A8435 High Efficiency Charge Pump White LED Driver Features and Benefits Description ▪ ▪ ▪ ▪ ▪ The A8435 high efficiency charge pump IC offers a simple, low-cost white LED driver solution for portable electronics display applications. Using a proprietary control scheme (1×, 1.5×), the A8435 can output well-matched currents for up to 4 LEDs, while maintaining the highest efficiency over most of the Li-ion battery lifetime. ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ Proprietary adaptive control scheme (1×, 1.5×) Maximum efficiency, over 92% 0.5% LED current matching 1 MHz operating frequency Flexible dimming control: ▫ Serial 11-level dimming, down to 5% ▫ PWM ▫ 2-bit parallel Drives up to 4 white LEDs 30 mA per LED 120 mA total continuous output Low input ripple and EMI Soft-start limits inrush current Short circuit protection Overvoltage protection Thermal shutdown protection Space-saving MLP-16 package: 3 × 3 mm footprint Very thin 0.75 mm nominal height package The A8435 accepts an input range of 2.7 to 5.5 V and delivers up to 30 mA for each of the four regulated current sources. The A8435 can deliver a total continuous output current of 120 mA, meeting the requirements of most Li-ion battery-powered white LED backlight applications. Outputs can also be tied together for WLED flash/torch applications. The A8435 offers flexible options for LED current driving. The LED current can be set by any of the following methods: (a) choosing an appropriate value for RSET, (b) 2-bit parallel control with 3 levels, (c) PWM control, or (d) serial programming The A8435 is available in a very thin profile 0.75 mm (nominal height) 3 × 3 mm QFN/MLP-16 package (ES), fitting the needs of space-conscious applications. Package: 16 pin QFN/MLP (suffix ES) Applications include: ▪ White LED backlights for cellular phones, PDAs ▪ Digital cameras, camcorders ▪ Portable audio devices ▪ Other portable device white LED backlighting ▪ 120 mA WLED flash/torch Approximate Scale Typical Applications VBATT 2.7 to 5.5 V VBATT 2.7 to 5.5 V C1 1 µF VIN VOUT VIN CIN 1 µF C1+ COUT 1 µF LED1 CIN 1 µF C1 1 µF C2+ A8435 C2– LED2 C2 1 µF Single-Wire On/Off and Dimming Control LED4 EN2 GND A8435 CTRL RSET LED2 LED3 EN1 LED4 EN2 ISET Figure 1. Typical Circuit. Dual wire control configuration: 2-bit parallel or PWM dimming. A8435-DS, Rev. 1 C2+ C2- LED3 EN1 NC CTRL On/Off and Dimming Control COUT 1 µF LED1 C1- C1– C2 1 µF VOUT C1+ GND ISET RSET Figure 2. Typical Circuit. Single wire control configuration. A8435 High Efficiency Charge Pump White LED Driver Selection Guide Part Number Packaging* Package Type A8435EESTR-T 7-in. reel, 1500 pieces/reel ES, 3 × 3 mm QFN/MLP-16 *Contact Allegro for additional packing options. Functional Block Diagram C2 1 µF C1 1 µF C1 – C1+ C2– C2+ VOUT VIN Fractional Charge Pump (1× and 1.5×) CIN 1 µF COUT 1 µF + – EN1 EN2 CTRL Minimum Select Control, Clock, and Reference LED1 LED2 LED3 Current Mirror LED4 + – ISET + – + – + – + – RSET GND Absolute Maximum Ratings Input or Output Voltage VIN, VOUT, C1+, C1–, C2+, and C2– pins...................... –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 Maximum Junction Temperature, TJ(max) ............................................. 150°C Storage Temperature, TS ................................................... –55°C to 150°C Package Thermal Characteristics RθJA = 68 °C/W, on a 4-layer board (vendor data; unverified) Additional information is available on the Allegro Web site. Package is lead (Pb) free, with 100% matte tin leadframe plating. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 2 A8435 High Efficiency Charge Pump White LED Driver 13 C1– 14 VIN 8 9 LED1 4 10 LED3 7 CTRL 11 GND EP LED2 3 6 EN1 12 NC 5 2 EN2 1 ISET C2+ VOUT 15 C2– 16 C1+ Pin-out Diagram LED4 (Top View) Terminal List Table Name Pin Number C1– 13 Function* Negative terminal of capacitor C1. C1+ 16 Positive terminal of capacitor C1. C2– 15 Negative terminal of capacitor C2. C2+ 1 Positive terminal of capacitor C2. CTRL 4 Brightness control scheme toggle. For 2-bit parallel or PWM dimming, leave open or tie to VIN (see table 1). For single-wire serial input dimming, connect to GND (see figure 2). EN1 3 When CTRL is open or HIGH: Enable and dimming control input 1 (see table 1). When CTRL is grounded: single-wire enable and dimming control (see table 1 and figure 2). (Do not leave unconnected.) EN2 5 When CTRL is open or HIGH: Enable and dimming control input 2 (see table 1). When CTRL is grounded: this pin disables shutdown. (Do not leave unconnected.) EP – Exposed metal pad on bottom side. Connect this to ground plane for better thermal performance. GND 11 Ground. ISET 6 Connect RSET resistor to ground to set desired constant current through LEDs. LED1 8 Current sink for LED1. Connect to VIN or VOUT if not used for LED. (Do not leave unconnected.) LED2 7 Current sink for LED2. Connect to VIN or VOUT if not used for LED. (Do not leave unconnected.) LED3 10 Current sink for LED3. Always connect this pin to LED. LED4 9 Current sink for LED4. Connect to VIN or VOUT if not used for LED. (Do not leave unconnected.) NC 12 No Connection. VIN 14 Power supply voltage input. VOUT 2 Charge pump voltage source output for connection to the LED anodes. * See Application Information section for cited figure and tables. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 3 A8435 High Efficiency Charge Pump White LED Driver ELECTRICAL CHARACTERISTICS1 VIN = VEN1 = VEN2 = 3.6 V, C1 = C2 = 1 μF, TA = –40 to 85°C, typical values at TA = 25°C (unless otherwise noted) Characteristics Symbol Test Conditions Min. Typ. Max. Input Voltage Range VIN Undervoltage Lockout Threshold UVLO Hysteresis Window VUVLO VIN falling, VUVLOHYS = 35 mV Units 2.7 – 5.5 V 2.25 2.45 2.60 V – 35 – mV Switching, TA = 25°C – 2.8 4 mA EN1 = EN2 = GND, TA = 25°C – 0.1 1 μA 2 – ms VUVLOHYS Quiescent Current IQ Soft-Start Completion Time tSS – ISET Bias Voltage VISETBIAS 0.56 0.6 0.64 V ISET Leakage in Shutdown VISETLKG – 0.01 1 μA ISET Current Range IISET EN1 = EN2 = VIN ISET to LEDx Current Ratio ILEDx / IISET IISET = 60 μA, EN1 = VIN, EN2 = GND CTRL = open or HIGH EN1 = GND, EN2 = VIN IISET = 60 μA, CTRL = LOW Full brightness 40 – 140 μA 190 219 245 A/A 105 121 137 A/A 51 60 69 A/A – 200 – A/A % ILED Accuracy EILED EN1 = EN2 = VIN, RSET = 4.3 kΩ – ±0.9 – LED Current Matching2 ΔILED VIN =3.6 V, ILED = 30 mA per LED – ±0.5 – % Regulation Voltage at LEDx (1.5×) VLED EN1 = EN2 = VIN – 150 – mV Open Loop Output Resistance3 ROUT 1× to 1.5× Mode Transition Voltage at LEDx VTrans Transition to Dropout Voltage Difference4 LED Leakage in Shutdown Oscillator Frequency Output Overvoltage ΔVdr VLEDLKG 1× mode: [(VIN – VOUT) / IOUT] – 1.1 – Ω 1.5× mode: [(1.5 × VIN – VOUT) / IOUT] – 3.6 – Ω VLEDx Falling – 100 – mV Measured as VTrans – VDropout – 60 – mV EN1 = EN2 = GND, VIN = 5.5 V, TA = 25°C – 0.01 1 μA – 1 – MHz – 5.74 – V V fosc Protection5 VOVP Open circuit at any LED that is programmed to be in the ON state CTRL, EN1, EN2 Input High Logic Threshold6 VIH 1.6 – – CTRL, EN1, EN2 Input Low Logic Threshold6 VIL – – 0.4 V Input High Current IIH VIH = VIN – – 1 μA VIL = GND Input Low Current IIL – – 1 μA EN1 Pulse Low Time7 tLO 0.5 – 500 μs EN1 Pulse High Time7 tHI 0.5 – – μs Initial EN1 Pulse High Time7 tHI(Init) First EN1 pulse after shutdown 100 – – μs Shutdown Delay7 tSHDN Falling edge of EN1 pulse – 2 3 ms Thermal-Shutdown Threshold TSHDN 20°C hysteresis – 165 – °C 1Specifications guaranteed by design over operating temperature range, –40°C to 85°C. 2LED current matching is defined as (I LEDX – ILED(AVG)) / ILED(AVG) . 3The Open Loop Output Resistance for 1.5× mode is measured with one of the LEDx pins tied to ground or open (thus its voltage is always less than 80 mV). 4Dropout Voltage, V Dropout, is defined as the LEDx-to-GND voltage at which ILEDx drops 10% below the value of ILEDX at VLEDX = 200 mV. 5Guaranteed by design. 6EN2 is not used when CTRL is tied to ground. 7Applies only when CTRL is tied to ground. See figure 3 in Application Information section. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 4 A8435 High Efficiency Charge Pump White LED Driver Performance Characteristics Tests performed using application circuit shown in figure 1: dual wire control; and VIN = 3.6 V, EN1 = EN2 = VIN, CIN = C1 = C2 = COUT = 1 μF, RSET = 7.5 kΩ, TA = 25°C (unless otherwise noted) Efficiency versus Supply Voltage Over Range of Dimming Levels, VIN Falling 100 90 Dimming Level (mA) 4.75 η (%) 80 9.8 17.6 (Full Brightness) 70 60 50 2.70 2.90 3.10 3.30 3.50 3.70 3.90 4.10 VIN (V) Supply Current versus Supply Voltage Over Range of Dimming Levels (mA) 120 100 VIN Rising VIN Falling 17.6 mA 60 VIN Rising VIN Falling 9.8 mA 40 VIN Rising 20 4.75 mA VIN Falling 0 2.70 2.90 3.10 3.30 3.50 3.70 3.90 4.10 VIN (V) LED Current versus Supply Voltage Matching Between LEDs <1% Over Range of VIN 20 19 18 17 ILED (mA) IBATT (mA) 80 16 15 14 13 12 11 10 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VIN (V) Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 5 A8435 High Efficiency Charge Pump White LED Driver Startup Response VEN Symbol C1 C2 C3 t Parameter VEN IBATT VOUT time Units/Division 5V 50 mA 2V 500 μs C1 IBATT C2 C3 VOUT t 2-Bit (EN1-EN2) Dimming Response Symbol C1 C2 t Conditions EN2 = VIN Parameter VEN1 IOUT time Units/Division 2V 50 mA 5 μs VEN C1 IOUT C2 t 11-Level Single-Wire Serial Dimming Response Symbol Parameter Units/Division C1 VEN1 2V C2 IOUT 50 mA C3 VOUT 2V t time 10 ms Conditions EN2 = CTRL = GND, apply control signal to EN1 C1 VEN1 IOUT C2 VOUT C3 t Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 6 A8435 High Efficiency Charge Pump White LED Driver Application Information Setting LED Current The LED current level, ILEDX, is set by the value chosen for the external resistor, RSET, which is connected to the ISET terminal. The full current (100%) level for ILEDX can be calculated using the following formulas: Setting Formula CTRL = Open or HIGH RSET (Ω) = 0.6 V × 219 / ILEDX CTRL = LOW RSET (Ω) = 0.6 V × 200 / ILEDX Dimming The A8435 offers serial, 2-bit parallel, and PWM dimming control. When the CTRL pin is pulled LOW, the EN1 pin accepts one-wire serial pulse input both to enable the part, and to select one of the 11 dimming levels, from 100% down to 5% (see table 1). With EN2 low, when EN1 is pulled high, the IC turns on. The initial LED current defaults to 100% after softstart is complete. The tLO must be < 500 ms to avoid shutdown. With EN2 high, the operation of EN1 is the same as when EN2 is low, except shutdown is disabled (TLO = ∞). Table 1. CTRL, EN1, and EN2 Pin States CTRL EN1 EN2 Open or HIGH LOW LOW Shutdown Brightness LED Current, ILED 0 Open or HIGH LOW HIGH 27% Brightness 60 × IISET Open or HIGH HIGH LOW 55% Brightness 121 × IISET Open or HIGH HIGH HIGH Full Brightness 219 × IISET LOW Adjustable; 11 levels of dimming from Pulse No 100% to 5% (see figure 3; 100% corinput effect responds to 200 × IISET) LOW LOW LOW Shutdown > 2 ms Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 7 A8435 High Efficiency Charge Pump White LED Driver When changing from one specific brightness level to another, the user may not want to keep the existing brightness level stored in memory. A simpler method is to program a shutdown and re-enable, followed by an appropriate number of pulses (from 100%) to reach the target brightness level. The total “LED off” time during shutdown, re-enable, and brightness programming can be kept sufficiently short such that no delay is discernable to the eye. Shutdown If the CTRL pin is unconnected or HIGH, the device enters the shutdown mode when EN1 and EN2 are pulled LOW. When configured to have a serial pulse dimming control (the CTRL pin is grounded), the EN1 and the EN2 pins must be pulled LOW for longer than tSHDN (2 ms typical) in order to enter shutdown mode. 0 EN1 tHI(Init) 2 3 4 tSS 100% IILEDX SHDN 1 5 The output is high impedance after shutdown. Disabling Unused LEDs If any WLED is not used, connect the corresponding pin to either VIN or VOUT to disable it. Never leave open any unused WLED pin. LED pins will sink 30 μA typical when connected to VIN or VOUT and the IC is enabled. LED3 must always be selected. For example, to drive 2 LEDs, select LED3 and one of either LED1, LED2, or LED4. 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. 6 t LO 90% 80% 70% 7 8 9 10 11 tSHDN t HI 100% 90% 60% 50% 40% 30% 20% 10% 5% SHDN Figure 3. Single-Wire Serial Dimming Control, at pin EN1; CTRL = LOW, EN2 = LOW. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 8 A8435 High Efficiency Charge Pump White LED Driver Package ES, 3 × 3 mm 16-Pin QFN/MLP 3.15 .124 2.85 .112 A B 16 1 Preliminary dimensions, for reference only (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 A 2 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 SEATING PLANE 0.08 [.003] C 16X 0.30 .012 0.18 .007 0.80 .031 0.70 .028 0.10 [.004] M C A B 0.05 [.002] M C 0.50 .020 0.20 .008 REF 0.30 .012 NOM 0.90 .035 NOM 0.05 .002 0.00 .000 0.50 .020 NOM 16 C 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 2 B 1.70 NOM .067 1 16 16X 0.20 .008 MIN 1.70 .067 NOM 0.23 x 0.23 .009 x .009 REF 3.10 .122 NOM 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 detailed 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 products are not authorized for use as critical components in life-support devices or systems without express written approval. 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. Copyright©2005, 2006 AllegroMicroSystems, Inc. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 9