LTC3230 5-LED Main/Sub Display Driver with Dual LDO FEATURES DESCRIPTION ■ The LTC®3230 is a low noise charge pump DC/DC converter designed to drive 4 Main LEDs and 1 Sub LED, plus two 200mA linear regulators to provide additional system power. The LTC3230 charge pump requires only four small ceramic capacitors and one current set resistor to form a complete LED power supply and current controller. ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Low Noise Charge Pump Provides High Efficiency with Automatic Mode Switching Multimode Operation: 1x, 1.5x, 2x Full-Scale Current Set Resistor Up to 125mA Total LED Current Single Wire Enable/Brightness Control for Main and Sub Display LEDs 32:1 Linear LED Brightness Control Dual 200mA Linear Regulators Four 25mA Low Dropout Main LED Current Sources One 25mA Low Dropout Sub LED Current Source Low Noise Constant Frequency Operation Low Shutdown Current: 3μA Internal Soft-Start Limits Inrush Current During Start-Up and Mode Switching Open/Short LED Protection No Inductors 20-Lead 3mm × 3mm QFN Package 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. Main and Sub full-scale current settings are programmed by a single external resistor. Charge pump efficiency is optimized based on the voltage across the LED current sources. The part powers up in 1x mode and automatically switches to the next higher mode, 1.5x and subsequently 2x, whenever any LED current source approaches dropout. Two 200mA linear regulators have independent enable and output voltage select pins. Each regulator can be set to one of three pre-selected output voltages with tri-level input pins. The regulators may be enabled independently of the charge pump. APPLICATIONS ■ Multi-LED Driver and Dual LDO Supplies for Cell Phone, PDA, Digital Camera and PND Applications The LTC3230 is available in a low profile (0.75mm) 3mm × 3mm 20-lead QFN package. , LT, LTC and LTM 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 APPLICATION C1 1mF C2 1mF Efficiency vs VIN Voltage 100 C3 2.2mF ENM ENS RSET 17.4k 1% LTC3230 C6 1mF D1 MLED1 MLED2 MLED3 MLED4 SLED LDO1 ENM ENS ENLDO1 ENLDO2 V1 V2 RSET 90 MAIN GND D2 C4 1mF LDO2 C5 1mF 1.5V 200mA 2.8V 200mA D3 SUB D4 D5 3230 TA01a EFFICIENCY (PLED/PIN) (%) VIN = 2.7V TO 5.5V C1P C1M C2P C2M 125mA CPO VIN 80 70 60 50 40 30 20 4 LEDs AT 9mA/LED VF = 3V TA = 25°C 10 0 3 ENM OR ENS SET BRIGHTNESS LEVEL ON OFF 3.2 3.4 3.6 3.8 VIN (V) 4 4.2 4.4 3230 TA01b 3230fa 1 LTC3230 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Notes 1-5) VIN, CPO....................................................... –0.3V to 6V ENM, ENS, ENLDO1, ENLDO2, V1, V2, LDO1, LDO2 ......................–0.3V to (VIN + 0.3V) ICPO (Note 2) ........................................................200mA LD01, LD02 (Note 3)............................................200mA MLED1-4, SLED, RSET.................................. –0.3V to 6V Operating Ambient Temperature Range (Note 4).................................................... –40°C to 85°C Junction Temperature ........................................... 125°C Storage Temperature Range................... –65°C to 150°C C2M C1M VIN C2P C1P TOP VIEW 20 19 18 17 16 15 LDO1 CPO 1 14 LDO2 ENLDO1 2 13 V1 21 ENLDO2 3 12 V2 RSET 4 11 ENM 7 8 9 10 SLED MLED2 MLED3 MLED4 6 MLED1 ENS 5 UD PACKAGE 20-LEAD (3mm × 3mm) PLASTIC QFN TJMAX = 125°C, θJA = 68°C/W EXPOSED PAD (PIN 21) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3230EUD#PBF LTC3230EUD#TRPBF LCYB 20-Lead (3mm × 3mm) Plastic QFN –40°C to 85°C Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, C1 = C2 = C4 = C5 = C6 = 1μF, RSET = 17.4k, ENM = ENS = high, ENLDO1 = ENLDO2 = low, unless otherwise noted. PARAMETER CONDITIONS MIN ● VIN Operating Voltage IVIN Operating Current ICPO = 0, 1x Mode ICPO = 0, 1.5x Mode ICPO = 0, 2x Mode VIN Shutdown Current ENM = ENS = ENLD02 = ENLD01 = Low TYP 2.7 MAX 5.5 0.48 1.2 1.6 ● 3 UNITS V mA mA mA 9 μA MLED1, MLED2, MLED3, MLED4 and SLED Currents LED Current Ratio (ILED/IRSET) 555 A/A LED Dropout Voltage Mode Switch Threshold, IMLED = 15mA 100 mV LED Current Matching Any Two MLED Outputs, IMLED = Full Scale 0.5 % MLED/SLED Current, 5-Bit Linear DAC 1 ENM/ENS Strobe (FS) 31 ENM/ENS Strobes (FS/31) 25.5 0.860 mA mA Unused LED Detection Threshold Voltage VCPO – MLED ● 200 780 mV Test Current LED Tied to CPO ● 39 178 μA 3230fa 2 LTC3230 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, C1 = C2 = C4 = C5 = C6 = 1μF, RSET = 17.4k, ENM = ENS = high, ENLDO1 = ENLDO2 = low, unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS CPO Short Circuit Detection ● Threshold Voltage 0.4 1.3 V Charge Pump (CPO) 1x Mode Output Voltage ICPO = 0mA VIN V 1.5x Mode Output Voltage ICPO = 0mA 4.5 V 2x Mode Output Voltage ICPO = 0mA 5.0 V 1.6 Ω 1.5x Mode Output Impedance VIN = 3.4V, VCPO = 4.6V (Note 6) 7.9 Ω 2x Mode Output Impedance VIN = 3.4V, VCPO = 5.1V (Note 6) 9.2 Ω Clock Frequency 0.9 MHz Mode Switching Delay 0.5 ms 1x Mode Output Impedance tEN Current Source Enable Time (ENM, ENS = High) (Note 7) ● 250 μs LDO1, LDO2 Bias per 1 LDO ENM = ENS = Low Additional DC Bias per LDO Output Voltage Accuracy IOUT = 100μA Current Limit ● –3 ● 280 125 μA 60 μA 475 3 % 750 mA VLDO = 1.8V, IOUT = 50mA 0.1 Load Regulation VIN = 3.6V, 100μA < ILDO < 200mA 0.65 % Dropout Voltage LDO2, VLDO = 3.3V, VIN – VLDO at VLDO 3% Down from VLDO Measureed at VIN = 4.3V 250 mV Line Regulation %/V V1, V2 VIL ● VIH ● 0.2 VIN – 0.2 V V Shutdown Input Current ENLDO1 = ENLDO2 = Low –1 1 μA Active Input Current ENLDO1 = ENLDO2 = High –3 3 μA 0.4 V ENM, ENS, ENLDO1, ENLDO2 VIL ● VIH ● 1.4 IIH VIH = 3.6V IIL VIL = 0V ● –1 tPWH High Pulse Width ● 0.2 tPWL Low Pulse Width tSD Low Time to Shutdown (ENM, ENS = Low) V 3 μA 1 μA ENM, ENS Timing μs 0.2 ● 250 VRSET ● 768 IRSET ● 20 μs μs RSET 800 832 mV 70 μA 3230fa 3 LTC3230 ELECTRICAL CHARACTERISTICS Note 4: The LTC3230 is guaranteed to meet performance specifications from 0°C to 85°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: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125°C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may result in device degradation or failure. Note 6: 1.5x mode output impedance is defined as (1.5VIN – VCPO)/IOUT. 2x mode output impedance is defined as (2VIN – VCPO)/IOUT. Note 7: If the part has been shut down then the initial enable time is about 100μs longer due to the bandgap start-up and charge pump soft-start times. Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. 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 125mA. Note 3: Based on long-term current density limitations. LD01 and LD02 have short circuit protection which limits current to no more than 750mA. Assumes an operating short circuit duty cycle less than 3% for durations less than 10 seconds. TYPICAL PERFORMANCE CHARACTERISTICS Dropout Time from Enable 1.5x Dropout Time when Enabled 2x 1.5x CPO 2V/DIV 1x CPO 2V/DIV TA = 25°C unless otherwise noted. 1.5x CPO Ripple 2x 1x VCPO 20mV/DIV AC COUPLED MODE RESET ENM 2V/DIV ENM 2V/DIV ENS = LOW 400μs/DIV ENS = HIGH 3230 G01 400μs/DIV 3230 G02 VIN = 3V 400ns/DIV ICPO = 80mA C1 = C2 = C6 = 1μF 1.5x Mode Charge Pump OpenLoop Output Resistance vs Temperature (1.5VIN – VCPO)/ICPO 1x Mode Switch Resistance vs Temperature 2x CPO Ripple 11 2.0 ICPO = 100mA 1.9 VIN = 3.6V 10 1.8 1.7 RESISTANCE (Ω) RESISTANCE (Ω) VCPO 20mV/DIV AC COUPLED 1.6 1.5 1.4 1.3 VIN = 3.6V 400ns/DIV ICPO = 80mA C1 = C2 = C6 = 1μF 3230 G04 3230 G03 1.2 VIN = 3V VCPO = 4.2V C1 = C2 = C6 = 1μF 9 8 7 6 1.1 1.0 –40 –15 35 10 TEMPERATURE (°C) 60 85 3230 G05 5 –40 –15 10 35 TEMPERATURE (°C) 60 85 3230 G06 3230fa 4 LTC3230 TYPICAL PERFORMANCE CHARACTERISTICS 2x Mode Charge Pump Open-Loop Output Resistance vs Temperature (2VIN – VCPO)/ICPO 1.5x Mode CPO Voltage vs Load Current 12 4.8 4.2 4.0 VIN = 3.2V VIN = 3.1V VIN = 3V 3.8 10 9 8 50 100 150 LOAD CURRENT (mA) 6 –40 200 –15 10 35 TEMPERATURE (°C) 5.0 4.5 960 4.0 60 40 20 VIN CURRENT (μA) 80 TA = 85°C 940 920 TA = 25°C 900 880 TA = –40°C 860 20 15 MLED/SLED PIN CURRENT (mA) TA = –40°C 3.0 2.5 2.0 1.5 1.0 820 0.5 0 2.7 25 TA = 85°C TA = 25°C 3.5 840 800 10 3.2 3.7 4.2 VIN (V) 4.7 5.2 2.7 4.7 3.7 VIN (V) 3230 G11 1x Mode No-Load VIN Current vs VIN Voltage 3230 G12 1.5x Mode Supply Current vs ICPO (IVIN – 1.5ICPO) 7 RSET = 17.4k 560 200 3230 G09 980 FREQUENCY (kHz) MLED/SLED DROPOUT VOLTAGE (mV) 100 100 50 150 LOAD CURRENT (mA) 0 VIN Shutdown Current vs VIN Voltage 3230 G10 2x Mode Supply Current vs ICPO (IVIN – 2ICPO) 5 VIN = 3.6V VIN = 3.6V 6 SUPPLY CURRENT (mA) 520 500 480 460 440 SUPPLY CURRENT (mA) 4 540 VIN CURRENT (μA) 4.2 85 60 1000 120 580 4.5 Oscillator Frequency vs VIN Voltage 140 5 4.6 3230 G08 VIN = 3.6V 0 VIN = 3.5V VIN = 3.4V VIN = 3.3V VIN = 3.2V VIN = 3.1V VIN = 3V 4.7 4.3 MLED/SLED Pin Dropout Voltage vs MLED/SLED Pin Current 0 4.8 4.4 3230 G07 160 VIN = 3.6V 7 3.6 0 CPO VOLTAGE (V) 4.4 C1 = C2 = C6 = 1μF 5.0 4.9 RESISTANCE (Ω) CPO VOLTAGE (V) 11 VIN = 3.3V VIN = 3.4V VIN = 3.5V VIN = 3.6V 5.1 VIN = 3V VCPO = 4.8V C1 = C2 = C6 = 1μF C1 = C2 = C6 = 1μF 4.6 2x Mode CPO Voltage vs Load Current 5 4 3 2 3 2 1 1 420 0 400 2.8 3.2 3.6 4 4.4 4.8 5.2 VIN (V) 3230 G13 0 100 50 LOAD CURRENT (mA) 150 3230 G14 0 0 100 50 LOAD CURRENT (mA) 150 3230 G15 3230fa 5 LTC3230 TYPICAL PERFORMANCE CHARACTERISTICS MLED/SLED Pin Current vs MLED/SLED Pin Voltage 25 VIN = 3.6V MLED/SLED CURRENT (mA) MLED/SLED PIN CURRENT (mA) 25 20 15 10 5 Efficiency vs VIN Voltage 90 VIN = 3.6V RSET = 17.7k 80 20 EFFICIENCY (PLED/PIN) (%) 30 MLED/SLED Current vs ENM/ENS Strobe Pulses 15 10 5 70 60 50 40 30 20 10 0 0 0.04 0.08 0.12 0.16 MLED/SLED PIN VOLTAGE (V) 0 0.20 16 8 24 NUMBER OF STROBE PULSES 0 3230 G16 2.7 0.35 0 0.30 –0.1 0.25 0.20 0.15 0.10 0.05 4.3 4.7 LDO2 50mV/DIV AC COUPLED –0.2 LDO1 50mV/DIV AC COUPLED –0.3 –0.4 60mA ILDO 50mA/DIV –0.5 10mA –0.6 –0.8 0 50 3.9 VIN (V) LDO1 and LDO2 Load Transient Response CLDO = 1μF –0.7 25 3.5 3.1 3230 G18 Output Voltage Accuracy vs Load Current % CHANGE FROM NO LOAD (%) DROPOUT VOLTAGE (V) 0 32 3230 G17 LDO2 Dropout Voltage vs Load Current 0 C1 = C2 = C6 = 1μF 5 LEDs AT 25mA/LED VF = 3.45V TA = 25°C 75 100 125 150 175 200 225 LOAD CURRENT (mA) 0 25 40μs/DIV 3230 G21 50 75 100 125 150 175 200 LOAD CURRENT (mA) 3230 G20 3230 G19 Output Voltage Accuracy vs Temperature LDO1 and LDO2 Current Limit vs Temperature 0.05 500 475 –0.05 LDO CURRENT LIMIT (mA) % CHANGE FROM 25°C (%) 0 –0.10 –0.15 –0.20 –0.25 –0.30 –0.35 450 425 400 375 –0.40 –0.45 –40 –20 0 40 20 TEMPERATURE (°C) 60 80 3230 G22 350 –40 –20 0 20 40 60 80 TEMPERATURE (°C) 100 120 3230 G23 3230fa 6 LTC3230 PIN FUNCTIONS CPO (Pin 1): Output of the Charge Pump Used to Power All LEDs. This pin is enabled or disabled using the ENM and ENS inputs. A 1μF X5R or X7R ceramic capacitor should be connected to ground. ENLDO1, ENLDO2 (Pins 2, 3): LDO1 and LDO2 Enables. Logic-level high enables LDO1 or LDO2. Logic-level low disables LDO1 or LDO2. RSET (Pin 4): LED Current Programming Resistor Pin. The RSET pin will servo to 0.8V. A resistor connected between RSET and GND is used to set the MLED and SLED full-scale current level. Connecting a resistor 10k or less will cause the LTC3230 to enter overcurrent shutdown. ENS, ENM (Pins 5, 11): SLED and MLED Enable and Output Control. The ENS and ENM pins are used to program the LED output currents. Pulse the ENS pin up to 31 times to decrement the internal 5-bit DAC which controls the Sub LED current from full scale to one LSB. Pulse the ENM pin up to 31 times to decrement the internal 5-bit DAC which controls the MLED1-4 LED currents from full scale to one LSB. The counters will stop at 1LSB when the number of strobes exceeds 31. The pin must be held high after the desired positive strobe edge and the data is transferred after a 150μs (typical) delay. Holding the ENS or ENM pin low will clear the counter for the selected display and reset the LED current to zero. If both inputs are held low for longer than 150μs (typical), the charge pump and LED current sources will go into shutdown. The charge pump mode is reset to 1x whenever ENS or ENM is held low or when the part is shut down. SLED (Pin 6): SLED Current Driver. SLED is the Sub current source output. The LED is connected between CPO (anode) and SLED (cathode). The current to the LED output is set via the ENS input. MLED1, MLED2, MLED3, MLED4 (Pins 7, 8, 9, 10): MLED1-4 Current Drivers. MLED1 to MLED4 are the Main current source outputs. The LEDs are connected between CPO (anodes) and MLED1-4 (cathodes). The current to the LED outputs are set via the ENM input. Any of the four LED outputs can be disabled by connecting the output directly to CPO. A 100μA current will flow through each directly connected LED output. V2, V1 (Pins 12, 13): LDO Output Voltage Select. V1 is used to set LDO1’s output voltage. V2 is used to set LDO2’s output voltage. Tie to VIN, GND or float. LDO Output voltages set by V1 and V2 are shown below. V1 GND FLOAT VIN LDO1 (V) 1.2 1.5 1.8 V2 GND FLOAT VIN LDO2 (V) 1.8 2.8 3.3 LDO2, LDO1 (Pins 14, 15): LDO Outputs. Bypass LDO1 and LDO2 with 1μF X5R or X7R ceramic capacitors to GND. C2M, C1M, C2P, C1P (Pins 16, 17, 19, 20): Charge Pump Flying Capacitor Pins. 1μF X5R or X7R ceramic capacitors should be connected from C1P to C1M and from C2P and C2M. VIN (Pin 18): Supply Voltage. This pin should be bypassed with a 2.2μF or greater low ESR ceramic capacitor. Exposed Pad (Pin 21): Ground. This pad must be connected directly to a low impedance ground plane for proper thermal and electrical performance. 3230fa 7 LTC3230 BLOCK DIAGRAM 20 17 C1P 19 C1M 16 C2M C2P GND 900kHz OSCILLATOR 18 21 VIN CPO 1 – + + 0.8V – 4 RSET TIMER ENABLE MAIN ENM 5-BIT DOWN COUNTER MLED1 7 MLED2 11 50ns FILTER 5-BIT LINEAR DAC MLED CURRENT SOURCES 8 MLED3 9 MLED4 10 TIMER 5 ENS ENABLE SUB 5-BIT DOWN COUNTER 50ns FILTER 5-BIT LINEAR DAC TIMER 3 SLED CURRENT SOURCES SLED 6 VIN SHUTDOWN ENLDO2 + – 2 + LDO1 – 12 14 ENLDO1 0.8V 13 LDO2 V1 LDO1 VOUT SELECT V2 LDO2 VOUT SELECT 15 GND 21 3230 BD 3230fa 8 LTC3230 OPERATION Power Management The LTC3230 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, VIN is connected directly to CPO. 1x mode provides maximum efficiency and minimum noise. The LTC3230 will remain in 1x mode until any 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 LTC3230 will switch into 1.5x mode. The CPO voltage will then start to increase and will attempt to reach 1.5x VIN up to 4.5V. Any subsequent dropout will cause the part to enter 2x mode. The CPO voltage will attempt to reach 2x VIN up to 5V. The part will be reset to 1x mode whenever the part is shut down or when either ENM or ENS is driven low. A 2-phase non-overlapping clock activates the charge pump switches. In 2x mode the flying capacitors are charged on alternate clock phases from VIN to minimize CPO voltage ripple. In 1.5x mode the flying capacitors are charged in series during the first clock phase and stacked in parallel on VIN during the second phase. This sequence of charging and discharging the flying capacitors continues at a constant frequency of 900kHz. LED Current Control The MLED and SLED currents are delivered by programmable current sources controlled by the ENM and ENS tPWH ≥ 200ns pins and by the value of the resistor on the RSET pin. There are four MLED current sources controlled by the ENM pin and one SLED current source controlled by the ENS pin. Full-scale current in the MLED and SLED pins are set by a resistor from the RSET pin to GND according to the following formula: MLED/SLED Full-Scale Output Current = 0.8 • 555 RSETT Thirty two linear current settings are available by applying up to 31 pulses when enabling the ENM and ENS pins. Each strobe counts down a 5-bit DAC to set the LED current. When the desired count is reached, leave the enable strobe high and the output current will be set to the programmed value after a typical delay of 150μs. If more than 31 strobes are received the counter will stop at one LSB. The output current will be set to zero if the enable is set low only after the 150μs delay. If the enable is toggled before the 150μs delay, the DAC counter will continue to count down and the current output will not be enabled until the start-up delay is finished. When both ENM and ENS are held low for more than 250μs (minimum) the LED drivers and charge pump will go into shutdown. See Figure 1 for timing information. If the charge pump is in either 1.5x or 2x modes, the falling edge of either ENM or ENS will reset the charge pump to 1x mode. tEN ≥ 250μs tSD ≥ 250μs ENM OR ENS 200ns < tPWL < 20μs PROGRAMMED CURRENT LED CURRENT SHUTDOWN ENM = ENS = LOW 3230 F01 Figure 1. Current Programming Timing Diagram 3230fa 9 LTC3230 OPERATION Charge Pump Soft-Start In shutdown, CPO is disconnected from VIN and is pulled down through a 14.3k resistor. When enabled, a weak switch connects VIN to CPO. This allows VIN to slowly charge the CPO output to prevent large charging currents. The LTC3230 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 50μs. Soft-start occurs at the start of both 1.5x and 2x modes. 1.5 • VIN – CPO for 1.5x mode and 2 • VIN – 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 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. Table 1. Charge Pump Output Regulation Voltages CHARGE PUMP MODE REGULATED VCPO 1.5x 4.5V 2x 5V When the LTC3230 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). ROL + – + 1.5VIN OR 2VIN CPO – 3230 F02 Figure 2. Charge Pump Thevenin Equivalent Open-Loop Circuit ROL is dependent on a number of factors including the switching term, 1/(2 • fOSC • CFLY), internal switch resistances and the non-overlap period of the switching circuit. However, for a given ROL, the amount of current available will be directly proportional to the advantage voltage of 1.5 • VIN – VCPO ROL For 2x mode, the available current is given by: IOUT = 2 • VIN – VCPO 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 increase in available current is achieved. Typical values of ROL as a function of temperature are shown in Figures 3 and 4. Mode Switching The LTC3230 will automatically switch from 1x mode to 1.5x mode and subsequently to 2x mode whenever a dropout condition is detected at any LED pin. Dropout occurs when a current source voltage becomes too low for the programmed current to be supplied. The time from dropout detection to mode switching is typically 0.5ms. The charge pump mode is reset back to 1x when the LED drivers are shut down (ENM = ENS = Low) or on the falling edge of either ENM or ENS. An internal comparator will not allow the main switches to connect VIN and CPO in 1x mode until the voltage at the CPO pin has decayed to less than or equal to the voltage at the VIN pin. LDO Operation Two independent low drop-out linear regulators are in the LTC3230. Each regulator may be independently enabled (ENLDO1 and ENLDO2) from each other and from the 3230fa 10 LTC3230 OPERATION charge pump function. Driving ENLDO1 and ENLDO2 high enable LDO1 and LDO2 respectively. When the charge pump is enabled, each LDO consumes an additional 60μA (typical) from VIN. If the charge pump is not enabled, one LDO consumes 125μA (typical) and the second uses 60μA (typical) additional current. The reference input to each LDO is ramped when enabled to provide an output soft-start lasting typically 100μs. When an LDO is disabled its output is pulled to ground through an 11.5k resistor. LDO output voltage is set using three-level input pins V1 and V2 as shown in Table 2. In shutdown mode all the circuitry is turned off and the LTC3230 draws a very low current from the VIN supply. When in shutdown, CPO is disconnected from VIN and is pulled to ground through a 14.3k resistor. The LTC3230 enters shutdown mode when both ENM and ENS pins are brought low for 250μs (minimum) and ENLDO1 and ENLDO2 are brought low. All enable pins ENM, ENS, ENLDO1 and ENLDO2 have internal pull-downs to define the shutdown state whenever the inputs are floating. Table 2. LDO1 and LDO2 Output Voltage Control V1 GND FLOAT VIN LDO1 (V) 1.2 1.5 1.8 V2 GND FLOAT VIN LDO2 (V) 1.8 2.8 3.3 RESISTANCE (Ω) 10 12 VIN = 3V VCPO = 4.2V C1 = C2 = C6 = 1μF 11 RESISTANCE (Ω) 11 Shutdown Current 9 8 7 6 5 –40 VIN = 3V VCPO = 4.8V C1 = C2 = C6 = 1μF 10 9 8 7 –15 10 35 TEMPERATURE (°C) 60 85 3230 G06 Figure 3. Typical 1.5x ROL vs Temperature 6 –40 –15 10 35 TEMPERATURE (°C) 60 85 3230 G08 Figure 4. Typical 2x ROL vs Temperature 3230fa 11 LTC3230 APPLICATIONS INFORMATION VIN and CPO Capacitor Selection The style and value of the capacitors used with the LTC3230 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 on both VIN and CPO. Tantalum and aluminum capacitors are not recommended due to high ESR. times. Since the nonoverlapping time is small (~10ns), 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 cause a higher input noise due to the higher ESR. Input noise can be further reduced by powering the LTC3230 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. The value of CCPO directly controls the amount of output ripple for a given load current. Increasing the size of CCPO will reduce the output ripple but will increase start-up time. The peak-to-peak output ripple of the 1.5x mode is approximately given by the expression: IOUT VRIPPLE(P-P) = 3 • fOSC • CCPO where fOSC is the oscillator frequency, typically 900kHz, 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 LTC3230. As shown in the Block Diagram, the LTC3230 uses a control loop to adjust the strength of the charge pump to match the required output current. The error signal for 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 0.6μF 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 CVIN controls the amount of ripple present at the input pin (VIN). The LTC3230’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 overlapping VBAT LTC3230 GND 3230 F05 Figure 5. 10nH Inductor Used for Input Noise Reduction 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 LTC3230. 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 at least 0.6μF 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 3230fa 12 LTC3230 APPLICATIONS INFORMATION of capacitor is needed to ensure minimum capacitances at all temperatures and voltages. • LED pads must be large and connected to the other layers of metal to ensure proper heat sinking. Table 3 shows a list of ceramic capacitor manufacturers and how to contact them. • The RSET pin is sensitive to noise and capacitance. The resistor should be placed near the part with minimum line width. Table 3. Recommended Capacitor Vendors AVX xww.avxcrp.com Kemet www.kemet.com Murata www.murata.com Taiyo Yuden www.t-yuden.com Vishay www.vishay.com Layout Considerations and Noise Due to the high switching frequency and the transient currents produced by the LTC3230, 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 high edge rate waveforms. The large dv/dt on these pins can couple energy to adjacent PCB runs. Magnetic fields can also be generated if the flying capacitors are not close to the LTC3230 (i.e., the loop area is large). To decouple capacitive energy transfer, a grounded PCB trace between the sensitive node and the LTC3230 pins will shield the sensitive node. For a high quality AC ground, the shield trace should be returned to a solid ground plane that extends all the way to the LTC3230. The following guidelines should be followed when designing a PCB layout for the LTC3230: • 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. • VIN and CPO traces must be wide to minimize inductance and handle high currents. 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 The efficiency of the LTC3230 depends upon the mode in which it is operating. Recall that the LTC3230 operates as a pass switch, connecting VIN to CPO, until dropout is detected at a 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 VLED • ILED VLED = = PIN VIN • IIN VIN 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 LTC3230 is negligible and the expression above is valid. Once dropout is detected at any LED pin, the LTC3230 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: η= PLED V •I V = LED LED = LED PIN VIN • 1.5 • IIN 1.5 • VIN 3230fa 13 LTC3230 APPLICATIONS INFORMATION In 2x boost mode as well, 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: η= PLED VLED • ILED V = = LED PIN VIN • 2 • IIN 2 • VIN Thermal Management For higher input voltages and maximum output current, there can be substantial power dissipation in the LTC3230. If the junction temperature increases above approximately 150°C the thermal shutdown circuitry will automatically deactivate the output current sources, charge pump and both LDOs. 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. Its built-in thermal shutdown circuitry will protect the LTC3230 from short term transient events. For continuous operation the maximum rated junction temperature is 125°C. The power dissipated by the device is made up of three components: 1. The LTC3230 IVIN operating current (found in the Electrical Characteristics table) multiplied by VIN. Given a thermal resistance, θJA, for the LTC3230 QFN package of 68°C/W, at an ambient temperature of 70°C the total power in the LTC3230 should be kept to less than 815mW. Applications in which the LDO output voltages are set to the lower range and which use a high VIN input voltage may require limiting the total current output to keep TJ less than 125°C at the upper ambient temperature corners. An example using the parameters in Table 4 shows an application that just meets the maximum junction temperature limit. An increase in VIN, for example, will require reducing the output current of the charge pump or LDO. Table 4. TJ Calculation Example Parameters VIN 3.6V Mode 1.5x VLED 3.3V ILEDTOTAL 100mA (20mA/LED) VLDO1 1.5V VLDO2 2.8V ILDO1 200mA ILDO2 200mA θJA 68°C/W TA 70°C Total Power Dissipation 799mW Internal Junction Temperature 124°C PQ = IQ • VIN 2. The sum of the LED currents multiplied by the difference between VIN • Mode and the LED forward voltage where Mode is 1, 1.5 or 2 depending on the charge pump mode. PCP = (VIN • Mode – VLED) • ILEDTOTAL 3. For each LDO, the product of the LDO output current and the difference between VIN and the LDO. PLDO = (VIN – VLDO1) • ILDO1 + (VIN – VLDO2) • ILDO2 3230fa 14 LTC3230 PACKAGE DESCRIPTION UD Package 20-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1720 Rev A) 0.70 ±0.05 3.50 ± 0.05 (4 SIDES) 1.65 ± 0.05 2.10 ± 0.05 PACKAGE OUTLINE 0.20 ±0.05 0.40 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 3.00 ± 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD R = 0.115 TYP 0.75 ± 0.05 R = 0.05 TYP PIN 1 TOP MARK (NOTE 6) PIN 1 NOTCH R = 0.20 TYP OR 0.25 × 45° CHAMFER 19 20 0.40 ± 0.10 1 2 1.65 ± 0.10 (4-SIDES) (UD20) QFN 0306 REV A 0.200 REF 0.00 – 0.05 NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 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 0.20 ± 0.05 0.40 BSC 3230fa 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 LTC3230 TYPICAL APPLICATION 3-LED Main and One LED Sub at 20mA Full Scale C1 1mF VIN = 2.7V TO 5.5V C2 1mF C1P C1M C2P C2M CPO VIN C3 2.2mF MAIN C6 1mF D1 LTC3230 MLED1 MLED2 MLED3 MLED4 SLED LDO1 LDO2 ENM ENS ENM ENS ENLDO1 ENLDO2 ENLDO1 ENLDO2 V1 V2 RSET RSET 21.5k D2 SUB D3 D5 MLED4 DISABLED 1.2V 3.3V C5 1mF 3230 TA02 C4 1mF GND ENM OR ENS SET BRIGHTNESS LEVEL ON OFF RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT®3023 Dual 100mA, Low Noise Micropower, LDO Dual Low Noise < 20μVRMS, Stable with 1μF Ceramic Capacitors, VIN: 1.8V to 20V, VOUT(MIN) = 1.22V, Dropout Voltage = 0.3V, IQ = 40μA, ISD < 1μA, VOUT = Adj., MS10, DFN Packages LT3024 Dual 100mA/500mA, Low Noise Micropower, LDO Dual Low Noise < 20μVRMS, Stable with 1μF/3.3μF Ceramic Capacitors, VIN: 1.8V to 20V, VOUT(MIN) = 1.22V, Dropout Voltage = 0.3V, IQ = 60μA, ISD < 1μA, VOUT = Adj., TSSOP16, DFN Packages LT3028 Dual 100mA/500mA, Low Noise Micropower, LDO Dual Low Noise < 20μVRMS, Stable with 1μF/3.3μF Ceramic Capacitors, VIN: 1.8V to 20V, VOUT(MIN) = 1.22V, Dropout Voltage = 0.3V/3.3μF, IQ = 60μA/65μA, with Independent Inputs ISD < 1μA, VOUT = Adj., TSSOP16, DFN Packages LTC3207 600mA Universal Multi-Output LED/CAM Driver VBAT: 2.9V to 5.5V, 12 Universal Individually Controlled LED Drivers, One Camera Driver, 4mm × 4mm QFN Package LTC3208 High Current Software Configurable Multidisplay LED Controller 95% Efficiency, VIN: 2.9V to 4.5V, 1A Output Current; Up to 17 LEDs for 5 Displays, 5mm × 5mm QFN Package LTC3209 600mA MAIN/Camera LED Controller Up to 8 LEDs, 94% Efficiency, VIN: 2.9V to 4.5V, 1x/1.5x/2x Boost Modes, 4mm × 4mm QFN Package LTC3210/ LTC3210-1/ LTC3210-2/ LTC3210-3 500mA MAIN/Camera LED Controller Up to 5 LEDs, 95% Efficiency, VIN: 2.9V to 4.5V, 1x/1.5x/2x Boost Modes, Exponential Brightness Control, “-1” Version Has 64-Step Linear Brightness Control, 3mm × 3mm QFN Package, “-2” Version Drives 4 Main LEDs, “-3” Drives 3 Main LEDs LTC3219 250mA Universal 9-Channel LED Driver 91% Efficiency, VIN: 2.9V to 5.5V, Up to 9 × 28mA LEDs, Universal LED Programmability, 3mm × 3mm QFN20 Package 3230fa 16 Linear Technology Corporation LT 0108 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 2007