19-4370; Rev 0; 11/08 EVALUATION KIT AVAILABLE High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP The MAX8831 integrates a 60mA, 28V PWM DC-DC step-up converter with five low-dropout LED current regulators for display and keypad backlighting in cell phones, PDAs, and other portable devices. The IC provides up to 90% efficiency over the entire input voltage range of 2.7V to 5.5V. The step-up converter operates at a fixed 2MHz switching frequency, enabling the use of very small external components to achieve a compact circuit area. For improved efficiency, the step-up converter automatically transitions to pulse-skipping mode at light loads. Each of the five current regulators accommodates up to 9 series LEDs (depending on LED string forward voltage), and is independently programmed using an I2C interface. Two of the current regulators (LED1, LED2) are intended to support display backlight functions and are programmable up to 25mA using a 128-step logarithmic dimming scheme. The other three regulators (LED3, LED4, LED5) are suitable for keyboard backlight functions or for driving signal indicators, and are programmable up to 5mA using a 32-step logarithmic dimming scheme. The low-current regulators (LED3, LED4, LED5) can be operated from the step-up converter or from a separate low-voltage source. The I2C interface controls all operational aspects of the current regulators, including: on/off state, LED current, ramp-up/ramp-down timers, and blink rate timers (LED3, LED4, LED5). The MAX8831 write/read addresses are factory programmed at 0x9A/0x9B (contact the factory for other address options). The MAX8831 features open/short LED fault detection, output overvoltage protection, thermal shutdown, and open-circuit Schottky diode detection, with the status of each fault monitored continually for readback through the I2C interface. The MAX8831 is available in a tiny 2mm x 2mm, 16-bump WLP package. Applications Features ♦ 28V Step-Up DC-DC Converter Integrated NMOS Power Switch > 90% Efficiency Fixed 2MHz Switching Pulse Skipping for Improved Light-Load Efficiency Tiny External Components ♦ I2C Programmable (0x9A Write/0x9B Read), Compatible with 1.8V Logic ♦ Two 25mA Regulators for Display Backlighting I2C-Programmable Output Current (50µA to 25.25mA) 128-Step Logarithmic Dimming Individually Programmable Ramp (Up/Down) Timers Low Dropout (200mV max) ♦ Three 5mA Current Regulators for Keypad Lighting I2C-Programmable Output Current (50µA to 5.0mA) 32-Step Logarithmic Dimming Individually Programmable Ramp (Up/Down) Timers Individual Blink Rate and Duty Cycle Timers Low Dropout (150mV max) ♦ Open/Short LED and Open-Circuit Diode Detection ♦ Thermal-Shutdown and Output Overvoltage Protection ♦ Ultra-Low 0.1mA Shutdown Current ♦ Tiny 2mm x 2mm, 16-Bump WLP Package Ordering Information PART MAX8831EWE+T Cell Phones TEMP RANGE PIN-PACKAGE -40°C to +85°C 16 WLP 2mm x 2mm +Denotes a lead(Pb)-free/RoHS-compliant package. PDAs Smartphones T = Tape and reel. ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com. 1 MAX8831 General Description MAX8831 High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP ABSOLUTE MAXIMUM RATINGS IN to GND ..............................................................-0.3V to +6.0V VDD, COMP to GND.....................................-0.3V to (VIN + 0.3V) SDA, SCL to GND.......................................-0.3V to (VDD + 0.3V) OUT, LX, LED1–LED5 to GND................................-0.3V to +30V ILX (Note 1) .....................................................................1.2ARMS PGND to GND .......................................................-0.3V to +0.3V Operating Temperature Range ...........................-40°C to +85°C Continuous Power Dissipation (TA = +70°C) 16-Bump, 2mm x 2mm WLP (derate 8.2mW/°C above +70°C ambient) ...................660mW Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Bump Temperature (soldering, reflow) ............................+260°C Note 1: LX has an internal clamp diode to PGND. Applications that forward bias this diode should take care not to exceed the power dissipation limits of the device. Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VIN = 3.6V, VGND = VPGND = 0V, VDD = 1.8V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) MAX UNITS IN Supply Voltage PARAMETER 2.7 5.5 V VDD Supply Voltage 1.6 5.5 V IN Undervoltage Lockout Threshold 2.4 2.6 V IN Quiescent Current CONDITIONS MIN No load, 2MHz switching IN Shutdown Current VDD = GND VDD Standby Current VSDA = VSCL = VDD IN Standby Current VSDA = VSCL = VDD OUT Leakage Current VIN = VOUT = 5.5V, VDD = GND TYP 1.5 TA = +25°C 0.1 TA = +85°C 0.1 TA = +25°C 0.1 TA = +85°C 0.1 TA = +25°C 2 TA = +85°C 2 TA = +25°C 0.01 TA = +85°C 0.1 mA 1 1 5 1 µA µA µA µA LED_ CURRENT REGULATORS LED_ Current Regulator Dropout Voltage (Note 2) ILED1 or ILED2 = 25mA setting ILED3 or ILED4 or ILED5 = 5.0mA setting ILED1 or ILED2 = 25.25mA setting LED_ Current Accuracy ILED3 or ILED4 or ILED5 = 5.0mA setting LED_ Leakage Current VLED_ = 5.5V, VDD = GND LX On-Resistance 2 150 mV -2 +2 TA = -40°C to +85°C -5 +5 TA = +25°C -2 +2 TA = -40°C to +85°C -5 +5 TA = +25°C 0.01 TA = +85°C 0.1 780 ILX = 200mA mV TA = +25°C LED_ Regulation Voltage N-CHANNEL SWITCH LX Current Limit 200 1 % % µA 0.35 V 860 mA 0.3 Ω _______________________________________________________________________________________ High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP (VIN = 3.6V, VGND = VPGND = 0V, VDD = 1.8V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER LX Leakage Current CONDITIONS VIN = VLX = 5.5V, VDD = GND MIN TYP MAX TA = +25°C 0.01 1 TA = +85°C 0.1 UNITS µA OSCILLATOR Operating Frequency Maximum Duty Cycle VLED1 or VLED2 = 0.2V Minimum On-Time Skip mode 1.8 2 2.2 MHz 87 92 100 % 30 ns -20 µA 20 kΩ COMP Soft-Start Charge Current COMP Input Resistance to GND Step-up converter off I2C INTERFACE SDA, SCL Logic Input High Voltage VDD = 1.6V to 5.5V SDA, SCL Logic Input Low Voltage VDD = 1.6V to 5.5V SDA Output Low Voltage ISDA = 3mA SDA, SCL Logic Input Current VIL = 0V or VIH = 5.5V 0.7 x VDD V 0.3 x VDD V V 0.03 0.4 TA = +25°C 0.01 1 TA = +85°C 0.1 µA FAULT PROTECTION Thermal Shutdown Temperature rising Thermal-Shutdown Hysteresis Output Overvoltage Threshold VOUT rising °C 20 °C 28 Output Overvoltage Hysteresis 30 V 120 mV 4 Open LED_ Sense Voltage LED_ enabled, measured at LED_ Shorted LED_ Sense Voltage LED_ enabled, measured at LED_, VOUT = 10V Open/Short LED Debounce Timer +160 100 VOUT - 2.2V V VOUT - 0.7V V 16 ms _______________________________________________________________________________________ 3 MAX8831 ELECTRICAL CHARACTERISTICS (continued) MAX8831 High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP I2C INTERFACE TIMING CHARACTERISTICS (VDD = 1.6V to 5.5V, TA = -40°C to +85°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 400 kHz I2C Clock Frequency fSCL Bus-Free Time Between STOP and START tBUF 1.3 Repeated START Condition Hold Time tHD_STA 0.6 0.1 µs Repeated START Condition Setup Time tSU_STA 0.6 0.1 µs STOP Condition Setup Time µs tSU_STO 0.6 0.1 µs SCL Clock Low Period tLOW 1.3 0.2 µs SCL Clock High Period tHIGH 0.6 0.2 µs SDA Hold Time tHD_DAT 0 0.01 µs SDA Setup Time tSU_DAT 100 50 ns Note 1: All devices are 100% production tested at TA = +25°C. Limits over the operating temperature range are guaranteed by design. Note 2: LED dropout voltage is defined as the LED_ to GND voltage when current into LED_ drops 10% from the value at VLED_ = 0.5V. 4 _______________________________________________________________________________________ High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP 95 80 85 4 LEDs: VOUT = 13.35V 5 LEDs: VOUT = 16.63V 6 LEDs: VOUT = 19.83V 7 LEDs: VOUT = 23.07V 8 LEDs: VOUT = 26.23V 80 75 80 75 4 LEDs: VOUT = 13.37V 5 LEDs: VOUT = 16.61V 6 LEDs: VOUT = 19.78V 7 LEDs: VOUT = 23.02V 8 LEDs: VOUT = 26.17V 65 3.0 3.5 4.0 4.5 5.0 65 5 LEDs: VOUT = 15.04V 6 LEDs: VOUT = 17.97V 7 LEDs: VOUT = 20.97V 8 LEDs: VOUT = 23.97V 9 LEDs: VOUT = 26.81V 55 50 2.5 5.5 70 60 60 2.5 3.0 3.5 4.0 4.5 5.0 5.5 2.5 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE (V) INPUT VOLTAGE (V) CONVERTER EFFICIENCY vs. INPUT VOLTAGE (LED3-TO-LED5 STRINGS) CONVERTER EFFICIENCY vs. INPUT VOLTAGE (LED1–LED5 STRINGS) CONVERTER EFFICIENCY vs. LED CURRENT (LED1 STRING) 86 LED1, LED2: 7 LEDs LED3 TO LED5: 8 LEDs VOUT = 23.86V 95 90 MAX8831 toc05 100 MAX8831 toc04 88 80 78 5 LEDs: VOUT = 15.21V 6 LEDs: VOUT = 18.11V 7 LEDs: VOUT = 21.02V 8 LEDs: VOUT = 24.01V 9 LEDs: VOUT = 26.93V 76 74 72 EFFICIENCY (%) EFFICIENCY (%) 82 85 LED1, LED2: 8 LEDs LED3 TO LED5: 8 LEDs VOUT = 26.81V 80 75 3.0 3.5 4.0 4.5 5.0 5.5 60 50 30 65 2.5 70 40 70 70 4 LEDs 6 LEDs 8 LEDs 80 90 84 2.5 3.0 3.5 4.0 4.5 5.0 0 5.5 5 10 15 20 INPUT VOLTAGE (V) LED CURRENT (mA) CONVERTER EFFICIENCY vs. LED CURRENT (LED1 AND LED2 STRINGS) LED1, LED2 CURRENT ACCURACY vs. LED CURRENT LED3-TO-LED5 CURRENT ACCURACY vs. LED CURRENT 70 60 50 40 8 6 ILED1 (ILED2 = 25.25mA) 4 2 0 -2 ILED2 (ILED1 = 25.25mA) -4 -6 LED1, LED2: 8 LEDs LED3 TO LED5: 9 LEDs AT 5mA -8 0 5 10 15 LED CURRENT (mA) 20 25 8 ILED5 (ILED4 = ILED3 = 5mA) 6 ILED4 (ILED5 = ILED3 = 5mA) 4 2 0 -2 ILED3 (ILED5 = ILED4 = 5mA) -4 -6 LED1, LED2: 8 LEDs AT 25.25mA LED3 TO LED5: 9 LEDs -8 -10 -10 30 25 10 LED CURRENT ACCURACY (%) 80 10 MAX8831 toc08 3 LEDs 5 LEDs 8 LEDs LED CURRENT ACCURACY (%) MAX8831 toc07 INPUT VOLTAGE (V) 90 5.5 MAX8831 toc06 INPUT VOLTAGE (V) 90 EFFICIENCY (%) 85 70 70 EFFICIENCY (%) 75 EFFICIENCY (%) EFFICIENCY (%) EFFICIENCY (%) 90 90 MAX8831 toc03 95 85 MAX8831 toc02 100 MAX8831 toc01 100 CONVERTER EFFICIENCY vs. INPUT VOLTAGE (LED3 STRING) CONVERTER EFFICIENCY vs. INPUT VOLTAGE (LED1 AND LED2 STRINGS) MAX8831 toc09 CONVERTER EFFICIENCY vs. INPUT VOLTAGE (LED1 STRING) 0 5 10 15 LED CURRENT (mA) 20 25 0 1 2 3 4 5 LED CURRENT (mA) _______________________________________________________________________________________ 5 MAX8831 Typical Operating Characteristics (VIN = 3.6V, VDD = 1.8V, CIN = 1µF, COUT = 1µF, CVDD = 0.1µF, CCOMP = 0.22µF, L = TOKO 1098AS-100M, ILED1 = ILED2 = 25.25mA, ILED3 = ILED4 = ILED5 = 5mA, unless otherwise noted.) Typical Operating Characteristics (continued) (VIN = 3.6V, VDD = 1.8V, CIN = 1µF, COUT = 1µF, CVDD = 0.1µF, CCOMP = 0.22µF, L = TOKO 1098AS-100M, ILED1 = ILED2 = 25.25mA, ILED3 = ILED4 = ILED5 = 5mA, unless otherwise noted.) LIGHT-LOAD SWITCHING WAVEFORMS HEAVY-LOAD SWITCHING WAVEFORMS MAX8831 toc10 MAX8831 toc11 100mV/div (AC-COUPLED) VIN 200mV/div (AC-COUPLED) VIN 20V/div 20V/div VLX 1V/div (AC-COUPLED) 20mA/div VOUT ILED1 100mV/div (AC-COUPLED) VOUT 4mA/div 0mA 0mA ILED2 20mA/div ILED1 = ILED2 = 25.25mA ILED1 = 2mA 0mA 200ns/div 200ns/div SOFT-START RESPONSE SHUTDOWN RESPONSE MAX8831 toc12 MAX8831 toc13 20V/div VOUT 20V/div VOUT 0V 0V IIN 200mA/div 200mA/div 0mA IIN ILED1 ILED2 0mA 20mA/div ILED1 20mA/div ILED2 20mA/div 20mA/div 0mA 0mA 20ms/div 40ms/div MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE 80 60 1.00 0.50 ILED1 (ILED2 = 25.25mA) 0 40 20 -1.00 0 -1.50 1.50 LED1, LED2: 8 LEDs AT 25.25mA LED3 TO LED5: 9 LEDs 1.00 ILED4 (ILED5 = ILED3 = 5mA) 0.50 0 ILED3 (ILED4 = ILED5 = 5mA) -0.50 -0.50 ILED2 (ILED1 = 25.25mA) -1.00 ILED5 (ILED4 = ILED3 = 5mA) 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) 6 LED1, LED2: 8 LEDs LED3 TO LED5: 9 LEDs AT 5mA LED CURRENT ACCURACY (%) 100 MAX8831 toc15 120 1.50 LED CURRENT ACCURACY (%) MAX8831 toc14 140 LED3-TO-LED5 CURRENT ACCURACY vs. INPUT VOLTAGE LED1, LED2 CURRENT ACCURACY vs. INPUT VOLTAGE MAX8831 toc16 ILED1 0V VLX 0V MAXIMUM OUTPUT CURRENT (mA) MAX8831 High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP 5.0 5.5 -1.50 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) 5.0 5.5 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) _______________________________________________________________________________________ 5.0 5.5 High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP LED1 RAMP-UP LED1 RAMP-DOWN MAX8831 toc17 MAX8831 toc18 10mA/div ILED1 ILED1 10mA/div 0mA 0mA RAMP-UP TIMES OF 128ms, 1024ms, AND 8192ms RAMP-DOWN TIMES OF 128ms, 1024ms, AND 8192ms 1s/div 1s/div LED3 RAMP-UP LED3 RAMP-DOWN MAX8831 toc19 MAX8831 toc20 2mA/div ILED3 ILED3 2mA/div 0mA 0mA RAMP-UP TIMES OF 128ms, 1024ms, AND 8192ms RAMP-DOWN TIMES OF 128ms, 1024ms, AND 8192ms 1s/div 1s/div LED3 BLINK TIMER LED3 BLINK TIMER + RAMP TIMER COMBINED MAX8831 toc21 MAX8831 toc22 2mA/div ILED3 0mA tON = 512ms, tOFF = 1024ms 400ms/div 2mA/div ILED3 0mA tON = 512ms, tOFF = 1024ms, RAMP-UP = 128ms, RAMP-DOWN = 128ms 400ms/div _______________________________________________________________________________________ 7 MAX8831 Typical Operating Characteristics (continued) (VIN = 3.6V, VDD = 1.8V, CIN = 1µF, COUT = 1µF, CVDD = 0.1µF, CCOMP = 0.22µF, L = TOKO 1098AS-100M, ILED1 = ILED2 = 25.25mA, ILED3 = ILED4 = ILED5 = 5mA, unless otherwise noted.) High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831 Pin Description PIN NAME FUNCTION A1 LED1 25mA LED Current Regulator. Connect LED1 to the cathode of the LED1 diode string. LED1 is high impedance in shutdown. A2 GND Analog Ground. Connect GND directly to PGND at the output capacitor as close as possible to the IC. A3 LED3 5mA LED Current Regulator. Connect LED3 to the cathode of the LED3 diode string. LED3 is high impedance in shutdown. A4 COMP Step-Up Compensation Node. Connect a 0.22µF ceramic capacitor from COMP to GND. The applied COMP capacitance stabilizes the converter and sets the soft-start time. COMP discharges to GND through a 20kΩ resistance when in shutdown. See the Compensation Network Selection section for more details. B1 LED2 25mA LED Current Regulator. Connect LED2 to the cathode of the LED2 diode string. LED2 is high impedance in shutdown. B2 LED5 5mA LED Current Regulator. Connect LED5 to the cathode of the LED5 diode string. LED5 is high impedance in shutdown. B3 LED4 5mA LED Current Regulator. Connect LED4 to the cathode of the LED4 diode string. LED4 is high impedance in shutdown. B4 SCL I2C Serial-Clock Input C1, D1 LX C2, D2 PGND C3 SDA I2C Serial-Data I/O. Data written on rising edge of SCL, data read on falling edge of SCL. C4 VDD I2C Input Buffer Supply. Connect a 0.1µF capacitor from VDD to GND as close as possible to the IC. Connect VDD to a 1.6V to 5.5V supply to enable the I2C interface. Drive VDD low to place the IC in shutdown. D3 IN Power-Supply Input. Bypass IN to GND with a 1µF ceramic capacitor placed as close as possible to the IC. D4 OUT LED Overvoltage Protection Input. Connect OUT to the positive terminal of the output capacitor. OUT monitors voltage at the LEDs. If an overvoltage condition is detected, all LED_ current regulators and the step-up converter are shut down. OUT is high impedance during shutdown. Step-Up Converter Switching Node. Connect an inductor between IN and LX. LX is high impedance in shutdown. Power Ground. Connect PGND directly to GND at the output capacitor as close as possible to the IC. Detailed Description The MAX8831 integrates a 60mA, 28V PWM DC-DC step-up converter with five low-dropout LED current regulators for display and keypad backlighting in cell phones, PDAs, and other portable devices. The IC provides up to 90% efficiency over the entire input voltage range of 2.7V to 5.5V. The step-up converter operates at a fixed 2MHz switching frequency, enabling the use of very small external components to achieve a compact circuit area. For improved efficiency, the step-up con- 8 verter automatically operates in pulse-skipping mode at light loads. Figure 1 displays the functional diagram of the MAX8831. Each current regulator accommodates up to 9 series LEDs (depending on LED string forward voltage), and is independently programmed using an I2C interface. Two of the current regulators (LED1, LED2) are intended to support display backlight functions and are programmable up to 25.25mA using a 128-step logarithmic dimming scheme. _______________________________________________________________________________________ High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831 OUT IN OSC UVLO AND BIAS OVP LX LX GND PWM LOGIC PGND COMP PGND LED1 REF SEL MIN VDD I2C INTERFACE LED2 SDA SCL 25mA CURRENT REGULATORS LED3 LED4 LED5 MAX8831 5mA CURRENT REGULATORS Figure 1. MAX8831 Functional Diagram _______________________________________________________________________________________ 9 The other three regulators (LED3, LED4, LED5) are suitable for keyboard backlight functions or for driving signal indicators, and are programmable up to 5.0mA using a 32-step logarithmic dimming scheme. The lowcurrent regulators (LED3, LED4, LED5) can be operated from the step-up converter or from a separate lowvoltage source. The I2C interface controls all operational aspects of the current regulators, including: on/off state, LED current, ramp-up/ramp-down timers, and blink rate timers (LED3, LED4, LED5). The MAX8831 I 2 C write/read addresses are factory set at 0x9A/0x9B (contact the factory for other address options). The IC features several protective features, including: open/short LED fault detection, output overvoltage protection, thermal shutdown, and open Schottky diode detection. The status of each fault is monitored continually for readback through the I2C interface. Fixed-Frequency Step-Up Controller The MAX8831’s fixed-frequency, current-mode, step-up controller automatically chooses the lowest active LED_ voltage to complete the feedback loop (Figure 1). Specifically, the difference between the lowest LED_ voltage and the 350mV reference is integrated by the error amplifier. The resulting error signal is compared to the external switch current plus slope compensation to terminate the switch on-time. As the load changes, the error amplifier sources or sinks current to COMP to adjust the required peak inductor current. The slopecompensation signal is added to the current-sense signal to improve stability at high duty cycles. At light loads, the MAX8831 automatically skips pulses to improve efficiency and to prevent overcharging the output capacitor. In SKIP mode, the inductor current ramps up for a minimum on-time of 20ns (typ), then discharges the stored energy to the output. The switch remains off until another pulse is needed to step-up the output voltage. When the MAX8831 is programmed by the I2C interface to use an alternate supply voltage for the LED3, LED4, or LED5 string (see the Low-Current Regulators (LED3, LED4, LED5) section), internal logic masks that LED_ input and it is not used to regulate the step-up converter output. High-Current Regulators (LED1, LED2) The MAX8831 contains two low-dropout (200mV max), 25.25mA linear current regulators (LED1, LED2) that can each drive up to 9 series LEDs (depending on LED string forward voltage) for display backlighting func- 10 LED1, LED2 CURRENT vs. ILED1, ILED2 CONTROL REGISTER VALUE 25 LED1, LED2 CURRENT (mA) MAX8831 High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP 20 15 10 5 0 0 20 40 60 80 100 120 140 ILED1, ILED2 CONTROL REGISTER VALUE (INTEGER) Figure 2. LED1, LED2 String Current vs. ILED1, ILED2 Control Register Value tions. Each high-current regulator is independently enabled and is programmable from 50µA to 25.25mA in 128 logarithmic steps (Table 1, Figure 2) using the I2C interface. Additionally, the I2C interface programs the ramp-up and ramp-down timers for each regulator to one of eight different timing settings. See the MAX8831 I2C Registers section for details on I2C control of the high-current regulators. Low-Current Regulators (LED3, LED4, LED5) The MAX8831 also contains three low-dropout (150mV max), 5.0mA linear current regulators (LED3, LED4, LED5) that can each drive up to 9 series LEDs for keypad backlighting or signal indicator functions. Each current regulator is independently enabled, and is programmable from 50µA to 5.0mA in 32 logarithmic steps (Table 2, Figure 3) using the I2C interface. Individual ramp-up and ramp-down timers are programmable for LED3, LED4, and LED5, with eight possible timing settings. The individual blink ON and blink OFF timers for each low-current regulator are also programmable, or these features can be disabled. See the MAX8831 I2C Registers section for details. The LED3, LED4, and LED5 low-current regulators can be powered from an alternate external source. By programming the BOOST_CNTL register, internal logic masks that LED_ input and it is not used to regulate the step-up converter output. ______________________________________________________________________________________ High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831 Table 1. LED1, LED2 Programmable Current Levels and Register Values ILED_CNTRL REGISTER VALUE ILED_CNTRL REGISTER VALUE ILED_CNTRL REGISTER VALUE ILED_ (mA) 0x00 0.05 0x2B 6.15 0x56 15.15 0x01 0.1 0x2C 6.35 0x57 15.35 0x02 0.2 0x2D 6.5 0x58 15.6 0x03 0.25 0x2E 6.7 0x59 15.8 0x04 0.35 0x2F 6.9 0x5A 16.05 0x05 0.45 0x30 7.1 0x5B 16.3 0x06 0.55 0x31 7.3 0x5C 16.5 0x07 0.65 0x32 7.45 0x5D 16.75 0x08 0.75 0x33 7.65 0x5E 17 ILED_ (mA) ILED_ (mA) 0x09 0.85 0x34 7.85 0x5F 17.25 0x0A 1 0x35 8.05 0x60 17.45 0x0B 1.1 0x36 8.25 0x61 17.7 0x0C 1.2 0x37 8.45 0x62 17.95 0x0D 1.35 0x38 8.65 0x63 18.2 0x0E 1.45 0x39 8.85 0x64 18.45 0x0F 1.6 0x3A 9.05 0x65 18.65 0x10 1.75 0x3B 9.25 0x66 18.9 0x11 1.85 0x3C 9.45 0x67 19.15 0x12 2 0x3D 9.65 0x68 19.4 0x13 2.15 0x3E 9.9 0x69 19.65 0x14 2.3 0x3F 10.1 0x6A 19.9 0x15 2.45 0x40 10.3 0x6B 20.15 0x16 2.6 0x41 10.5 0x6C 20.4 0x17 2.75 0x42 10.7 0x6D 20.65 0x18 2.9 0x43 10.9 0x6E 20.9 0x19 3.05 0x44 11.15 0x6F 21.15 0x1A 3.2 0x45 11.35 0x70 21.4 0x1B 3.35 0x46 11.55 0x71 21.65 0x1C 3.5 0x47 11.8 0x72 21.9 22.15 0x1D 3.65 0x48 12 0x73 0x1E 3.85 0x49 12.2 0x74 22.4 0x1F 4 0x4A 12.45 0x75 22.65 0x20 4.15 0x4B 12.65 0x76 22.9 0x21 4.35 0x4C 12.85 0x77 23.15 0x22 4.55 0x4D 13.1 0x78 23.4 0x23 4.7 0x4E 13.3 0x79 23.7 0x24 4.9 0x4F 13.55 0x7A 23.95 0x25 5.05 0x50 13.75 0x7B 24.2 ______________________________________________________________________________________ 11 Table 1. LED1, LED2 Programmable Current Levels and Register Values (continued) ILED_CNTRL REGISTER VALUE ILED_ (mA) ILED_CNTRL REGISTER VALUE ILED_ (mA) ILED_CNTRL REGISTER VALUE ILED_ (mA) 0x26 5.25 0x51 14 0x7C 24.45 0x27 5.45 0x52 14.2 0x7D 24.7 0x28 5.6 0x53 14.45 0x7E 25 0x29 5.8 0x54 14.65 0x7F 25.25 0x2A 5.95 0x55 14.9 — — Soft-Start From shutdown, once any LED_ is enabled through the I2C interface, the IC prepares for soft-start. CCOMP is quickly pulled to 1V by an internal pullup clamp. Since the LED_ feedback node voltage is less than the regulation threshold (0.35V typ), 40µA current is sourced from the error amplifier (Figure 1) and further charges CCOMP. Once VCOMP reaches 1.25V, the step-up converter starts switching at a reduced duty cycle. As VCOMP rises, the step-up converter duty cycle increases. When VLED_ reaches 0.35V (typ), the error amplifier stops sourcing current to CCOMP, soft-start ends, and the control loop achieves regulation as VLED_ settles. The VCOMP where the IC exits soft-start depends on the load. A 2.5V upper limit to VCOMP is imposed to aid in transient recovery and to allow maximum output for low input voltages. CCOMP is discharged to GND through a 20kΩ internal resistor whenever the step-up converter is turned off, allowing the device to reinitiate soft-start when it is enabled. See the Typical Operating Characteristics for an example of soft-start operation. Off, Shutdown, and Standby The MAX8831 is considered OFF when VIN is below the V UVLO threshold and V DD is below 1.6V. With V IN above the VUVLO threshold, and with VDD low, the IC enters the shutdown state and disables its internal reference. During shutdown, the MAX8831 holds all registers in reset, the step-up converter and all LED current drivers are off, and supply current is reduced to 0.1µA (typ). LX and LED1–LED5 are high impedance when the step-up converter is off. While the n-channel MOSFET is turned off, the step-up regulator’s output is connected to IN through the external inductor and Schottky diode. With a valid supply voltage applied to VDD (greater than 1.6V) and with VIN above VUVLO, the IC enters a standby condition, whereby it is ready to accept I2C commands. The step-up converter turns on when any current regulator is enabled with an I2C command. 12 LED3, LED4, LED5 CURRENT vs. ILED3, ILED4, ILED5 CONTROL REGISTER VALUE 5 LED3, LED4, LED5 CURRENT (mA) MAX8831 High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP 4 3 2 1 0 0 4 8 12 16 20 24 28 ILED3, ILED4, ILED5 CONTROL REGISTER VALUE (INTEGER) Figure 3. LED3, LED4, LED5 String Current vs. ILED3, ILED4, ILED5 Control Register Value Open/Shorted LED Detection The MAX8831 includes two fault-detection comparators on each LED_ input to detect an open or shorted LED condition. One comparator monitors LED_ voltage and indicates an open LED_ fault when VLED_ falls below 100mV. The other comparator detects when LED_ voltage rises above VOUT - 0.7V, indicating a shorted LED fault. The fault detection comparators are enabled only when the corresponding LED_ current regulator is enabled. Once a fault is detected, the two comparators provide a single bit output (1 = fault, 0 = no fault) to the STAT1 register (bits 0–4), corresponding to the appropriate LED regulator. A debounce time of 16ms (typ) is applied from when a fault condition is detected. At the end of the 16ms debounce time, the status is latched in to the status register and the respective current regulator is disabled. If an open LED condition occurs on a current regulator that is included in the adaptive output voltage ______________________________________________________________________________________ High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP ILED_CNTRL REGISTER VALUE ILED_(mA) 0x00 0x01 ILED_CNTRL REGISTER VALUE ILED_(mA) 0.05 0x10 1.75 0.1 0x11 1.90 0x02 0.15 0x12 2.10 0x03 0.20 0x13 2.25 0x04 0.25 0x14 2.40 0x05 0.30 0x15 2.60 0x06 0.35 0x16 2.80 0x07 0.45 0x17 3.00 0x08 0.55 0x18 3.25 0x09 0.65 0x19 3.50 0x0A 0.80 0x1A 3.70 0x0B 0.95 0x1B 3.90 0x0C 1.10 0x1C 4.15 0x0D 1.25 0x1D 4.40 0x0E 1.40 0x1E 4.70 0x0F 1.60 0x1F 5.00 regulation, the output voltage starts to rise. Depending on the converter output voltage and load condition, the output voltage can reach the OVP threshold before the 16ms debounce timer expires. In this case, the converter disables all current regulators, forces the IC into standby mode, and the status register indicates only an OVP fault. If the BOOST_CNTL register is programmed to power LED3, LED4, or LED5 from an alternate source, only open LED detection is enabled for LED3, LED4, or LED5. Output Overvoltage Protection The MAX8831 protects the LEDs from excessive voltage by initiating overvoltage protection (OVP) when VOUT rises above 28V (min). When OVP occurs, the MAX8831 turns off the LED current regulators by resetting all ON/OFF control register bits to 0, causing the IC to enter standby status and turn off the step-up converter. Bit 0 (OVP) of the STAT2 register is updated to a 1 to indicate that an OVP event has occurred. The stepup converter automatically restarts after an OVP event when VOUT decreases below 25V (typ). The MAX8831 detects an open external Schottky diode by sensing VOUT before turning on the step-up converter. If VOUT is above 0.8V (typ), the MAX8831 allows the step-up converter to turn on. If VOUT is less than 0.8V (typ), indicating that the external Schottky diode is open, the MAX8831 is put into standby state, the ON/OFF control register bits for the LEDs are set low, and the step-up converter stops switching. Bit 2 (OSDD) of the STAT2 register is updated to a 1 to indicate that an open Schottky diode event has occurred. Thermal-Shutdown Protection When the junction temperature exceeds +160°C (typ), the ON/OFF control register bits for all LEDs are reset to low and the MAX8831 enters standby mode and the step-up converter stops switching. Bit 1 (TSD) of the STAT2 register is updated to a 1 to indicate that thermal shutdown has occurred. System States and Fault Handling The MAX8831 implements two fault registers (STAT1, STAT2) to provide users with fault indication through the I2C interface. The STAT1 register indicates a fault condition for each LED_ string, whether a shorted or open LED_ fault has occurred. In the event of an LED_ fault, the corresponding bit in the STAT1 register is latched and the ON/OFF control bit for that current regulator is cleared. An I2C read of the STAT1 register causes all STAT1 bits to be cleared and the corresponding string to be reenabled. If the fault is persistent, then the corresponding bit in the STAT1 register is set again. All open/short fault monitors are subject to a 16ms blanking period to ensure that the MAX8831 does not respond to a false fault occurrence. The second status register, STAT2, reports the following global system faults: output overvoltage-protection detection (OVP), thermal-shutdown detection (TSD), and open Schottky diode detection (OSDD). If a TSD, OVP, or OSDD fault occurs, the IC enters standby mode, the step-up converter stops switching, and all the current regulators are shut down by clearing their ON/OFF control bits. Once standby occurs, the MAX8831 does not transition back to the ON state until the STAT2 register is read, clearing the fault indication, and an I2C command enabling one or more current regulators is received. See Figure 4 for a state diagram of the MAX8831. ______________________________________________________________________________________ 13 MAX8831 Open Schottky Diode Detection Table 2. LED3, LED4, and LED5 Programmable Current Levels and Register Values MAX8831 High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP VDD INVALID FROM ANY CONDITION SHUTDOWN VDD INVALID. INTERNAL REFERENCE, BIAS, AND OSCILLATOR ARE OFF; I2C REGISTER IS IN RESET. VDD VALID STANDBY I2C READY. INTERNAL REFERENCE, BIAS, AND OSCILLATOR ARE OFF. I2C LED_ ENABLE COMMAND RECEIVED ALL CURRENT REGULATORS DISABLED ALL CURRENT REGULATORS DISABLED USING I2C ENABLE BIT CLEARED FOR FAULTED LED_ STRING AND STAT1 REGISTER IS UPDATED WITH FAULT CONDITION. LED SHORT OR OPEN FAULT ONE OR MORE CURRENT REGULATORS ENABLED ON BOOST CONVERTER AND LEDs ARE ON, INTERNAL REFERENCE, BIAS, AND OSCILLATOR ARE ON. VIN < VUVLO UVLO CHECK I2C READY. INTERNAL REFERENCE, BIAS AND OSCILLATOR ARE OFF. VIN > VUVLO ENABLE BIT CLEARED FOR ALL LED_, AND STAT2 REGISTER IS UPDATED WITH FAULT CONDITION. TSD OR OVP FAULT SCHOTTKY DIODE DETECTED SCHOTTKY DIODE NOT DETECTED OPEN SCHOTTKY DIODE DETECTION INTERNAL REFERENCE, BIAS, AND OSCILLATOR ARE ON. Figure 4. State Diagram of Global Faults 14 ______________________________________________________________________________________ High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831 SDA tSU,DAT tBUF tSU,STA tHD,DAT tLOW tHD,STA tSU,STO SCL tHIGH tHD,STA REPEATED START CONDITION START CONDITION STOP CONDITION STOP CONDITION Figure 5. I2C Interface Timing Diagram SCL output. Each transmission consists of a START condition (Figure 6) sent by a master, followed by the MAX8831 7-bit slave address plus a R/W bit, a register address byte, 1 or more data bytes, and finally a STOP condition (Figures 5 and 6). SDA START and STOP Conditions SCL S P START CONDITION STOP CONDITION Figure 6. I2C START and STOP Conditions Both SCL and SDA remain high when the interface is not busy. The master signals the beginning of a transmission with a START (S) condition by transitioning SDA from high to low while SCL is high. When the master has finished communicating with the slave, it issues a STOP (P) condition by transitioning the SDA from low to high while SCL is high. The bus is then free for another transmission (Figure 6). I2C Interface Bit Transfer MAX8831 operates as an I2C slave that receives sends data through an I 2 C-compatible, 2-wire One data bit is clocked onto SDA on the falling edge of SCL and is read on the rising edge of SCL. The data on the SDA line must remain stable while SCL transitions (Figure 7). The and interface. The LED1–LED5 current settings, ramp and blink-rate timers, and other configuration parameters are set using the I2C serial interface. See the register definitions for more details. The interface uses a serial-data line (SDA) and a serialclock line (SCL) to achieve bidirectional communication between master(s) and slave(s). A master (typically a microcontroller) initiates all data transfers to and from the MAX8831, and generates the SCL clock that synchronizes the data transfer (Figure 5). The MAX8831 SDA line operates as both an input and an open-drain output. A pullup resistor, typically 4.7kΩ, is required on SDA. The MAX8831 SCL line operates only as an input. A pullup resistor, typically 4.7kΩ, is required on SCL if there are multiple masters on the 2-wire interface, or if the master in a single-master system has an open-drain Acknowledge The acknowledge bit is a clocked 9th bit that the recipient uses to handshake receipt of each byte of data (Figure 8). Thus, each byte transferred effectively requires 9 bits. The master generates the 9th clock pulse, and the recipient pulls down SDA during the acknowledge clock pulse, such that the SDA line is stable low during the high period of the clock pulse. When the master is transmitting to the MAX8831, the MAX8831 generates the acknowledge bit because it is the recipient. When the MAX8831 is transmitting to the master, the master generates the acknowledge bit because it is the recipient. ______________________________________________________________________________________ 15 MAX8831 High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP SDA BY TRANSMITTER D7 D0 D6 NOT ACKNOWLEDGE SDA SDA BY RECEIVER ACKNOWLEDGE SCL SCL 1 DATA LINE STABLE, CHANGE OF DATA DATA IS VALID IS ALLOWED 8 2 S START CONDITION Figure 7. I2C Bit Transfer CLOCK PULSE FOR ACKNOWLEDGMENT Figure 8. I2C Acknowledge 1 SDA 9 0 0 1 1 0 1 ACK R/W LSB MSB SCL Figure 9. MAX8831 Default Slave Address S S AS P 7-BIT SLAVE ADDRESS 0 AS COMMAND BYTE AS DATA BYTE AS P START BIT ACKNOWLEDGE SLAVE STOP BIT Figure 10. I2C Single-Byte Write MAX8831 Slave Address Message Format for Writing The MAX8831 has a 7-bit-long slave address (Figure 9). The eighth bit following the 7-bit slave address is the R/W bit. It is low for a write command, high for a read command. The slave addresses available for the MAX8831 are 1001101X (with a write/read address of 0x9A/0x9B). Contact the factory for other I2C address options. A write to the MAX8831 comprises the transmission of the MAX8831’s slave address with the R/W bit set to zero (0x9A), followed by at least 1 byte of information. The first byte of information is the command byte (Figure 10), which determines which register of the MAX8831 is to be written by the next byte, if received. If a STOP condition is detected after the command byte is received, the MAX8831 takes no further action beyond storing the command byte. Any bytes received after the command byte are data bytes. The first data 16 ______________________________________________________________________________________ High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP 7-BIT SLAVE ADDRESS 0 LAST DATA BYTE AS COMMAND BYTE AS S AS P P FIRST DATA BYTE AS MAX8831 S AS START BIT ACKNOWLEDGE SLAVE STOP BIT Figure 11. I2C Multiple-Byte Write S 7-BIT SLAVE ADDRESS 0 DATA BYTE AM COMMAND BYTE AS P S AS AM P S A 7-BIT SLAVE ADDRESS 1 AS START BIT ACKNOWLEDGE SLAVE ACKNOWLEDGE MASTER STOP BIT Figure 12. I2C Single-Byte Read 7-BIT SLAVE ADDRESS S FIRST DATA BYTE S AS AM P 0 AS COMMAND BYTE AS S AM LAST DATA BYTE AM P 7-BIT SLAVE ADDRESS 1 AS START BIT ACKNOWLEDGE SLAVE ACKNOWLEDGE MASTER STOP BIT Figure 13. I2C Multiple-Byte Read byte goes into the internal register of the MAX8831 selected by the command byte. If multiple data bytes are transmitted before a STOP condition is detected, these bytes are stored in subsequent MAX8831 internal registers because the command byte address autoincrements (Figure 11). bytes from the MAX8831, by first writing the read command (0x9B) to the MAX8831 (Figures 12 and 13). When performing read-after-write verification, reset the command byte’s address since the stored byte address is autoincremented after the write. Message Format for Reading The MAX8831 contains 19 registers that are accessible through the I2C interface (Table 3). See the register descriptions for more details. The register contents are reset to the default RESET values (shown in Table 3) if VDD goes low. The MAX8831 is read using the MAX8831’s internally stored command byte as an address pointer, the same way the stored command byte is used as an address pointer for a write. The pointer autoincrements after each data byte is read, using the same rules as for a write. Thus, a read is initiated by first configuring the MAX8831’s command byte by writing the command byte corresponding to the beginning register address to be read. The master can now read n consecutive MAX8831 I2C Registers ON/OFF Control Register The ON/OFF control register (ON/OFF_CNTL) enables and disables the LED1–LED5 current regulators (Table 4). Write a 1 to the LED#_EN bit to enable that ______________________________________________________________________________________ 17 MAX8831 High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP LED_ current regulator. Write a 0 to the LED#_EN bit to disable that LED_ current regulator. Overvoltage, open Schottky diode, and thermal-shutdown faults automatically clear all LED#_EN bits to turn off all LED current regulators. LED_ Ramp Control Registers The LED_ ramp control registers (LED1_RAMP_CNTL to LED5_RAMP_CNTL) contains the timing information for each LED current regulator’s ramp-up and rampdown rate. The registers at locations 0x03 to 0x07 program the ramp rates of the LED1 to LED5 current regulators, respectively. The ramp-up and ramp-down rates are programmable with eight different timing selections. See Table 5. LED_ Current Control Registers The LED_ current control registers (ILED1_CNTL to ILED5_CNTL) program the individual LED1 to LED5 current regulators (see Tables 1 and 2 for programmable values). Registers located at 0x0B and 0x0C program the current of the LED1 and LED2 current regulators (Table 6). Registers located at 0x0D, 0x0E, and 0x0F program the current of the LED3, LED4, and LED5 current regulators, respectively (Table 7). LED3, LED4, and LED5 Blink Control Registers The blink control registers (LED3_BLINK_CNTL to LED5_BLINK_CNTL) contain the blink control timing data for the LED3, LED4, and LED5 current regulators. The registers allow enabling of the blink function and control the on- and off-time of the blink sequence. The registers located at 0x17, 0x18, and 0x19 control the blink timing of the LED3, LED4, and LED5 current regulators, respectively. See Table 8. The LED1 and LED2 current regulators do not have blink functionality. Boost Control Register The boost control register (BOOST_CNTL) determines if the LED3, LED4, or LED5 current regulators are included in the step-up converter regulation loop. If programmed to be powered from the step-up converter, LED_ is included in the feedback loop. Otherwise, if LED_ is programmed to be powered from an alternate source, LED_ is not included in the feedback loop. LED3, LED4, and LED5 are high impedance in shutdown. If the BOOST_CNTL bits are programmed to power LED3, LED4, or LED5 from an alternate source, open LED detection is enabled only for that current regulator. See Table 9. The LED1 and LED2 inputs are always in the feedback loop and are not programmable with the boost control register. 18 LED_ Status Registers The LED_ status registers (STAT1, STAT2) indicate the fault conditions of the MAX8831 IC and LEDs and are read-only registers. The STAT1 register indicates a fault condition for each LED_ string, whether a shorted or open LED_ fault is causing the fault condition. The second status register, STAT2, reports the following global system faults: output overvoltage-condition detection (OVP), thermal-shutdown condition detection (TSD), and open Schottky diode detection (OSDD). See Tables 10 and 11. See the Open/Shorted LED Detection, Output Overvoltage Protection, Open Schottky Diode Detection, Thermal-Shutdown Protection, and System States and Fault Handling sections for more details. Chip ID The CHIP ID registers (CHIP_ID1 and CHIP_ID2) contains MAX8831 die type and mask revision data. These registers are read-only registers. See Tables 12 and 13. Applications Information Inductor Selection The MAX8831 is optimized for a 10µH inductor, although larger or smaller inductors can be used. Using a smaller inductor results in discontinuous current-mode operation over a larger range of output power, whereas use of a larger inductor results in continuous conduction for most of the operating range. To prevent core saturation, ensure that the inductor’s saturation current rating exceeds the peak inductor current for the application. For larger inductor values and continuous conduction operation, calculate the worst-case peak inductor current with the following formula: IPEAK = VOUT × IOUT(MAX) 0.9 × VIN(MIN) + VIN(MIN) × 0.5μs 2 ×L Otherwise, for small values of L in discontinuous conduction operation, IPEAK is 860mA (typ). Table 14 provides a list of recommended inductors. Capacitor Selection Ceramic X5R or X7R dielectric capacitors are recommended for best operation. When selecting ceramic capacitors in the smallest available case size for a given value, ensure that the capacitance does not degrade significantly with DC bias. Generally, ceramic capacitors with high values and very small case size have poor DC bias characteristics. ______________________________________________________________________________________ High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP not returning to minimum current before turning off during the blink OFF time. The blink ON and blink OFF timers (tON_BLINK and tOFF_BLINK) are programmed according to the following equations as guidance: Diode Selection The high switching frequency of the MAX8831 demands a high-speed rectification diode for optimum efficiency. A Schottky diode is recommended due to its fast recovery time and low forward voltage drop. Ensure that the diode’s average and peak current rating exceeds the average output current and peak inductor current. In addition, the diode’s reverse breakdown voltage must exceed VOUT. Compensation Network Selection The step-up converter is compensated for stability through an external compensation network from COMP to GND. The compensation capacitor is typically 0.22µF for most applications. Note that higher CCOMP values increase soft-start duration, as well as the time delay between enabling the step-up converter to initiating soft-start. Combining BLINK Timer and RAMP Functions When using the ramp functionality of LED3, LED4, and LED5 in combination with the blink timer, it is recommended to keep the ramp-up timer shorter than the blink ON timer and the ramp-down timer shorter than the blink OFF timer. See Figure 14. Failing to comply with this restriction results in LED_ current not reaching maximum value during blink ON time, and LED_ current tON_BLINK t ON _ BLINK ≥ tLED _ RU t OFF _ BLINK ≥ 32 (LED _ CODE + 1) tLED _ RD 32 (LED _ CODE + 1) Where tLED_RU is the LED_ ramp-up time, tLED_RD is the LED_ ramp-down time, and LED_CODE is the decimal equivalent of the ILED_CNTL register value of Table 2. Using the LED3, LED4, and LED5 BOOST_CNTRL Bit The default setting of the BOOST_CNTL bits (low) include the LED3, LED4, and LED5 current regulators in the step-up converter minimum voltage select feedback circuit. This is intended for multi-LED strings powered from the step-up converter. For single LED indicator lights, set the respective BOOST_CNTL bit high, connect the LED anode to the battery or other voltage source, and connect the LED cathode to the respective LED_ input. Ensure the voltage source is high enough to satisfy VF of the LED plus 150mV (current regulator dropout voltage). If BOOST_CNTL bits are set to high for LED3, LED4, and LED5 and LED1 and LED2 are not enabled, the step-up converter does not turn on when LED3, LED4, or LED5 is enabled. tOFF_BLINK tON_BLINK BLINK TIMERS ILED = ILED_CNTL REGISTER SETTING ILED_ = OFF t= tLED_RU 32 t= tLED_RU 32 Figure 14. Combined Timing Characteristics of RAMP and BLINK Timers ______________________________________________________________________________________ 19 MAX8831 The typical value for the input capacitor is 1µF, and the typical value for the output capacitor is 1µF. Higher value capacitors can reduce input and output ripple, but at the expense of size and higher cost. MAX8831 High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP Table 3. MAX8831 Register Map COMMAND/ ADDRESS BYTE (HEX) TYPE (READ/WRITE) REGISTER RESET VALUES ON/OFF_CNTL 0x00 R/W 0x00 LED current regulator ON/OFF control LED1_RAMP_CNTL 0x03 R/W 0x00 LED1 ramp control LED2_RAMP_CNTL 0x04 R/W 0x00 LED2 ramp control LED3_RAMP_CNTL 0x05 R/W 0x00 LED3 ramp control LED4_RAMP_CNTL 0x06 R/W 0x00 LED4 ramp control LED5_RAMP_CNTL 0x07 R/W 0x00 LED5 ramp control ILED1_CNTL 0x0B R/W 0x00 LED1 current sink control ILED2_CNTL 0x0C R/W 0x00 LED2 current sink control ILED3_CNTL 0x0D R/W 0x00 LED3 current sink control ILED4_CNTL 0x0E R/W 0x00 LED4 current sink control ILED5_CNTL 0x0F R/W 0x00 LED5 current sink control LED3_BLINK_CNTL 0x17 R/W 0x00 LED3 blink rate control LED4_BLINK_CNTL 0x18 R/W 0x00 LED4 blink rate control LED5_BLINK_CNTL 0x19 R/W 0x00 LED5 blink rate control BOOST_CNTL 0x1D R/W 0x00 Adaptive step-up converter control STAT1 0x2D R N/A Status register1 STAT2 0x2E R N/A Status register2 CHIP_ID1 0x39 R 0x07 Die type information CHIP_ID2 0x3A R 0x0B Mask revision information REGISTER 20 FUNCTION ______________________________________________________________________________________ High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831 Table 4. ON/OFF_CNTL Register (Address 0x00) BIT NAME B7 (MSB) — B6 DESCRIPTION BIT NAME DESCRIPTION Reserved for future use B2 LED3_EN 0 = Disable LED3 current regulator 1 = Enable LED3 current regulator — Reserved for future use B1 LED2_EN 0 = Disable LED2 current regulator 1 = Enable LED2 current regulator B5 — Reserved for future use B4 LED5_EN 0 = Disable LED5 current regulator 1 = Enable LED5 current regulator B0 (LSB) LED1_EN 0 = Disable LED1 current regulator 1 = Enable LED1 current regulator B3 LED4_EN 0 = Disable LED4 current regulator 1 = Enable LED4 current regulator Table 5. LED#_RAMP_CNTL Registers (Addresses: 0x03, 0x04, 0x05, 0x06, 0x07) BIT NAME B7 (MSB) — Reserved for future use B6 — Reserved for future use B5 B4 LED#_RAMP_DOWN [2:0] B3 B2 B1 LED#_RAMP_UP [2:0] B0 (LSB) DESCRIPTION Programs LED# current ramp-down rate using bits [5:3] as follows: 000 64ms 001 128ms 010 256ms 010 512ms 100 1024ms 101 2048ms 110 4096ms 111 8192ms Sets LED# current ramp-up rate using bits [2:0] as follows: 000 64ms 001 128ms 010 256ms 010 512ms 100 1024ms 101 2048ms 110 4096ms 111 8192ms #Indicates the selected LED current regulator (1, 2, 3, 4, or 5). ______________________________________________________________________________________ 21 MAX8831 High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP Table 6. ILED#_CNTL Registers for LED1, LED2 (Addresses: 0x0B, 0x0C) BIT NAME B7 (MSB) — DESCRIPTION Table 7. ILED#_CNTL Registers for LED3, LED4, LED5 (0x0D, 0x0E, 0x0F) BIT Reserved for future use NAME DESCRIPTION B7 (MSB) — Reserved for future use B6 B6 — Reserved for future use B5 B5 — Reserved for future use B4 B3 B4 ILED# [6:0] Programs LED# current as indicated in Table 1 B3 B2 B2 B1 B1 B0 (LSB) B0 (LSB) ILED# [4:0] Programs LED# current as indicated in Table 2 #Indicates selected LED current regulator (3, 4, or 5). #Indicates selected LED current regulator (1 or 2). Table 8. LED#_BLINK_CNTL Registers (Addresses: 0x17, 0x18, 0x19) BIT NAME B7 (MSB) — B6 LED#_BLINK_EN B5 — B4 LED#_TOFF_BLINK[1:0] B3 B2 B1 — LED#_TON_BLINK[1:0] B0 (LSB) DESCRIPTION Reserved for future use 0 1 LED# blink function disabled LED# blink function enabled Reserved for future use Programs LED# blink OFF timer using bits [4:3] as follows: 00 LED# blink OFF timer set to 1024ms 01 LED# blink OFF timer set to 2048ms 10 LED# blink OFF timer set to 4096ms 11 LED# blink OFF timer set to 8192ms Reserved for future use Programs LED# blink ON timer using bits [1:0] as follows: 00 LED# blink ON timer set to 256ms 01 LED# blink ON timer set to 512ms 10 LED# blink ON timer set to 1024ms 11 LED# blink ON timer set to 2048ms #Indicates selected LED current regulator (3, 4, or 5). 22 ______________________________________________________________________________________ High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP BIT NAME BIT NAME B7 (MSB) — Reserved for future use B7 (MSB) — Reserved for future use B6 — Reserved for future use B6 — Reserved for future use B5 — Reserved for future use B5 — Reserved for future use B4 B3 B2 DESCRIPTION Table 10. STAT1 Register (Address 0x2D) 0 = LED5 is powered from high-voltage STEP-UP converter. 1= LED5 is powered from LED5_BOOST_CNTL an alternate power source. VLED5 is not used as an input for the feedback loop. 0 = LED4 is powered from high-voltage STEP-UP converter. 1 = LED4 is powered from LED4_BOOST_CNTL an alternate power source. VLED4 is not used as an input for the feedback loop. 0 = LED3 is powered from high-voltage STEP-UP converter. 1 = LED3 is powered from LED3_BOOST_CNTL an alternate power source.VLED3 is not used as input for the feedback loop. B1 Reserved for future use B0 (LSB) Reserved for future use B4 B3 B2 B1 B0 (LSB) DESCRIPTION LED5_FAULT 0 = No open or short is detected for LED5 1 = Open or short is detected for LED5 LED4_FAULT 0 = No open or short is detected for LED4 1 = Open or short is detected for LED4 LED3_FAULT 0 = No open or short is detected for LED3 1 = Open or short is detected for LED3 LED2_FAULT 0 = No open or short is detected for LED2 1 = Open or short is detected for LED2 LED1_FAULT 0 = No open or short is detected for LED1 1 = Open or short is detected for LED1 ______________________________________________________________________________________ 23 MAX8831 Table 9. BOOST_CNTL Register (Address: 0x1D) MAX8831 High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP Table 11. STAT2 Register (Address 0x2E) BIT NAME Table 12. CHIP_ID1 Register (Address: 0x39) DESCRIPTION B7 (MSB) Reserved for future use B6 Reserved for future use B5 Reserved for future use B4 Reserved for future use B3 Reserved for future use B2 Open Schottky diode detection 0 = Schottky diode is present 1 = Schottky diode is missing B1 B0 (LSB) OSDD TSD OVP Thermal-shutdown detection 0 = No thermal shutdown occurred 1 = MAX8831 has entered thermal shutdown since the last read operation of this register Output overvoltage detection 0 = No overvoltage protection has occurred 1 = MAX8831 has entered over voltage protection since last read operation of this register PCB Layout Due to fast switching waveforms and high current paths, careful PCB layout is required. Minimize trace lengths between the IC and the inductor, the diode, the input capacitor, and the output capacitor. Minimize trace lengths between the input and output capacitors and the MAX8831 GND terminal, and place input and output capacitor grounds as close together as possible. Use separate power ground and analog ground copper areas, and connect them together at the output capacitor ground. Keep traces short, direct, and wide. Keep noisy traces, such as the LX node trace, away from sensitive analog circuitry. For improved thermal performance, maximize the copper area of the LX and PGND traces. Refer to the MAX8831 EV Kit for an example layout. 24 BIT B7 (MSB) B6 B5 B4 B3 B2 B1 B0 (LSB) NAME DESCRIPTION DIE_TYPE[7:4] BCD character 0 DIE_TYPE[3:0] BCD character 7 Table 13. CHIP_ID2 Register (Address 0x3A) BIT NAME DESCRIPTION B7 (MSB) B6 B5 B4 DASH [7:4] BCD character 0 B3 B2 B1 B0 (LSB) MASK_REV [3:0] BCD character B Table 14. Recommended Inductors for the MAX8831 Circuit PART L (µH) DCR (mΩ) ISAT (A) SIZE (mm) TOKO 1098AS-100M 10 290 0.75 2.8 x 3.0 x 1.2 TOKO 1069AS-220M 22 570 0.47 3 x 3 x 1.8 FDK MIP3226D100M 10 160 0.9 3.2 x 2.6 x 1.0 Coilcraft EPL2014472ML 4.7 231 650 2.0 x 2.0 x 1.45 Coilcraft DO2010472ML 4.7 800 650 2.0 x 2.0 x 1.0 ______________________________________________________________________________________ High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP L1 10μH D1 D2–D9 D10–D17 D18–D26 D27–D35 MAX8831 VIN 2.7V TO 5.5V D36–D44 C1 1μF OUT LX LX C2 1μF MAX8831 PGND IN PGND SCL SDA VDD 1.6V TO 5.5V VDD LED1 C3 0.1μF LED2 LED3 COMP LED4 C4 0.22μF LED5 GND Figure 15. MAX8831 Applications Circuit ______________________________________________________________________________________ 25 High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831 Typical Operating Circuit VIN 2.7V TO 5.5V VOUT UP TO 28V 10μH UP TO 25.25mA/LED UP TO 5.0mA/LED 1μF OUT LX LX 1μF MAX8831 PGND IN PGND SCL SDA VDD 1.6V TO 5.5V VDD LED1 0.1μF LED2 LED3 COMP LED4 0.22μF LED5 GND Chip Information PROCESS: BiCMOS 26 ______________________________________________________________________________________ High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP TOP VIEW (BUMPS ON BOTTOM) 1 2 3 4 + MAX8831 A B C D Package Information For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. A1 A2 A3 A4 LED1 GND LED3 COMP B1 B2 B3 B4 LED2 LED5 LED4 SCL C1 C2 C3 C4 LX PGND SDA VDD D1 D2 D3 D4 LX PGND IN OUT PACKAGE TYPE PACKAGE CODE DOCUMENT NO. 16 WLP W162B2+1 21-0200 WLP Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 27 © 2008 Maxim Integrated Products Boblet is a registered trademark of Maxim Integrated Products, Inc. MAX8831 Pin Configuration