, C1 = C4 = 4.7µF, unless otherwise noted. MIN 92.5 TYP 102.5 6.96 1 540 26 1.73 1 140 104.9 28.1 0.24 0.32 0.46 0.63 0.89 1.22 1.74 2.42 3.47 4.73 6.7 9.47 13.56 19.05 27.06 0.35 2 2.2 4.53 5.02 0.9 MAX 112.5 UNITS mA mA % mV mA mA % mV mA mA mA mA mA mA mA mA mA mA mA mA mA mA mA mA mA White LED Current (CAM1-4), 4-Bit Linear DAC Full-Scale LED Current CAM = 1V Minimum (1LSB) LED Current CAM = 1V LED Current Matching Any Two CAM Outputs, 50% FS LED Dropout Voltage ILED = FS White LED Current (AUX1-4, AUX Outputs Assigned to AUX DAC), 4-Bit Linear DAC Full-Scale LED Current AUX = 1V Minimum (1LSB) LED Current AUX = 1V LED Current Matching LED Dropout Voltage Two AUX Outputs, 50% FS ILED = FS ● 23 28.5 Full-Scale AUX LED Current AUX Connected to CAM DAC, AUX = 1V Full-Scale AUX LED Current AUX Connected to SUB or MAIN DAC, AUX = 1V RGB LED Current (RED, GREEN, BLUE), 4-Bit Exponential DAC DAC Code 0001 RED, GREEN, BLUE = 1V DAC Code 0010 RED, GREEN, BLUE = 1V DAC Code 0011 RED, GREEN, BLUE = 1V DAC Code 0100 RED, GREEN, BLUE = 1V DAC Code 0101 RED, GREEN, BLUE = 1V DAC Code 0110 RED, GREEN, BLUE = 1V DAC Code 0111 RED, GREEN, BLUE = 1V DAC Code 1000 RED, GREEN, BLUE = 1V DAC Code 1001 RED, GREEN, BLUE = 1V DAC Code 1010 RED, GREEN, BLUE = 1V DAC Code 1011 RED, GREEN, BLUE = 1V DAC Code 1100 RED, GREEN, BLUE = 1V DAC Code 1101 RED, GREEN, BLUE = 1V DAC Code 1110 RED, GREEN, BLUE = 1V DAC Code 1111 RED, GREEN, BLUE = 1V Charge Pump (CPO) 1x Mode Output Impedance 1.5x Mode Output Impedance VBAT = 3V, VCPO = 4.2V (Note 5) 2x Mode Output Impedance VBAT = 3V, VCPO = 4.8V (Note 5) CPO Voltage Regulation 1.5x Mode, ICPO = 2mA 2x Mode, ICPO = 2mA CLOCK Frequency SDA, SCL, ENRGBS, CAMHL VIL, (Low Level Input Voltage) VIH, (High Level Input Voltage) VOL, Digital Output Low (SDA) IPULLUP = 3mA IIH SDA, SCL, ENRGBS, CAMHL = DVCC IIL SDA, SCL, ENRGBS, CAMHL = 0V Serial Port Timing (Notes 6, 7) tSCL Clock Operating Frequency tBUF Bus Free Time Between Stop and Start Condition tHD,STA Hold Time After (Repeated) Start Condition ● ● ● ● ● ● 0.6 1.2 0.3 • DVCC V V MHz V V V µA µA kHz µs µs 3208fa 0.7 • DVCC 0.18 –1 –1 0.4 1 1 400 1.3 0.6 3 LTC3208 ELECTRICAL CHARACTERISTICS PARAMETERS tSU,STA tSU,STO tHD,DAT(OUT) tHD,DAT(IN) tSU,DAT tLOW tHIGH tf tr tSP CONDITIONS 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 Rise Time Spike Suppression Time The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VBAT = 3.6V, DVCC = 3V, ENRGBS = Hi, RREF = 24k, C2 = C3 = 2.2µF, C1 = C4 = 4.7µF, unless otherwise noted. MIN 0.6 0.6 0 0 100 1.3 0.6 20 20 50 TYP MAX UNITS µs µs ns ns ns µs µs ns ns ns 900 300 300 Note 1: Absolute Maximum Ratings are those values beyond which the MTBF of a device may be impaired. Note 2: Based on long-term current density limitations. Assumes an operating duty cycle of ≤10% under absolute maximum conditions for durations less than 10 seconds. Max charge pump current for continuous operation is 500mA. Note 3: Based on long-term current density limitations. Note 4: The LTC3208E is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the –40°C to 85°C ambient operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 5: 1.5x mode output impedance is defined as (1.5VBAT – VCPO)/IOUT. 2x mode output impedance is defined as (2VBAT – VCPO)/IOUT. Note 6: All values are referenced to VIH and VIL levels. Note 7: Guaranteed by Design. TYPICAL PERFOR A CE CHARACTERISTICS Mode Switch Dropout Times 5V 1x 1.5x VCPO 1V/DIV 2x TA = 25°C VBAT = 3.6V 250µs/DIV 3208 G01 4 UW 1.5x Mode CPO Ripple TA = 25°C VBAT = 3.6V ICPO = 400mA CCPO = 4.7µF VCPO 20mV/DIV AC COUPLED VCPO 20mV/DIV AC COUPLED 2x Mode CPO Ripple TA = 25°C VBAT = 3.6V ICPO = 400mA CCPO = 4.7µF 500ns/DIV 3208 G02 500ns/DIV 3208 G03 3208fa LTC3208 TYPICAL PERFOR A CE CHARACTERISTICS LED Pin Dropout Voltage vs LED Pin Current 600 LED PIN DROPOUT VOLTAGE (mV) 500 SWITCH RESISTANCE (Ω) 0.40 VBAT = 3.6V 0.35 VBAT = 3.9V 0.30 400 300 200 100 0 10 20 30 40 50 60 70 80 LED CURRENT (mA) 90 100 3208 G04 VBAT = 3.6V TA = 25°C SWITCH RESISTANCE (Ω) 1.5x Mode CPO Voltage vs Load Current 4.8 4.6 3.6V CPO VOLTAGE (V) 4.4 3.2V 4.2 4.0 3.8 C2 = C3 = 2.2µF C4 = 4.7µF TA = 25°C 3.6 0 100 200 300 400 LOAD CURRENT (mA) VBAT = 3V 3.3V 3.1V 3.4V 3.5V SWITCH RESISTANCE (Ω) 2.8 2.4 2.2 2.0 1.8 1.6 –40 CPO VOLTAGE (V) Oscillator Frequency vs Supply Voltage 940 930 DVCC SHUTDOWN CURRENT (µA) 920 FREQUENCY (kHz) 910 900 890 880 870 860 850 840 2.7 3.0 4.2 3.3 3.6 3.9 VBAT SUPPLY VOLTAGE (V) 4.5 3208 G10 TA = 25°C TA = –40°C 0.3 TA = 85°C VBAT SHUTDOWN CURRENT (µA) TA = 85°C UW 1x Mode Switch Resistance vs Temperature 0.45 ICPO = 200mA VBAT = 3.3V 2.5 1.5x Mode Charge Pump Open-Loop Output Resistance vs Temperature (1.5VBAT – VCPO)/ICPO VBAT = 3V VCPO = 4.2V C2 = C3 = 2.2µF 2.3 C4 = 4.7µF 2.1 1.9 1.7 0.25 –40 –15 10 35 TEMPERATURE (°C) 60 85 3208 G05 1.5 –40 –15 10 35 TEMPERATURE (°C) 60 85 3208 G06 2x Mode Charge Pump OpenLoop Output Resistance vs Temperature (2VBAT – VCPO)/ICPO VBAT = 3V VCPO = 4.8V 2.6 C2 = C3 = 2.2µF C4 = 4.7µF 5.2 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 2x Mode CPO Voltage vs Load Current VBAT = 3V VBAT = 3.1V VBAT = 3.2V VBAT = 3.3V VBAT = 3.4V VBAT = 3.5V VBAT = 3.6V 500 3208 G07 –15 10 35 TEMPERATURE (°C) 60 85 3208 G08 C2 = C3 = 2.2µF 4.3 C4 = 4.7µF TA = 25°C 4.2 0 100 200 300 400 500 600 700 800 LOAD CURRENT (mA) 3208 G09 DVCC Shutdown Current vs DVCC Voltage 0.4 VBAT = 3.6V TA = –40°C 8.5 7.5 6.5 5.5 4.5 3.5 2.5 VBAT Shutdown Current vs VBAT Voltage DVCC = 3V TA = 85°C 0.2 TA = 25°C 0.1 TA = 25°C TA = –40°C 0 2.7 3.0 3.3 3.6 3.9 DVCC VOLTAGE (V) 4.2 4.5 3208 G11 1.5 2.7 3.0 3.3 3.6 3.9 VBAT VOLTAGE (V) 4.2 4.5 3208 G12 3208fa 5 LTC3208 TYPICAL PERFOR A CE CHARACTERISTICS 1x Mode No Load VBAT Current vs VBAT Voltage 300 290 280 SUPPLY CURRENT (mA) VBAT CURRENT (µA) 270 260 250 240 230 220 210 200 2.7 0 3.0 3.3 3.6 3.9 VBAT VOLTAGE (V) 4.2 4.5 3208 G13 TA = 25°C SUPPLY CURRENT (mA) CAM Pin Current vs CAM Pin Voltage 120 100 CAM PIN CURRENT (mA) RGB LED CURRENT (mA) 80 60 40 20 0 VBAT = 3.6V TA = 25°C 30 CAM LED CURRENT (mA) 0 0.2 0.4 0.6 0.8 CAM PIN VOLTAGE (V) AUX LED Current vs Input Code 28 V = 3.6V 26 T BAT 25°C A= 24 RREF = 24.3k 22 20 18 16 14 12 10 8 6 4 2 0 0123456789ABCDEF HEX CODE 3208 G21 MAIN/SUB LED CURRENT (mA) AUX LED CURRENT (mA) MAIN/SUB INL (LSB) 6 UW 3208 G16 1.5x Mode Supply Current vs ICPO (IVBAT – 1.5ICPO) 40 VIN = 3.6V TA = 25°C 25 2x Mode Supply Current vs ICPO (IVBAT – 2ICPO) VIN = 3.6V TA = 25°C 30 20 15 20 10 10 5 0 200 400 600 LOAD CURRENT (mA) 800 3208 G14 0 0 100 200 300 400 500 600 700 800 LOAD CURRENT (mA) 3208 G15 RGB LED Current vs Input Code VBAT = 3.6V TA = 25°C 25 RREF = 24.3k 20 15 10 5 0 110 CAM LED Current vs Input Code VBAT = 3.6V 100 TA = 25°C 90 RREF = 24.3k 80 70 60 50 40 30 20 10 0 1.0 0123456789ABCDEF HEX CODE 3208 G17 0123456789ABCDEF HEX CODE 3208 G18 Main/Sub LED Current vs Input Code 28 V = 3.6V 26 T BAT 25°C A= 24 RREF = 24.3k 22 20 18 16 14 12 10 8 6 4 2 0 0 10 20 30 40 50 60 70 80 90 A0 B0 C0 D0 E0 F0 FF HEX CODE 3208 G19 Main/Sub INL 1.0 0.8 0.6 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8 –1.0 1 80 HEX CODE FF 3208 G20 3208fa LTC3208 PI FU CTIO S CAM1-4 (Pins 1, 2, 3, 4): Current Source Outputs for the CAM Display White LEDs. The LEDs on the CAM display can be set from 0mA to 102mA in 16 steps via software control and internal 4-bit linear DAC. Two 4-bit registers are available. One is used to program the high camera current and the second the low camera current. These registers can be selected via the serial port or the CAMHL pin. Each output can be disabled by connecting the output to CPO. Setting data in REGF to 0 disables all CAM outputs. (See Applications Information.) AUX1-4 (Pins 5, 6, 7, 8): Current Source Outputs for the AUX Display White LEDs. When used as a separate display, the LED current sources of the AUX display can be set from 0mA to 26mA in 16 steps via software control and internal 4-bit linear DAC. In addition, these outputs can be connected individually as needed to the CAM, SUB or MAIN displays and driven from each display’s associated DAC. AUX 1, 2 and 3 can be disabled by connecting the output to CPO. AUX 4 can be used as an open drain I2C controlled logic output but cannot be disabled by connecting to CPO when configured as logic output. Setting data in REGE and REGB2 to 0 disables all AUX outputs. (See Applications Information.) CAMHL (Pin 9): Logic Input. Selects CAM high register when asserted High and CAM Low Register when low. The high to low transition automatically resets the charge pump mode to 1x. SCL (Pin 10): I2C Clock Input. The logic level for SCL is referenced to DVCC. SDA (Pin 11): I2C Data Input for the Serial Port. Serial data is shifted in one bit per clock to control the LTC3208. The logic level is referenced to DVCC. VBAT3, 2, 1 (Pins 12, 24, 30): Supply Voltage for the Entire Device. Three separate pins are used to isolate the charge pump from the analog sections to reduce noise. All pins must be connected together externally and bypassed with a 4.7µF low ESR ceramic capacitor. The 4.7µF bypass capacitor should be connected close to VBAT2. A 0.1µF capacitor should be connected close to VBAT3. RREF (Pin 13): Controls the Maximum Amount of LED Current for all Displays. The RREF voltage is 1.215V. An external resistor to ground sets the reference currents for all display DACs and support circuits. Since this resistor biases all circuits within the LTC3208, the value is limited to a range of 22k to 30k. DVCC (Pin 14): Supply Voltage for all Digital I/O Lines. This pin sets the logic reference level of the LTC3208. A UVLO circuit on the DVCC pin forces all registers to all 0s whenever DVCC is below the DVCC UVLO threshold. Bypass to GND with a 0.1µF capacitor. MAIN1-4 (Pins 15,16,17,18): Current Source Outputs for the MAIN Display White LEDs. The LEDs on the MAIN display can be set from 0µA to 27.5mA in 256 steps via software control and internal 8-bit linear DAC. Each output can be disabled externally by connecting the output to CPO. Setting data in REGC to 0 disables all MAIN outputs. SUB2, SUB1 (Pins 19, 20): Current Source Outputs for the SUB Display White LEDs. The LEDs on the SUB display can be set from 0µA to 27.5mA in 256 steps via software control and an internal 8-bit linear DAC. Each output can be disabled externally by connecting the output to CPO. Setting the data in REGD to 0 disables all SUB outputs. U U U 3208fa 7 LTC3208 PI FU CTIO S BLUE, GRN, RED (Pins 21, 22, 23): Current Source Outputs for the RGB Illuminator LEDs. The RGB currents can be independently set via the serial port. Currents up to 27mA can be programmed over 16 steps via the three internal 4-bit exponential DACs. These outputs can also be used as open drain I2C controlled logic outputs. When configured this way, these outputs cannot be externally disabled by connecting to CPO. Setting data to 0 in REGA1 disables RED, REGA2 disables GREEN and REGB1 disables BLUE. GND (Pins 25, 33): System Ground. Connect Pin 25 and exposed pad Pin 33 directly to a low impedance ground plane. C2M, C1M, C2P, C1P (Pins 26, 27, 29, 31): Charge Pump Flying Capacitor Pins. 2.2µF X7R or X5R ceramic capacitors should be connected from C1P to C1M and C2P to C2M. ENRGBS (Pin 28): Logic Input. This pin is normally high and is used to enable or disable the RED, GREEN and BLUE LEDs or the SUB LEDs. The selection between RGB or SUB is made via an internal programmable bit. When the pin is toggled from low (disable) to high (enable), the LTC3208 illuminates either the RGB display with a color combination that was previously programmed, or the SUB display at its previously programmed current. The logic level is referenced to DVCC. CPO (Pin 32): Output of the Charge Pump Used to Power All LEDs. A 4.7µF X5R or X7R ceramic capacitor should be connected to ground. 8 U U U 3208fa LTC3208 BLOCK DIAGRA W C1P 31 C1M 27 C2P 29 C2M 26 900kHz OSCILLATOR 25 GND VBAT2 24 32 CPO VBAT3 12 CHARGE PUMP VBAT1 30 – + ENABLE CP 16 MAIN2 15 MAIN1 + 17 MAIN3 – RREF 13 DVCC 14 ENRGBS 28 1.215V CONTROL LOGIC MASTER/ SLAVE REG MAIN CURRENT SOURCES SUB CURRENT SOURCES AUX CURRENT SOURCES CAM CURRENT SOURCES RGB CURRENT SOURCES 4 18 MAIN4 2 19 SUB2 4 20 SUB1 CAMHL 9 4 5 AUX1 SDA 11 SCL 10 V SHIFT REGISTER 3 6 AUX2 23 RED 22 GRN 21 BLUE 1 CAM1 2 CAM2 3 CAM3 4 CAM4 8 AUX4 7 AUX3 3208 BD OPERATIO Power Management The LTC3208 uses a switched capacitor charge pump to boost CPO to as much as 2 times the input voltage up to 5V. The part starts up in 1x mode. In this mode, VBAT1,2 are connected directly to CPO. This mode provides maximum efficiency and minimum noise. The LTC3208 will remain in this mode until an LED current source drops out. Dropout occurs when a current source voltage becomes too low for the programmed current to be supplied. When dropout is detected, the LTC3208 will switch into 1.5x mode. The CPO voltage will then start to increase and will attempt to reach 1.5x VBAT up to 4.5V. Any subsequent dropout will cause the part to enter the 2X mode. The CPO voltage will attempt to reach 2x VBAT up to 5V. The part will be reset to U 1x mode whenever a DAC data bit is updated via the I2C port or on the falling edge of the CAMHL signal. A two-phase nonoverlapping clock activates the charge pump switches. In the 2x mode the flying capacitors are charged on alternate clock phases from VBAT to minimize input current ripple and CPO voltage ripple. In 1.5x mode the flying capacitors are charged in series during the first clock phase and stacked in parallel on VBAT during the second phase. This sequence of charging and discharging the flying capacitors continues at a constant frequency of 900kHz. The currents delivered by the LED current sources are controlled by an associated DAC. Each DAC is programmed via the I2C port. The full scale DAC currents are set by RREF. The value of RREF is limited to the range of 22k to 30k. 3208fa 9 LTC3208 OPERATIO Soft-Start Initially, when the part is in shutdown, a weak switch connects VBAT to CPO. This allows VBAT1,2 to slowly charge the CPO output capacitor and prevent large charging currents to occur. The LTC3208 also employs a soft-start feature on its charge pump to prevent excessive inrush current and supply voltage droop when switching into the step-up modes. The current available to the CPO pin is increased linearly over a typical period of 150µs. Soft start occurs at the start of both 1.5x and 2x mode changes. Charge Pump Strength SWITCH RESISTANCE (Ω) When the LTC3208 operates in either 1.5x mode or 2x mode, the charge pump can be modeled as a Thevenin-equivalent circuit to determine the amount of current available from the effective input voltage and effective open-loop 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 nonoverlap period of the switching circuit. However, for a given ROL, the amount of current available will be directly proportional to the advantage voltage of 1.5VBAT - CPO for 1.5x mode and 2VBAT -CPO for 2x mode. 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 for 1.5x mode 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, for 1.5x mode the available current is given by: IOUT = 1.5VBAT – VCPO ROL ROL SWITCH RESISTANCE (Ω) Figure 1. Charge Pump Thevenin–Equivalent Open-Loop Circuit 3208fa 10 U For 2X mode, the available current is given by: IOUT = 2VBAT – VCPO ROL (2) Notice that the advantage voltage in the 2x case is 3.1V • 2 – 3.8V – 0.1V = 2.3V. ROL is higher in 2x mode, but a significant overall increase in available current is achieved. Typical values of ROL as a function of temperature are shown in Figure 2 and Figure 3. 2.5 VBAT = 3V VCPO = 4.2V C2 = C3 = 2.2µF 2.3 C4 = 4.7µF 2.1 1.9 1.7 1.5 –40 –15 10 35 TEMPERATURE (°C) 60 85 3208 F02 Figure 2. Typical 1.5x ROL vs Temperature 2.8 VBAT = 3V VCPO = 4.8V 2.6 C2 = C3 = 2.2µF C4 = 4.7µF 2.4 2.2 2.0 1.8 (1) 1.6 –40 –15 + CPO 10 35 TEMPERATURE (°C) 60 85 3208 F03 + – 1.5VBAT OR 2VBAT Figure 3. Typical 2x ROL vs Temperature – 3208 F01 LTC3208 OPERATIO Shutdown Current Shutdown occurs when all the current source data bits have been written to zero or when DVCC is below the DVCC UVLO threshold. Although the LTC3208 is designed to have very low shutdown current, it will draw about 3µA from VBAT when in shutdown. Internal logic ensures that the LTC3208 is in shutdown when DVCC is grounded. Note, however, that all of the logic signals that are referenced to DVCC (SCL, SDA, ENRGBS, CAMHL) will need to be at DVCC or below (i.e., ground) to avoid violation of the absolute maximum specifications on these pins. Serial Port The microcontroller compatible I2C serial port provides all of the command and control inputs for the LTC3208. Data on the SDA input is loaded on the rising edge of SCL. D7 is loaded first and D0 last. There are seven data registers, one address register and one sub-address register. Once all address bits have been clocked into the address register acknowledgment occurs. The sub-address register is then written followed by writing the data register. Each data register has a sub-address. After the data register has been written a load pulse is created after the stop bit. The load pulse transfers all of the data held in the data registers to the DAC registers. The stop bit can be delayed until all of the data master registers have been written. At this point the LED current will be changed to the new settings. The serial port uses static logic registers so there is no minimum speed at which it can be operated. MAIN and SUB Current Sources There are four MAIN current sources and two SUB current sources. Each bank of current sources has an 8-bit linear DAC for current control. The output current range is 0 to 27.5mA in 256 steps. The current sources are disabled when a block receives an all zero data word. The supply current for that block is reduced to zero. In addition each individual LED output can be connected to CPO to turn off that particular current source output and reduce operating current of the disabled output to typically 10µA. U Camera Current Sources There are four CAM current sources. This bank of current sources has a 4-bit linear DAC for current control. The output current range is 0 to 102mA in 16 steps. The current sources are disabled when the block receives an all zero data word. The supply current for the block is reduced to zero. In addition each individual LED output can be connected to CPO to turn off that particular current source output and reduce operating current of the disabled output to typically 10µA. RGB Illuminators The RED, GREEN and BLUE LEDs can be individually set from 0µA to 27mA in 16 steps via three 4-bit exponential DACs. The current sources are individually disabled when an all-zero data word is received. The supply current for the current source is reduced to zero. These outputs can also be used as open drain logic control outputs. For this reason they will not be disabled when connected to CPO. Auxiliary Current Sources There are four AUX current sources. This bank of current sources has a 4-bit linear DAC for current control. The output current range is 0mA to 26mA in 16 steps. In addition, each current source can be independently connected to the CAM, SUB or MAIN DAC outputs. The selection is made through the I2C port. The output current will then match the corresponding selected current source bank. In this case a range of 0mA to 27.5mA for SUB and MAIN or 0mA to 102mA for CAM will be achieved. The current sources are disabled when the block receives an all-zero data word in both REGE and REGB2. The supply current for the block is reduced to zero. AUX 1, 2 and 3 LED outputs can be connected to CPO to turn off that particular current source output and reduce operating current of the disabled output to typically 10µA. AUX 4 can be used as an open drain logic output and for this reason will not be disabled if connected to CPO. 3208fa 11 LTC3208 OPERATIO Disabling Current Source Outputs Unused CAM, SUB and MAIN outputs can be disabled by using two different methods depending on the application requirement. If the entire group is to be disabled (ie MAIN), then the data register for that group is written to zero. The unused outputs can be open circuit. If one or more of the group outputs is to be enabled then the unused outputs must be connected to CPO to prevent a false dropout signal from occurring. AUX has a mixture of disable requirements. If AUX is not used then the data register is written to zero and all outputs can be left open circuit. If one or more output is to be enabled then AUX1, AUX2 and AUX3 can be disabled by connecting the unused output to CPO. AUX 4 cannot be disabled by connecting to CPO but can be left open circuit if XRGBDROP is set high. This setting removes the dropout detector from the AUX4 output but also removes the dropout detectors from the RED, GRN and BLUE LED outputs. To avoid disabling the RED, GRN and BLUE dropout detectors, AUX4 should be one of the enabled outputs whenever a mixture of enabled and disabled AUX outputs are used. RED, GRN and BLUE outputs are disabled by writing the unused output register to zero. The unused output can be left open circuit. CAMHL The CAMHL pin quickly selects the camera high register for flash applications without reaccessing the I2C port. When low, the CAM current range will be controlled by the camera low 4-bit register. When CAMHL is asserted high, the current range will be set by the camera high 4-bit register. ENRGBS Pin The ENRGBS pin can be used to enable or disable the LTC3208 without re-accessing the I2C port. This might be useful to indicate an incoming phone call without waking 12 U the microcontroller. ENRGBS can be software programmed as an independent control for either the RGB display or the SUB display. Options REGG bit G1 determines which display ENRGBS controls. When bit G1 is 0, the ENRGBS pin controls the RGB display. If it is set to 1, then ENRGBS controls the SUB display. To use the ENRGBS pin, the I2C port must first be configured to the desired setting. For example, if the ENRGBS pin will be used to control the SUB display, then a nonzero code must reside in REGD and Command register REGG bit G1 must be set to 1. Now when ENRGBS is high (DVCC), the SUB display will be on with the REGD setting. When ENRGBS is low the SUB display will be off. If no other displays are programmed to be on, the entire chip will be in shutdown. Likewise if ENRGBS will be used to enable the RGB display, then a nonzero code must reside in one of the RED, GREEN or BLUE registers REGA1, REGA2 or REGB1, and options register REGG bit G1 is set to 0. Now when ENRGBS is high (DVCC), the RGB display will light with the programmed color. When ENRGBS is low, the RGB display will be off. If no other displays are programmed to be on, the entire chip will be in shutdown. If options register REGG bit G1 is set to 1 (SUB display control), then ENRGBS will have no effect on the RGB display. Likewise, if bit G1 is set to 0 (RGB display control), then ENRGBS will have no effect on the SUB display. If the ENRGBS pin is not used, it must be connected to DVCC. It should not be grounded or left floating. Thermal Protection The LTC3208 has built-in overtemperature protection. At internal die temperatures of around 150°C thermal shutdown will occur. This will disable all of the current sources and charge pump until the die has cooled by about 15°C. This thermal cycling will continue until the fault has been corrected. 3208fa LTC3208 OPERATIO U Mode Switching The LTC3208 will automatically switch from 1x mode to 1.5x mode and subsequently to 2x mode whenever a dropout condition is detected at an LED pin. Dropout occurs when a current source voltage becomes too low for the programmed current to be supplied. The dropout delay is typically 400µs. The mode will automatically switch back to 1x whenever a data bit is updated via the I2C port or when the CAMHL pin switches from high to low. I2C Interface The LTC3208 communicates with a host (master) using the standard I2C 2-wire interface. The Timing Diagram (Figure 5) 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 LTC3208 is a receive-only (slave) device. 1 . 215V RGB fullscale LED current ( Amps) = • 533 RREF SUB-ADDRESS ADDRESS 0 START SDA 0 0 1 1 0 1 1 0 ACK S7 S6 S5 S4 S3 S2 S1 S0 ACK 7 1 6 2 5 3 4 4 3 5 2 6 1 7 0 8 ACK 0 1 1 0 1 1 WR 0 S7 S6 S5 S4 S3 S2 S1 S0 7 6 5 4 3 2 1 0 STOP DATA BYTE RREF Current Set Resistor The current set resistor is connected between RREF and ground. The value of this resistor should typically be near 24k since all of the DAC reference currents and support circuit currents are related to this set current. This input is protected against shorts to ground or low value resistors