AOZ1934/1935 High Efficiency Boost 20-, 30- LED Driver General Description Features The AOZ1934/5 is an ideal power solution for white LED backlighting for medium to small size LCD panels. It is a highly integrated step up DC-DC converter with input voltage range from 2.7V to 25V, accommodating 1-, 2-, 3-, or 4-cell lithium ion batteries or 3.3V, 5V, 12V or 20V regulated supplies. The AOZ1934/5 integrates a 40V power MOSFET as well as compensation and soft start circuitry, which results in a simpler and smaller solution with much fewer external components. A high switching frequency (800kHz) allows the use of a smaller inductor and capacitor to further reduce the solution size. Wide input range: 2.7V to 25V Each of the regulated current sinks in the AOZ1934/5 provides 20mA factory programmed current. With a maximum of 40V at the output of the step-up converter, each string can connect up to ten LEDs in series, for a total of 20 LEDs for AOZ1934 and 30 LEDs for AOZ1935. The AOZ1934/5 is equipped with fast PWM dimming control for wide dimming range and has an enable pin for IC ON/OFF control. Various protection features are built into the AOZ1934/5, including cycle-by-cycle input current limit protection, output over-voltage protection, LED fault (open or short) protection and thermal shutdown protection. The leakage current in shutdown mode is 0.1µA. The AOZ1934/5 is available in a 16-lead 3 x 3 x 0.75mm thin QFN package. Drive up to 30 LEDs – AOZ1934 up to 20 LEDs (10s2p) – AOZ1935 up to 30 LEDs (10s3p) Up to 92% efficiency High frequency step-up converter (800kHz) Highly integrated solution – Integrated 40V Power MOSFET – Internal compensation and soft start Integrated current sinks: AOZ1934 – 2 channels, AOZ1935 – 3 channels – ±2% Typ. current accuracy – 1.5% Typ. current matching PWM dimming with <1µs delay time Low operating quiescent current (500µA) LED open/short protection Both internal fixed and external adjustable Over-voltage protection Cycle-by-cycle inductor current limit (2.5A) 0.1µA shutdown current Green Package: 3 x 3 QFN-16 -40°C to +85°C temperature range Applications Netbook Tablet PCs GPS Portable media players 1-, 2-, 3-, 4-cell Li Ion LED applications Rev. 1.2 June 2013 www.aosmd.com Page 1 of 15 AOZ1935 Typical Application Circuit LED Power Input Voltage Range: 3V to 25V L = 4.7µH C OUT C IN 10µF 1µF White LEDs AOZ1935 VIN IC Supply: 2.7V to 5.5V LX AVCC Up to 10 in series OV C AVCC 1µF VOUT S1 Enable PWM Dimming Control EN S2 PWM S3 GND PAD PGND Ordering Information Part Number Ambient Temperature Range Package Environmental AOZ1934QI* -40°C to +85°C 3x3 QFN-16 Green Product AOZ1935QI -40°C to +85°C 3x3 QFN-16 Green Product *Contact manufacturer for product availability AOS Green Products use reduced levels of Halogens, and are also RoHS compliant. Please visit www.aosmd.com/media/AOSGreenPolicy.pdf for additional information. Rev. 1.2 June 2013 www.aosmd.com Page 2 of 15 AOZ1935 Pin Configuration VIN AVCC PGND PGND 13 OV 12 VOUT 11 14 15 16 1 LX 2 LX PAD S1 10 3 PWM S2 9 4 NC 8 7 S3* GND 6 5 EN NC 3x3 QFN-16 (Bottom View) Pin Description Pin Number Pin Name 1, 2 LX 3 PWM 4, 5 NC Not internally connected 6 EN IC enable 7 GND 8 S3* Regulated output current sink #3* 9 S2 Regulated output current sink #2 10 S1 Regulated output current sink #1 11 VOUT 12 OV Over voltage feedback sense pin. Programmable with a resistor divider, this pin has an internal 1.2V threshold 13 VIN Boost converter power supply’s input voltage sense pin 14 AVCC Input supply pin for the IC 15, 16 PGND Power Ground pin PAD Pin Function Switching node of the step-up converter Pulse width controlled dimming input. Connect this pin to AVCC when not used Analog Ground pin Output voltage sense pin Exposed Backside Paddle. Connect to ground for electrical and thermal usage. PAD is internally connected to Analog Ground pin. *S3 is only for the AOZ1935. Rev. 1.2 June 2013 www.aosmd.com Page 3 of 15 AOZ1935 Functional Block Diagram Backlight Unit LED Power Input 3V to 25V LX VOUT Converter Control PGND Over Voltage Control OV Up to 10 LEDs in Series VIN S1 ICC Supply 2.7V to 5.5V AVCC IC Bias, Vref Voltage Optimizing Control S2 GND S3* *S3 is only for the AOZ1935 Enable PWM Brightness Control EN Constant Current Control Logic Control PWN AOZ1934/35 Rev. 1.2 June 2013 www.aosmd.com Page 4 of 15 AOZ1935 Absolute Maximum Ratings (TA=25C unless otherwise noted(1) Exceeding the Absolute Maximum ratings may damage the device. Symbol Value Unit Boost Converter Input Voltage -0.3 to 28 V AVCC IC Input Voltage -0.3 to 6 V LX, Sx High Voltage Nodes -0.3 to 44 V VOUT Output Voltage Node -0.3 to 44 VIN EN, PWM, OV Description Input Nodes -0.3 to AVCC+0.3 V TJ Operating Temperature Range -40 to 150 C TS Storage Temperature Range -65 to 150 C 300 C 2 kV TLEAD ESD Maximum Soldering Temperature (at leads, 10 seconds) Human Body Model Note: 1.Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions specified is not implied. Only one Absolute Maximum rating should be applied at any one time. Thermal Capabilities Symbol Description Ambient(2) Value Unit 50 C/W JA Thermal Resistance – Junction to PD Maximum Power Dissipation at TA 25C 2.0 W Derating Factor Above TA = 25C -20 mW/C PD / T Note: 2. Junction to Ambient thermal resistance is highly dependent on PCB layout. Values are based on thermal properties of the device when soldered to an EV board. Rev. 1.2 June 2013 www.aosmd.com Page 5 of 15 AOZ1935 Electrical Characteristics Symbol Parameter Condition Min. Typ. Max. Units IC SUPPLY Boost Converter Input Range 2.7 25 V AVCC IC Supply Voltage Range 2.7 5.5 V UVLO IC Supply Under Voltage Lockout 2.65 V VIN UVLOHYST IQ ISHDN_AVCC ISHDN_VIN Rising Edge 2.5 UVLO Hysteresis 0.15 V IC Standby Current Not Switching 0.5 mA IC Operating Current Switching 1.15 mA AVCC Pin Shutdown Current EN = GND 0.1 1.0 µA VIN Pin Shutdown Current EN = GND 0.1 1.0 µA STEP-UP CONVERTER NMOS On-resistance 0.35 Ω ILIM Peak NMOS Current Limit 2.5 A FSW Oscillator Frequency 800 kHz Dmax Maximum Duty Cycle 95 % VOV OV Pin Threshold 1.2 V VOVP Internal OVP – VOUT Threshold 40 V Start-up Time 1 ms RDS(ON) TS 92 CURRENT SINK ID Output Current Accuracy Output current matching(3) V_sov Current Sink Over-voltage Threshold TFAULT Current Sink Fault Delay Current Setting = 20mA (DATA = 1), TA=25°C ±1 ±4 Current Setting = 20mA (DATA = 1) ±1 ±6 Current Setting = 20mA (DATA = 1) 1.5 3.5 PWM 100% Duty Cycle % % 6.0 V 80 ms CONTROL VTH-L EN, PWM Pin Logic Low Threshold VTH-H EN, PWM Pin Logic High Threshold TPWM(ON)_MIN 0.4 V 1.4 Minimum PWM On Time V 1 100 µs FPWM PWM Dimming Frequency 30000 Hz TJ-TH IC Junction Thermal Shutdown Threshold 150 °C IC Junction Thermal Shutdown Hysteresis 15 C Note: 3.The device is guaranteed to meet performance specifications over the –40°C to +85°C operating temperature range by design, characterization and correlation with statistical process controls. 4.The current matching between channels is defined as |Id-Iavg|max/Iavg . Rev. 1.2 June 2013 www.aosmd.com Page 6 of 15 AOZ1935 Typical Operating Characteristics Electrical Efficiency 100 95 Efficiency (%) 90 85 80 75 70 65 60 55 50 2 7 12 17 22 27 Vin (V) LED Current Regulation 22.90 22.85 LED Current (mA) 22.80 22.75 22.70 22.65 22.60 22.55 22.50 22.45 22.40 2.7 7.7 12.7 17.7 Input Voltage (V) 22.7 PWM Dimming Linearity Average LED Current (mA) 20 15 10 DBRIT = 1kHZ DBRIT = 100HZ DBRIT = 30kHZ 5 0 0 10 20 30 40 50 60 70 80 90 100 PWM Duty Cycle(%) Rev. 1.2 June 2013 www.aosmd.com Page 7 of 15 AOZ1935 Typical Operating Characteristics (Continued) Start-up Waveform Switching Waveform (VIN = 5V, Full Brightness) (VIN = 2.7V, Full Brightness) EN 2V/div LX 20V/div Vout 20V/div IS3 20mA/div IL 1A/div 400µs/div 1µs/div Switching Waveform Switching Waveform (VIN = 3.6V, Full Brightness) (VIN = 5V, Full Brightness) LX 20V/div LX 20V/div IL 1A/div IL 1A/div 1µs/div 1µs/div Switching Waveform Switching Waveform (VIN = 12V, Full Brightness) (VIN = 25-V, Full Brightness) LX 20V/div LX 20V/div IL 1A/div IL 1A/div 1µs/div Rev. 1.2 June 2013 1µs/div www.aosmd.com Page 8 of 15 AOZ1935 Typical Operating Characteristics (Continued) PWM Dimming 10% PWM Dimming 10% (VIN = 3.6V, Frequency = 20kHz) (VIN = 5V, Frequency = 20kHz) DPWM 5V/div DPWM 5V/div VS1 20V/div VS1 20V/div IS1 20mA/div IS1 20mA/div IL 1A/div IL 1A/div 10µs/div 10µs/div PWM Dimming 50% PWM Dimming 50% (VIN = 3.6V, Frequency = 20kHz) (VIN = 5V, Frequency = 20kHz) DPWM 5V/div DPWM 5V/div VS1 20V/div VS1 20V/div IS1 20mA/div IS1 20mA/div IL 1A/div IL 1A/div 10µs/div 10µs/div PWM Dimming 90% PWM Dimming 90% (VIN = 3.6V, Frequency = 20kHz) (VIN = 5V, Frequency = 20kHz) DPWM 5V/div DPWM 5V/div VS1 20V/div VS1 20V/div IS1 20mA/div IS1 20mA/div IL 1A/div IL 1A/div 10µs/div Rev. 1.2 June 2013 10µs/div www.aosmd.com Page 9 of 15 AOZ1935 Typical Operating Characteristics (Continued) Output, Short-to-Ground LED Open Protection (VIN = 5V, Full Brightness) (VIN = 5V, Full Brightness) VS3 5V/div VS3 5V/div Vout 20V/div Vout 20V/div IS3 20mA/div IS3 20mA/div IL 1A/div IL 1A/div 40ms/div 2s/div LED Short Protection (VIN = 5V, Full Brightness) VS3 5V/div Vout 20V/div IS3 20mA/div IL 1A/div 20ms/div Rev. 1.2 June 2013 www.aosmd.com Page 10 of 15 AOZ1935 Detailed Description The AOZ1934/5 is a unique current regulated step-up (boost) converter. Two (or three for AOZ1935) current regulating devices are integrated to drive two or three strings of LEDs. Unused channels need to be connected to ground (GND). The voltage step-up is accomplished by a boost topology, using an inductor-based DC-DC switching converter, in which the inductor serves as an energy storage device in the system. By integrating a high voltage optimized MOSFET, the AOZ1934/5 internal switching frequency is 800kHz while still maintaining high power efficiency. Unlike a traditional DC-DC boost converter with a fixed output voltage, the AOZ1934/5 dynamically changes its output voltage regulation parameters depending on the load. The use of unique control schemes maintains accurate current regulation in each current sink while leaving the output voltage at a minimum, increasing the overall conversion efficiency. The internal step-up converter dynamically controls the voltage at the output high enough to drive the LED string with the highest total forward voltage. The wide input voltage range, from 2.7V to 25V, allows maximum system flexibility; battery powered devices using 1-, 2-, 3- or 4-cell Li Ion packs can share the same power architecture. A low power 2.7V to 5.5V input to supply the IC bias circuitry is required at AVCC pin. LED brightness control is based on the popular PWM dimming scheme via the PWM pin. The EN pin provides ON/OFF control of the IC. By asserting a logic high on the EN pin, the converter is enabled and will regulate each of the current sinks at the factory programmed current setting. Application Information Power Up Sequence It’s recommended to power up Vin, AVCC, and PWM dimming in sequence, and EN pin needs to ramp up simultaneously or later than AVCC, in order to avoid latch-off, or mis-operation of device. We do not assume any liability or responsibility for any loss or damage arising from misuse or inappropriate use of the product. Current Dimming Using PWM Pin AOZ1934/5 allows maximum flexibility with a PWM signal control input which can be used for dimming. The IC must remain Enabled at EN pin during PWM dimming, which means the step-up converter is active to reduce the response time. Combining this with the fast response of the step-up converter, each LED channel can typically Rev. 1.2 June 2013 recover from no current within 1µs. This allows very short PWM on-time or a duty-cycle with fine resolution. Assume a 50µs minimum on-time for a 100Hz PWM signal, a 200:1 ratio can be achieved by PWM. The minimum PWM on-time of 1s is required in AOZ1934/5’s application, this means minimum PWM duty cycle of 2% for 20kHz dimming frequency and 0.02% for 200Hz dimming frequency. The amplitude of PWM signal should not be higher than AVCC, otherwise test mode will be triggered. Fault Protection (LED Open or Short) Each current sink is protected against LED short or open conditions. If an LED short circuit condition arises, the current sink continues to regulate until VSINK > VSOV (6V). When any sink node voltage goes above VSOV for more than 80ms (while PWM dimming signal remains high), that channel’s current sink will be turned off, and other channels will still work if they don’t trigger this fault condition. For example, if one or more LEDs on a channel are shorted, that channel’s sink voltage will increase. If the voltage goes above 6V for more than 80ms, the Current Sink Fault Protection will be triggered and only this faulty string will be disabled by shutting off this current sink. All other channels will continue normal operation if they don’t have a fault condition. When PWM dimming control is used, the 80ms fault delay is accumulated only when PWM signal is high; the PWM low time is not counted into the fault delay, so the delay time will be 80ms / DPWM (DPWM is the duty cycle of the PWM signal). In case of an LED failing open, the current sink voltage of the failed string will go close to ground and dominate the boost converter control loop. As a result the output voltage will move up to the over-voltage threshold, set internally to 40V or by the external resistor divider, whichever is lower. Once the over-voltage incident is flagged internally, the faulty channel(s) will be disabled. Then the output voltage of the boost converter will go back to normal level. During the entire process, the rest of the LED strings (healthy LED strings) would continue normal operation. The fault conditions are reset when the IC is powered down and up again. Output Over-Voltage Protection (OVP) AOZ1934/5 has built in over-voltage protection function with 40V threshold at VOUT pin. This level is suitable for applications with ten series LEDs per string. However, for applications with fewer series LEDs, the user can choose www.aosmd.com Page 11 of 15 AOZ1935 to program a lower over-voltage threshold using the OV pin. The internal reference voltage to trigger OVP at OV pin is 1.2V; a resistor divider can be connected as shown in the following figure and the over voltage threshold can be derived as R V OUT_OV = 1.2 1 + ------1- R 2 To limit the leakage current through the divider, make sure 10M > R1+R2 > 1M. The lower value of the internal 40V OVP and the external OVP set by the resistor divider determines the system OVP value. Thermal Shutdown Thermal shutdown feature is also included in the AOZ1934/5. When IC junction temperature (TJ) reaches 150C, the IC will immediately enter shutdown mode. Once TJ drops 15C to around 135C, the IC will be back to normal operation. Inductor Selection A 4.7µH to 10µH inductor is recommended for all the applications. If high efficiency is a critical requirement, a low DCR inductor should be selected. The inductor’s saturation current rating should also exceed the peak input current. Rev. 1.2 June 2013 Capacitor Selection Small size ceramic capacitors with low ESR are ideal for all the applications. A 10uF input capacitor at VIN, a 1µF input capacitor at AVCC and a 1µF output capacitor at VOUT are suggested. The voltage rating of these capacitors should exceed the maximum possible voltage at the corresponding pins. For example, for the application of 3P10S LEDs from input voltage range of 5V to 22V and AVCC = 3.3V, a 25V capacitor is recommended at the VIN pin, a 50V capacitor is recommended at the VOUT pin, and a 10V capacitor is recommended at the AVCC pin. Diode Selection Using a schottky diode is recommended because of its low forward voltage drop and fast reverse recovery time. The current rating of the schottky diode should exceed the peak current of the boost converter. The voltage rating should also exceed the target output voltage. For applications driving 10 LEDs in series, 50V voltage rating schottky diode is recommended. Layout Considerations PCB layout is very important for high frequency switching regulators in order to keep the loop stable and minimize noise. The AVCC pin’s capacitor should be very close to the IC to get the best decoupling. The path of the inductor, schottky diode and output capacitor should be kept as short as possible to minimize noise and ringing. Please see the AOZ1934/5 evaluation document for detailed PCB layout guidelines. www.aosmd.com Page 12 of 15 AOZ1935 Package Dimensions, QFN-16 3mm x 3mm x 0.75mm D D1 9 12 12 9 8 13 13 8 E1 E Pin 1 Dot By Marking 5 5 16 16 Pin 1 Identification L 1 4 4 TOP VIEW 1 e Detail "A" R0.3(4X)max Round corner b BOTTOM VIEW Detail "B" C A S Detail “A” SIDE VIEW A1 A2 Detail “B” Dimensions in millimeters Symbols A A1 A2 b C D D1 E E1 e L S Min. 0.65 0.000 0.154 0.18 2.95 2.95 0.45 0.30 Nom. 0.75 0.025 0.203 0.23 0.3 Ref. 3.00 1.7 Ref. 3.00 1.7 Ref. 0.50 0.40 0.25 Ref Max. 0.85 0.050 0.280 0.30 3.05 3.05 0.55 0.50 Dimensions in inches Symbols A A1 A2 b C D D1 E E1 e L S Min. 0.026 0.000 0.006 0.007 Nom. Max. 0.030 0.033 0.001 0.002 0.008 0.011 0.009 0.012 0.012 Ref. 0.116 0.118 0.120 0.067 Ref. 0.116 0.118 0.120 0.067 Ref. 0.018 0.020 0.022 0.012 0.016 0.020 0.010 Ref. Note: 1. Controlling dimension is millimeter, converted inch dimensions are not necessarily exact. Rev. 1.2 June 2013 www.aosmd.com Page 13 of 15 AOZ1935 Tape and Reel Dimensions, QFN-16 3mm x 3mm x 0.75mm Carrier Tape D0 D1 P1 E1 K0 E2 E B0 T P2 A0 P0 Feeding Direction UNIT: mm Package DFN 3x3 EP A0 3.40 ±0.10 B0 K0 3.35 ±0.10 1.10 ±0.10 D0 1.50 +0.10/-0 D1 E E1 E2 P0 P1 P2 T 1.50 +0.10/-0 12.00 ±0.30 1.75 ±0.10 5.50 ±0.05 8.00 ±0.10 4.00 ±0.10 2.00 ±0.05 0.30 ±0.05 Reel W1 S G N M K V R H W UNIT: mm Tape Size Reel Size M N W W1 H K S G R V 12mm ø330 ø330.0 ±0.50 ø97.00 ±0.10 13.00 ±0.30 17.40 ±1.00 ø13.0 +0.50/-0.20 10.60 2.00 ±0.50 — — — Leader/Trailer and Orientation Trailer Tape 300mm min. Rev. 1.2 June 2013 Components Tape Orientation in Pocket www.aosmd.com Leader Tape 500mm min. Page 14 of 15 AOZ1935 Part Marking AOZ1935QI (3 x 3 QFN-16) Assembly Lot Code Part Number Code I 0 8 W Week Code & Year Code Extension Code Option Code Assembly Location Code LEGAL DISCLAIMER Alpha and Omega Semiconductor makes no representations or warranties with respect to the accuracy or completeness of the information provided herein and takes no liabilities for the consequences of use of such information or any product described herein. Alpha and Omega Semiconductor reserves the right to make changes to such information at any time without further notice. This document does not constitute the grant of any intellectual property rights or representation of non-infringement of any third party’s intellectual property rights. LIFE SUPPORT POLICY ALPHA AND OMEGA SEMICONDUCTOR PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body or (b) support or sustain life, and (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury of the user. Rev. 1.2 June 2013 2. A critical component in any component of a life support, device, or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. www.aosmd.com Page 15 of 15