LM3537 LM3537 8-Channel WLED Driver with Four Integrated LDOs Literature Number: SNVS634A LM3537 8-Channel WLED Driver with Four Integrated LDOs General Description Features The LM3537 is a highly integrated LED driver capable of driving 8 LEDs in parallel for single display backlighting applications. Independent LED control allows for a subset of the main display LEDs to be selected for partial illumination applications. I2C-compatible control allows full configurability of the backlighting function. The LM3537 provides multi-zone Ambient Light Sensing allowing autonomous backlight intensity control in the event of changing ambient light conditions. A PWM input is also provided to give the user a means to adjust the backlight intensity dynamically based upon the content of the display. Four integrated LDOs are fully configurable through I2C capable of addressing point-of-load regulation needs for functions such as integrated camera modules. The LDOs can be powered from main battery source, or by a fixed output voltage of an external buck converter (post regulation) leading to higher conversion efficiency. The LM3537 provides excellent efficiency without the use of an inductor by operating the charge pump in a gain of 3/2 or in Pass Mode. The proper gain for maintaining current regulation is chosen, based on LED forward voltage, so that efficiency is maximized over the input voltage range. LM3537 is offered in a tiny 30-bump micro-SMD package: 2.02 mm x 2.52 mm x 0.60 mm, 0.40 mm pitch. Lighting: ■ 8-channel backlight capability ■ Internal ALS engine; PWM input to support CABC ■ Built-in power supply and gain control for ambient light sensor ■ Up to 90% efficiency ■ Adaptive charge pump with 1x and 1.5x gains for maximum efficiency ■ 128 dimming steps for group A, exponential or linear dimming selectable by register setup ■ 8 linear dimming states for group B LDOs: ■ 4 Programmable LDOs (300 mA/150 mA output currents) ■ Default startup voltage states ■ Low dropout voltage: 100 mV typ. at 150 mA load current ■ LDO input voltage = 1.8V to VIN_A ■ Overload protection Combined Common Features: ■ Wide input voltage range: 2.7V to 5.5V ■ I2C-compatible serial interface ■ 2 general-purpose outputs Applications ■ Smartphone lighting ■ MP3 players, gaming devices ■ Digital cameras Typical Application Circuit 30108301 © 2011 National Semiconductor Corporation 301083 www.national.com LM3537 8-Channel WLED Driver with Four Integrated LDOs October 17, 2011 LM3537 Connection Diagrams 30–Bump micro SMD Package Top View 30108341 XY – Date Code TT – Die Traceability ABCD – Product Identification 30108302 Pin Descriptions Bump Name Description C5 VIN_A Input voltage for LED driver and sensor interface. Input range: 2.7V to 5.5V. E5 VIN_B Input voltage for the regulators. This must be connected to the same voltage supply as VIN_A F5 VIN_C Input voltage (power rail) for the LDO regulators. 1.8V ≤ VIN_C ≤ VIN_A B1 SCL Serial interface clock B3 SDA Serial interface data A1 HWEN B2 PWM External PWM Input - Allows the current sinks to be turned on and off at a frequency and duty cycle externally controlled. Minimum on-time pulse width = 15 µsec. E4 SBIAS Power supply for a light sensor. Leave unconnected if not used. E3 GPO1 General purpose output. Can be used as a sensor gain control signal. When functioning as a general purpose output, it is open drain and requires an external pullup. Leave unconnected if not used. E2 GPO2 General purpose output. Can be used as a sensor gain control signal. When functioning as a general purpose output, it is open drain and requires an external pullup. Leave unconnected if not used. Hardware enable pin. High = normal operation, low = RESET D5 ALS Ambient Light Sensor input. Connect to ground if not used. F3 GND Regulator ground A2 PGND LED driver and charge pump ground F2 LDO4 Programmable VOUT of 1.2-3.3 V. Max load = 150 mA. F4 LDO3 Programmable VOUT of 1.2-3.3 V. Max load = 150 mA. E1 LDO2 Programmable VOUT of 1.2-3.3 V. Max load = 150 mA. www.national.com 2 Name LM3537 Bump Description F1 LDO1 C3 D8 Programmable VOUT of 1.2-3.3 V. Max load = 300 mA. C4 D7/INT D4 D6 LED driver D3 D5 LED driver D2 D4 LED driver D1 D3 LED driver C1 D2 LED driver C2 D1 LED driver B5 VOUT Charge pump output B4 C2- Flying capacitor 2 negative terminal A4 C2+ Flying capacitor 2 positive terminal A3 C1- Flying capacitor 1 negative terminal A5 C1+ Flying capacitor 1 positive terminal LED driver LED driver/ ALS interrupt (mode of operation is selected via register). In ALS interrupt mode, a pullup resistor is required. A '0’ means a change has occurred, while a ‘1’ means no ALS adjustment has been made. Ordering Information Order Information LM3537TME LM3537TMX Package TMD30AEA 3 Supplied As 250 Units, Tape & Reel 3000 Units, Tape & Reel www.national.com LM3537 Absolute Maximum Ratings (Note 1, Note Operating Rating VIN_A, VIN_B Input Voltage Range LED Voltage Range VIN_C Input Voltage Range (Note: must stay > VOUTLDO + 0.3V) Junction Temperature (TJ) Range Ambient Temperature (TA) Range (Note 6) 2) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VIN_A, VIN_B , VIN_C pin voltage Voltage on Logic Pins (SCL, SDA, GPO1, GPO2, HWEN, PWM) LED driver (D1 to D8) Pin Voltages Voltage on All Other Pins Continuous Power Dissipation (Note 3) Junction Temperature (TJ-MAX) Storage Temperature Range Maximum Lead Temperature (Soldering) ESD Rating (Note 5) Human Body Model (Note 1, Note 2) -0.3V to 6.0V -0.3V to (VIN_A+0.3V) with 6.0V max -0.3V to (VOUT+0.3V) with 6.0V max -0.3V to (VIN_A +0.3V) with 6.0V max Internally Limited 2.7V to 5.5V 2.0V to 4.0V 1.8V to VIN_B −30°C to +110°C −30°C to +85°C Thermal Properties Junction-to-Ambient Thermal Resistance (θJA), TMD30 Package (Note 7) 45°C/W If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales/Office/Distributors for availability and specifications. 150°C -40°C to +150°C (Note 4) 2 kV ESD Caution Notice National Semiconductor recommends that all integrated circuits be handled with appropriate ESD precautions. Failure to observe proper ESD handling techniques can result in damage to the device. Charge Pump and LED Drivers Electrical Characteristics (Note 2, Note 8) Limits in standard typeface are for TJ = 25°C, and limits in boldface type apply over the operating ambient temperature range (−30°C to +85°C). Unless otherwise specified: VIN_A = 3.6V; VHWEN = VIN_A; VDx = 0.4V; GroupA = GroupB = Fullscale Current; C1 = C2 = CIN_A= COUT= 1.0 µF. (Note 9) Symbol IDx IDx- Min Typ Max Units Output Current Regulation GroupA Parameter 2.7V ≤ VIN_A ≤ 5.5V 8 LEDs in GroupA −7.5% 25 +7.5% mA Output Current Regulation GroupB 2.7V ≤ VIN_A ≤ 5.5V 4 LEDs in GroupB −7.5% 25 +7.5% mA Output Current Regulation All LED Drivers Enabled All LED Drivers on BankA (Note 10) 3.2V ≤ VIN_A ≤ 5.5V VLED = 3.6V BankA current code = 1111101b, exp dimming scale LED Current Matching (Note 11) 2.7V ≤ VIN ≤ 5.5V LED Current = Fullscale current MATCH Condition 22.3 DxA mA GroupA (8 LEDs) 0.8 3 GroupB (4 LEDs) 0.4 3 % VDxTH VDx 1x to 3/2x Gain Transition Threshold VDx Falling 135 mV VHR Current sink Headroom Voltage Requirement (Note 12) IDx = 95% ×IDx (nom.) (IDx (nom) ≈ 20 mA) 100 mV ROUT Open-Loop Charge Pump Output Resistance (Note 20) Gain = 3/2 2.4 Gain = 1 0.5 Gain = 1.5x, No Load. Current through VIN_A pin. Sensor Bias OFF 2.9 4.4 Gain = 1x, No Load. Current through VIN_A pin. Sensor Bias OFF 1.1 2.4 IQ Quiescent Supply Current mA ISB Standby Supply Current HWEN = 1.8V. All registers in factory defaults state. Current through VIN_A pin. 1.2 ISD Shutdown Supply Current HWEN = 0V. Current through VIN_A pin. 0.2 www.national.com 4 Ω µA 1.0 µA Parameter fSW Switching Frequency tSTART Startup Time VALS ALS Reference Voltage RALS Condition 1.1 (Note 16) Internal ALS Resistor Typ Max Units 1.3 1.6 MHz 250 µs −6% 1.0 +6% RALS register setting = 00010b −6% 10.1 +6% RALS register setting = 00100b −6% 5.0 +6% Min Typ Max Logic Interface Characteristics Symbol Min V kΩ (Note 2, Note 8) Parameter Condition Units I2C-Compatible Interface Timing Specifications (SCL, SDA) (Note 13) t1 SCL (Clock Period) t2 Data In Setup Time to SCL High t3 Data Out stable After SCL Low t4 SDA Low Setup Time to SCL Low (Start) t5 SDA High Hold Time After SCL High (Stop) (Note 14) 2.5 µs 100 ns 0 ns 100 ns 100 ns I2C-Compatible Interface Voltage Specifications (SCL, SDA) VIL Input Logic Low "0" 2.7V ≤ VIN_A ≤ 5.5V 0 0.45 V VIH Input Logic High "1" 2.7V ≤ VIN_A ≤ 5.5V 1.25 VIN_A V VOL Output Logic Low "0" ILOAD = 3mA 400 mV Logic inputs HWEN and PWM VHWEN HWEN Voltage Thresholds 2.7V ≤ VIN_A ≤ 5.5V Reset VPWM PWM Voltage Thresholds 2.7V ≤ VIN_A ≤ 5.5V 0 0.45 1.2 VIN_A LEDs Off 0 0.45 LEDs On 1.2 VIN_A Normal Operation V V ALS interrupt VOL-INT Interrupt Output Logic Low '0' ILOAD = 3mA 400 mV 0.5 V Logic outputs GPO1, GPO2 (Note 19) VOL Output Low Level IOUT = 3 mA VOH Output High Level IOUT = −2 mA 0.3 VOUT_S −0.5 VOUT _S − 0.3 V Voltage Regulators Electrical Characteristics (Note 2, Note 8) Unless otherwise noted, VIN_A= VIN_B = VIN_C = 3.6V, CIN_A = 1 µF, CIN_B = 100 nF, CIN_C = 2.2 µF, CLDOX= 1 µF, HWEN = high. Limits in standard typeface are for TJ = 25°C, and limits in boldface type apply over the operating ambient temperature range (-30°C to +85°C). (Note 17) Symbol Parameter Condition Min Typ Max Units LDO1 VOUT Output Voltage Accuracy IOUTLDO = 1 mA, VOUTLDO = 2.80V Default Output Voltage IOUT VDO ΔVOUT −2 +2 −3 +3 2.80 Output Current 1.8V ≤ VIN_C ≤ 5.5V Output Current Limit (short circuit) VOUTLDO = 0V 600 Dropout Voltage IOUTLDO = 300 mA 220 Line Regulation VOUTLDO + 0.5V ≤ VIN_C ≤ 4.5V IOUTLDO = 1 mA 2 Load Regulation 1 mA ≤ IOUTLDO ≤ 300 mA 20 5 % V 300 mA mA 300 mV mV www.national.com LM3537 Symbol LM3537 Symbol PSRR Parameter Condition Min f = 100Hz, CLDO1 = 1 µF, Power Supply Ripple Rejection Ratio IOUTLDO = 20 mA Output Voltage = 1.20V Typ Max 65 Units dB LDO2, LDO3, LDO4 Output Voltage Accuracy VOUT Default Output Voltage IOUT VDO ΔVOUT PSRR IOUTLDO = 1 mA, VOUTLDO = 2.80V −2 +2 −3 +3 LDO2 1.80 LDO3 1.80 LDO4 2.80 Output Current 1.8V ≤ VIN_C ≤ 5.5V Output Current Limit (short circuit) VOUTLDO = 0V 400 Dropout Voltage IOUTLDO = 150 mA 100 Line Regulation VOUTLDO + 0.5V ≤ VIN_C ≤ 4.5V IOUTLDO = 1mA 2 Load Regulation 1mA ≤ IOUTLDO ≤ 150 mA 10 V V 150 f = 100 Hz, CLDOX = 1µF, Power Supply Ripple Rejection Ratio IOUTLDO = 20 mA Output Voltage = 1.20V % mA mA 200 mV mV 65 dB LDO Combined Common Electrical Characteristics IGND All LDOs Disabled 0.2 1 One LDO Enabled 70 130 Ground Pin Current (GND and PGNDNote: IOUTLDOX = 0mA Two LDOs Enabled pin) Three LDOs Enabled 100 tSTARTUP Turn-on Time from Shut-down (Note 15) TTransient Startup Transient Overshoot µA 130 Four LDOs Enabled µA 160 CLDOX = 1µF, IOUTLDO = 150 mA VOUT = 2.8V. Enable of First LDO 130 CLDOX = 1 µF, IOUTLDO = 150 mA VOUT = 2.8V. Enable of Each Subsequent LDO after First Enabled 70 µs CLDOX = 1 µF, IOUTLDO = 150 mA 30 mV Sensor Interface Electrical Characteristics Unless otherwise noted, VIN_A = 3.6V, CIN_A = 1 µF, CIN_B = 100 nF, CIN_C = 2.2 µF, CSEN= 1 µF, HWEN = high. Limits in standard typeface are for TJ = 25°C, and limits in boldface type apply over the operating ambient temperature range (−30°C to +85°C). Symbol Parameter Condition Min Typ Max Units 20 mA SBIAS IOUT_S VOUT_S IQIF SBIAS Output Current SBIAS Output Voltage Sensor Interface Quiescent Supply Current (Note 18, Note 20) www.national.com 2.7V ≤ VIN_A ≤ 5.5V. VOUT_S < (VIN_A +0.3V) 2.7V ≤ VIN_A ≤ 5.5V. IOUT_S = 1.0 mA. 2.4V option selected via register. −5% 3.3V ≤ VIN_A ≤ 5.5V. IOUT_S = 1.0 mA. 3.0V option selected via register. −5% No Load 2.4 V 3.0 35 6 +5% +5% µA LM3537 30108313 FIGURE 1. Timing Parameters Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operation of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the Electrical Characteristics tables. Note 2: All voltages are with respect to the potential at the GND pins. Note 3: Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ = 160°C (typ.) and disengages at TJ = 155°C (typ.). Note 4: For detailed soldering specifications and information, please refer to National Semiconductor Application Note 1112: Micro SMD Wafer Level Chip Scale Package (AN-1112). Note 5: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. (MIL-STD-883 3015.7) Note 6: In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may have to be derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP = 110°C), the maximum power dissipation of the device in the application (PD-MAX), and the junction-to ambient thermal resistance of the part/package in the application (θJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (θJA × PD-MAX). Note 7: Junction-to-ambient thermal resistance is highly dependent on application and board layout. In applications where high maximum power dissipation exists, special care must be paid to thermal dissipation issues in board design. For more information, please refer to National Semiconductor Application Note 1112: Micro SMD Wafer Level Chip Scale Package (AN-1112). Note 8: Min and Max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the most likely norm. Note 9: CIN_X, COUT, CLDOX, CSEN, C1, and C2 : Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics. Note 10: The total output current can be split between the two groups (IDx = 25 mA Max). Under maximum output current conditions, special attention must be given to input voltage and LED forward voltage to ensure proper current regulation. The maximum total output current for the LM3537 should be limited to 180 mA. Note 11: For the two groups of current sinks on a part (group A and group B), the following are determined: the maximum sink current in the group (MAX), the minimum sink current in the group (MIN), and the average sink current of the group (AVG). For each group, two matching numbers are calculated: (MAX-AVG)/ AVG and (AVG-MIN)/AVG. The largest number of the two (worst case) is considered the matching figure for the group. The matching figure for a given part is considered to be the highest matching figure of the two groups. The typical specification provided is the most likely norm of the matching figure for all parts. Note 12: For each Dx pin, headroom voltage is the voltage across the internal current sink connected to that pin. For group A and B current sinks, VHRx = VOUT -VLED. If headroom voltage requirement is not met, LED current regulation will be compromised. Note 13: SCL and SDA should be glitch-free in order for proper device control to be realized. See Figure 1 for timing specification details. Note 14: SCL is tested with a 50% duty-cycle clock. Note 15: Time needed for VOUTLDO to reach 95% of final value. Note 16: Turn-on time is measured from the moment the charge pump is activated until the VOUT crosses 90% of its target value. Note 17: CIN_C, CLDOX : Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics. Note 18: In addition to Quiescent Supply Current (IQ) drawn by the charge pump. (See Table Charge Pump and LED Drivers Electrical Characteristics.) Note 19: VOUT_S = SBIAS pin output voltage. The voltage level of the GPOs depends on the sbias_en-bit: '1'; GPOs will behave as push-pull outputs and will reference the high-side to the voltage of SBIAS. '0'; GPOs will act as open-drain outputs (default). In the open-drain configuration, they can be high-side referenced to any voltage equal to, or less than, the VIN_A of the LM3537. Output High Level (VOH) specification is valid only for push-pull -type outputs. Note 20: Guaranteed by design. 7 www.national.com LM3537 Typical Performance Characteristics Unless otherwise specified: VIN_A,B,C = 3.6V, CIN_A = COUT = 1.0 µF, CIN_B = 0.1 µF, CIN_C = 4.7 µF, C1 = C2= 1.0 µF, CLDOx= 1.0 µF, TA = 25°C. Regulator 1 (300 mA) Output Voltage vs Output Current VSET = 2.80V Regulator 2,3,4 (150 mA) Output Voltage vs Output Current VSET = 1.80V 30108319 30108320 Power Supply Rejection Ratio, VOUT = 1.20V, ILOAD = 20 mA Power Supply Rejection Ratio, VOUT = 1.20V, ILOAD = 20 mA VIN_C is shorted to VIN_A, VIN_B Signal Applied on VIN_C, VIN_A and VIN_B Clear. 30108321 www.national.com 30108322 8 LM3537 Load Transient. VOUT setting = 1.80V ILOAD 1mA to 150mA to 1mA; tRISE= tFALL= 5µs Line Transient Response VOUT setting = 1.80V,, ILOAD 1mA 30108342 30108343 Regulator Enable Response; Enable of First Regulator (1mA load, 1.80V) via Reg. Write Regulator Enable Response; Enable of First Regulator (150mA load, 2.80V) via Reg. Write 30108344 30108345 Regulator 2,3,4 Short Circuit Current VOUT setting = 1.80V Regulator 1 Short Circuit Current VOUT setting = 2.80V 30108346 30108347 9 www.national.com LM3537 Shutdown Supply Current HWEN = 0V. Current through VIN_A pin Standby Supply Current HWEN = 1.8V. Current through VIN_A pin 30108348 30108349 Quiescent Current vs Input Voltage 1× Gain Quiescent Current vs Input Voltage 3/2× Gain 3/2× Gain 30108355 30108354 LED Current Matching Distribution. 6 Drivers on Group A, Output Set to 25 mA. (Note 11) Charge Pump 1.5x Efficiency vs Load Current 30108353 30108352 www.national.com 10 LM3537 Block Diagram 30108303 11 www.national.com LM3537 '0' alerting the controller. Available resistor values are shown in Table 1 below. Circuit Description OVERVIEW The LM3537 is a white LED driver system based upon an adaptive 3/2× - 1× CMOS charge pump capable of supplying up to 180 mA of total output current. With two separately controlled groups of constant current sinks, the LM3537 is an ideal solution for platforms requiring a single white LED driver for main display and sub display (or keypad). The tightly matched current sinks ensure uniform brightness from the LEDs across the entire small-format display. Each LED is configured in a common anode configuration, with the peak drive current set to 25 mA. An I2C-compatible interface is used to enable the device and vary the brightness within the individual current sink groups. For group A, 128 brightness control levels are available (user defined linear or exponential dimming curve). Group B has 8 linearly-spaced analog brightness levels. The LM3537 provides an input for an Ambient Light Sensor to adaptively adjust the diode current based on ambient conditions, and a PWM pin to allow the diode current to be pulse width modulated to work with a display driver utilizing dynamic or content adjusted backlight control (DBC or CABC). Additionally, the device provides 20 mA power supply output for the sensor. The GPOs can also be configured to serve as a gain control interface for sensors with HW-controlled gain. The LM3537 also integrates three 150-mA LDO and one 300mA LDO voltage regulators, which can be turned on/off using separate enable bits on each LDO. Each LDO operates with a power rail input voltage range between 1.8 V and 5.5V allowing them to be supplied from the battery or a step-down converter. Furthermore, the regulated output voltages can be adjusted through the serial bus. TABLE 1. ALS Resistor Values CIRCUIT COMPONENTS Charge Pump The input to the 3/2× - 1× charge pump is connected to the VIN_A pin, and the regulated output of the charge pump is connected to the VOUT pin. The operating input voltage range of the LM3537 is 2.7V to 5.5V. The device’s regulated charge pump has both open-loop and closed-loop modes of operation. When the device is in open loop, the voltage at VOUT is equal to the gain times the voltage at the input. When the device is in closed loop, the voltage at VOUT is regulated to 4.2V (typ.). The charge pump gain transitions are actively selected to maintain regulation based on LED forward voltage and load requirements. Diode Current Sinks The matched current outputs are generated with a precision current mirror that is biased off the charge pump output. Matched currents are ensured with the use of tightly matched internal devices and internal mismatch cancellation circuitry. There are eight regulated current sinks configurable into 2 different lighting regions. r_als [3] r_als [2] r_als [1] r_als [0] RALS (typ) Value Unit 1 1 1 1 1 0.651 kΩ 1 1 1 1 0 0.672 kΩ 1 1 1 0 1 0.695 kΩ 1 1 1 0 0 0.720 kΩ 1 1 0 1 1 0.747 kΩ 1 1 0 1 0 0.776 kΩ 1 1 0 0 1 0.806 kΩ 1 1 0 0 0 0.840 kΩ 1 0 1 1 1 0.876 kΩ 1 0 1 1 0 0.916 kΩ 1 0 1 0 1 0.960 kΩ 1 0 1 0 0 1.01 kΩ 1 0 0 1 1 1.06 kΩ 1 0 0 1 0 1.12 kΩ 1 0 0 0 1 1.19 kΩ 1 0 0 0 0 1.26 kΩ 0 1 1 1 1 1.34 kΩ 0 1 1 1 0 1.44 kΩ 0 1 1 0 1 1.55 kΩ 0 1 1 0 0 1.68 kΩ 0 1 0 1 1 1.83 kΩ 0 1 0 1 0 2.02 kΩ 0 1 0 0 1 2.24 kΩ 0 1 0 0 0 2.52 kΩ 0 0 1 1 1 2.88 kΩ 0 0 1 1 0 3.36 kΩ 0 0 1 0 1 4.03 kΩ 0 0 1 0 0 5.00 kΩ 0 0 0 1 1 6.72 kΩ 0 0 0 1 0 10.1 kΩ 0 0 0 0 1 20.2 kΩ 0 0 0 0 0 HighZ -- Automatic Gain Change GPO pins of the LM3537 can be configured to serve as a gain control interface for sensors with HW controlled gain, like ROHM BH1600-series. Please see Table 2. LM3537 changes sensor gain automatically based on ambient light intensity changes. Ambient Light Sensing (ALS) and Interrupt The LM3537 provides an Ambient Light Sensing input for use with ambient backlight control. Connecting the anode of a photo diode to this pin and configuring the appropriate ALS resistor, the LM3537 can be configured to adjust the LED current to five unique settings corresponding to four adjustable light region trip points. Additionally, when the LM3537 determines that an ambient condition has changed, the interrupt pin, when connected to a pullup resistor will toggle to a www.national.com r_als [4] 12 OUTPUT PIN STATUS GPO1 GPO2 autogain_en = "0" Can be set to "1" or Can be set to "1" or "0" with REG 52H, "0" with REG 52H, bit gpo1 bit gpo2 autogain_en = "1" (enables autogain functionality) LOW GAIN 0 1 autogain_en = "1" (enables autogain functionality) HIGH GAIN 1 0 The ambient light sensing circuit has 4 configurable Ambient Light Boundaries (ZB0 – ZB3) programmed through the four 8-bit Zone Boundary Registers. These zone boundaries define 5 ambient brightness zones. The ambient light sensor input has a 0 to 1V operational input voltage range. The Typical Application Circuit shows the LM3537 with an ambient light sensor (ROHM, BH1621FVC). If the internal ALS Resistor Select Register is set to 0x14 (1.44 kΩ), this circuit will convert 0 to 1000 LUX light into approximately a 0 to 850 mV linear output voltage (high-gain mode). The voltage at the active ambient light sensor input is com- 30108317 FIGURE 2. ALS Zone to LED Brightness Mapping ALS Zone transitions with AutoGain is shown in Figure 3. When the light intensity increases, the LM3537 configures the sensor for low-gain mode. Transition from Zone2 to Zone3 triggers the shift to lower gain mode. When the light intensity decreases, the LM3537 configures the sensor to high-gain mode. The trip point to this transition is set by the ALS LOW_to_HIGH_TP register, and it should be set lower than the Zone2 to Zone3 transition, in order to have hysteresis. Zone3 to Zone2 transition trip point must be set separately for lower gain mode, by the ALS ZONE BOUNDARY Z3_to_Z2 register. This register value should be set higher than the ALS LOW_to_HIGH_TP. In low-gain mode the sensor will have a lower output current which helps save battery power. Highgain mode will allow better resolution, but will result higher output current. Thus, there is a trade-off between increased resolution and increased power consumption. High-gain mode is the default mode of operation after enabling the autogain. 13 www.national.com LM3537 pared against the 8-bit values programmed into the Zone Boundary Registers (ALS ZONE BOUNDARY#0 - ALS ZONE BOUNDARY#3 ). When the ambient light sensor output crosses one of the programmed thresholds the internal ALS circuitry will smoothly transition the LED current to the new 7bit brightness level as programmed into the appropriate Zone Target Register (ALS BRIGHTNESS ZONE#0 to ALS BRIGHTNESS ZONE#4). Ambient light sensor samples are averaged and then further processed by the discriminator block to provide rejection of noise and transient signals. The averager is configurable with 8 different averaging times to provide varying amounts of noise and transient rejection. The discriminator block algorithm has a maximum latency of two averaging cycles; therefore, the averaging time selection determines the amount of delay that will exist between a steady state change in the ambient light conditions and the associated change of the backlight illumination. For example, the A/D converter samples the ALS inputs at 16 kHz. If the averaging time is set to 800 ms, the averager will send the updated zone information to the discriminator every 800 ms. This zone information contains the average of approximately 12800 samples (800 ms × 16 kHz). Due to the latency of 2 averaging cycles, when there is a steady state change in the ambient light, the LED current will begin to transition to the appropriate target value after approximately 1600 ms have elapsed. ALS Zone to LED Brightness Mapping principle without AutoGain is shown in below. Here, the exponential dimming scheme is used. TABLE 2. Sensor Gain Control REGISTER SETTING LM3537 30108350 FIGURE 3. ALS Zone transitions with AutoGain. The higher X-axis is for increasing light intensity, while the lower axis is for decreasing light intensity (Note 21) Note 21: There are some limits in Zone transitions when the autogain is enabled, for example a direct transition from the lowest Zone0 to the highest Zone4 (and vice versa) is not possible, because the device must go through the gain change process first. Countdown Timer The ALS engine includes a pre-defined countdown timer function. This function is targeted to applications where it's favorable to only increase through the zones; i.e., the LM3537 will stick to the highest zone reached, but won't allow transitions to lower Zones until the countdown has completed. At the end of every countdown, the timer sets the countdown timer flag (reg 40H), and after that, any Zone transition to a lower Zone re-loads the timer and starts the next timer period. See Table 3 and Figure 4 for details. TABLE 3. Countdown Timer Pre-defined Countdown Timer Function TIMER[1] TIMER[0] 0 0 Countdown timer is disabled 0 1 10s countdown timer is enabled (stick to the highest zone for 10s). 1 0 Always stick to the highest zone the ALS reached. 1 1 Always stick to the highest zone the ALS reached. www.national.com Timer Function 14 LM3537 30108315 FIGURE 4. Countdown timer principle. Solid line shows the ALS operation when the timer is disabled. Dashed line shows the operation when the 10s timer is enabled. Dotted line shows the operation when the device sticks to the highest zone. PWM Input A PWM (Pulse Width Modulation) pin is provided on the LM3537 to allow a display driver utilizing dynamic backlight control (DBC), to adjust the LED brightness based on the content. The PWM input can be turned on or off (Acknowledge or Ignore) and the polarity can be flipped (active high or active low) through the I2C interface. The current sinks of the LM3537 require approximately 15 µs to reach steady-state target current. This turn-on time sets the minimum usable PWM pulse width for DBC. The external PWM input is effective for group A LEDs only. Configurable Gain Transition Delay To optimize efficiency, the LM3537 has a user-selectable gain transition delay that allows the part to ignore short duration input voltage drops. By default, the LM3537 will not change gains if the input voltage dip is shorter than 3 to 6 milliseconds. There are four selectable gain transition delay ranges available on the LM3537. Hardware Enable (HWEN) The LM3537 has a hardware enable/reset pin (HWEN) that allows the device to be disabled by an external controller without requiring an I2C write command. Under normal operation, the HWEN pin should be held high (logic '1') to prevent an unwanted reset. When the HWEN is driven low (logic '0'), all internal control registers reset to the default states, and the part becomes disabled. Please see the Electrical Characteristics section of the datasheet for required voltage thresholds. LED Forward Voltage Monitoring The LM3537 has the ability to switch gains (1x or 3/2x) based on the forward voltage of the LED load. This ability to switch gains maximizes efficiency for a given load. Forward voltage monitoring occurs on all diode pins. At higher input voltages, the LM3537 will operate in pass mode, allowing the VOUT voltage to track the input voltage. As the input voltage drops, the voltage on the Dx pins will also drop (VDX = VVOUT – VLEDx). Once any of the active Dx pins reaches a voltage approximately equal to 150 mV, the charge pump will switch to the gain of 3/2. This switch-over ensures that the current through the LEDs never becomes pinched off due to a lack of headroom across the current sinks. Once a gain transition occurs, the LM3537 will remain in the gain of 3/2 until an I2C write to the part occurs. At that time, the LM3537 will re-evaluate the LED conditions and select the appropriate gain. Only active Dx pins will be monitored. Low Dropout Voltage Regulators The four low dropout voltage regulators are designed to operate with small-size ceramic input and output capacitors. They can operate with power rail voltages down to 1.8V. The LDOs 2, 3 and 4 offer a typical dropout voltage of 100 mV at 150 mA output current. The single, higher-current LDO 1 offers a typical dropout voltage of 220 mV at 300mA output current. The LDOs are enabled by the EN_LDO1, EN_LDO2, EN_LDO3 and EN_LDO4 bits (see Table 5 for details). summarizes the supported output voltages. At startup, the LDOs are off but are preset to 1.8V (for LDO2 and LDO3) and 2.8V (for LDO1 and LDO4). 15 www.national.com LM3537 TABLE 4. Regulator Voltage Options LDOX_VOUT[4] LDOX_VOUT[3] LDOX_VOUT[2] LDOX_VOUT[1] LDOX_VOUT[0] Output Voltage (typ.) 1 1 1 1 1 3.30V 1 1 1 1 0 3.20V 1 1 1 0 1 3.10V 1 1 1 0 0 3.00V 1 1 0 1 1 2.95V 1 1 0 1 0 2.90V 1 1 0 0 1 2.85V 1 1 0 0 0 2.80V 1 0 1 1 1 2.75V 1 0 1 1 0 2.70V 1 0 1 0 1 2.65V 1 0 1 0 0 2.60V 1 0 0 1 1 2.55V 1 0 0 1 0 2.50V 1 0 0 0 1 2.40V 1 0 0 0 0 2.20V 0 1 1 1 1 2.00V 0 1 1 1 0 1.90V 0 1 1 0 1 1.85V 0 1 1 0 0 1.80V 0 1 0 1 1 1.75V 0 1 0 1 0 1.70V 0 1 0 0 1 1.65V 0 1 0 0 0 1.60V 0 0 1 1 1 1.55V 0 0 1 1 0 1.50V 0 0 1 0 1 1.45V 0 0 1 0 0 1.40V 0 0 0 1 1 1.35V 0 0 0 1 0 1.30V 0 0 0 0 1 1.25V 0 0 0 0 0 1.20V www.national.com 16 should be equal to VIN_A, and at least 0.3V above the output voltage of the regulators. 30108314 FIGURE 5. LDO Block Diagram. VIN_B supplies internal circuitry. VIN_C, the power input voltage, is regulated to the fixed output voltage. and STOP conditions. The I2C bus is considered busy after a START condition and free after a STOP condition. During data transmission, the I2C master can generate repeated START conditions. A START and a repeated START conditions are equivalent function-wise. The data on SDA must be stable during the HIGH period of the clock signal (SCL). In other words, the state of SDA can only be changed when SCL is LOW. I2C-Compatible Interface STOP AND START CONDITIONS The LM3537 is controlled via an I2C-compatible interface. START and STOP ) conditions classify the beginning and the end of the I2C session. A START condition is defined as SDA transitioning from HIGH to LOW while SCL is HIGH. A STOP condition is defined as SDA transitioning from LOW to HIGH while SCL is HIGH. The I2C master always generates START 30108356 FIGURE 6. Start and Stop Sequences 17 www.national.com LM3537 The power input voltage applied between VIN_C and GND should be at least 0.3V above the output voltage of the regulators. The bias input voltage applied between VIN_B and GND LM3537 WRITE and R/W = 1 indicates a READ. The second byte following the chip address selects the register address to which the data will be written. The third byte contains the data for the selected register. I2C-COMPATIBLE CHIP ADDRESS The chip address for the LM3537 is 0111000 (38h). After the START condition, the I2C master sends the 7-bit chip address followed by a read or write bit (R/W). R/W= 0 indicates a 30108357 FIGURE 7. Chip Address pulse. The LM3537 pulls down SDA during the 9th clock pulse, signifying an acknowledge. An acknowledge is generated after each byte has been received. Figure 8 is an example of a write sequence to the DIODE ENABLE register of the LM3537. TRANSFERRING DATA Every byte on the SDA line must be eight bits long, with the most significant bit (MSB) transferred first. Each byte of data must be followed by an acknowledge bit (ACK). The acknowledge related clock pulse (9th clock pulse) is generated by the master. The master releases SDA (HIGH) during the 9th clock 30108358 FIGURE 8. Write Sequence to the LM3537 www.national.com 18 LM3537 Internal Registers of LM3537 The LM3537 is controlled by a set of registers through the two-wire serial interface port. Table 5 below lists device registers and their addresses together with a short description. TABLE 5. Control Register Map Hex Addr. 00 10 Register Name Bit(s) Read/ Write Default Value After Reset Bit Mnemonic and Description MASTER ENABLE [2] R/W xxxxx0xx group_A_en Master enable for all the LEDs, which are assigned to group A. '1' = LEDs ON '0' = LEDs OFF. [1] R/W xxxxxx0x group_B_en Master enable for all the LEDs, which are assigned to group B. '1' = LEDs ON '0' = LEDs OFF. [0] W xxxxxxx0 softw_rst Writing = '1' to this register bit resets all the registers to factory defaults. After writing, this bit is forced back to '0' automatically. [7] R/W 0xxxxxxx enD8 ON/OFF Control for D8 output [6] R/W x0xxxxxx enD7 ON/OFF Control for D7 output [5] R/W xx0xxxxx enD6 ON/OFF Control for D6 output [4] R/W xxx0xxxx enD5 ON/OFF Control for D5 output [3] R/W xxxx0xxx enD4 ON/OFF Control for D4 output [2] R/W xxxxx0xx enD3 ON/OFF Control for D3 output [1] R/W xxxxxx0x enD2 ON/OFF Control for D2 output [0] R/W xxxxxxx0 enD1 ON/OFF Control for D1 output DIODE ENABLE 19 www.national.com LM3537 Hex Addr. 20 30 40 Register Name Bit(s) Read/ Write Default Value After Reset Bit Mnemonic and Description CONFIGURATION [7] R/W 0xxxxxxx D7_int Enables the Interrupt Pin. 1 = interrupt output enabled. 0 = interrupt output disabled, LED driver operation. Reading the 0x40 register clears the interrupt. [6] R/W x0xxxxxx lin Selects between linear and exponential dimming curve. Effective for Group A only. 1 = linear dimming curve. 0 = exponential dimming curve. [5] R/W xx1xxxxx D8_A Assign D8 diode to Group A Writing a '1' assigns D8 to BankA (default) and a '0' assigns D8 to Group B. [4] R/W xxx1xxxx D7_A Assign D7 diode to Group A Writing a '1' assigns D7 to BankA (default) and a '0' assigns D7 to Group B. [3] R/W xxxx1xxx D6_A Assign D6 diode to Group A Writing a '1' assigns D6 to BankA (default) and a '0' assigns D6 to Group B. [2] R/W xxxxx1xx D5_A Assign D5 diode toGroup A . Writing a '1' assigns D5 to BankA (default) and a '0' assigns D5 to Group B. [1] R/W xxxxxx0x pwm_p PWM input polarity. Writing a '0' = active high (default) and a '1' = active low. [0] R/W xxxxxxx0 pwm_en PWM input enable. Writing a '1' = Enable, and a '0' = Ignore (default). [7:6] R/W 00xxxxxx gt Charge pump gain transition filter. The value stored in this register determines the filter time used to make a gain transition in the event of an input line VIN_A step. Filter Times (typ.) = ‘00’ = 3-6ms, ‘01’ = 0.8-1.5ms, ‘10’ = 20µs, '11' = 1µs, [5:3] R/W xx000xxx rd Diode current ramp down step time: ‘000’ = 6µs, ‘001’ = 0.77ms, ‘010’ = 1.5ms, ‘011’ = 3ms, ‘100’ = 6ms, ‘101’ = 12ms, ‘110’ = 25ms, ‘111’ = 50ms [2:0] R/W xxxxx000 ru Diode current ramp up step time : ‘000’ = 6µs, ‘001’ = 0.77ms, ‘010’ = 1.5ms, ‘011’ = 3ms, ‘100’ = 6ms, ‘101’ = 12ms, ‘110’ = 25ms, ‘111’ = 50ms [7:6] R 00xxxxxx rev Stores the silicon revision value. LM3537 = '00' [5] R xx0xxxxx als_gain Gain_status indicator: '1' = high gain, '0' = low gain. [4] R xxx0xxxx timerflag At the end of every countdown, the timer sets the timerflag ='1'. The flag bit is cleared once the 0x40 register has been read. [3] R xxxx0xxx zoneflag ALS transition flag. '1' = Transition has occurred. '0' = No transition. The flag bit is cleared once the 0x40 register has been read. [2:0] R xxxxx000 zone ALS Zone information: '000’ = Zone0, ‘001’ = Zone1, ‘010’ = Zone2, ‘011’ = Zone3, ‘100’ = Zone4. Other combinations not used. OPTIONS ALS ZONE READBACK www.national.com 20 50 51 Register Name ALS CONTROL ALS RESISTOR Bit(s) Read/ Write Default Value After Reset Bit Mnemonic and Description [7:5] R/W 000xxxxx ave Sets averaging time for the ALS sampling. Need two to three averaging periods to make transition decision.‘000’ = 25ms, ‘001’ = 50ms, ‘010’ = 100ms, ‘011’ = 200ms, ‘100’ = 400ms, ‘101’ = 800ms, ‘110’ = 1.6s, ‘111’ = 3.2s. [4:3] R/W xxx00xxx timer Pre-defined countdown timer function. '00' = countdown timer is disabled '01' = 10s countdown timer is enabled (stick to the highest zone for 10s) '10' = Always stick to the highest zone the ALS reached '11' = Always stick to the highest zone the ALS reached. At the end of every countdown, the timer sets the countdown timerflag (reg 40H), and after that, a Zone transition to a lower Zone re-loads the timer and starts the next timer period. [2] R/W xxxxx0xx als_en Enables ALS monitoring. Writing a '1' enables the ALS monitoring circuitry and a '0' disables it. This feature can be enabled without having the current sinks or charge pump active. The ALS value is updated in register 0x40 ALS ZONE READBACK. [1] R/W xxxxxx0x als_en_a Enable ALS on Group A. Writing a '1' enables ALS control of diode current and a '0' (default) forces the Group A current to the value stored in the Group A brightness register. The als_en bit must be set to a '1' for the ALS block to control the Group A brightness. [0] R/W xxxxxxx0 als_en_b Enable ALS on Group B. Writing a '1' enables ALS control of diode current and a '0' (default) forces the Group B current to the value stored in the Group B brightness register. The als_en bit must be set to a '1' for the ALS block to control the Group B brightness. The ALS function for Group B is different than Group A in that the ALS will only enable and disable the Group B diodes depending on the ALS zone chosen by the user. Group A utilizes the 5 different zone brightness registers (Addresses 0x70 to 0x74). [4:0] R/W xxx00010 r_als Sets the internal ALS resistor value. See Table 1for details. 21 www.national.com LM3537 Hex Addr. LM3537 Hex Addr. 52 Register Name ALS CONFIG Bit(s) Read/ Write Default Value After Reset Bit Mnemonic and Description [7] R/W 0xxxxxxx autogain_en '1' = Enables autogain for the external ambient light sensor. '0' = disables autogain and GPO's are controlled by the gpo1 and gpo2 -bits. See Table 2 for details. [6] R/W x0xxxxxx sbias_en '1' = External sensor power output enabled. '0' = External sensor power output disbaled. Note: '1' -> GPOs will behave as push-pull CMOS outputs referenced to voltage on SBIAS. '0 '-> GPOs will act as open-drain outputs (default). [5] R/W xx0xxxxx sbias_volt Sensor bias output voltage selection. '1' = 3.0V output voltage. '0' = 2.4V output voltage. [3] R/W xxxx0xxx cp_en Writing = '1' to this register bit enables the Charge-Pump block. Forces the LM3537 to operate in the gain of 1.5x. This mode DOES NOT require the Dx current sinks to be enabled for operation. [2] R/W xxxxx0xx pass_en Writing = '1' to this register bit forces the LM3537 to operate in the gain of 1x (pass-mode). This mode DOES NOT require the Dx current sinks to be enabled for operation. Note: 1.5x gain (cp_en bit) has a higher priority. [1] R/W xxxxxx0x gpo1 '0' = GPO1 pin state is low. '1' = GPO1 pin state is high. Effective only when the autogain is disabled. (Note 19) [0] R/W xxxxxxx0 gpo2 '0' = GPO2 pin state is low. '1' = GPO2 pin state is high. Effective only when the autogain is disabled. (Note 19) 60 ALS ZONE BOUNDARY#0 [7:0] R/W 00110011 zb0 Sets Zone0 to Zone1 transition trip point 61 ALS ZONE BOUNDARY#1 [7:0] R/W 01100110 zb1 Sets Zone1 to Zone2 transition trip point 62 ALS ZONE BOUNDARY#2 [7:0] R/W 10011001 zb2 Sets Zone2 to Zone3 transition trip point 63 ALS ZONE BOUNDARY#3 [7:0] R/W 11001100 zb3 Sets Zone3 to Zone4 transition trip point 64 ALS LOW to HIGH [7:0] TP R/W 00001011 LtoH Sets the trip point for low gain to high gain transition. Effective only when autogain = '1'. 65 ALS ZONE BOUNDARY Z3 to Z2 [7:0] R/W 00010000 zb3to2 Zone3 to Zone2 transition trip point when the autogain is enabled. 70 ALS BRIGHTNESS [6:0] ZONE#0 R/W x0111100 z0b Sets the Zone Brightness code for Zone0. 71 ALS BRIGHTNESS [6:0] ZONE#1 R/W x1001101 z1b Sets the Zone Brightness code for Zone1. 72 ALS BRIGHTNESS [6:0] ZONE#2 R/W x1011001 z2b Sets the Zone Brightness code for Zone2. 73 ALS BRIGHTNESS [6:0] ZONE#3 R/W x1100110 z3b Sets the Zone Brightness code for Zone3. www.national.com 22 Register Name Bit(s) Read/ Write Default Value After Reset LM3537 Hex Addr. Bit Mnemonic and Description 74 ALS BRIGHTNESS [6:0] ZONE#4 R/W x1110010 z4b Sets the Zone Brightness code for Zone4. A0 GROUP A BRIGHTNESS [6:0] R/W x0000000 dxa Sets Brightness for Group A. 128 steps, 1111111=Fullscale. B0 GROUP B BRIGHTNESS [5:3] R/W xx000xxx alsZT Sets the Brightness Zone boundary used to enable and disable Group B diodes based upon ambient lighting conditions. [2:0] R/W xxxxx000 dxb Sets Brightness for Group B. 8 steps, 111 = Fullscale. [3] R/W xxxx0xxx en_ldo4 '1' = Regulator 4 enabled. '0' = Regulator 4 disbaled. [2] R/W xxxxx0xx en_ldo3 '1' = Regulator 3 enabled. '0' = Regulator 3 disbaled. [1] R/W xxxxxx0x en_ldo2 '1' = Regulator 2 enabled. '0' = Regulator 2 disbaled. [0] R/W xxxxxxx0 en_ldo1 '1' = Regulator 1 enabled. '0' = Regulator 1 disbaled. C0 LDO ENABLE C1 LDO1 VOUT [4:0] R/W xxx11000 ldo1_vout Regulator 1 output voltage programming. See Table 4 for voltage options. C2 LDO2 VOUT [4:0] R/W xxx01100 ldo2_vout Regulator 2 output voltage programming. C3 LDO3 VOUT [4:0] R/W xxx01100 ldo3_vout Regulator 3 output voltage programming. C4 LDO4 VOUT [4:0] R/W xxx11000 ldo4_vout Regulator 4 output voltage programming. 23 www.national.com LM3537 dimming curve current can be approximated by the following equation (where N = the decimal value stored in the Group A Brightness register): Current Control Registers A0 GROUP A BRIGHTNESS This is the LED driver current control register for Group A. The register is effective when the ALS isn't used. The resolution is 7 bits, so in linear dimming mode the step size from zero up to full brightness is fixed (25.0mA/127) = 197 µA. Exponential dimming scheme provides a more fine-grained level of control over low level LED currents. Group A exponential 30108304 Current vs. code is shown below. 30108351 FIGURE 9. LED current (typ.) vs. register code, exponential dimming curve B0 GROUP B BRIGHTNESS Bits [2:0] set the GroupB Brightness Levels, as shown in below: TABLE 6. Group B Brightness Levels dxb[2] dxb[1] dxb[0] GroupB LED Current (typ.) 1 1 1 25.0 mA 1 1 0 17.5 mA 1 0 1 15.0 mA 1 0 0 12.5 mA 0 1 0 10.0 mA 0 1 0 7.5 mA 0 0 1 5.0 mA 0 0 0 2.5 mA www.national.com 24 LED CONFIGURATIONS The LM3537 has a total of 8 current sinks capable of sinking 180mA of total diode current. These 8 current sinks are configured to operate in one or two independently controlled lighting regions. GroupA has eight dedicated current sinks, while GroupB has 0 by default. However, drivers D5 to D8 can be assigned to either GroupA or GroupB one-by-one through a setting in the configuration register. With this added flexibility, the LM3537 is capable of supporting applications requiring from 4 to 7 LEDs for main display lighting, while still providing additional current sink(s) that can be used for a wide variety of lighting functions. CAPACITOR SELECTION The LM3537 circuit requires 11 external capacitors for proper operation. Surface-mount multi-layer ceramic capacitors are recommended. These capacitors are small, inexpensive and have very low equivalent series resistance (ESR <20 mΩ typ.). Tantalum capacitors, OS-CON capacitors, and aluminum electrolytic capacitors are not recommended for use with the LM3537 due to their high ESR, as compared to ceramic capacitors. For most applications, ceramic capacitors with X7R or X5R temperature characteristic are preferred for use with the LM3537. These capacitors have tight capacitance tolerance (as good as ±10%) and hold their value over temperature (X7R: ±15% over -55°C to 125°C; X5R: ±15% over -55°C to 85°C). Capacitors with Y5V or Z5U temperature characteristic are generally not recommended for use with the LM3537. Capacitors with these temperature characteristics typically have wide capacitance tolerance (+80%, -20%) and vary significantly over temperature (Y5V: +22%, -82% over -30°C to +85°C range; Z5U: +22%, -56% over +10°C to +85°C range). Under some conditions, a nominal 1µF Y5V or Z5U capacitor could have a capacitance of only 0.1µF. Such detrimental deviation is likely to cause Y5V and Z5U capacitors to fail to meet the minimum capacitance requirements of the LM3537. Table 7 below lists recommended external capacitors from some leading ceramic capacitor manufacturers. It is strongly recommended that the LM3537 circuit be thoroughly evaluated early in the design-in process with the mass-production capacitors of choice. This will help ensure that any variability in capacitance does not negatively impact circuit performance. PARALLEL CONNECTED AND UNUSED OUTPUTS Connecting the outputs in parallel does not affect internal operation of the LM3537 and has no impact on the Electrical Characteristics and limits previously presented. The available diode output current, maximum diode voltage, and all other specifications provided in the Electrical Characteristics table apply to this parallel output configuration, just as they do to the standard LED application circuit. All Dx current sinks utilize LED forward voltage sensing circuitry to optimize the charge-pump gain for maximum efficiency. If some of the drivers are not going to be used, make sure that the enable bits in the DIODE ENABLE register are set to '0' to ensure optimal efficiency. THERMAL PROTECTION Internal thermal protection circuitry disables the LM3537 when the junction temperature exceeds 160°C (typ.). This feature protects the device from being damaged by high die temperatures that might otherwise result from excessive power dissipation. The device will recover and operate normally when the junction temperature falls below 155°C (typ.). It is TABLE 7. Suggested Capacitors Model Type Vendor Voltage Rating Package Size 1 µF for COUT , CLDO1, CLDO2, CLDO3, CLDO4, CSEN, C1, C2 and CIN_A (Note 22) C1005X5R1A105K Ceramic X5R TDK 10V 0402 LMK105BJ105KV-F Ceramic X5R Taiyo Yuden 10V 0402 GRM155R61A105K Ceramic X5R Murata 10V 0402 GRM155R61A104K Ceramic X5R Murata 10V 0402 LMK105BJ104KV-F Ceramic X5R Taiyo Yuden 10V 0402 C1005X5R1A104K Ceramic X5R TDK 10V 0402 JMK105BJ225MV-F Ceramic X5R Taiyo Yuden 6.3V 0402 GRM155R60J225ME15D Ceramic X5R Murata 6.3V 0402 0.1 µF for CIN_B (Note 22) 2.2 µF for CIN_C Note 22: The recommended voltage rating for these capacitors is 10V to account for DC bias capacitance losses. 25 www.national.com LM3537 important that the board layout provide good thermal conduction to keep the junction temperature within the specified operating ratings. Application Information LM3537 Physical Dimensions inches (millimeters) unless otherwise noted The dimension for X1, X2 and X3 are as given: — X1 = 2,015mm ±0.030 mm — X2 = 2,517mm ±0.030 mm — X3 = 0.600 mm ±0.075 mm TMD30: 30-Bump micro SMD www.national.com 26 LM3537 Notes 27 www.national.com LM3537 8-Channel WLED Driver with Four Integrated LDOs Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: www.national.com Products Design Support Amplifiers www.national.com/amplifiers WEBENCH® Tools www.national.com/webench Audio www.national.com/audio App Notes www.national.com/appnotes Clock and Timing www.national.com/timing Reference Designs www.national.com/refdesigns Data Converters www.national.com/adc Samples www.national.com/samples Interface www.national.com/interface Eval Boards www.national.com/evalboards LVDS www.national.com/lvds Packaging www.national.com/packaging Power Management www.national.com/power Green Compliance www.national.com/quality/green Switching Regulators www.national.com/switchers Distributors www.national.com/contacts LDOs www.national.com/ldo Quality and Reliability www.national.com/quality LED Lighting www.national.com/led Feedback/Support www.national.com/feedback Voltage References www.national.com/vref Design Made Easy www.national.com/easy www.national.com/powerwise Applications & Markets www.national.com/solutions Mil/Aero www.national.com/milaero PowerWise® Solutions Serial Digital Interface (SDI) www.national.com/sdi Temperature Sensors www.national.com/tempsensors SolarMagic™ www.national.com/solarmagic PLL/VCO www.national.com/wireless www.national.com/training PowerWise® Design University THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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