LTC3210 MAIN/CAM LED Controller in 3mm × 3mm QFN DESCRIPTIO U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Low Noise Charge Pump Provides High Efficiency with Automatic Mode Switching Multimode Operation: 1x, 1.5x, 2x Individual Full-Scale Current Set Resistors Up to 500mA Total Output Current Single Wire EN/Brightness Control for MAIN and CAM LEDs (8 Brightness Steps) 64:1 Brightness Control Range for MAIN Display Four 25mA Low Dropout MAIN LED Outputs One 400mA Low Dropout CAM LED Output Low Noise Constant Frequency Operation* Low Shutdown Current: 3µA Internal Soft-Start Limits Inrush Current During Startup and Mode Switching Open/Short LED Protection No Inductors 3mm × 3mm 16-Lead Plastic QFN Package U APPLICATIO S ■ Multi-LED Light Supply for Cellphones/DSCs/PDAs , 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®3210 is a low noise charge pump DC/DC converter designed to drive four MAIN LEDs and one high current CAM LED for camera lighting. The LTC3210 requires only four small ceramic capacitors and two current set resistors to form a complete LED power supply and current controller. Built-in soft-start circuitry prevents excessive inrush current during start-up and mode changes. High switching frequency enables the use of small external capacitors. Independent MAIN and CAM full-scale current settings are programmed by two external resistors. Shutdown mode and current output levels are selected via two logic inputs. The full-scale current through the LEDs is programmed via external resistors. ENM and ENC are toggled to adjust the LED currents via internal counters and DACs. The part is shut down when both ENM and ENC are low for 150µs (typ). The 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 LTC3210 is available in a 3mm × 3mm 16-lead QFN package. U TYPICAL APPLICATIO C2 2.2µF 4-LED MAIN Display Efficiency vs VBAT Voltage C3 2.2µF 100 C1P VBAT C1M C2P MAIN CAM CPO VBAT C1 2.2µF C2M C4 2.2µF LTC3210 MLED1 MLED2 MLED3 ENM ENM MLED4 ENC ENC CLED RM 30.1k 1% RC GND 24.3k 1% 3210 TA01 EFFICIENCY (PLED/PIN) (%) 90 80 70 60 50 40 30 20 4 LEDs AT 9mA/LED 10 (TYP VF AT 9mA = 3V, NICHIA NSCW100) TA = 25°C 0 3.0 3.2 3.4 3.6 3.8 4.0 4.2 VBAT (V) 4.4 3210 TA01b 3210f 1 LTC3210 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) VBAT, CPO to GND ........................................ –0.3V to 6V ENM, ENC ................................... –0.3V to (VBAT + 0.3V) ICPO (Note 2) ........................................................600mA IMLED1-4 .................................................................30mA ICLED (Note 2) ......................................................450mA CPO Short-Circuit Duration .............................. Indefinite Operating Temperature Range (Note 3) ...–40°C to 85°C Storage Temperature Range...................–65°C to 125°C C2M C1M VBAT C2P TOP VIEW 16 15 14 13 C1P 1 12 GND CPO 2 11 CLED 17 ENM 3 10 ENC MLED1 4 RC 6 7 8 MLED2 MLED3 MLED4 RM 9 5 UD PACKAGE 16-LEAD (3mm × 3mm) PLASTIC QFN TJMAX = 125°C, θJA = 68°C/W EXPOSED PAD IS GND (PIN 17) MUST BE SOLDERED TO PCB ORDER PART NUMBER UD PART MARKING LTC3210EUD LBXH 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, C1 = C2 = C3 = C4 = 2.2µF, RM = 30.1k, RC = 24.3k, ENM = high, unless otherwise noted. PARAMETER CONDITIONS MIN ● VBAT Operating Voltage IVBAT Operating Current ICPO = 0, 1x Mode, MLED LSB Setting ICPO = 0, 1.5x Mode ICPO = 0, 2x Mode VBAT Shutdown Current ENM = ENC = LOW ● LED Current Ratio (IMLED/IRM) IMLED = Full Scale ● LED Dropout Voltage Mode Switch Threshold, IMLED = Full Scale LED Current Matching Any Two Outputs, IMLED = Full Scale MLED Current, 3-Bit Exponential DAC 1 ENM Strobe (FS) 2 ENM Strobes 3 ENM Strobes 4 ENM Strobes 5 ENM Strobes 6 ENM Strobes 7 ENM Strobes (FS/64) TYP 2.9 MAX 4.5 0.375 2.5 4.5 UNITS V mA mA mA 3 6 µA 515 567 A/A MLED1, MLED2, MLED3, MLED4 Current 463 100 mV 1 % 20 10 5 2.5 1.25 0.625 0.312 mA mA mA mA mA mA mA 3210f 2 LTC3210 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.VBAT = 3.6V, C1 = C2 = C3 = C4 = 2.2µF, RM = 30.1k, RC = 24.3k, ENM = high, unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS 6750 7500 8250 A/A CLED Current ● LED Current Ratio (ICLED/IRC) ICLED = Full Scale LED Dropout Voltage Mode Switch Threshold, ICLED = Full Scale 500 mV CLED Current, 3-Bit Linear DAC 1 ENC Strobe (FS) 7 ENC Strobes (FS/7) 380 54 mA mA 1x Mode Output Voltage ICPO = 0mA VBAT V 1.5x Mode Output Voltage ICPO = 0mA 4.55 V 2x Mode Output Voltage ICPO = 0mA 5.05 V 0.5 Ω Charge Pump (CPO) 1x Mode Output Impedance 1.5x Mode Output Impedance VBAT = 3.4V, VCPO = 4.6V (Note 4) 3.15 Ω 2x Mode Output Impedance VBAT = 3.2V, VCPO = 5.1V (Note 4) 3.95 Ω CLOCK Frequency 0.8 MHz Mode Switching Delay 0.4 ms ENC, ENM VIL ● VIH ● 1.4 ENM = ENC = 3.6V ● 10 ENM = ENC = 0V ● –1 tPW Minimum Pulse Width ● 60 tSD Low Time to Shutdown (ENC and ENM = Low) ● 50 150 250 µs tEN Current Source Enable Time (ENC or ENM = High) (Note 5) ● 50 150 250 µs VRM, VRC ● 1.16 1.20 1.24 V IRM, IRC ● 70 µA IIH IIL 0.4 V V 15 20 µA 1 µA ENC, ENM Timing ns RM, RC Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may become 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. Maximum current for continuous operation is 300mA. Note 3: The LTC3210E 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 4: 1.5x mode output impedance is defined as (1.5VBAT – VCPO)/IOUT. 2x mode output impedance is defined as (2VBAT – VCPO)/IOUT. Note 5: If the part has been shut down then the initial enable time is about 100µs longer due to the bandgap enable time. 3210f 3 LTC3210 U W TYPICAL PERFOR A CE CHARACTERISTICS Dropout Time from Shutdown EN 2V/DIV Dropout Time When Enabled 2X CPO 1V/DIV TA = 25°C unless otherwise stated. 1.5X VBAT = 3.6V ICPO = 200mA CCPO = 2.2µF 2X CPO 1V/DIV 1X 1.5x CPO Ripple 1.5X 1X ENC 2V/DIV MODE RESET VCPO 50mV/DIV AC COUPLED MODE RESET ENM = HIGH 500µs/DIV 250µs/DIV 3210 G01 SWITCH RESISTANCE (Ω) 0.65 VCPO 20mV/DIV AC COUPLED 0.60 VBAT = 3.3V 0.55 VBAT = 3.6V 0.50 VBAT = 3.9V 0.45 500ns/DIV 3210 G04 0.40 –40 3.8 VBAT = 3.2V VBAT = 3.1V VBAT = 3V 3.6 0 100 10 35 TEMPERATURE (°C) 60 3.4 3.2 3.0 2.8 2.6 2.4 –40 85 200 300 400 LOAD CURRENT (mA) 500 4.4 85 3210 G06 C2 = C3 = C4 = 2.2µF 5.0 4.0 3.8 3.6 VBAT = 3.6V 4.9 4.8 VBAT = 3.5V 4.7 VBAT = 3.4V 4.6 VBAT = 3.3V 4.5 VBAT = 3.2V 4.4 3.4 VBAT = 3.1V 4.3 4.2 10 60 5.1 4.2 –15 35 2x Mode CPO Voltage vs Load Current 5.2 3.2 –40 10 TEMPERATURE (˚C) VBAT = 3V VCPO = 4.8V C2 = C3 = C4 = 2.2µF 35 60 85 TEMPERATURE (˚C) 3210 G07 –15 3210 G05 CPO VOLTAGE (V) VBAT = 3.6V OPEN LOOP OUTPUT RESISTANCE (Ω) CPO VOLTAGE (V) VBAT = 3.3V VBAT = 3.4V VBAT = 3.5V 4.2 4.0 4.6 C2 = C3 = C4 = 2.2µF 4.4 –15 VBAT = 3V VCPO = 4.2V C2 = C3 = C4 = 2.2µF 3.6 2x Mode Charge Pump Open-Loop Output Resistance vs Temperature (2VBAT – VCPO)/ICPO 1.5x Mode CPO Voltage vs Load Current 4.6 3.8 ICPO = 200mA OPEN LOOP OUTPUT RESISTANCE (Ω) 0.70 VBAT = 3.6V ICPO = 200mA CCPO = 2.2µF 3210 G03 1.5x Mode Charge Pump Open-Loop Output Resistance vs Temperature (1.5VBAT – VCPO)/ICPO 1x Mode Switch Resistance vs Temperature 2x CPO Ripple 4.8 500ns/DIV 3210 G02 3210 G08 VBAT = 3V 0 100 300 400 200 LOAD CURRENT (mA) 500 3210 G09 3210f 4 LTC3210 U W TYPICAL PERFOR A CE CHARACTERISTICS CLED Pin Dropout Voltage vs CLED Pin Current MLED Pin Dropout Voltage vs MLED Pin Current 300 200 100 0 100 150 200 250 300 350 CLED PIN CURRENT (mA) 400 850 VBAT = 3.6V 90 840 80 70 60 50 40 30 770 0 760 800 780 TA = 25°C 2 0 4 6 8 10 12 14 16 18 20 MLED PIN CURRENT (mA) 2.7 TA = 85°C 20 4.5 VBAT = 3.6V RM = 33.2k RC = 24.3k 740 720 700 680 660 640 2.0 4.2 1.5x Mode Supply Current vs ICPO (IVBAT – 1.5ICPO) SUPPLY CURRENT (mA) VBAT CURRENT (µA) 3.0 3.3 3.6 3.9 VBAT VOLTAGE (V) 3.0 3210 G12 760 TA = –40°C 15 10 5 620 600 3.9 3.6 3.3 VBAT VOLTAGE (V) 4.2 4.5 0 3.0 2.7 3.6 3.9 3.3 VBAT VOLTAGE (V) 4.2 3210 G13 0 100 300 400 200 LOAD CURRENT (mA) 500 3210 G15 CLED Pin Current vs CLED Pin Voltage 2x Mode Supply Current vs ICPO (IVBAT – 2ICPO) 20 4.5 3210 G14 400 VBAT = 3.6V VBAT = 3.6V 360 15 CLED PIN CURRENT (mA) 3.0 SUPPLY CURRENT (mA) VBAT SHUTDOWN CURRENT (µA) TA = –40°C 790 1x Mode No Load VBAT Current vs VBAT Voltage 4.0 1.5 2.7 800 3210 G11 5.0 2.5 TA = 85°C 810 10 VBAT Shutdown Current vs VBAT Voltage 3.5 820 780 20 3210 G10 4.5 TA = 25°C 830 FREQUENCY (kHz) 400 50 Oscillator Frequency vs VBAT Voltage 100 VBAT = 3.6V MLED PIN DROPOUT VOLTAGE (mV) CLED PIN DROPOUT VOLTAGE (mV) 500 TA = 25°C unless otherwise stated. 10 5 320 280 240 200 160 120 80 40 0 0 100 300 400 200 LOAD CURRENT (mA) 500 3210 G16 0 0 0.2 0.6 0.8 0.4 CLED PIN VOLTAGE (V) 1 3210 G17 3210f 5 LTC3210 U W TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise stated. MLED Pin Current vs MLED Pin Voltage CLED Current vs ENC Strobe Pulses 22 400 VBAT = 3.6V 20 18 16 CLED CURRENT (mA) MLED PIN CURRENT (mA) VBAT = 3.6V RC = 24.3k 350 14 12 10 8 6 300 250 200 150 100 4 50 2 0 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 MLED PIN VOLTAGE (V) 0 0 7 6 4 3 2 5 NUMBER OF ENC STROBE PULSES 3210 G18 3210 G19 MLED Current vs ENM Strobe Pulses Efficiency vs VBAT Voltage 20 90 VBAT = 3.6V RM = 33.2k 18 80 EFFICIENCY (PLED /PIN) (%) 16 MLED CURRENT (mA) 1 14 12 10 8 6 4 70 60 50 40 30 20 10 2 0 0 0 4 5 6 3 2 7 NUMBER OF ENM STROBE PULSES 1 3210 G20 300mA LED CURRENT (TYP VF AT 300mA = 3.1V, AOT-2015HPW TA = 25°C 2.9 3.05 3.2 3.35 3.5 3.65 3.8 3.95 4.1 4.25 4.4 VBAT (V) 3210 G21 3210f 6 LTC3210 U U U PI FU CTIO S C1P, C2P, C1M, C2M (Pins 1, 16, 14, 13): Charge Pump Flying Capacitor Pins. A 2.2µF X7R or X5R ceramic capacitor should be connected from C1P to C1M and C2P to C2M. CPO (Pin 2): Output of the Charge Pump Used to Power All LEDs. This pin is enabled or disabled using the ENM and ENC inputs. A 2.2µF X5R or X7R ceramic capacitor should be connected to ground. ENM, ENC (Pins 3, 10): Inputs. The ENM and ENC pins are used to program the LED output currents. Each input is strobed up to 7 times to decrement the internal 3-bit DACs from full-scale to 1LSB. The counter will stop at 1 LSB if the strobing continues. The pin must be held high after the final desired positive strobe edge. The data is transferred after a 150µs (typ) delay. Holding the ENM or ENC pin low will set the LED current to 0 and will reset the counter after 150µs (typ). If both inputs are held low for longer than 150µs (typ) the part will go into shutdown. The charge pump mode is reset to 1x whenever ENC goes low or when the part is in shutdown mode. MLED1, MLED2, MLED3, MLED4 (Pins 4, 5, 6, 7): Outputs. MLED1 to MLED4 are the MAIN current source outputs. The LEDs are connected between CPO (anodes) and MLED1-4 (cathodes). The current to each LED output is set via the ENM input, and the programming resistor connected between RM and GND. Each of the four LED outputs can be disabled by connecting the output directly to CPO. A 10µA current will flow through each directly connected LED output. RM, RC (Pins 8, 9): LED Current Programming Resistor Pins. The RM and RC pins will servo to 1.2V. Resistors connected between each of these pins and GND are used to set the CLED and MLED current levels. Connecting a resistor 12k or less will cause the LTC3210 to enter overcurrent shutdown. CLED (Pin 11): Output. CLED is the CAM current source output. The LED is connected between CPO (anode) and CLED (cathode). The current to the LED output is set via the ENC input, and the programming resistor connected between RC and GND. GND (Pin 12): Ground. This pin should be connected to a low impedance ground plane. VBAT (Pin 15): Supply voltage. This pin should be bypassed with a 2.2µF, or greater low ESR ceramic capacitor. Exposed Pad (Pin 17): This pad should be connected directly to a low impedance ground plane for optimal thermal and electrical performance. 3210f 7 LTC3210 W BLOCK DIAGRA C1P C1M C2P C2M 1 14 16 13 800kHz OSCILLATOR 12 GND VBAT 15 2 CPO 4 MLED1 5 MLED2 6 MLED3 7 MLED4 CHARGE PUMP – + + ENABLE CP 1.215V – TIMER ENABLE MAIN 500Ω RM 8 ENM 3 3-BIT DOWN COUNTER 250k + – 3-BIT EXPONENTIAL DAC MLED CURRENT SOURCES 4 1.215V TIMER SHUTDOWN TIMER ENABLE CAM 500Ω RC 9 ENC 10 250k 3-BIT DOWN COUNTER 3-BIT LINEAR DAC CLED CURRENT SOURCE 11 CLED 3210 BD 3210f 8 LTC3210 U OPERATIO Power Management The LTC3210 uses a switched capacitor charge pump to boost CPO to as much as 2 times the input voltage up to 5.1V. The part starts up in 1x mode. In this mode, VBAT is connected directly to CPO. This mode provides maximum efficiency and minimum noise. The LTC3210 will remain in 1x 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 LTC3210 will switch into 1.5x mode. The CPO voltage will then start to increase and will attempt to reach 1.5x VBAT up to 4.6V. Any subsequent dropout will cause the part to enter the 2x mode. The CPO voltage will attempt to reach 2x VBAT up to 5.1V. The part will be reset to 1x mode whenever the part is shut down or when ENC goes low. 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 800kHz. current is achieved ENM is stopped high. The output current then changes to the programmed value after 150µs (typ). The counter will stop when the LSB is reached. The output current is set to 0 when ENM is toggled low after the output has been enabled. If strobing is started within 150µs (typ), after ENM has been set low, the counter will continue to count down. After 150µs (typ) the counter is reset. The CLED current is delivered by a programmable current source. Eight linear current settings (0mA to 380mA, RC = 24.3k) are available by strobing the ENC pin. Each positive strobe edge decrements a 3-bit down counter which controls a 3-bit linear DAC. When the desired current is reached, ENC is stopped high. The output current then changes to the programmed value after 150µs (typ). The counter will stop when the LSB is reached. The output current is set to 0 when ENC is toggled low after the output has been enabled. If strobing is started within 150µs (typ) after ENC has been set low, the counter will continue to count down. After 150µs (typ) the counter is reset. The full-scale output current is calculated as follows: MLED full-scale output current = (1.215V/(RM + 500)) • 515 CLED full-scale output current = (1.215V/(RC + 500)) • 7500 LED Current Control The MLED currents are delivered by the four programmable current sources. Eight current settings (0mA to 20mA, RM = 30.1k) are available by strobing the ENM pin. Each positive strobe edge decrements a 3-bit down counter which controls an exponential DAC. When the desired tPW ≥ 60ns When both ENM and ENC are held low for 150µs (typ) the part will go into shutdown. See Figure 1 for timing information. ENC resets the mode to 1x on a falling edge. tEN 150µs (TYP) tSD 150µs (TYP) ENM OR ENC PROGRAMMED CURRENT LED CURRENT ENM = ENC = LOW SHUTDOWN 3210 F01 Figure 1. Current Programming and Shutdown Timing Diagram 3210f 9 LTC3210 U OPERATIO Soft-Start 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. Initially, when the part is in shutdown, a weak switch connects VBAT to CPO. This allows VBAT to slowly charge the CPO output capacitor to prevent large charging currents. The LTC3210 also employs a soft-start feature on its charge pump to prevent excessive inrush current and supply 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. From Figure 2, for 1.5x mode the available current is given by: IOUT = Charge Pump Strength and Regulation Regulation is achieved by sensing the voltage at the CPO pin and modulating the charge pump strength based on the error signal. The CPO regulation voltages are set internally, and are dependent on the charge pump modes as shown in Table 1. For 2x mode, the available current is given by: (2V – VCPO ) IOUT = BAT ROL Notice that the advantage voltage in this 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. Table 1. Charge Pump Output Regulation Voltages Charge Pump Mode Regulated VCPO 1.5x 4.55V 2x 5.05V (1.5VBAT – VCPO ) ROL Typical values of ROL as a function of temperature are shown in Figure 3 and Figure 4. Shutdown Current When the LTC3210 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 2). In shutdown mode all the circuitry is turned off and the LTC3210 draws a very low current from the VBAT supply. Furthermore, CPO is weakly connected to VBAT. The LTC3210 enters shutdown mode when both the ENM and ENC pins are brought low for 150µs (typ). ENM and ENC have 250k internal pull down resistors to define the shutdown state when the drivers are in a high impedance state. 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. ROL + – 1.5VBAT OR 2VBAT + CPO – Figure 2. Charge Pump Thevenin-Equivalent Circuit 3210f 10 LTC3210 U OPERATIO Thermal Protection The LTC3210 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. Mode Switching The LTC3210 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 time from drop-out detection to mode switching is typically 0.4ms. The part is reset back to 1x mode when the part is shut down (ENM = ENC = Low) or on the falling edge of ENC. An internal comparator will not allow the main switches to connect VBAT and CPO in 1x mode until the voltage at the CPO pin has decayed to less than or equal to the voltage at the VBAT pin. 4.6 VBAT = 3V VCPO = 4.2V 3.6 C2 = C3 = C4 = 2.2µF OPEN LOOP OUTPUT RESISTANCE (Ω) OPEN LOOP OUTPUT RESISTANCE (Ω) 3.8 3.4 3.2 3.0 2.8 2.6 2.4 –40 –15 10 35 TEMPERATURE (˚C) 60 85 3210 F03 4.4 VBAT = 3V VCPO = 4.8V C2 = C3 = C4 = 2.2µF 4.2 4.0 3.8 3.6 3.4 3.2 –40 –15 10 35 60 85 TEMPERATURE (˚C) 3210 F04 Figure 3. Typical 1.5x ROL vs Temperature Figure 4. Typical 2x ROL vs Temperature 3210f 11 LTC3210 U W U U APPLICATIO S I FOR ATIO VBAT, CPO Capacitor Selection The style and value of the capacitors used with the LTC3210 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 (3 f0SC • C CPO ) (3) Where fOSC is the LTC3210 oscillator frequency or typically 800kHz and CCPO is the output storage capacitor. The output ripple in 2x mode is very small due to the fact that load current is supplied on both cycles of the clock. Both style and value of the output capacitor can significantly affect the stability of the LTC3210. As shown in the Block Diagram, the LTC3210 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 1.3µF of capacitance over all conditions. In addition, excessive output capacitor ESR >100mΩ will tend to degrade the loop stability. Multilayer ceramic chip capacitors typically have exceptional ESR performance and when combined with a tight board layout will result in very good stability. As the value of CCPO controls the amount of output ripple, the value of CVBAT controls the amount of ripple present at the input pin(VBAT). The LTC3210’s 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 (~35ns), 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 LTC3210 through a very small series inductor as shown in Figure 5. 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. VBAT LTC3210 GND 3210 F05 Figure 5. 10nH Inductor Used for Input Noise Reduction (Approximately 1cm of Board Trace) 3210f 12 LTC3210 U W U U APPLICATIO S I FOR ATIO Flying Capacitor Selection Layout Considerations and Noise 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 LTC3210. Ceramic capacitors should always be used for the flying capacitors. Due to the high switching frequency and the transient currents produced by the LTC3210, 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 capacitors control the strength of the charge pump. In order to achieve the rated output current it is necessary to have at least 1.6µF 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. Capacitors may also have a very poor voltage coefficient causing them to lose 60% or more of their capacitance when 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, over rated 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. The flying capacitor pins C1P, C2P, C1M and C2M will have 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 LTC3210 (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 LTC3210 pins. For a high quality AC ground, it should be returned to a solid ground plane that extends all the way to the LTC3210. Table 2 shows a list of ceramic capacitor manufacturers and how to contact them: Table 2. Recommended Capacitor Vendors AVX www.avxcorp.com Kemet www.kemet.com Murata www.murata.com Taiyo Yuden www.t-yuden.com Vishay www.vishay.com The following guidelines should be followed when designing a PCB layout for the LTC3210: • 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 must be placed close to the part. • The flying capacitors must be placed close to the part. The traces from the pins to the capacitor pad should be as wide as possible. • VBAT, CPO traces must be wide to minimize inductance and handle high currents. • LED pads must be large and connected to other layers of metal to ensure proper heat sinking. • RM and RC pins are sensitive to noise and capacitance. The resistors should be placed near the part with minimum line width. 3210f 13 LTC3210 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= P LED PIN The efficiency of the LTC3210 depends upon the mode in which it is operating. Recall that the LTC3210 operates as a pass switch, connecting VBAT to CPO, until dropout is detected at the LED 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 PIN = (VLED • ILED ) VLED = (VBAT • IBAT ) VBAT 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 LTC3210 is negligible and the expression above is valid. Once dropout is detected at any LED pin, the LTC3210 enables the charge pump in 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: PLED (VLED • ILED ) VLED ηIDEAL = = = 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 PIN = (VLED • ILED ) VLED = (VBAT • (2)• ILED ) (2 • VBAT ) Thermal Management For higher input voltages and maximum output current, there can be substantial power dissipation in the LTC3210. If the junction temperature increases above approximately 150°C the thermal shut down 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. 3210f 14 LTC3210 U PACKAGE DESCRIPTIO UD Package 16-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1691) 0.70 ±0.05 3.50 ± 0.05 1.45 ± 0.05 2.10 ± 0.05 (4 SIDES) PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 ± 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD PIN 1 NOTCH R = 0.20 TYP OR 0.25 × 45° CHAMFER R = 0.115 TYP 0.75 ± 0.05 15 16 PIN 1 TOP MARK (NOTE 6) 0.40 ± 0.10 1 1.45 ± 0.10 (4-SIDES) 2 (UD16) QFN 0904 0.200 REF 0.00 – 0.05 NOTE: 1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WEED-2) 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 0.15mm 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 3210f 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. 15 LTC3210 U TYPICAL APPLICATIO 3-LED MAIN, One LED Camera C2 2.2µF C1P VBAT C3 2.2µF C1M C2P CAM CPO VBAT C1 2.2µF MAIN C2M C4 2.2µF LTC3210 MLED1 MLED2 MLED3 ENM ENM MLED4 ENC ENC CLED RM RC 30.1k 1% MLED4 DISABLED 3210 TA02 GND 24.3k 1% RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1618 Constant Current, 1.4MHz, 1.5A Boost Converter VIN: 1.6V to 18V, VOUT(MAX) = 36V, IQ = 1.8mA, ISD < 1µA, MS Package LTC3205 250mA, 1MHz, Multi-Display LED Controller VIN: 2.8V to 4.5V, VOUT(MAX) = 5.5V, IQ = 50µA, ISD < 1µA, QFN Package LTC3206 400mA, 800kHz, Multi-Display LED Controller VIN: 2.8V to 4.5V, VOUT(MAX) = 5.5V, IQ = 50µA, ISD < 1µA, QFN Package LTC3208 High Current Software Configurable Multi-Display LED Controller VIN: 2.9V to 4.5V, VOUT = 5.1V, IQ = 250µA, ISD < 1µA, 17 Current Sources (MAIN, SUB, RGB, CAM, AUX), 5 × 5 QFN Package LTC3209-1/ LTC3209-2 600mA Main/Camera/AUX LED Controller VIN: 2.9V to 4.5V, IQ = 400µA, Up to 94% Efficiency, 4mm × 4mm QFN-20 Package LTC3210-1 MAIN/CAM LED Controller with 64-Step Brightness Control VIN: 2.9V to 4.5V, IQ = 400µA, 3-Bit DAC Brightness Control for MAIN and CAM LEDs, 3mm × 3mm QFN Package LTC3214 500mA Camera LED Charge Pump VIN: 2.9V to 4.5V, Single Output, 3 × 3 DFN Package LTC3215 700mA Low Noise High Current LED Charge Pump VIN: 2.9V to 4.4V, VOUT(MAX) = 5.5V, IQ = 300µA, ISD < 2.5µA, DFN Package LTC3216 1A Low Noise High Current LED Charge Pump with Independent Flash/Torch Current Control VIN: 2.9V to 4.4V, VOUT(MAX) = 5.5V, IQ = 300µA, ISD < 2.5µA, DFN Package LTC3217 600mA Low Noise Multi-LED Camera Light VIN: 2.9V to 4.4V, IQ = 400µA, Four 100mA Outputs, QFN Package LTC3440/LTC3441 600mA/1.2A IOUT, 2MHz/1MHz, Synchronous Buck-Boost DC/DC Converter VIN: 2.4V to 5.5V, VOUT(MAX) = 5.25V, IQ = 25µA/50µA, ISD <1µA, MS/DFN Packages LTC3443 600mA/1.2A IOUT, 600kHz, Synchronous Buck-Boost DC/DC Converter VIN: 2.4V to 5.5V, VOUT(MAX) = 5.25V, IQ = 28µA, ISD <1µA, DFN Package LTC3453 1MHz, 800mA Synchronous Buck-Boost High Power LED Driver VIN(MIN): 2.7V to 5.5V, VIN(MAX): 2.7V to 4.5V, IQ = 2.5mA, ISD < 6µA, QFN Package LT3467/LT3467A 1.1A (ISW), 1.3/2.1MHz, High Efficiency Step-Up DC/DC Converters with Integrated Soft-Start VIN: 2.4V to 16V, VOUT(MAX) = 40V, IQ = 1.2mA, ISD < 1µA, ThinSOT Package LT3479 3A, 42V, 3.5MHz Boost Converter VIN: 2.5V to 24V, VOUT(MAX) = 40V, IQ = 2µA, ISD < 1µA DFN, TSSOP Packages 3210f 16 Linear Technology Corporation LT 0106 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2006