KIT ATION EVALU LE B A IL A AV 19-0847; Rev 0; 11/07 Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN Features ♦ High-Efficiency Charge Pump for Up to Four White LEDs Independent Adaptive Voltage Supply for Each LED 24mA to 0.1mA Dimming Range 1% (typ) Current Accuracy and 0.3% Current Matching Low 65µA (typ) Quiescent Current ♦ Dual 200mA Low-Noise, High PSRR LDOs 16 Different Output Voltage Combinations Up to 3.3V High 60dB PSRR at 10kHz ♦ Flexible Single-Wire Control for Dimming and LDO Output Voltage ♦ Low 0.5µA (typ) Shutdown Mode ♦ Soft-Start Limits Inrush Current ♦ Thermal Shutdown and Open- and Short-Circuit Protection ♦ Tiny 16-Pin, 3mm x 3mm Thin QFN Package (0.8mm max Height) with Exposed Paddle The MAX8822 includes soft-start, thermal shutdown, open- and short-circuit protection. Ordering Information Applications White LED Backlighting Cell Phones and Smartphones Typical Operating Circuit 1μF 16 Thin QFN-EP* (3mm x 3mm) AFW T1633-5 Pin Configuration TOP VIEW LED2 4.7μF MAX8822 GND LED3 C2N LED1 IN MAX8822ETE+ LED2 C2P PKG CODE LED1 C1N TOP MARK LDO1 C1P PIN-PACKAGE Note: The device is specified over the -40°C to +85°C extended temperature range. +Denotes a lead-free package. *EP = Exposed paddle. INPUT 2.7V TO 5.5V 1μF PART 12 11 10 9 LED3 LED4 LDO2 13 ENLED 14 NEG ENLED MAX8822 ENLDO 15 2.2μF ENLDO VLDO2 LDO2 EP 1μF 1μF + 1 2 3 4 C2P VLDO1 LDO1 C1P REF 0.1μF GND REF 16 IN SERIALPULSE CONTROL INTERFACE 8 LED4 7 NEG 6 C1N 5 C2N UP TO 24mA/LED THIN QFN (3mm x 3mm) ________________________________________________________________ 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 MAX8822 General Description The MAX8822 drives up to four white light-emitting diodes (LEDs) with regulated constant current for display backlighting in cell phones, digital cameras, PDAs, and other handheld devices. By utilizing a proprietary negative 0.5x inverting charge pump and innovative independent low-dropout (LDO) adaptive current regulators, very high efficiency is achieved over the full 1-cell Li+ battery voltage range, even with large LED VF mismatch. The 1MHz fixed-frequency switching allows for tiny external components. The regulation scheme is optimized to ensure low EMI and low input ripple. Two 200mA, low-noise, high power-supply-rejection-ratio (PSRR) LDOs with programmable output voltages are included on-chip to provide power to camera modules or other devices. The MAX8822 features a single-wire, serial-pulse controllogic interface that programs LED current and the output voltages of the LDOs. The LED dimming range is pseudo-logarithmic from 24mA to 0.1mA in 31 steps. LDO output voltages are programmable in 16 different combinations to meet various camera module requirements. MAX8822 Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN ABSOLUTE MAXIMUM RATINGS IN, C1N, C2N, REF, ENLED, ENLDO, LDO1, LDO2 to GND...............................................................-0.3V to +6.0V IN, REF, ENLED, ENLDO, LDO1, LDO2 to NEG ...............................................................-0.3V to +6.0V LED_, C1N, C2N to NEG .............................-0.3V to (VIN + 0.3V) C1P, C2P to GND ........................................-0.3V to (VIN + 0.3V) NEG to GND ..........................................................-6.0V to +0.3V NEG, LDO1, LDO2 Short-Circuit Current to GND ......Continuous Continuous Power Dissipation (TA = +70°C) 16-Pin Thin QFN 3mm x 3mm (derate 14.7mW/°C above +70°C) .............................1177mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C 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 = 0V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER CONDITIONS IN Operating Voltage Undervoltage Lockout (UVLO) Threshold MIN 2.7 VIN rising 2.25 UVLO Hysteresis Shutdown Supply Current TYP 2.45 MAX UNITS 5.5 V 2.65 V 100 ENLED = ENLDO = GND TA = +25°C 0.5 TA = +85°C 0.5 mV 5 µA Charge pump inactive, ILED1 = ILED2 = ILED3 = ILED4 = 0.1mA 65 Charge pump active, VIN = 2.7V, 1MHz switching, ILED1 = ILED2 = ILED3 = ILED4 = 0.1mA 1.4 mA Thermal-Shutdown Threshold 160 °C Thermal-Shutdown Hysteresis 20 °C IN Operating Supply Current 100 µA SERIAL-PULSE CONTROL Logic Input-High Voltage (VIH) VIN = 2.7V to 5.5V Logic Input-Low Voltage (VIL) VIN = 2.7V to 5.5V 1.4 V 0.4 TA = +25°C 0.01 TA = +85°C 0.1 1 V µA Logic Input Current VIL = 0V or VIH = 5.5V tSHDN See Figures 1 and 2 (Note 2) 2.5 tLO See Figures 1 and 2 0.5 500 µs tHI See Figures 1 and 2 0.5 500 µs tINIT First high pulse from shutdown (Figures 1 and 2) 100 µs tHOLD Pulse width to latch EN_ count (Figures 1 and 2) (Note 3) 2.5 ms ms CHARGE PUMP Switching Frequency Soft-Start Time 1 MHz 0.5 ms 5 V Charge-Pump Regulation Voltage (VIN - VNEG) Open-Loop NEG Output Resistance (VNEG - 0.5 x VIN) / INEG 2.8 NEG Shutdown Discharge Resistance All LEDs off, EN_ = GND 10 2 _______________________________________________________________________________________ 5.0 Ω kΩ Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN (VIN = 3.6V, VGND = 0V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER CONDITIONS MIN TYP MAX UNITS 24.0 mA CURRENT REGULATOR (LED1–LED4) Programmable Current Range Current Accuracy 0.1 ILED_ = 24mA, TA = +25°C -2 ILED_ = 24mA, TA = -40°C to +85°C -3 ILED_ = 0.1mA, TA = +25°C LED_ Dropout Voltage ILED_ = 24mA (Note 4) LED_ Current Regulator Switchover Threshold (Inactive to Active) VLED_ falling LDO_ Output Current +2 +3 Charge pump inactive 60 120 Charge pump active 80 250 150 175 125 100 All LEDs off, ENLED = GND % ±5 LED_ Current Regulator Switchover Hysteresis LED_ Shutdown Leakage Current ±1 TA = +25°C 0.01 TA = +85°C 0.1 mV mV mV 5 µA (Note 5) 200 Current Limit VLDO = 0V 220 LDO1 Dropout Voltage ILDO1 = 200mA, VLDO1 = 2.8V (Notes 5 and 6) 150 250 mV LDO2 Dropout Voltage ILDO2 = 200mA, VLDO2 = 2.8V (Notes 5 and 6) 300 550 mV Line Regulation 3.4V ≤ VIN < 5.5V, ILDO = 100mA 1 mV/V Load Regulation 50µA < ILDO < 200mA 0.1 mV/mA Power-Supply Rejection ΔVOUT/ΔVIN 10Hz to 10kHz, CLDO = 1µF, ILDO = 30mA 60 dB Output Noise Voltage (RMS) 100Hz to 100kHz, CLDO = 1µF, ILDO = 30mA 45 µVRMS LDO1 Output Voltage ILDO1 = 100mA (Note 7) mA 750 ENLDO count = 5 1.2 ENLDO count = 6, 13 1.8 ENLDO count = 1, 3, 7, 9, 14 2.716 2.800 ENLDO count = 2, 4, 8, 15 3.3 ENLDO count = 1, 2 1.2 ENLDO count = 3, 4, 10 1.5 2.884 mA V LDO2 Output Voltage ILDO2 = 100mA (Note 7) Ground Current ILDO = 500µA 50 µA Shutdown Output Impedance ENLDO = GND 1 kΩ ENLDO count = 5, 6, 7, 8, 11 ENLDO count = 9, 12 1.746 1.800 1.854 V 2.8 Limits are 100% production tested at TA = +25°C. Specifications over the operating temperature range are guaranteed by design. Hold EN_ low for at least 2.5ms to guarantee shutdown. Hold EN_ high for at least 2.5ms to latch EN count. LED dropout voltage is defined as the LED_ to GND voltage when current into LED_ drops 10% from the value at VLED = 0.5V. Guaranteed by design, not production tested. LDO dropout voltage is defined as VIN - VOUT when VOUT has dropped 100mV below the initial value of VOUT when VIN = VOUT + 0.8V. Note 7: LDO output voltage corresponds to the LDO output voltage programmed by pulsing ENLDO low by the given count and then holding ENLDO high for greater than tHOLD to set the voltage value. See Figure 2. Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: _______________________________________________________________________________________ 3 MAX8822 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VIN = 3.6V, VEN_ = VIN, Circuit of Typical Operating Circuit, TA = +25°C, unless otherwise noted.) 14.4mA/LED 50 6.4mA/LED 40 1.6mA/LED 60 50 40 80 1.6mA/LED 70 60 50 30 30 20 20 20 10 10 VIN FALLING 2.7 3.0 3.3 3.6 3.9 4.2 10 VIN FALLING 0 2.7 3.0 3.3 3.6 3.9 6.4mA/LED 40 30 0 VIN FALLING 0 2.7 4.2 3.0 3.3 3.6 3.9 4.2 SUPPLY VOLTAGE (V) SUPPLY VOLTAGE (V) SUPPLY VOLTAGE (V) EFFICIENCY vs. Li+ BATTERY VOLTAGE (4 MATCHED WLEDs) EFFICIENCY vs. Li+ BATTERY VOLTAGE (4 MISMATCHED WLEDs) EFFICIENCY vs. Li+ BATTERY VOLTAGE (4 MISMATCHED WLEDs) 6.4mA/LED 1.6mA/LED 60 50 80 14.4mA/LED 70 1.6mA/LED 60 3.8 3.7 3.6 3.5 3.4 3.0 20.8mA/LED 70 6.4mA/LED 60 40 40 4.2 3.9 80 50 50 40 MAX8822 toc06 90 4.2 3.9 3.8 3.7 3.6 4.2 3.9 3.5 3.4 3.0 3.8 3.7 3.6 3.5 3.4 3.0 Li+ BATTERY VOLTAGE (V, TIME-WEIGHTED) Li+ BATTERY VOLTAGE (V, TIME-WEIGHTED) SUPPLY CURRENT vs. SUPPLY VOLTAGE (4 WLEDs) SUPPLY CURRENT vs. SUPPLY VOLTAGE (RGB MODULE) INPUT VOLTAGE RIPPLE vs. SUPPLY VOLTAGE (4 WLEDs) 100 20.8mA/LED 80 14.4mA/LED 60 40 6.4mA/LED 20 RGB MODULE: LUMEX SML-LX3632SISUGSBC, VIN FALLING 20.8mA/LED 80 60 14.4mA/LED 40 6.4mA/LED 20 1.6mA/LED 1.6mA/LED 0 3.0 3.3 3.6 SUPPLY VOLTAGE (V) 3.9 4.2 2.4 2.0 20.8mA/LED 1.6 1.2 14.4mA/LED 0.8 0.4 6.4mA/LED 0 0 2.7 VIN FALLING, MISMATCHED LEDs 2.8 INPUT VOLTAGE RIPPLE (mVRMS) 120 100 SUPPLY CURRENT (mA) VIN FALLING MISMATCHED LEDs MAX8822 toc07 140 MAX8822 toc08 Li+ BATTERY VOLTAGE (V, TIME-WEIGHTED) MAX8822 toc09 70 EFFICIENCY (%) 80 90 EFFICIENCY (%) 14.4mA/LED 100 MAX8822 toc05 20mA/LED 90 100 MAX8822 toc04 100 4 70 20.8mA/LED 90 EFFICIENCY (%) 20.8mA/LED 60 80 EFFICIENCY (%) EFFICIENCY (%) 80 14.4mA/LED 90 100 MAX8822 toc02 90 EFFICIENCY (%) 100 MAX8822 toc01 100 70 EFFICIENCY vs. SUPPLY VOLTAGE (4 MISMATCHED WLEDs) EFFICIENCY vs. SUPPLY VOLTAGE (4 MISMATCHED WLEDs) MAX8822 toc03 EFFICIENCY vs. SUPPLY VOLTAGE (4 MATCHED WLEDs) SUPPLY CURRENT (mA) MAX8822 Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN 2.7 3.0 3.3 3.6 SUPPLY VOLTAGE (V) 3.9 4.2 2.7 3.0 3.3 3.6 SUPPLY VOLTAGE (V) _______________________________________________________________________________________ 3.9 4.2 Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN TYPICAL OPERATING WAVEFORMS (CHARGE PUMP INACTIVE) LED CURRENT MATCHING vs. SUPPLY VOLTAGE MAX8822 toc11 MAX8822 toc10 17.0 16.8 LED CURRENT (mA) 16.6 VIN 10mV/div (AC-COUPLED) IIN 100mA (AC-COUPLED) 10mA/div 16.4 16.2 16.0 15.8 15.6 24mA (AC-COUPLED) 10mA/div ILED1 15.4 15.2 4 LEDs, 24mA/LED, VIN = 3.8V 16mA/LED, VIN FALLING 15.0 2.7 3.1 3.5 3.9 4.3 4.7 5.1 400ns/div 5.5 SUPPLY VOLTAGE (V) TYPICAL OPERATING WAVEFORMS (CHARGE PUMP ACTIVE) STARTUP AND SHUTDOWN MAX8822 toc13 MAX8822 toc12 5V/div 0V VENLED VIN 10mV/div (AC-COUPLED) IIN 100mA (AC-COUPLED) 10mA/div ILED1 VIN 24mV/div (AC-COUPLED) IIN 100mA/div 24mA (AC-COUPLED) 10mA/div 4 LEDs, 24mA/LED, VIN = 3.2V 0A ILED_ = 24mA ILED_TOTAL 0A 400ns/div 1ms/div SERIAL-PULSE CONTROL DIMMING RESPONSE SERIAL-PULSE CONTROL LDO VOLTAGE PROGRAMMING MAX8822 toc14 MAX8822 toc15 5V/div 7 PULSES 0V VENLED 24mA 0 5V/div VENLDO 0A 1.8V 8 PULSES 14.4mA 10mA/div ILED1 100mA/div 1V/div ILDO2 0V 3.3V 50mA/div IIN 4 LEDs 1ms/div 0A 2V/div ILDO1 0V ILDO1 = ILDO2 = 100mA 400μs/div _______________________________________________________________________________________ 5 MAX8822 Typical Operating Characteristics (continued) (VIN = 3.6V, VEN_ = VIN, Circuit of Typical Operating Circuit, TA = +25°C, unless otherwise noted.) Typical Operating Characteristics (continued) (VIN = 3.6V, VEN_ = VIN, Circuit of Typical Operating Circuit, TA = +25°C, unless otherwise noted.) LINE-TRANSIENT RESPONSE (NO MODE CHANGE) LINE-TRANSIENT RESPONSE (MODE CHANGE) MAX8822 toc16 VIN 3.7V IIN MAX8822 toc17 4.2V 500mV/div (AC-COUPLED) VIN 100mA/div IIN 3.4V ILED_TOTAL 100mA/div 0mA ILED_TOTAL 100mA/div 0mA 0mA ILED_ = 24mA ILED_ = 24mA 1ms/div 1ms/div LDO1 LOAD TRANSIENT LDO2 LOAD TRANSIENT MAX8822 toc18 VLDO1 MAX8822 toc19 20mV/div (AC-COUPLED) ILDO1 VLDO2 20mV/div (AC-COUPLED) 150mA 150mA 50mA/div 50mA/div 10mA ILDO2 10mA VLDO2 = 1.8V VLDO1 = 2.8V 20μs/div POWER-SUPPLY REJECTION RATIO vs. FREQUENCY LDO OUTPUT NOISE IOUT = 10mA COUT = 1μF MAX8822 toc21 80 MAX8822 toc20 20μs/div 70 60 50 40 50μV/div 30 20 10 VLDO = 2.8V, ILDO = 28mA 0 0.01 0.1 1 10 100 1000 400μs/div FREQUENCY (kHz) 6 3.8V 500mV/div (AC-COUPLED) 100mA/div 0mA PSRR (dB) MAX8822 Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN _______________________________________________________________________________________ Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN PIN NAME FUNCTION 1 IN Supply Voltage Input. Bypass IN to GND with a 4.7µF ceramic capacitor placed as close as possible to the IC. The input voltage range is 2.7V to 5.5V. 2 GND Ground. Connect to system ground. GND is used for charge-pump switching currents. 3 C1P Transfer Capacitor 1 Positive Connection. Connect a 1µF ceramic capacitor from C1P to C1N. 4 C2P Transfer Capacitor 2 Positive Connection. Connect a 1µF ceramic capacitor from C2P to C2N. 5 C2N Transfer Capacitor 2 Negative Connection. Connect a 1µF ceramic capacitor from C2P to C2N. 6 C1N Transfer Capacitor 1 Negative Connection. Connect a 1µF ceramic capacitor from C1P to C1N. 7 NEG Charge-Pump Output. Bypass NEG to GND with a 2.2µF ceramic capacitor placed as close as possible to the IC. 8–11 LED4–LED1 LED Current Regulators. Connect LED_ to the cathodes of the external LEDs. LED_ is high impedance in shutdown. Connect any unused LED_ to IN to disable the corresponding current regulator. LED_ current is programmed by pulsing ENLED as described in the LED Dimming Control section. 12 LDO1 LDO1 Output. Bypass LDO1 to GND with a 1µF ceramic capacitor placed as close as possible to the IC. The LDO1 and LDO2 output voltage combination is selected by pulsing ENLDO low. See the LDO1/LDO2 Output Voltage Control section. 13 LDO2 LDO2 Output. Bypass LDO2 to GND with a 1µF ceramic capacitor placed as close as possible to the IC. The LDO1 and LDO2 output voltage combination is selected by pulsing ENLDO low. See the LDO1/LDO2 Output Voltage Control section. 14 ENLED WLED Enable and Dimming Control Input. Pulse ENLED low to program LED_ current. Hold ENLED low for at least 2.5ms to place the LED drivers in shutdown. See the LED Dimming Control section. 15 ENLDO LDO Enable and Voltage Control Input. Pulse ENLDO low to program the output voltage of both LDO1 and LDO2 to one of sixteen different combinations. Hold ENLDO low for at least 2.5ms to place the LDOs in shutdown. See the LDO1/LDO2 Output Voltage Control section. 16 REF Reference. Bypass REF to GND with a 0.1µF ceramic capacitor placed as close as possible to the IC. VREF regulates to 1.2V (typ). — EP Exposed Paddle. Connect EP to GND. For good thermal dissipation, solder the exposed paddle to the power ground plane. _______________________________________________________________________________________ 7 MAX8822 Pin Description MAX8822 Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN 1 3 2 1 4 2 13 3 14 tINIT = 120μs tHI = 500ns TO 500μs tLO = 500ns TO 500μs ENLED tHOLD tINIT INTERNAL CURRENT SHDN SETTING 24.0mA 22.4mA 20.8mA tHOLD tLO tHI 2.5ms tSHDN 2.5ms 2.5ms 19.2mA 24.0mA 22.4mA 20.8mA 5.6mA SHDN 4.8mA 19.2mA ILED_ 4.8mA SHDN SHDN Figure 1. Timing Characteristics for LED Serial-Pulse Control Interface 0 1 2 2 1 3 3 12 13 tINIT = 120μs tHI = 500ns TO 500μs tLO = 500ns TO 500μs ENLDO tHOLD t INIT tHOLD 2.5ms tLO tHI 2.5ms INTERNAL LDO1 SETTING SHDN 0V 2.8V 3.3V 2.8V 2.8V 3.3V 2.8V 0V 1.8V INTERNAL LDO2 SETTING SHDN 0V 1.2V 1.2V 1.5V 1.2V 1.2V 1.5V 2.8V 0V tSHDN 2.5ms SHDN 2.8V 1.8V VLDO1 SHDN SHDN 1.5V VLDO2 0V SHDN SHDN Figure 2. Timing Characteristics for LDO Serial-Pulse Control Interface Detailed Description The MAX8822 drives up to four white LEDs (WLEDs) with regulated constant current for display backlighting in cell phones, cameras, PDAs, and other handheld devices. The IC also includes two low-noise, high-PSRR, 200mA LDOs for powering camera modules or other devices. Figure 3 depicts the MAX8822 block diagram. The MAX8822 IC utilizes a 0.5x inverting charge pump and extremely low-dropout current regulators to achieve high efficiency over the full 1-cell Li+ battery 8 voltage range. The charge pump remains inactive unless the LED current regulators require additional voltage to prevent them from entering dropout. To maximize efficiency, the current regulators operate with as little as 150mV voltage drop. Additionally, each LED current regulator is independently monitored and switched, ensuring the least possible power consumption to extend battery life (see the Adaptive Current Regulator Switchover section for details). _______________________________________________________________________________________ Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN C4 1μF C1P VIN C1N C2P C2N C5 2.2μF NEG NEG LDO1 IN INPUT 2.7V TO 5.5V MAX8822 C3 1μF C1 4.7μF C6 1μF 0.5x INVERTING CHARGE PUMP LDO2 GND C7 1μF LOW-DROPOUT LINEAR REGULATORS REF C2 0.1μF UVLO, THERMAL SHUTDOWN BANDGAP REF SEL MIN ENLDO SERIALPULSE CONTROL INTERFACE ENLED LDO VOLTAGE CONTROL NEG LED CURRENT CONTROL VIN LED1 D1 LED2 INDEPENDENT, ADAPTIVE CURRENT REGULATORS LED3 LED4 D2 D3 D4 MAX8822 EP Figure 3. MAX8822 Functional Block Diagram and Application Circuit _______________________________________________________________________________________ 9 MAX8822 Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN MAX8822 MAX8822 LED CURRENT CONTROL NEG LED CURRENT CONTROL VIN NEG ILED_ ILED_ LED_ LED_ CURRENT REGULATOR VLED_ > SWITCHOVER THRESHOLD Figure 4. Current Regulator Returning to GND The LED current and LDO output voltages are programmed using a serial-pulse control interface. Pulse ENLED low (as discussed in the LED Dimming Control section) to decrease the LED current from 24mA to 0.1mA, or hold ENLED low for at least 2.5ms to place the LED current regulators in shutdown mode. LED dimming is controlled in 31 pseudo-logarithmic steps. Pulse ENLDO low (as discussed in the LDO1/LDO2 Output Voltage Control section) to choose LDO1 and LDO2 output voltages from one of 16 combinations including off. Drive both ENLED and ENLDO low for at least 2.5ms to place the IC in low-power (0.5µA typ) shutdown mode. The MAX8822 includes soft-start, thermal shutdown, and open- and short-circuit protection. Adaptive Current Regulator Switchover When VIN is higher than the forward voltage of an LED plus the 150mV (typ) dropout voltage of the current regulator, the LED current returns through GND (Figure 4). If this condition is satisfied for all four WLEDs, the charge pump remains inactive. When VIN drops such that the current regulator voltage (VLED_) cannot be maintained above the dropout voltage for any of the individual LEDs, the charge pump activates and generates a voltage on NEG that is no greater than 5V (typ) below VIN. For any current regulator that is detected at the switchover threshold voltage of 150mV (typ, VIN falling), internal circuitry switches that current regulator’s return path from GND to NEG to provide enough voltage across that regulator to overcome dropout (Figure 5). When VLED_ rises to 250mV (typ), the return of that current regulator is switched back from NEG to GND. Each current regulator is independently monitored to detect when switchover is required. Since the LED current is switched for only the individual LED current regulators requiring higher voltage, power consumption is minimized. 10 VIN CURRENT REGULATOR VLED_ < SWITCHOVER THRESHOLD Figure 5. Current Regulator Returning to NEG LED Dimming Control The MAX8822 uses a serial-pulse control interface to program the intensity of the LEDs. The dimming range is pseudo-logarithmic from 24mA to 0.1mA in 31 steps. All active LED current regulators are programmed to the same value, with a 1% (typ) current accuracy and 0.3% current matching between regulators. To program the LED current, pulse ENLED (500ns to 500µs pulse width), as shown in Figure 1. An internal register accumulates the pulse count on the rising edge of the ENLED pulse. See Table 1 for the LED current values and the corresponding ENLED pulse count. Once the desired pulse count is met, hold ENLED high for at least 2.5ms (tHOLD) to internally latch the pulse-count value and enable the LED_ current at the programmed level. If ENLED is pulsed more than 31 times before latching, the pulse count restarts at 1 on the 32nd rising edge. To program a new LED current level, follow the previous sequence from the beginning. Drive ENLED low for greater than 2.5ms (typ) to place the LED current regulators in shutdown. When the MAX8822 starts up with ENLED high, the LEDs turn on at full brightness. If dimming control is not required, ENLED works as a simple on/off logic control. Drive ENLED high for at least 2.5ms to enable the LED current regulators, or drive ENLED low for at least 2.5ms for shutdown. The LED drivers operate at 100% brightness and off under these conditions. ______________________________________________________________________________________ Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN ENLED PULSE COUNT* PROGRAMMED LED_ CURRENT (mA) ENLED PULSE COUNT* PROGRAMMED LED_ CURRENT (mA) 1 24.0 17 2.8 2 22.4 18 2.4 3 20.8 19 2.0 4 19.2 20 1.6 5 17.6 21 1.4 6 16.0 22 1.2 7 14.4 23 1.0 8 12.8 24 0.8 9 11.2 25 0.7 10 9.6 26 0.6 11 8.0 27 0.5 12 6.4 28 0.4 13 5.6 29 0.3 14 4.8 30 0.2 15 4.0 31** 0.1 16 3.2 — — *Rising edge. **If ENLED is pulsed more than 31 times, the pulse count restarts at 1 on the 32nd rising edge. Low LED Current Levels The MAX8822 internally generates a PWM signal to obtain higher resolution at lower currents. As LED current is set below 6.4mA, the IC adjusts not only LED DC current, but the duty cycle is controlled by the PWM signal. The frequency of the PWM dimming signal is set at 1kHz with a minimum duty cycle of 1/16 to avoid the LED flickering effect to human eyes. Table 2 shows the current level and the corresponding duty cycle. Table 2. Internal PWM Duty Cycle vs. LED Set Current DUTY CYCLE (n/16th) ILED (mA) DUTY CYCLE (n/16th) ILED (mA) 16 6.4 12 1.2 14 5.6 10 1.0 12 4.8 8 0.8 LDO1/LDO2 Output Voltage Control 10 4.0 7 0.7 Similar to the LED dimming control structure, the MAX8822 uses serial-pulse control to program the output voltages of LDO1 and LDO2 to one of sixteen different combinations. To program the LDO voltages, pulse ENLDO low (500ns to 500µs pulse width), as shown in Figure 2. An internal register accumulates the pulse count on the rising edge of the ENLDO pulse. An initial pulse (tINIT) is required to enable the LDOs from shutdown. See Table 3 for LDO voltage combinations and the corresponding ENLDO pulse count. When the desired pulse count is met, hold ENLDO high for at least 2.5ms (tHOLD) to internally latch the pulse-count value and program the LDO output voltages at the desired level. If ENLDO is pulsed for more than 15 counts, LDO1 and LDO2 are off when the count is 16 3.2 6 0.6 14 2.8 5 0.5 12 2.4 4 0.4 10 2.0 3 0.3 16 1.6 2 0.2 14 1.4 1 0.1 latched (the count does not roll over). To program new LDO_ output voltages, follow the previous sequence from the beginning. Do not include the initial tINIT pulse when programming LDO voltages unless enabling the LDOs from shutdown (the OFF setting is not shutdown). Pulling ENLDO low for greater than 2.5ms places the LDOs in shutdown. ______________________________________________________________________________________ 11 MAX8822 Table 1. ENLED Pulse Count and Programmed LED_ Current MAX8822 Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN Table 3. ENLDO Pulse Count and LDO1 and LDO2 Output Voltage Selection has cooled by 20°C (typ) and resets the LEDs and LDOs in the default condition of I LED_ = 24mA and VLDO1 = VLDO2 = 0V. ENLDO PULSE COUNT* PROGRAMMED LDO1 VOLTAGE (V) PROGRAMMED LDO2 VOLTAGE (V) 0** 0 0 1 2.8 1.2 2 3.3 1.2 3 2.8 1.5 4 3.3 1.5 5 1.2 1.8 6 1.8 1.8 7 2.8 1.8 8 3.3 1.8 9 2.8 2.8 Input Ripple 10 0 1.5 11 0 1.8 12 0 2.8 13 1.8 0 For LED drivers, input ripple is more important than output ripple. The amount of input ripple depends on the source supply’s output impedance. Add a lowpass filter to the input of the MAX8822 to further reduce input ripple. Alternatively, increasing CIN reduces input ripple. 14 2.8 0 15*** 3.3 0 *Rising edge. **Initial pulse is only required to enable LDOs from shutdown. ***If ENLDO is pulsed for more than 15 counts,VLDO1 and VLDO2 are 0V (not shutdown) when the count is latched (the count does not roll over). Power-Up LED Short Detection and Open-Fault Protection The MAX8822 contains special circuitry to detect an LED_ short-circuit condition at startup only, and disables that current regulator to avoid wasting battery power. If an LED fails short-circuit detection after startup, that current regulator continues current-regulated operation until IC power is cycled and the short circuit is detected during the subsequent startup. An open-circuit LED failure drives the voltage on the corresponding LED current-regulator output below the switchover threshold, enabling the charge pump. Applications Information Using Fewer Than Four LEDs The MAX8822 can operate with fewer than four LEDs. Disable the unused current regulator by connecting LED_ to IN. If an unused LED_ is not connected to IN, the MAX8822 operates as if an open LED has been detected. In this condition, the open-circuit LED_ drives the voltage on the corresponding output below the switchover threshold, enabling the charge pump. Shutdown Mode Component Selection The MAX8822 features a shutdown mode to reduce power consumption. Hold ENLED low for at least 2.5ms to place the LEDs in shutdown. LED shutdown pulls NEG to GND through a 10kΩ internal resistor. Hold ENLDO low for at least 2.5ms to place the LDOs in shutdown. LDO shutdown pulls LDO_ to GND through a 1kΩ internal resistor. The MAX8822 consumes only 0.5µA of supply current when both the LED current regulators and LDOs are in shutdown mode. Ceramic capacitors are recommended due to their small size, low cost, and low ESR. Select ceramic capacitors that maintain their capacitance over temperature and DC bias. Capacitors with X5R or X7R temperature characteristics generally perform well. Recommended values are shown in the Typical Operating Circuit. Using a larger value input capacitor helps to reduce input ripple (see the Input Ripple section). LDO and LED Thermal Shutdown The MAX8822 includes two thermal-limit circuits that protect the IC from temperatures exceeding +160°C (typ). The first circuit monitors the internal LED_ regulator temperature and shuts down the entire IC when the temperature limit is violated. The second circuit monitors the internal LDO temperature and shuts down only the LDOs when the temperature limit is violated. The thermal-shutdown condition clears after temperature 12 The LDO output capacitor size affects LDO stability. A 1µF ceramic capacitor is recommended to maintain stability for load currents up to 200mA. PCB Layout and Routing The MAX8822 is a high-frequency switched-capacitor voltage regulator. For best circuit performance, use a solid ground plane and place all capacitors as close as possible to the IC. Use large traces for the powersupply inputs to minimize losses due to parasitic trace ______________________________________________________________________________________ Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN Chip Information PROCESS: BiCMOS ______________________________________________________________________________________ 13 MAX8822 resistance and to route heat away from the device. The exposed paddle lowers the thermal resistance of the package by providing a direct-heat conduction path from the die to the printed circuit board (PCB). Connect the exposed paddle to the GND plane directly under the IC, but do not rely on EP for ground functions. For good thermal dissipation, solder the exposed paddle to the power ground plane. Refer to the MAX8822 evaluation kit data sheet for an example PCB layout. Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) (NE - 1) X e E MARKING 12x16L QFN THIN.EPS MAX8822 Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN E/2 D2/2 (ND - 1) X e D/2 AAAA e CL D D2 k CL b 0.10 M C A B E2/2 L E2 0.10 C C L C L 0.08 C A A2 A1 L L e e PACKAGE OUTLINE 8, 12, 16L THIN QFN, 3x3x0.8mm 21-0136 14 ______________________________________________________________________________________ I 1 2 Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN PKG 8L 3x3 12L 3x3 16L 3x3 REF. MIN. NOM. MAX. MIN. NOM. MAX. MIN. NOM. MAX. A 0.70 0.75 0.80 0.70 0.75 0.80 0.70 0.75 0.80 b 0.25 0.30 0.35 0.20 0.25 0.30 0.20 0.25 0.30 D 2.90 3.00 3.10 2.90 3.00 3.10 2.90 3.00 3.10 E 2.90 3.00 3.10 2.90 3.00 3.10 2.90 3.00 3.10 0.75 0.45 0.65 0.30 e L 0.65 BSC. 0.35 0.55 0.50 BSC. 0.55 0.50 BSC. 0.40 N 8 12 16 ND 2 3 4 NE 2 3 4 0 A1 A2 k 0.02 0.05 0 0.20 REF 0.25 - 0.02 0.05 0 0.20 REF - 0.25 - EXPOSED PAD VARIATIONS 0.02 0.50 0.05 0.20 REF - 0.25 - PKG. CODES TQ833-1 D2 E2 PIN ID JEDEC MIN. NOM. MAX. MIN. NOM. MAX. 0.25 0.70 1.25 0.25 0.70 1.25 0.35 x 45° WEEC WEED-1 T1233-1 0.95 1.10 1.25 0.95 1.10 1.25 0.35 x 45° T1233-3 0.95 1.10 1.25 0.95 1.10 1.25 0.35 x 45° WEED-1 T1233-4 0.95 1.10 1.25 0.95 1.10 1.25 0.35 x 45° WEED-1 WEED-2 T1633-2 0.95 1.10 1.25 0.95 1.10 1.25 0.35 x 45° T1633F-3 0.65 0.80 0.95 0.65 0.80 0.95 0.225 x 45° WEED-2 T1633FH-3 0.65 0.80 0.95 0.65 0.80 0.95 0.225 x 45° WEED-2 T1633-4 0.95 1.10 1.25 0.95 1.10 1.25 0.35 x 45° WEED-2 T1633-5 0.95 1.10 1.25 0.95 1.10 1.25 0.35 x 45° WEED-2 - NOTES: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES. N IS THE TOTAL NUMBER OF TERMINALS. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.20 mm AND 0.25 mm FROM TERMINAL TIP. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS . DRAWING CONFORMS TO JEDEC MO220 REVISION C. MARKING IS FOR PACKAGE ORIENTATION REFERENCE ONLY. NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY. WARPAGE NOT TO EXCEED 0.10mm. PACKAGE OUTLINE 8, 12, 16L THIN QFN, 3x3x0.8mm 21-0136 I 2 2 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 ____________________ 15 © 2007 Maxim Integrated Products Boblet is a registered trademark of Maxim Integrated Products, Inc. MAX8822 Package Information (continued) (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)