A8434 6-Channel High Efficiency Charge Pump White LED Driver Features and Benefits Description ▪ Proprietary adaptive control scheme (1×, 1.5×, 2×) ▪ 0.5% typical WLED current matching ▪ Drives up to 6 white LEDs ▫ Main display backlight (up to 6 WLEDs) ▫ Main display and sub display backlight ▫ Main display and low-current flash/torch ▪ 30 mA per WLED ▪ 2× serial dimming interfaces ▪ 320 mA charge pump capability ▪ Low EMI design and soft start function ▪ Short circuit, overvoltage, thermal shutdown protection ▪ 0.75 mm nominal height (very thin profile), 3 × 3 mm footprint packages The A8434 high efficiency charge pump ICs offer a simple, low-cost WLED (white LED) driver solution for driving up to six WLEDs in various application configurations, either all six backlighting a single display, or for multiple displays, such as four WLEDs as the main display backlight, with the other two WLEDs used for backlighting a sub display or a low-current flash/torch. Using a proprietary control scheme (1×, 1.5×, and 2×), the A8434 can deliver well-matched WLED current while maintaining the highest efficiency and low EMI. The WLED current is regulated over the entire range of Li+ battery voltage to provide uniform intensity. WLED brightness and on/off can be controlled for the main display and sub display/torch through 2 single-wire serial interface pins. The A8434 is available in an QFN/MLP-16 space-conserving (3 × 3 mm footprint) ES package. Package: 16 pin QFN/MLP (suffix ES) Applications include: ▪ ▪ ▪ ▪ White LED backlights for cellular phones, PDAs Digital cameras, camcorders Portable audio devices and MP3s Other portable device white LED backlighting Approximate scale 1:1 Typical Applications VBATT 2.7 to 5.5 V COUT 1 µF VIN CIN 1 µF C1 1 µF C2 1 µF RSET C1+ LED1 C1– LED2 C2+ A8434 LED3 C2– LED4 ISET GND LED6 D4 VBATT 2.7 to 5.5 V CIN 1 µF C1 1 µF COUT 1 µF VIN VOUT C1+ LED1 C1– Figure 1.6 × 30 mA WLED display C2 1 µF RSET On/Off and Dimming Control LED2 C2+ A8434 LED3 C2– LED4 ISET D1 LED1 LED2 D3 D4 D5 LED5 ENM D6 ENS GND RSET On/Off and Dimming Control LED5 ENM ENS GND LED6 D1 D2 D3 D4 D5 D6 VIN>Vf(max)+0.2 V, Vf = LED forward drop D2 LED6 D1-D4 Main Display; D5-D6 Sub Display Figure 2. 4 × 30 mA main with 2 × 30 mA sub display 8434-DS, Rev. 1 VOUT C1+ C2+ A8434 LED3 C2– LED4 ISET D3 D5 VIN C1– D2 D6 ENS CIN 1 μF D1 LED5 ENM On/Off and Dimming Control VIN VOUT Figure 3. High efficiency current sink 6-Channel High Efficiency Charge Pump White LED Driver A8434 Functional Block Diagram C2 1 μF C1 1 μF C1 − C1+ C2− C2+ VOUT VIN Fractional Charge Pump (1×, 1.5×, and 2×) CIN 1 μF COUT 1 μF + − ENM Control, Clock, and Reference ENS Minimum Select LED1 LED2 LED3 Current Mirror LED4 LED5 LED6 + − ISET + − + − + − + − + − + − RSET GND Absolute Maximum Ratings Input or Output Voltage VIN, VOUT, C1+, C1– , C2+, C2– to GND ..................... –0.3 to 6 V All other pins..................................................... –0.3 to VIN + 0.3 V VOUT Short Circuit to GND ....................................................Continuous Operating Ambient Temperature, TA ..................................... –40°C to 85°C Junction Temperature, TJ(max).............................................................. 150°C Storage Temperature, TS ................................................... –55°C to 150°C Package Thermal Characteristics ES Package RθJA = 68 °C/W (vendor data, on 4-layer PCB; unverified) Additional information is available on the Allegro website. The device package is lead (Pb) free, with 100% matte tin leadframe plating. Use the following complete part number when ordering: Part Number Packaging* Package Type A8434EESTR-T 7-in. reel, 1500 pieces/reel ES, 3 × 3 mm MLP-16 *Contact Allegro for additional packing options. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 2 6-Channel High Efficiency Charge Pump White LED Driver A8434 Pin-out Diagram 13 C1– 14 VIN 8 9 LED4 4 10 LED2 7 ENS 11 LED1 EP LED5 3 6 ISET 12 GND 5 2 ENM 1 LED6 C2+ VOUT 15 C2– 16 C1+ ES Package LED3 (Top View) Terminal List Table Name C1– C1+ C2– C2+ ENS ENM EP GND Number 13 16 15 1 4 5 – 12 ISET 3 LED1, LED2, LED3, and LED4 8, 9, 10, and 11 LED5 and LED6 6 and 7 VIN 14 VOUT 2 Function Negative terminal of capacitor C1. Connect capacitor C1 between C1+ and C1–. Positive terminal of capacitor C1. Negative terminal of capacitor C2 Positive terminal of capacitor C2. Connect capacitor C2 between C2+ and C2–. Enable and dimming control input for sub display WLED group. Enable and dimming control input for main display WLED group. Exposed metal pad on bottom side. Connect this to ground plane for better thermal performance. Ground. Connect RSET resistor to ground to set desired constant current through main and sub WLEDs. ILED(max) = 220 x 0.6 V / RSET Current sink for main display WLEDs. If not used, connect to VOUT, but do not leave open. If left open, the IC works in 2 × mode. Current sink for sub display WLEDs. If not used, connect to VOUT, but do not leave open. If left open, the IC works in 2 × mode. Power supply voltage input. Charge pump output voltage for display backlight and flash/torch LED anodes. Connect a 1 μF capacitor, COUT, between VOUT and GND (see figure 2). Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 3 6-Channel High Efficiency Charge Pump White LED Driver A8434 ELECTRICAL CHARACTERISTICSa VIN = ENM = ENS = 3.6 V, C1 = C2 = 1 μF, CIN = COUT = 1 μF, RSET = 6.49 kΩ, TA = –40°C to +85°C; typical values are at TA = 25°C; unless otherwise noted Characteristics Input Voltage Range Undervoltage Lockout Threshold UVLO Hysteresis Window Symbol VIN VUVLO VUVLOHYS Test Conditions VIN falling Switching in 1.5× or 2.0× mode; TA = 25°C Min. 2.7 Typ. Max. Units – 5.5 V 2.25 – – 2.45 60 6 2.60 – – V mV mA Quiescent Current IQ – 0.1 2 μA Soft-start Completion Time tss – 0.4 – ms ISET Bias Voltage VISETBIAS – 0.6 – V ISET Leakage in Shutdown ISET Current Range ISET to LEDx Current Ratio for LED1 through LED6 VISETLKG ISET ILEDx/IISET 100% setting, ISET = 60 μA – 40 – 0.01 – 220 1 140 – μA μA A/A EILEDERR ILED Accuracy for LED1 through LED6b ENS = ENM = GND; TA = 25°C ENS = ENM = VIN – ±1.6 – % LED Current Matching for LED1 through LED4c ΔILED14 ENS = GND, ENM = VIN – ±0.5 – % LED Current Matching for LED5 and LED6c ΔILED56 ENS = VIN, ENM = GND – ±0.5 – % Regulation Voltage at LEDx (1.5× and 2× modes) VREG ENS = ENM = VIN – 250 – mV 1× mode to 1.5× or 1.5× to 2× mode transition voltage at LEDx Vtrans VLEDx falling – 150 – mV Transition–Dropout Deltad ΔVdr Measured as Vtrans – Vdropout – 40 – mV 1× mode (VIN – VOUT) / IOUT – 1 – Ω 1.5× mode (1.5 × VIN – VOUT) / IOUT – 2.5 – Ω 2× mode (2 × VIN – VOUT) / IOUT – 5 – Ω ENS = ENM = GND, VIN = 5.5 V – 0.01 1 μA – 1 – MHz – – 6.0 V V Open Loop Output Resistancee LED Leakage in Shutdown Oscillator Frequency ROUT VLEDLKG fosc Output Overvoltage Protection (guaranteed by design) Vovp Open circuit at any LED that is programmed to be in the ON state ENS and ENM Input High Threshold VIH Input high logic threshold 1.4 – – ENS and ENM Input Low Threshold VIL Input low logic threshold – – 0.4 V Input High Current IIH VIH=VIN – – 1 μA Input Low Current IIL VIL= GND – – 1 μA ENM and ENS Pulse Low Time (figure 5) tLO 0.5 – 250 μs ENM and ENS Pulse High Time (figure 5) tHI 0.5 – – μs 50 – – μs ENM and ENS Initial Pulse High Time (figure 5) tINIHI First ENM or ENS pulse after shutdown Shutdown or Dimming Reset Delay tSHDN Falling edge of ENS and/or ENM – 0.5 – ms Thermal Shutdown Threshold TTSD 20oC hysteresis – 165 – oC aSpecifications for the range TA = –40°C to 85°C are guaranteed by design. bI accuracy is defined as ( ISET × 220 – ILEDAVG ) / (ISET × 220). LED cLED current matching is defined as (I LEDx – ILEDAVG) / ILEDAVG . dDropout voltage V dropout is defined as LEDx-to-GND voltage at which ILEDx drops 10% below the value of ILEDx when VLEDx = 300 eThe open loop output resistance, R OUT, for 1.5 × mode is measured when one of the LEDx pins is tied to ground or open (thus its mV. voltage is always less than 80 mV). Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 4 6-Channel High Efficiency Charge Pump White LED Driver A8434 Performance Characteristics Tests performed using application circuit shown in figure 2 TA = 25°C, VIN = 3.6 V (unless otherwise noted) Efficiency versus Supply Voltage Efficiency versus Supply Voltage VIN falling, Vf = 3.4 V at 20 mA VIN falling, Vf = 3.1 V at 10 mA 100.0 100.0 90.0 80.0 90.0 85.0 Main 75.0 75.0 Main 65.0 Main + Sub 65.0 60.0 Main + Sub 55.0 60.0 55.0 2.7 Sub 80.0 70.0 70.0 3.1 3.5 3.9 4.3 VIN (V) 4.7 5.1 50.0 2.7 5.5 3.1 3.9 4.3 4.7 5.1 5.5 16 18 RSET versus LED Current 1.2 30 1.1 25 ILED per Channel (mA) VHI 1.0 0.9 0.8 VLO 0.7 0.6 0.5 2.7 3.5 VIN (V) Logic Level V ENx (V) Eff (%) 85.0 95.0 Sub Eff (%) 95.0 RSET = 6.65 kΩ 20 RSET = 8.87 kΩ 15 10 5 3.1 3.5 3.9 4.3 4.7 5.1 5.5 4 6 8 VIN (V) 10 12 14 RSET (kΩ) Dimming on ENM and ENS Enable Pulses versus Total Current, LED1 through LED6 VENM and VENS C1 ILED1-6 C2 t Symbol C1 C2 t Parameter VENM ILED16 time Units/Division 0.5 V 50 mA 50 ms Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 5 6-Channel High Efficiency Charge Pump White LED Driver A8434 Performance Characteristics Tests performed using application circuit shown in figure 2 TA = 25°C, VIN = 3.6 V (unless otherwise noted) Turn ON LED1 through LED6 to 1X Mode VIN = 4.0 V, IOUT = 120 mA, VF = 3.4 V VENM and VENS C2 VOUT C1 IOUT C4 t Symbol C2 C1 C4 t Parameter VENM and VENS VOUT IOUT time Units/Division 5.00 V 2.00 V 100 mA 1 ms Turn ON LED1 through LED6 to 1.5X Mode VIN = 3.0 V, IOUT = 120 mA, VF = 3.4 V VENM and VENS C2 VOUT C1 IOUT C4 t Symbol C2 C1 C4 t Parameter VENM and VENS VOUT IOUT time Units/Division 5.00 V 2.00 V 100 mA 1 ms Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 6 6-Channel High Efficiency Charge Pump White LED Driver A8434 Performance Characteristics Tests performed using application circuit shown in figure 2 TA = 25°C, VIN = 3.6 V (unless otherwise noted) LED1 through LED6 ON, 2X Mode VIN = 2.7 V, IOUT = 120 mA, VF = 3.6 V VOUT(RIPPLE) C3 IIN(RIPPLE) C4 t Symbol C3 C4 t Parameter VOUT(RIPPLE) IIN(RIPPLE) time Units/Division 50 mV 50 mA 500 ns LED1 through LED6 ON, 1.5X Mode LED1 through LED4 on, 1.5X Mode VIN = 3.6 V, IOUT = 120 mA, VF = 3.6 V VIN = 3.6 V, IOUT = 80 mA, VF = 3.6 V VOUT(RIPPLE) C3 VOUT(RIPPLE) C3 IIN(RIPPLE) C4 IIN(RIPPLE) C4 t Symbol C3 C4 t Parameter VOUT(RIPPLE) IIN(RIPPLE) time t Units/Division 20 mV 50 mA 500 ns Symbol C3 C4 t Parameter VOUT(RIPPLE) IIN(RIPPLE) time Units/Division 20 mV 50 mA 500 ns Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 7 6-Channel High Efficiency Charge Pump White LED Driver A8434 Application Information Setting LED Current Transitions Between 1.5× and 2× Modes Use the following formula to set the display backlight LED full current (100%) using RSET on LED1 through LED6. The maximum current through one LED should not exceed 30 mA: The transition from 1.5× to 2× mode depends upon dropout conditions. When operating in 2× mode, the IC switches back to 1.5× mode every 130 ms, and then reenters 2× mode again if necessary. Furthermore, when in 2× mode, whenever a channel disabling is sensed (that is, whenever ENM is held low for > 0.5 ms with ENF high, or vice versa), the IC automatically reverts to 1.5× mode, and then reenters 2× mode again if necessary. RSET = 0.6 V × 220 / ILEDx where RSET is in Ω and ILEDx in amperes. Transitions Between 1× and 1.5× or 2× Modes The A8434 adaptively selects operating mode. When VIN is sufficiently high to maintain VLEDx > 150 mV, the A8434 operates in 1 × mode unless, as VIN drops, the LEDx nodes fall below the 150 mV threshold. When VLEDx falls below 150 mV, the IC enters 1.5× mode. Dimming When the A8434 switches from 1× to 2× mode, it first switches to 1.5× mode for a typical duration of 1 ms before entering 2× mode. When ENM is initially pulled up from shutdown, after a softstart, the current for the WLEDs is programmed to 100% of the setting current, which is determined by the current through the ISET pin. Each subsequent pulse reduces the backlight LEDs current by 10%, and the 10th pulse reduces the current by 5%. The next pulse restores 100% (full) brightness. Figure 5 shows the timing diagram for ENM control. Main Display LED1 through LED4 Dimming. The main display WLEDs (LED1 through LED4) brightness and on/off can be controlled using digital input at the ENM pin. The ENM pin accepts one-wire serial pulse input to enable the A8434 and to set up to 11 dimming levels, from 100% down to 5%. When operating in 1.5× mode, if VOUT < VIN, then the IC switches back to 1× mode every 130 ms, and then reenters 1.5× mode again if necessary. 95.0 90.0 Eff (%) 80.0 75.0 70.0 VIN Rising VIN Falling 85.0 65.0 60.0 55.0 50.0 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2 VIN (V) Figure 4. Mode change transition 0 tHI(Init) 1 2 3 4 5 6 7 8 9 10 11 ENM or ENS tSS 100% IILEDx t LO 90% 80% 70% tSHDN t HI 100% 90% 60% 50% SHDN 40% 30% 20% 10% 5% SHDN or Dimming Reset Figure 5. Single-Wire Serial Dimming Control; at pins ENM and ENS. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 8 6-Channel High Efficiency Charge Pump White LED Driver A8434 Sub Display LED5 and LED6 Operation. The sub display backlight LEDs (LED5 and LED6) brightness and on/off can be controlled using digital input at the ENS pin. The ENS pin accepts one-wire serial pulse input to enable the A8434 and to set up to 11 dimming levels, from 100% down to 5%. When ENS is initially pulled up from shutdown, after a soft-start, the current for the backlight LEDs is programmed to 100% of the setting current, which is determined by the current through the ISET pin. Each subsequent pulse reduces the LED current by 10%, and the 10th pulse reduces the current by 5%. The next pulse restores 100% (full) brightness. Figure 5 shows the timing diagram for ENS control. Simultaneous Dimming of All 6 LEDs For larger displays 6 LEDs can be grouped together. The LEDs LED1 through LED6 can be dimmed simultaneously by connecting ENM and ENS together and applying serial pulses for dimming, as shown in figure 1. Absolute Level Operation Some applications require dimming to a specific level, regardless of the present level of dimming. For example, if the IC should dim to 30%, this can be done with 7 steps, as shown in figure 5, irrespective of the dimming level in effect. This can be achieved by pulling corresponding ENx pin low for time greater than tSHDN and then applying pulses as shown in figure 5 (7 for 30% dimming). If the pulses are applied within 2-3 ms, the display flicker is not visible. The procedure is shown in figure 6. Shutdown When the ENM or ENS pin is pulled low for 0.5 ms or longer, the corresponding display channels are shut off and dimming is reset to 100% upon the next ENM or ENS going high edge. When both ENM and ENS are pulled low for 0.5 ms or longer, the A8434 enters the shutdown mode. Short Circuit Protection The A8434 is protected against short circuits on the output. When VOUT is externally pulled below 1.2 V, the IC enters short circuit mode. The A8434 resumes normal operation when the short circuit is removed. ∆t > tSHDN Rapid pulse pattern C1 VENM ENx pulled low Symbol C1 C2 C3 t Parameter VENM VOUT IOUT time Units/Division 2.00 V 2.00 V 50 mA 0.5 ms C2 VOUT 100% C3 ISET counter resets 30% IOUT t Figure 6. Absolute Dimming Level Setting. With ENM pulled low longer the tSHDN, pulsing the corresponding ENx pin sets an absolute target level. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 9 6-Channel High Efficiency Charge Pump White LED Driver A8434 Overvoltage Protection Note: In shutdown mode (ENM = ENS = 0 V for > 0.5 ms), the The A8434 is protected up to 4.9 V supply voltage, against accidental overvoltage caused by an open LED. When any LED opens, VOUT will increase till 6 V. Remaining LEDs will continue to function normally. Normal operation will be resumed when the fault is removed. total leakage current is < 1μA. Thermal Shutdown The IC is internally protected against overtemperature. The overtemperature limit is set to 165°C nominal. The IC shuts down LED Disconnection Every LEDx pin has a disable subcircuit, as shown in figure 7. The A8434 compares the voltage on each LED pin, and if the voltage on the pin is greater than either VOUT – 0.4 V or VIN – 0.4 V, then the corresponding LED pin is disabled. If any WLED is not used, connect the corresponding pin to VOUT. Never leave open any unused WLED pin. LED pins will sink 20 μA typical when connected to VOUT and the corresponding LED group (main or sub) is enabled. when the junction temperature exceeds 165°C and automatically turns on again when the IC cools. Component Selection Ceramic capacitors with X5R or X7R dielectric are recommended for the input capacitor, CIN, the output capacitor, COUT, and the charge pump capacitors, C1 and C2. A8434 VBATT VIN 1×, 1.5×, 2× Charge Pump VOUT CIN COUT LED Disable Block One of six blocks – + VIN – 0.4 LED1 – + D1 D2 VOUT – 0.4 Current Sink D3 D4 D5 D6 Figure 7. LED disable subcircuit. Subcircuit for one LEDx pin shown. A similar block is connected to each LEDx pin. 10 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 6-Channel High Efficiency Charge Pump White LED Driver A8434 Package ES, 3 × 3 mm16-Pin QFN/MLP 3.15 .124 2.85 .112 A B 16 1 All dimensions reference only, not for tooling use (reference JEDEC MO-220WEED-4) Dimensions in millimeters U.S. Customary dimensions (in.) in brackets, for reference only Dimensions exclusive of mold flash, gate burrs, and dambar protrusions Exact case and lead configuration at supplier discretion within limits shown A Terminal #1 mark area 2 A 3.15 .124 2.85 .112 B Exposed thermal pad (reference only, terminal #1 identifier appearance at supplier discretion) C Reference land pattern layout (reference IPC7351 QFN50P300X300X80-17W4M); adjust as necessary to meet application process requirements and PCB layout tolerances; when mounting on a multilayer PCB, thermal vias at the exposed thermal pad land can improve thermal dissipation (reference EIA/JEDEC Standard JESD51-5) 16X 16X 0.30 .012 0.18 .007 0.50 .020 NOM 16 C 0.80 .031 0.70 .028 0.10 [.004] M C A B 0.05 [.002] M C 0.50 .020 0.30 .012 NOM 0.90 .035 NOM SEATING PLANE 0.08 [.003] C 0.20 .008 REF 0.05 .002 0.00 .000 1.70 .067 NOM C 0.50 .020 0.30 .012 1 1.70 .067 NOM 12X 0.20 .008 MIN 4X 0.20 .008 MIN 3.10 .122 NOM 4X 0.20 .008 MIN 1.70 .067 NOM 2 B 1.70 NOM .067 1 16 0.23 x 0.23 .009 x .009 REF 3.10 .122 NOM Copyright ©2006, Allegro MicroSystems, Inc. The products described here are manufactured under one or more U.S. patents or U.S. patents pending. Allegro MicroSystems, Inc. reserves the right to make, from time to time, such departures from the detail specifications as may be required to permit improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the information being relied upon is current. Allegro’s products are not to be used in life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the failure of that life support device or system, or to affect the safety or effectiveness of that device or system. The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringement of patents or other rights of third parties which may result from its use. For the latest version of this document, visit our website: www.allegromicro.com 11 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com