LTC3208 High Current Software Configurable Multidisplay LED Controller DESCRIPTIO U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 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 U 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. 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. U TYPICAL APPLICATIO C2 2.2mF 4-LED MAIN Display Efficiency vs Input Voltage C3 2.2mF 100 VBAT C1 4.7mF MAIN MAIN1-4 ENRGBS ENABLE DISABLE LOW HI CAMHL RREF 24.3k 1% RGB AUX C4 4.7mF LTC3208 SCL/SDA CAMERA CPO VBAT1,2,3 I2C SUB 4 SUB1-2 2 CAM1-4 4 RGB 3 AUX1-4 GND 4 3208 TA01a EFFICIENCY (PLED/PIN) (%) 90 C1P C1M C2P C2M 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 TA01b 3208fa 1 LTC3208 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) GND C2M C1M ENRGBS C2P VBAT1 CPO C1P TOP VIEW 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 24 VBAT2 CAM2 2 23 RED CAM3 3 22 GRN 21 BLUE CAM4 4 33 AUX1 5 20 SUB1 AUX2 6 19 SUB2 AUX3 7 18 MAIN4 17 MAIN3 AUX4 8 MAIN2 MAIN1 DVCC RREF VBAT3 SDA SCL CAMHL 9 10 11 12 13 14 15 16 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 UH PART MARKING LTC3208EUH 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. ELECTRICAL CHARACTERISTICS 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 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 CONDITIONS MIN ● ICPO = 0, 1x Mode, LEDs Disabled ICPO = 0, 1.5x Mode ICPO = 0, 2x Mode 4.5 1.5 5.5 1 ● 1.5 1 3.2 DVCC = 1.8V ● ● 1.195 22 1.215 Reference Resistor Range MAIN, SUB = 1V MAIN, SUB = 1V Any Two MAIN or SUB Outputs, 50% FS ● 25.3 27.5 108 1 ILED = FS MAX 280 4.7 7 ● DVCC = 1.8V, Serial Port Idle TYP 2.9 180 1.235 30 29.7 UNITS V µA mA mA V µA V V µA V k mA µA % mV 3208fa 2 LTC3208 ELECTRICAL CHARACTERISTICS 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 CONDITIONS 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 Two AUX Outputs, 50% FS LED Dropout Voltage ILED = FS 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 MIN TYP MAX UNITS ● 92.5 102.5 6.96 1 540 112.5 mA mA % mV ● 23 26 1.73 28.5 mA mA ● 0.6 1 % 140 mV 104.9 28.1 mA mA 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 mA mA mA mA mA mA mA mA mA mA mA mA mA mA mA 0.35 2 2.2 4.53 5.02 0.9 V V MHz ● ● 0.3 • DVCC 0.7 • DVCC ● ● ● 1.2 0.18 –1 –1 0.4 1 1 400 1.3 0.6 V V V µA µA kHz µs µs 3208fa 3 LTC3208 ELECTRICAL CHARACTERISTICS 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 CONDITIONS MIN tSU,STA tSU,STO tHD,DAT(OUT) tHD,DAT(IN) tSU,DAT tLOW tHIGH tf tr tSP 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 0.6 0.6 0 0 100 1.3 0.6 20 20 50 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. TYP MAX 900 300 300 UNITS µs µs ns ns ns µs µs ns ns ns 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. U W TYPICAL PERFOR A CE CHARACTERISTICS Mode Switch Dropout Times 1.5x Mode CPO Ripple 5V 1x 1.5x 2x Mode CPO Ripple TA = 25°C VBAT = 3.6V ICPO = 400mA CCPO = 4.7µF 2x VCPO 20mV/DIV AC COUPLED VCPO 1V/DIV VCPO 20mV/DIV AC COUPLED TA = 25°C VBAT = 3.6V ICPO = 400mA CCPO = 4.7µF TA = 25°C VBAT = 3.6V 250µs/DIV 3208 G01 500ns/DIV 3208 G02 500ns/DIV 3208 G03 3208fa 4 LTC3208 U W TYPICAL PERFOR A CE CHARACTERISTICS LED Pin Dropout Voltage vs LED Pin Current 0.45 VBAT = 3.6V TA = 25°C 2.5 ICPO = 200mA 500 400 300 200 VBAT = 3.3V 0.40 VBAT = 3.6V 0.35 VBAT = 3.9V 0.30 10 20 30 40 50 60 70 80 LED CURRENT (mA) 0.25 –40 90 100 –15 10 35 TEMPERATURE (°C) 60 2.1 1.9 1.5 –40 85 3.2V VBAT = 3V 3.3V 3.1V 4.0 3.8 C2 = C3 = 2.2µF C4 = 4.7µF TA = 25°C 3.6 0 100 200 300 400 LOAD CURRENT (mA) 5.1 5.0 2.4 2.2 2.0 1.6 –40 500 –15 10 35 TEMPERATURE (°C) 60 940 0.4 DVCC SHUTDOWN CURRENT (µA) TA = –40°C TA = 25°C 900 TA = 85°C 880 870 860 85 3.0 4.5 3208 G09 VBAT Shutdown Current vs VBAT Voltage 8.5 TA = –40°C TA = 85°C 0.3 0.2 TA = 25°C 0.1 850 840 2.7 4.6 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) VBAT = 3.6V 930 890 4.7 DVCC Shutdown Current vs DVCC Voltage Oscillator Frequency vs Supply Voltage 910 4.8 3208 G08 3208 G07 920 4.2 3.3 3.6 3.9 VBAT SUPPLY VOLTAGE (V) 4.5 3208 G10 VBAT = 3V VBAT = 3.1V VBAT = 3.2V VBAT = 3.3V VBAT = 3.4V VBAT = 3.5V VBAT = 3.6V 4.9 4.4 1.8 VBAT SHUTDOWN CURRENT (µA) 4.2 85 5.2 VBAT = 3V VCPO = 4.8V 2.6 C2 = C3 = 2.2µF C4 = 4.7µF CPO VOLTAGE (V) 3.5V SWITCH RESISTANCE (Ω) 4.6 3.4V 60 2x Mode CPO Voltage vs Load Current 2.8 4.8 4.4 10 35 TEMPERATURE (°C) 3208 G06 2x Mode Charge Pump OpenLoop Output Resistance vs Temperature (2VBAT – VCPO)/ICPO 1.5x Mode CPO Voltage vs Load Current 3.6V –15 3208 G05 3208 G04 CPO VOLTAGE (V) VBAT = 3V VCPO = 4.2V C2 = C3 = 2.2µF 2.3 C4 = 4.7µF 1.7 100 0 FREQUENCY (kHz) SWITCH RESISTANCE (Ω) SWITCH RESISTANCE (Ω) LED PIN DROPOUT VOLTAGE (mV) 600 1.5x Mode Charge Pump Open-Loop Output Resistance vs Temperature (1.5VBAT – VCPO)/ICPO 1x Mode Switch Resistance vs Temperature 0 2.7 3.0 3.3 3.6 3.9 DVCC VOLTAGE (V) 4.2 4.5 3208 G11 DVCC = 3V 7.5 6.5 TA = 85°C 5.5 4.5 3.5 TA = 25°C TA = –40°C 2.5 1.5 2.7 3.0 3.3 3.6 3.9 VBAT VOLTAGE (V) 4.2 4.5 3208 G12 3208fa 5 LTC3208 U W TYPICAL PERFOR A CE CHARACTERISTICS 1.5x Mode Supply Current vs ICPO (IVBAT – 1.5ICPO) 1x Mode No Load VBAT Current vs VBAT Voltage 40 TA = 25°C 290 SUPPLY CURRENT (mA) VBAT CURRENT (µA) 280 270 260 250 240 230 25 VIN = 3.6V TA = 25°C VIN = 3.6V TA = 25°C 20 30 SUPPLY CURRENT (mA) 300 2x Mode Supply Current vs ICPO (IVBAT – 2ICPO) 20 10 15 10 5 220 210 200 2.7 0 3.3 3.6 3.9 VBAT VOLTAGE (V) 3.0 4.2 4.5 0 200 400 600 LOAD CURRENT (mA) CAM Pin Current vs CAM Pin Voltage 110 RGB LED CURRENT (mA) 40 VBAT = 3.6V 100 TA = 25°C 90 RREF = 24.3k CAM LED CURRENT (mA) VBAT = 3.6V TA = 25°C 25 RREF = 24.3k 100 CAM PIN CURRENT (mA) CAM LED Current vs Input Code 30 VBAT = 3.6V TA = 25°C 60 100 200 300 400 500 600 700 800 LOAD CURRENT (mA) 3208 G15 RGB LED Current vs Input Code 80 0 3208 G14 3208 G13 120 0 800 20 15 10 20 5 0 0 80 70 60 50 40 30 20 10 0 0.2 1.0 0.4 0.6 0.8 CAM PIN VOLTAGE (V) 0 0 1 2 3 4 5 6 7 8 9 A B C D E F HEX CODE 0 1 2 3 4 5 6 7 8 9 A B C D E F HEX CODE 3208 G16 3208 G17 Main/Sub LED Current vs Input Code 3208 G21 Main/Sub INL 28 V = 3.6V 26 T BAT A = 25°C 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 1.0 0.8 0.6 MAIN/SUB INL (LSB) MAIN/SUB LED CURRENT (mA) AUX LED CURRENT (mA) AUX LED Current vs Input Code 28 V = 3.6V 26 T BAT A = 25°C 24 RREF = 24.3k 22 20 18 16 14 12 10 8 6 4 2 0 0 1 2 3 4 5 6 7 8 9 A B C D E F HEX CODE 3208 G18 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8 –1.0 1 80 HEX CODE FF 3208 G20 3208fa 6 LTC3208 U U U 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. 3208fa 7 LTC3208 U U U 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. 3208fa 8 LTC3208 W BLOCK DIAGRA VBAT1 30 C1P C1M C2P C2M 31 27 29 26 900kHz OSCILLATOR 25 GND VBAT2 24 32 CPO VBAT3 12 CHARGE PUMP – 15 MAIN1 + ENABLE CP 16 MAIN2 + 17 MAIN3 – RREF 13 DVCC 14 1.215V ENRGBS 28 CAMHL CONTROL LOGIC MASTER/ SLAVE REG 9 V SDA 11 SHIFT REGISTER MAIN CURRENT SOURCES 4 SUB CURRENT SOURCES 2 AUX CURRENT SOURCES 4 CAM CURRENT SOURCES 4 18 MAIN4 19 SUB2 20 SUB1 5 AUX1 6 AUX2 RGB CURRENT SOURCES 3 SCL 10 23 22 21 1 2 3 4 8 7 RED GRN BLUE CAM1 CAM2 CAM3 CAM4 AUX4 AUX3 3208 BD U 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 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 U OPERATIO Soft-Start For 2X mode, the available current is given by: 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. IOUT = 2VBAT – VCPO ROL 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 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: 1.5VBAT – VCPO ROL VBAT = 3V VCPO = 4.2V C2 = C3 = 2.2µF 2.3 C4 = 4.7µF 2.1 1.9 1.7 1.5 –40 + – 1.5VBAT OR 2VBAT 10 35 TEMPERATURE (°C) 60 85 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 ROL –15 3208 F02 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). SWITCH RESISTANCE (Ω) Charge Pump Strength IOUT = (2) + CPO –15 10 35 TEMPERATURE (°C) 60 85 3208 F03 Figure 3. Typical 2x ROL vs Temperature – 3208 F01 Figure 1. Charge Pump Thevenin–Equivalent Open-Loop Circuit 3208fa 10 LTC3208 U OPERATIO Shutdown Current Camera Current Sources Shutdown occurs when all the current source data bits have been written to zero or when DVCC is below the DVCC UVLO threshold. 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. 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. 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. 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. 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 U 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 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 12 LTC3208 U OPERATIO RREF Current Set Resistor Mode Switching 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. 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. This input is protected against shorts to ground or low value resistors <10k. When a fault is detected the reference current amplifier is current limited. In addition, the current source outputs and charge pump are disabled. 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. Fullscale LED Current Equations I2C Interface 1 . 215V AUX fullscale LED current ( Amps ) = • 518 RREF SUB / MAIN fullscale LED current ( Amps ) = CAM fullscale LED current ( Amps ) = 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. 1 . 215V • 543 RRE F 1 . 215V • 202 5 RREF The LTC3208 is a receive-only (slave) device. 1 . 215V RGB fullscale LED current ( Amps) = • 533 RREF SUB-ADDRESS ADDRESS DATA BYTE WR 0 0 1 1 0 1 1 0 SDA 0 0 1 1 0 1 1 0 SCL 1 2 3 4 5 6 7 8 S7 S6 S5 S4 S3 S2 S1 S0 7 6 5 4 3 2 1 0 ACK S7 S6 S5 S4 S3 S2 S1 S0 ACK 7 6 5 4 3 2 1 0 ACK 9 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 9 START STOP 9 3208 FO4 Figure 4. Bit Assignments SDA tSU, STA tSU, DAT tLOW tHD, STA tHD, DAT tBUF tSU, STO 3208 F05 SCL tHIGH tHD, STA START CONDITION tr tSP tf REPEATED START CONDITION STOP CONDITION START CONDITION Figure 5. Timing Parameters 3208fa 13 LTC3208 U OPERATIO Write Word Protocol Used By the LTC3208 Sub-Address Byte 1 7 1 1 8 1 S SLAVE ADDRESS WR A *SUB-ADDRESS A 8 1 1 DATA BYTE A P** S = Start Condition, Wr = Write Bit = 0, A = Acknowledge, P = Stop Condition *The sub-address uses only the first 3 bits, D0, D1 and D2. **Stop can be delayed until all of the data registers have been written. MSB S7 X X X X X X X X S6 X X X X X X X X S5 X X X X X X X X S4 X X X X X X X X S3 X X X X X X X X S2 0 0 0 0 1 1 1 1 S1 0 0 1 1 0 0 1 1 LSB S0 0 1 0 1 0 1 0 1 REGISTER NONE REGA REGB REGC REGD REGE REGF REGG REGA, RED LED and GREEN LED 4-Bit DAC Data, Register Sub-Address = 001 MSB A7 GRN D3 REGA2 A6 A5 GRN D2 GRN D1 LSB A4 GRN D0 MSB A3 RED D3 REGA1 A2 A1 RED D2 RED D1 LSB A0 RED D0 REGB, BLUE LED and AUXILIARY 4-Bit DAC Data, Register Sub-Address = 010 MSB B7 AUX D3 REGB2 B6 AUX D2 B5 AUX D1 LSB B4 AUX D0 MSB B3 BLUE D3 REGB1 B2 BLUE D2 B1 BLUE D1 LSB B0 BLUE D0 C2 MAIN D2 C1 MAIN D1 LSB C0 MAIN D0 D2 SUB D2 D1 SUB D1 LSB D0 SUB D0 REGC, MAIN LED 8-Bit DAC Data, Register Sub-Address = 011 MSB C7 MAIN D7 C6 MAIN D6 C5 MAIN D5 C4 MAIN D4 C3 MAIN D3 REGD, SUB LED 8-Bit DAC Data, Register Sub-Address = 100 MSB D7 SUB D7 D6 SUB D6 D5 SUB D5 D4 SUB D4 D3 SUB D3 3208fa 14 LTC3208 U OPERATIO REGE, AUXILIARY LED 8-Bit MUX Data, Selects DAC for Each AUX Output, Register Sub-Address = 101 AUX4 AUX3 AUX2 AUX1 E7 0 E6 0 SELECT AUX E5 0 E4 0 SELECT AUX E3 0 E2 0 SELECT AUX E1 0 E0 0 SELECT AUX 0 1 1 0 MAIN SUB 0 1 1 0 MAIN SUB 0 1 1 0 MAIN SUB 0 1 1 0 MAIN SUB 1 1 CAM 1 1 CAM 1 1 CAM 1 1 CAM REGF, CAMERA LED 4-Bit High and 4-Bit Low DAC Data, Register Sub-Address = 110 MSB F7 CAM D3 HIGH BITS F6 CAM D2 F5 CAM D1 LSB MSB LOW BITS LSB F4 CAM D0 F3 CAM D3 F2 F1 F0 CAM D2 CAM D1 CAM D0 G4 G3 G2 G1 LSB G0 DTH1 XRGBDROP SCAMHILO SELRGBS Not Used REGG, Options Byte, Sub-Address = 111 MSB G7 Force2x G6 Force1p5 G5 DTH2 SELRGBS (G1) 1 0 Selects SUB displays for control by the ENRGBS pin Selects RGB displays for control by the ENRGBS pin SCAMHILO (G2) 1 0 Selects CAM high register, disables CAMHL pin Selects CAM low register, enables CAMHL pin XRGBDROP (G3) 1 0 Disables RGB and AUX4 dropout signals when outputs used as logic signals Enables RGB and AUX4 dropout signals DTH1 (G4) DTH2 (G5) Force1p5 (G6) 0 0 1 0 1 0 Test hook, must always be 0 Test hook, must always be 0 Forces charge pump into 1.5x mode Enables mode logic to control mode changes based on dropout signal Forces charge pump into 2x mode, overrides Force1p5 signal Enables mode logic to control mode changes based on dropout signal Force2x (G7) 3208fa 15 LTC3208 U OPERATIO Bus Speed Bus Write Operation 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. The master initiates communication with the LTC3208 with a START condition and a 7-bit address followed by the Write Bit R/W = 0. If the address matches that of the LTC3208, the LTC3208 returns an Acknowledge. The master should then deliver the most significant sub-address byte for the data register to be written. Again the LTC3208 acknowledges and then the data is delivered starting with the most significant bit. This cycle is repeated until all of the required data registers have been written. Any number of data latches can be written. Each data byte is transferred to an internal holding latch upon the return of an Acknowledge. After all data bytes have been transferred to the LTC3208, 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 LTC3208 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 global STOP condition can be sent and the LTC3208 will update all registers with the data that it had received. 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. Byte Format Each byte sent to the LTC3208 must be 8 bits long followed by an extra clock cycle for the Acknowledge bit to be returned by the LTC3208. The data should be sent to the LTC3208 most significant bit (MSB) first. Acknowledge The Acknowledge signal is used for handshaking between the master and the slave. An Acknowledge (active LOW) generated by the slave (LTC3208) 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 LTC3208 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 LTC3208 to recognize the address since it is a write only device. This effectively forces the address to be 8 bits long where the least significant bit of the address is 0. If the correct seven bit address is given but the R/W bit is 1, the LTC3208 will not respond. In certain circumstances the data on the I2C bus may become corrupted. In these cases the LTC3208 responds appropriately by preserving only the last set of complete data that it has received. For example, assume the LTC3208 has been successfully addressed and is receiving data when a STOP condition mistakenly occurs. The LTC3208 will ignore this stop condition and will not respond until a new START condition, correct address, sub-address and new set of data and STOP condition are transmitted. Likewise, if the LTC3208 was previously addressed and sent valid data but not updated with a STOP, it will respond to any STOP that appears on the bus with only one exception, independent of the number of REPEAT-START’s that have occurred. If a REPEAT-START is given and the LTC3208 successfully acknowledges its address, it will not respond to a STOP until all bytes of the new data have been received and acknowledged. Shared data registers will have all 8 bits rewritten since a common acknowledge signal writes these registers. The shared registers include REGA, REGB and REGF. 3208fa 16 LTC3208 U W U U APPLICATIO S I FOR ATIO VBAT, CPO Capacitor Selection The value and type of capacitors used with the LTC3208 determine several important parameters such as regulator control loop stability, output ripple, charge pump strength and minimum start-up time. To reduce noise and ripple, it is recommended that low equivalent series resistance (ESR) ceramic capacitors are used for both CVBAT and CCPO. Tantalum and aluminum capacitors are not recommended due to high ESR. The value of CCPO directly controls the amount of output ripple for a given load current. Increasing the size of CCPO will reduce output ripple at the expense of higher start-up current. The peak-to-peak output ripple of the 1.5X mode is approximately given by the expression VRIPPLE P−P = IOUT 3fOSC • CCPO value of CVBAT controls the amount of ripple present at the input pin (VBAT). The LTC3208 input current will be relatively constant while the charge pump is either in the input charging phase or the output charging phase but will drop to zero during the clock nonoverlap times. Since the nonoverlap time is small (~25ns), these missing “notches” will result in only a small perturbation on the input power supply line. Note that a higher ESR capacitor such as tantalum will have higher input noise due to the higher ESR. Therefore, ceramic capacitors are recommended for low ESR. Input noise can be further reduced by powering the LTC3208 through a very small series inductor as shown in Figure 6. A 10nH inductor will reject the fast current notches, thereby presenting a nearly constant current load to the input power supply. For economy, the 10nH inductor can be fabricated on the PC board with about 1cm (0.4”) of PC board trace. (3) Where fOSC is the LTC3208 oscillator frequency or typically 900kHz and CCPO is the output storage capacitor. VBAT The output ripple in 2x mode is very small due to the fact that load current is supplied on both cycles of the clock. GND Both value and type of output capacitor can significantly affect the stability of the LTC3208. As shown in the block diagram, the LTC3208 uses a control loop to adjust the strength of the charge pump to match the required output current. The error signal of the loop is stored directly on the output capacitor. The output capacitor also serves as the dominant pole for the control loop. To prevent ringing or instability, it is important for the output capacitor to maintain at least 2.2µF of capacitance over all conditions. In addition, excessive output capacitor ESR will tend to degrade the loop stability. The closed loop output resistance is about 80m . For a 100mA load current change, the error signal will change by about 8mV. If the output capacitor has 80m or more of ESR, the closed loop frequency response will cease to roll off in a simple one-pole fashion and poor load transient response or instability may occur. Multilayer ceramic chip capacitors typically have exceptional ESR performance. MLCCs combined with a tight board layout will result in very good stability. As the value of CCPO controls the amount of output ripple, the LTC3208 3208 F06 Figure 6. 10nH Inductor Used for Input Noise Reduction (Approximately 1cm of Board Trace) Flying Capacitor Selection Warning: Polarized capacitors such as tantalum or aluminum should never be used for the flying capacitors since their voltage can reverse upon start-up of the LTC3208. Ceramic capacitors should always be used for the flying capacitors. The flying capacitors control the strength of the charge pump. In order to achieve the rated output current it is necessary to have 2.2µF of capacitance for each of the flying capacitors. Capacitors of different materials lose their capacitance with higher temperature and voltage at different rates. For example, a ceramic capacitor made of X7R material will retain most of its capacitance from – 40°C to 85°C, whereas a Z5U or Y5V style capacitor will lose considerable capacitance over that range. Z5U and Y5V capacitors may also have a very poor voltage coefficient causing them to lose 60% or more of their capacitance when 3208fa 17 LTC3208 U W U U APPLICATIO S I FOR ATIO the rated voltage is applied. Therefore, when comparing different capacitors, it is often more appropriate to compare the amount of achievable capacitance for a given case size rather than comparing the specified capacitance value. For example, overrated voltage and temperature conditions, a 1µF, 10V, Y5V ceramic capacitor in a 0603 case may not provide any more capacitance than a 0.22µF, 10V, X7R available in the same case. The capacitor manufacturer’s data sheet should be consulted to determine what value of capacitor is needed to ensure minimum capacitances at all temperatures and voltages. Table 1 shows a list of ceramic capacitor manufacturers and how to contact them: Table 1. Recommended Capacitor Vendors AVX Kemet Murata Taiyo Yuden Vishay www.avxcorp.com www.kemet.com www.murata.com www.t-yuden.com www.vishay.com The following guidelines should be followed when designing a PCB layout for the LTC3208. • The exposed pad should be soldered to a large copper plane that is connected to a solid, low impedance ground plane using plated, through-hole vias for proper heat sinking and noise protection. • Input and output capacitors (C1 and C4) must be placed close to the part. • The flying capacitors (C2 and C3) must be placed close to the part. The traces running from the pins to the capacitor pads should be as wide as possible. • VBAT, CPO traces must be made wide to minimize inductance and handle the high currents. • LED pads must be large and connected to other layers of metal to ensure proper heat sinking. GND PLANE LAYER CPO GND CONNECT TO GND PLANE LAYER ALL VIAS LABELED GND ARE CONNECTED TO GND PLANE LAYER C2 Layout Considerations and Noise Due to its high switching frequency and the transient currents produced by the LTC3208, careful board layout is necessary. A true ground plane and short connections to all capacitors will improve performance and ensure proper regulation under all conditions. The flying capacitor pins C1P, C2P, C1M and C2M will have very high edge rate waveforms. The large dv/dt on these pins can couple energy capacitively to adjacent PCB runs. Magnetic fields can also be generated if the flying capacitors are not close to the LTC3208 (i.e., the loop area is large). To decouple capacitive energy transfer, a Faraday shield may be used. This is a grounded PCB trace between the sensitive node and the LTC3208 pins. For a high quality AC ground, it should be returned to a solid ground plane that extends all the way to the LTC3208. ALL VIAS LABELED VBAT ARE CONNECTED TO VBAT PLANE LAYER C3 VBAT GND GND C4 VBAT PLANE LAYER C1 1 VBAT GND VBAT PLANE LAYER VBAT C6 C5 RREF GND GND R1 DVCC GND GND PLANE LAYER 3208 F07 Figure 7. PC Board Layout Example 3208fa 18 LTC3208 U W U U APPLICATIO S I FOR ATIO Power Efficiency To calculate the power efficiency (η) of a white LED driver chip, the LED power should be compared to the input power. The difference between these two numbers represents lost power whether it is in the charge pump or the current sources. Stated mathematically, the power efficiency is given by: η= PLED PIN (4) The efficiency of the LTC3208 depends upon the mode in which it is operating. Recall that the LTC3208 operates as a pass switch, connecting VBAT to CPO, until dropout is detected at the ILED pin. This feature provides the optimum efficiency available for a given input voltage and LED forward voltage. When it is operating as a switch, the efficiency is approximated by: η= PLED VLED • ILED VLED = = PIN VBAT • IBAT VBAT (5) since the input current will be very close to the sum of the LED currents. At moderate to high output power, the quiescent current of the LTC3208 is negligible and the expression above is valid. Once dropout is detected at any LED pin, the LTC3208 switches the charge pump to 1.5x mode. In 1.5x boost mode, the efficiency is similar to that of a linear regulator with an effective input voltage of 1.5 times the actual input voltage. This is because the input current for a 1.5x charge pump is approximately 1.5 times the load current. In an ideal 1.5x charge pump, the power efficiency would be given by: ηIDEAL = PLED VLED • ILED VLED = = PIN VBAT • 1.5 • ILED 1.5 • VBAT Similarly, in 2x boost mode, the efficiency is similar to that of a linear regulator with an effective input voltage of 2 times the actual input voltage. In an ideal 2x charge pump, the power efficiency would be given by: ηIDEAL = PLED V •I V = LED LED = LED PIN VBAT • 2 • ILED 2 • VBAT Thermal Management For higher input voltages and maximum output current, there can be substantial power dissipation in the LTC3208. If the junction temperature increases above approximately 150°C, the thermal shutdown circuitry will automatically deactivate the output current sources and charge pump. To reduce maximum junction temperature, a good thermal connection to the PC board is recommended. Connecting the Exposed Pad to a ground plane and maintaining a solid ground plane under the device will reduce the thermal resistance of the package and PC board considerably. 3208fa 19 LTC3208 U TYPICAL APPLICATIO S 6-LED MAIN, RGB Plus Low/High Current 8-LED Camera Light VBAT C2 2.2µF C3 2.2µF C1P C1M C2P C2M VBAT1 C1 4.7µF MAIN CAMERA RGB CPO C4 4.7µF LTC3208 VBAT2 MAIN1-4 VBAT3 0.1µF I2C DVCC 0.1µF SCL/SDA SUB1-2 DVCC CAM1-4 AUX1-4 ENRGBS ENABLE DISABLE RGB CAMHL RREF LOW HI 4 2 4 4 3 3208 TA02 GND 24.3k 1% MAIN and SUB Backlight, Keypad Backlight, Camera Light and Camera Indicator C2 2.2µF C3 2.2µF C1P C1M C2P C2M VBAT VBAT1 C1 4.7µF MAIN SUB CAMERA CAMERA INDICATOR KEYPAD CPO C4 4.7µF LTC3208 VBAT2 VBAT3 0.1µF MAIN1-4 SUB1-2 2 I C DVCC SCL/SDA CAM1-2 DVCC CAM3-4 0.1µF 4 2 2 2 RED AUX1 ENABLE DISABLE ENRGBS AUX2 AUX3 CAMHL LOW HI RREF AUX4 GRN NC BLUE NC GND 3208 TA03 GRN AND BLUE DATA REGISTERS SET TO ALL 0s 24.3k 1% 3208fa 20 LTC3208 U TYPICAL APPLICATIO S 6-LED MAIN, 4-LED Camera Light, 7-LED Fun Lights VBAT C2 2.2µF C3 2.2µF C1P C1M C2P C2M VBAT1 C1 4.7µF MAIN CAMERA FUN LIGHTS CPO C4 4.7µF LTC3208 VBAT2 MAIN1-4 VBAT3 0.1µF I2C DVCC SCL/SDA SUB1-2 DVCC CAM1-4 0.1µF AUX1-4 ENRGBS ENABLE DISABLE RGB 4 2 4 4 3 3208 TA04 CAMHL LOW HI RREF GND 24.3k 1% 6-LED MAIN, RGB Plus Low/High Current 8-LED Camera Light with Tone Generator C2 2.2µF C3 2.2µF C1P C1M C2P C2M VBAT VBAT1 C1 4.7µF MAIN CAMERA RGB CPO C4 4.7µF LTC3208 VBAT2 VBAT3 MAIN1-4 0.1µF I2C DVCC SCL/SDA SUB1-2 DVCC CAM1-4 0.1µF AUX1-4 ENRGBS ENABLE DISABLE RGB 4 2 4 4 3 CAMHL LOW HI RREF GND TONE CONTROL 24.3k 1% 3208 TA05 3208fa 21 LTC3208 U TYPICAL APPLICATIO S 6-LED MAIN, 4-LED Camera Light, 4-LED Fun Lights with Vibrator Motor VBAT C2 2.2µF C3 2.2µF C1P C1M C2P C2M VBAT1 C1 4.7µF MAIN CAMERA FUN LIGHTS CPO C4 4.7µF LTC3208 VBAT2 BATT VBAT3 0.1µF I2C MAIN1-4 SCL/SDA SUB1-2 DVCC DVCC CAM1-4 0.1µF AUX1-4 ENRGBS ENABLE DISABLE RGB CAMHL LOW HI 4 2 VIBRATOR MOTOR 4 4 3 3208 TA06 RREF GND 24.3k 1% 10-LED MAIN with RED Camera Indicator, CAM Displays Disabled VBAT C2 2.2µF C3 2.2µF C1P C1M C2P C2M VBAT1 C1 4.7µF MAIN CPO C4 4.7µF LTC3208 CAMERA INDICATOR VBAT2 VBAT3 0.1µF I2C DVCC MAIN1-4 SCL/SDA SUB1-2 DVCC AUX1-4 0.1µF CAM1-4 ENABLE DISABLE ENRGBS CAMHL LOW HI RREF 4 2 4 4 NC CAM DISABLED RED 3208 TA07 GRN NC BLUE NC GRN, BLUE AND CAM DATA REGISTERS SET TO ALL 0s GND 24.3k 1% 3208fa 22 LTC3208 U PACKAGE DESCRIPTIO UH Package 32-Lead Plastic QFN (5mm × 5mm) (Reference LTC DWG # 05-08-1693) 0.70 ±0.05 5.50 ±0.05 4.10 ±0.05 3.45 ±0.05 (4 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC RECOMMENDED SOLDER PAD LAYOUT 5.00 ± 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD PIN 1 NOTCH R = 0.30 TYP OR 0.35 × 45° CHAMFER R = 0.115 TYP 0.75 ± 0.05 0.00 – 0.05 31 32 0.40 ± 0.10 PIN 1 TOP MARK (NOTE 6) 1 2 3.45 ± 0.10 (4-SIDES) (UH32) QFN 1004 0.200 REF NOTE: 1. DRAWING PROPOSED TO BE A JEDEC PACKAGE OUTLINE M0-220 VARIATION WHHD-(X) (TO BE APPROVED) 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.20mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 0.25 ± 0.05 0.50 BSC 3208fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 23 LTC3208 U TYPICAL APPLICATIO 6-LED MAIN, 800mA Camera LED, Plus RGB Driver C2 2.2µF C3 2.2µF MAIN C1P C1M C2P C2M C1 4.7µF CAMERA INDICATOR CPO VBAT1 VBAT C4 4.7µF LTC3208 VBAT2 C5 0.1µF DVCC D1 VBAT3 MAIN1-4 I2C SCL/SDA DVCC C6 0.1µF SUB1-2 CAM1-4 AUX1-4 ENABLE DISABLE LOW HI ENRGBS RGB CAMHL RREF GND 4 2 R G B 4 4 3 3208 TA08 D1 = Lumiled LXCL-PWF1 24.3k 1% RELATED PARTS PART NUMBER LT®1618 DESCRIPTION Constant Current, Constant Voltage, 1.4MHz High Efficiency Boost Regulator LTC1911-1.5 250mA (IOUT), 1.5MHz High Efficiency Step-Down Charge Pump LT1932 Constant Current, 1.2MHz High Efficiency White LED Boost Regulator LT1937 Constant Current, 1.2MHz High Efficiency White LED Boost Regulator LTC3200-5 LTC3205 Low Noise, 2MHz Regulated Charge Pump White LED Driver Low Noise, 1.7MHz Regulated Charge Pump White LED Driver Low Noise, 1.5MHz Regulated Charge Pump White LED Driver Multidisplay LED Controller LTC3206 I2C Multidisplay LED Controller LTC3216 1A High Current, Low Noise, White LED Driver LTC3251 500mA (IOUT), 1MHz to 1.6MHz Spread Spectrum Step-Down Charge Pump LTC3201 LTC3202 LTC3405/LTC3405A 300mA (IOUT), 1.5MHz Synchronous Step-Down DC/DC Converter LTC3406/LTC3406B 600mA (IOUT), 1.5MHz Synchronous Step-Down DC/DC Converter LTC3440 600mA (IOUT), 2MHz Synchronous Buck-Boost DC/DC Converter LT3465/LT3465A 1.2MHz/2.7MHz with Internal Schottky COMMENTS Up to 16 White LEDs, VIN: 1.6V to 18V, VOUT(MAX) = 34V, IQ = 1.8mA, ISD ≤1µA, 10-Lead MS Package 75% Efficiency, VIN: 2.7V to 5.5V, VOUT(MIN) = 1.5V/1.8V, IQ = 180µA, ISD ≤10µA, MS8 Package Up to 8 White LEDs, VIN: 1V to 10V, VOUT(MAX) = 34V, IQ = 1.2mA, IS ≤1µA, ThinSOTTM Package Up to 4 White LEDs, VIN: 2.5V to 10V, VOUT(MAX) = 34V, IQ = 1.9mA, ISD ≤1µA, ThinSOT, SC70 Packages Up to 6 White LEDs, VIN: 2.7V to 4.5V, VOUT(MAX) = 5V, IQ = 8mA, ISD ≤1µA, ThinSOT Package Up to 6 White LEDs, VIN: 2.7V to 4.5V, VOUT(MAX) = 5V, IQ = 6.5mA, ISD ≤1µA, 10-Lead MS Up to 8 White LEDs, VIN: 2.7V to 4.5V, VOUT(MAX) = 5V, IQ = 5mA, ISD ≤1µA, 10-Lead MS Package 92% Efficiency, VIN: 2.8V to 4.5V, IQ = 50µA, ISD ≤ 1µA, 4mm × 4mm QFN Package 92% Efficiency, 400mA Continuous Output Current. Up to 11 White LEDs in 4mm x 4mm QFN Package 93% Efficiency, VIN: 2.9V to 4.4V, 1x/1.5x/2x Boost Modes, Independent Low/High Current Programming 85% Efficiency, VIN: 3.1V to 5.5V, VOUT: 0.9V to 1.6V, IQ = 9µA, ISD ≤1µA, 10-Lead MS Package 95% Efficiency, VIN: 2.7V to 6V, VOUT(MIN) = 0.8V, IQ = 20µA, ISD ≤1µA, ThinSOT Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 20µA, ISD ≤1µA, ThinSOT Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 2.5V, IQ = 25µA, ISD ≤1µA, 10-Lead MS Package Up to 6 White LEDs, VIN: 12.7V to 16V, VOUT(MAX) = 34V, IQ = 1.9mA, ISD <1µA, ThinSOT Package ThinSOT is a trademark of Linear Technology Corporation. 3208fa 24 Linear Technology Corporation LT 0106 REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2005