LM3435 Compact Sequential Mode RGB LED Driver with I2C Control Interface General Description Key Specifications The LM3435, a Synchronously Rectified non-isolated Flyback Converter, features all required functions to implement a highly efficient and cost effective RGB LED driver. Different from conventional Flyback converter, LEDs connect across the VOUT pin and the VIN pin through internal passing elements at corresponding LED pins. Thus, voltage across LEDs can be higher than, equal to or lower than the input supply voltage. ● Support up to 2A LED current ● Typical ±3% LED current accuracy ● Integrated N-Channel main and P-Channel synchronous Load current to LEDs is up to 2A with voltage across LEDs ranging from 2.0V to 4.5V. Integrated N-Channel main MOSFET, P-Channel synchronous MOSFET and three N-Channel current regulating pass switches allow low component count, thus reducing complexity and minimize board size. The LM3435 is designed to work exceptionally well with ceramic output capacitors with low output ripple voltage. Loop compensation is not required resulting in a fast load transient response. Non-overlapping RGB LEDs are driven sequentially through individual control. Output voltage hence can be optimized for different forward voltage of LEDs during the nonoverlapping period. I2C interface eases the programming of the individual RGB LED current up to 1,024 levels per channel. The LM3435 is available in the thermally enhanced LLP-40 package. ● ● ● ● ● MOSFETs 3 Integrated N-Channel current regulating pass switches LED Currents programmable via I2C bus independently Input voltage range 2.7V - 5.5V Thermal shutdown Thermally enhanced LLP-40 package Features ● Sequential RGB driving mode ● Low component count and small solution size ● Stable with ceramic and other low ESR capacitors, no loop ● ● ● ● ● compensation required Fast transient response Programmable converter switching frequency up to 1 MHz MCU interface ready with I2C bus Peak current limit protection for the switcher LED fault detection and reporting via I2C bus Applications ● Li-ion batteries / USB Powered RGB LED driver ● Pico / Pocket RGB LED Projector PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. 301625 SNVS724B Copyright © 1999-2012, Texas Instruments Incorporated LM3435 Typical Application Circuit 30162501 2 Copyright © 1999-2012, Texas Instruments Incorporated LM3435 Connection Diagram 30162502 Top View 40-pin Leadless Leadframe Package (LLP) 5.0 x 5.0 x 0.8mm, 0.4mm pitch NS Package Number SQF40A Ordering Information Order Number Spec. Package Type NSC Package Drawing Supplied As LM3435SQ NOPB LLP-40 SQF40A 1000 Units, Tape and Reel LM3435SQX NOPB LLP-40 SQF40A 4500 Units, Tape and Reel Copyright © 1999-2012, Texas Instruments Incorporated 3 LM3435 Pin Descriptions 4 Pin Name Type Description Application Information 1, 2, 38, 39, 40 PGND Ground Power Ground Ground for power devices, connect to GND. 3 CG Output GREEN LED capacitor Connect a capacitor to Ground for GREEN LED. Minimum 1nF. 4 CB Output BLUE LED capacitor Connect a capacitor to Ground for BLUE LED. Minimum 1nF. 5 CR Output RED LED capacitor Connect a capacitor to Ground for RED LED. Minimum 1nF. 6 IREFG Output Current Reference for GREEN LED Connect a resistor to Ground for GREEN LED current reference generation. 7 IREFB Output Current Reference for BLUE LED Connect a resistor to Ground for BLUE LED current reference generation. 8 IREFR Output Current Reference for RED LED Connect a resistor to Ground for RED LED current reference generation. 9 GND Ground Ground 10, 29 SGND Ground I2C Ground Ground for I2C control, connect to GND. VDD for I2C control. 11 SVDD Power I2C VDD 12 SDATA Input / Output DATA bus Data bus for I2C control. 13 SCLK Input CLOCK bus Clock bus for I2C control. 14, 15, 16, 17, 37 VIN Power Input supply voltage Supply pin to the device. Nominal input range is 2.7V to 5.5V. 18 GCTRL Input GREEN LED control On/Off control signal for GREEN LED. Internally pull-low. 19 BCTRL Input BLUE LED control On/Off control signal for BLUE LED. Internally pull-low. 20 RCTRL Input RED LED control On/Off control signal for RED LED. Internally pull-low. 21, 22 RLED Output RED LED cathode Connect RED LED cathode to this pin. 23, 24 BLED Output BLUE LED cathode Connect BLUE LED cathode to this pin. 25, 26 GLED Output GREEN LED cathode Connect GREED LED cathode to this pin. 27 FAULT Output Fault indicator Pull-up when LED open or short is being detected. 28 EN Input Enable pin Internally pull-up. Connect to a voltage lower than 0.2 x VIN to disable the device. 30, 31, 32 VOUT Input / Output Output voltage Connect anodes of LEDs to this pin. 33 RT Input ON-time control An external resistor connected from VOUT to this pin sets the main MOSFET on-time, hence determine the switching frequency. 34, 35, 36 SW Output Switch node Internally connected to the drain of the main N-channel MOSFET and the P-channel synchronous MOSFET. Connect to the output inductor. EP EP Ground Exposed Pad Thermal connection pad, connect to the GND pin. Copyright © 1999-2012, Texas Instruments Incorporated LM3435 Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and specifications. VIN to GND VOUT, RT to VIN RLED, GLED, BLED to VIN SW to GND SW to GND (Transient) -0.3V to 6.0V -0.3V to 5.5V -0.3V to 5.5V -0.3V to 11.5V -2V to 13V (<100 ns) -0.3V to 6.0V All other inputs to GND ESD Rating (Note 2) Human Body Model Storage Temperature Junction Temperature (TJ) Operating Ratings ±1.5 kV -65°C to +150°C -40°C to +125°C (Note 1) Supply Voltage Range (VIN) Junction Temp. Range (TJ) 2.7V to 5.5V -40°C to +125°C 28°C/W Thermal Resistance (θJB) (Note 3) Electrical Characteristics Specification with standard type are for TA = TJ = +25°C only; limits in boldface type apply over the full Operating Junction Temperature (TJ) range. Minimum and Maximum are guaranteed through test, design or statistical correlation. Typical values represent the most likely parametric norm at TJ = +25°C, and are provided for reference purposes only. Unless otherwise stated the following conditions apply: VIN = 5V and VOUT – VIN = 3V. Symbol Parameter Conditions IIN IIN operating current IIN-SD IIN Shutdown current Min Typ Max Units No switching 5 10 mA VEN = 0V 8 30 µA 1 µA Supply Characteristics I2C ISVDD SVDD standby supply current VSVDD = 5V, VINUVLO VIN under-voltage lock-out VIN decreasing VINUVLO_hys VIN under-voltage lock-out hysteresis VIN increasing EN Pin input threshold VEN rising Bus idle V 2.5 0.2 V Enable Input VEN V 0.8 x VIN VEN falling IEN Enable Pull-up Current 0.2 x VIN VEN = 0V 5 V µA Logic Inputs (RCTRL, GCTRL and BCTRL) VCTRL CTRL pins input threshold VCTRL rising (VIN = 2.7V to 5.5V) V 1.35 VCTRL falling (VIN = 2.7V to 5.5V) 0.63 Switching Characteristics RDS-M-ON Main MOSFET RDS(ON) VGS(MAIN) =VIN = 5.0V ISW(sink) = 100mA 0.04 0.1 Ω RDS-S-ON Syn. MOSFET RDS(ON) VGS(SYN) = VOUT - 5.0V ISW(source) = 100mA 0.06 0.2 Ω 6 8.5 A Current Limit ICL Peak current limit through main MOSFET threshold ON/OFF Timer tON ON timer pulse width tON-MIN ON timer minimum pulse width Copyright © 1999-2012, Texas Instruments Incorporated RRT = 499 kΩ 750 ns 80 ns 5 LM3435 Symbol Parameter tOFF OFF timer minimum pulse width Conditions Min Typ Max 155 Units ns RGB Driver Characteristics (RLED, BLED and GLED) RDS(RED) Red LED Switch RDS VOUT - VIN = 3.3V ILED = 1.5A I2C code = 3FFh 0.1 0.2 Ω RDS(BLU) Blue LED Switch RDS VOUT - VIN = 3.3V ILED = 1.5A I2C code = 3FFh 0.1 0.2 Ω RDS(GRN) Green LED Switch RDS VOUT - VIN = 3.3V ILED = 1.5A I2C code = 3FFh 0.1 0.2 Ω ILEDMAX Max. LED current (Note 4) VIN = 4.5V to 5.5V, I1.5A,3FFh Current accuracy (3FFh) VIN = 2.7V to 5.5V 1.455 1.425 I1.5A,1FFh Current (1FFh) I1.5A,001h Current (001h) RIREF = 16.5 kΩ, VOUT – VIN = 2.4V (RLED), 3.3V (GLED/BLED) VIN = 2.7V to 5.5V, IOH = -100µA VIN – 0.1 V VIN = 2.7V to 5.5V, IOH = -5mA VIN – 0.5 V 2 A 0°C ≤ TA ≤ 50°C 1.5 1.545 A 1.575 A 0.8 A 1.2 mA FAULT Output Characteristics VOH VOL Output high voltage Output low voltage VIN = 2.7V to 5.5V, IOL = 100µA 0.1 V VIN = 2.7V to 5.5V, IOL = 5mA 0.5 V Thermal Shutdown TSD Thermal shutdown temperature TJ rising 163 °C TSD-HYS Thermal shutdown temperature hysteresis TJ falling 20 °C I2C Logic Interface Electrical Characteristics (1.7 V < SVDD < VIN ) Logic Inputs SCL, SDA VIL Input Low Level VIH Input High Level IL Logic Input Current fSCL Clock Frequency 0.2 x SVD D 0.8 x SVDD V V -1 1 µA 400 kHz Logic Output SDA VOL Output Low Level ISDA = 3mA IL Output Leakage Current VSDA = 2.8V 0.3 0.5 V 2 µA Note 1: Absolute Maximum Ratings are limits which damage to the device may occur. Operating ratings are conditions under which operation of the device is intended to be functional. For guaranteed specifications and test conditions, see the electrical characteristics. Note 2: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. Note 3: θJB is junction-to-board thermal characteristic parameter. For packages with exposed pad, θJB is significantly dependent on PC boards. So, only when the PC board under end-user environments is similar to the 2L JEDEC board, the corresponding θJB can be used to predict the junction temperature. θJB value is obtained by NS Thermal Calculator© for reference only. Note 4: Maximum LED current measured at VIN = 4.5V to 5.5V with heat sink on top of LM3435 with no air flow at 0°C ≤ TA ≤ 50°C. Operating conditions differ from the above is not guaranteed. 6 Copyright © 1999-2012, Texas Instruments Incorporated LM3435 Typical Performance Characteristics All curves taken at VIN = 5V with configuration in typical application for driving one red (OSRAM LRW5AP-KZMX), one green (OSRAM LTW5AP-LZMY) and one blue (OSRAM LBW5AP-JYKX) LEDs with IOUT per channel = 1.5A under TA = 25°C, unless otherwise specified. IIN-SD vs VIN IIN (no switching) vs VIN 12 6.0 125°C 5.5 25°C 8 125°C 5.0 IIN (mA) IIN-SD (μA) 10 6 -40°C 4 25°C 4.5 -40°C 4.0 2 3.5 0 3.0 2 3 4 VIN (V) 5 6 2 3 4 VIN (V) 5 6 30162505 30162506 ISVDD vs VIN RDS-M-ON vs VIN 25 70 60 125°C RDS-M-ON (mΩ) ISVDD (nA) 20 25°C 15 10 -40°C 5 125°C 50 25°C 40 30 -40°C 0 20 2 3 4 VSVDD (V) 5 6 2 3 4 VIN (V) 5 30162504 30162503 RDS-S-ON vs VIN RIREFx vs ILEDx 90 2.5 80 125°C 70 2.0 25°C ILEDx(A) RDS-S-ON (mΩ) 6 60 50 -40°C 40 1.5 1.0 0.5 30 0.0 2 3 4 VIN (V) 5 6 30162507 Copyright © 1999-2012, Texas Instruments Incorporated 5 15 25 35 RIREFx (kΩ) 45 55 30162531 7 LM3435 ILED(RED) vs VIN RDS(RED) vs VIN 160 1.54 RDS(RED) (mΩ) ILED(RED) (A) 140 125°C 1.52 25°C 1.50 -40°C 125°C 120 25°C 100 80 -40°C 1.48 60 1.46 40 2 3 4 VIN (V) 5 6 2 3 4 VIN (V) 5 30162508 30162509 ILED(GRN) vs VIN RDS(GRN) vs VIN 160 1.54 140 -40°C RDS(GRN) (mΩ) 125°C 1.52 ILED(GRN) (A) 6 1.50 25°C 1.48 125°C 120 25°C 100 80 -40°C 60 1.46 40 2 3 4 VIN (V) 5 6 2 3 4 VIN (V) 5 30162510 6 30162511 ILED(BLU) vs VIN RDS(BLU) vs VIN 160 1.54 140 125°C 1.50 RDS(BLU) (mΩ) ILED(BLU) (A) 1.52 -40°C 25°C 125°C 120 25°C 100 80 -40°C 1.48 60 1.46 40 2 3 4 VIN (V) 5 6 2 30162512 8 3 4 VIN (V) 5 6 30162513 Copyright © 1999-2012, Texas Instruments Incorporated LM3435 RED Efficiency vs VIN @ TA = 25°C GREEN Efficiency vs VIN @ TA = 25°C 100 GREEN EFFICIENCY, ηGRN(%) RED EFFICIENCY, ηRED(%) 100 90 80 70 60 50 90 80 70 60 50 2 3 4 VIN (V) 5 6 2 3 4 VIN (V) 30162528 BLUE Efficiency vs VIN @ TA = 25°C 5 6 30162529 Power Up Transient BLUE EFFICIENCY, ηBLU(%) 100 90 80 70 60 50 2 3 4 VIN (V) 5 6 30162530 RGB Sequential Mode Operation 30162524 10ms/DIV Color Transition Delay 30162525 1ms/DIV Copyright © 1999-2012, Texas Instruments Incorporated 30162526 100µs/DIV 9 LM3435 Simplified Functional Block Diagram 30162514 Operation Description INTRODUCTION The LM3435 is a sequential LED driver for portable and pico projectors. The device is integrated with three high current regulators, low side MOSFETs and a synchronous flyback DC-DC converter. Only single LED can be enabled at any given time. The DC-DC converter quickly adjusts the output voltage to an optimal level based on each LED’s forward voltage. This minimizes the power dissipation at the current regulators and maximizes the system efficiency. The I2C compatible synchronous serial interface provides access to the programmable functions and registers of the device. I2C protocol uses a two-wire interface for bi-directional communications between the devices connected to the bus. The two interface lines are the Serial Data Line (SDA), and the Serial Clock Line (SCL). These lines should be connected to a positive supply, via a pull-up resistor and remain HIGH even when the bus is idle. Every device on the bus is assigned an unique address and acts as either a Master or a Slave depending on whether it generates or receives the serial clock (SCL). SYNCHRONOUS FLYBACK CONVERTER The LM3435 integrates a synchronous flyback DC-DC converter to power the three-channel current regulator. The LEDs are connected across VOUT of the flyback converter and VIN through an internal power MOSFET connecting to corresponding LED channel. The maximum current to LED is 2A and the maximum voltage across VOUT and VIN is limited at around 4.7V. The LM3435 integrates the main N-channel MOSFET, the synchronous P-channel MOSFET of the flyback converter and three N-channel MOSFETs as internal passing elements connecting to LED channels in order to minimize the solution components count and PCB space. The flyback converter of LM3435 employs a proprietary Projected On-Time (POT) control scheme to determine the on-time of the main N-channel MOSFET with respect to the input and output voltages together with an external switching frequency setting resistor connected to RT pin, RRT. POT control use information of the current passing through RRT from VOUT, voltage information of VOUT and VIN to find an appropriate on-time for the circuit operations. During the on-time period, the inductor connecting to the flyback converter is charged up and the output capacitor is discharged to supply power to the LED. A cycle-by-cycle current limit of typical 6A is imposed on the main N-channel MOSFET for protection. After the on-time period, the main N-channel MOSFET is turned off and the synchronous P-channel MOSFET is turned on in order to discharge the inductor. The off state will last until VOUT is dropped below a reference voltage. Such reference voltage is derived from the required LED current to be regulated at a particular LED channel. The flyback converter under POT control can maintain a fairly constant switching frequency that depends mainly on value of the resistor connected across VOUT and RT pins, RRT. The relationship between the flyback converter switching frequency, FSW and RRT is approximated by the following relationship: 10 Copyright © 1999-2012, Texas Instruments Incorporated LM3435 RRT in Ω and FSW in kHz In addition, POT control requires no external compensation and achieves fast transient response of the output voltage changes that perfectly matches the requirements of a sequential RGB LED driver. The POT flyback converter only operates at Continuous Conduction Mode. Dead-time between main MOSFET and synchronous MOSFET switching is adaptively controlled by a minimum non-overlap timer to prevent current shoot through. Initial VOUT will be regulated at around 3.2V to 3.5V above VIN before any control signals being turned on. Three small capacitors connected to CR, CG and CB pins are charged by an internal current source and act as soft-start capacitors of the flyback converter during start-up. Once initial voltage of VOUT is settled, the capacitors will be used as a memory element to store the VOUT information for each channel respectively. This information will be used for VOUT regulation of respective LED channel during channel switching. In between the channel switching, a small I2C programmable blank out time of 5 µs to 35 µs is inserted so that the LED current is available after the correct VOUT for the color is stabilized. This control scheme ensures the minimal voltage headroom for different color LED and hence best conversion efficiency can be achieved. HIGH CURRENT REGULATORS The LM3435 contains three internal current regulators powered by the output of the synchronous Flyback Converter, VOUT. Three low side power MOSFETs are included. These current regulators control the current supplied to the LED channels individually and maintain accurate current regulation by internal feedback and control mechanism. The regulation is achieved by a Gm-C circuit comparing the sensing voltage of the internal passing N-channel MOSFET and an internal LED current reference voltage generated from the external reference current setting resistor, RIREFx connect to IREFG, IREFB or IREFR pin, of the corresponding LED channel. The nominal maximum LED current is governed by the equation in below: RIREFx in Ω and ILEDx in Ampere The LED current setting can be in the range of 0.5A up to 2A maximum. The nominal maximum of the device is 1.5A and for applications need higher than 1.5A LED current, VIN and thermal constrains must be complied. The actual LED current can be adjusted on-the-fly by the internal ten bits register for individual channel. The content of these registers are user programmable via I2C bus connection. The user can control the LED output current on-the-fly during normal operation. The resolution is 1 out of 1024 part of the LED current setting. The user can program the registers in the range of 1(001H) to 1023(3FFH) for each channel independently, provided the converter is not entered the Discontinuous Conduction Mode. Whenever the converter operation entered the Discontinuous Conduction Mode, the regulation will be deteriorated. A value of “0” may cause false fault detection, so it must be avoided. SEQUENTIAL MODE RGB TIMING LM3435 is a sequential mode RGB driver dedicatedly designed for pico and portable projector applications. By using this device, the system only require one power driver stage for three color LEDs. With LM3435, only single LED can be enabled at any given time period and the DC-DC converter can quickly adjusts the output voltage to an optimized level by controlling the current flowing into the respective LED channel. This approach minimizes the power dissipation of the internal current regulator and effectively maximizes the system efficiency. Timing of the RGB LEDs depends solely on the RCTRL, GCTRL and BCTRL inputs. The Timing Chart in below shows a typical timing of two cycles of even RGB scan. In real applications, the RGB sequence is totally controlled by the system or the video processor. It’s not mandatory to follow the simple RGB sequence, but for any change instructed by the I2C control will only take place at the falling edge of the corresponding CTRL signal. 30162520 RGB Control Signals Timing Chart PRIORITIES OF LED CONTROL SIGNALS The LM3435 does not support color overlapping mode operation. At any instant, only one LED will be enabled even overlapping control signals applied to the control inputs. The decision logics of the device determine which LED channel should be enabled in case overlapping control signals are detected at the control inputs. The GREEN channel has the higher priority over BLUE channel and the RED channel has the lowest priority. However, if a low priority channel is already turned on before the high priority channel Copyright © 1999-2012, Texas Instruments Incorporated 11 LM3435 control signal comes in, the low priority channel will continue to take the control until the control signal ceased. The timing diagram in below illustrates some typical cases during operation. 30162521 Priorities of LED Control Signals LED OPEN FAULT REPORTING The fly-back converter tries to keep VOUT to the forward voltage required by the LED with the desired LED current output. However, if the LED channel is being opened no matter it is due to LED failure or no connection, the fly-back converter will limit the VOUT voltage at around 4.7V above VIN. Once such voltage is achieved, an open-fault-suspect signal will go high. If this open-faultsuspect signal is being detected at 3 consecutive falling edges of the opened channel control signal, “Fault” pin will be latched high and the corresponding channel open fault will be reported through I2C. The open fault report can be removed either by pulling EN pin low for less than 100ns (a true shutdown will be triggered if the negative pulse on EN is more than 100ns) or by writing a “0” to “bit 0” of the I2C register ”05h”. The “Fault” pin will be cleared and the I2C fault register will be reset. In order to reinstate the fault reporting feature, the system need to write a “1” to “bit 0” of the I2C register “05h”. LED SHORT FAULT REPORTING If the VOUT is prohibited to regulate at a potential higher than 1.5V above VIN at a LED channel, such LED is considered being shorted and a short-fault-suspect signal will go high. If this short-fault-suspect signal is being detected at 3 consecutive falling edges of the shorted channel control signal, “Fault” pin will be latched high and the corresponding channel short fault will be reported through I2C. The short fault report can be removed either by pulling EN pin low for less than 100ns (a true shutdown will be triggered if the negative pulse on EN is more than 100ns) or by writing a “0” to “bit 0” of the I2C register ”05h”. The “Fault” pin will be cleared and the I2C fault register will be reset. In order to reinstate the fault reporting feature, the system need to write a “1” to “bit 0” of the I2C register “05h”. Persistently short of LED can cause permanent damage to the device. Whenever the short fault is detected, the system should turn off the faulty channel immediately by pulling the corresponding PWM control pin to GND. THERMAL SHUTDOWN Internal thermal shutdown circuitry is included to protect the device in the event that the maximum junction temperature is exceeded. The threshold for thermal shutdown in LM3435 is around 160°C and it will be resumed to normal operation again once the temperature cools down to below around 140°C. I2C Compatible Interface INTERFACE BUS OVERVIEW The I2C compatible synchronous serial interface provides access to the programmable functions and registers on the device. This protocol uses a two-wire interface for bi-directional communications between the devices connected to the bus. The two interface lines are the Serial Data Line (SDA), and the Serial Clock Line (SCL). These lines should be connected to a positive supply, via a pull-up resistor and remain HIGH even when the bus is idle. Every device on the bus is assigned a unique address and acts as either a Master or a Slave depending on whether it generates or receives the serial clock (SCL). DATA TRANSACTIONS One data bit is transferred during each clock pulse. Data is sampled during the high state of the serial clock (SCL). Consequently, throughout the clock’s high period, the data should remain stable. Any changes on the SDA line during the high state of the SCL and in the middle of a transaction, aborts the current transaction. New data should be sent during the low SCL state. This protocol permits a single data line to transfer both command/control information and data using the synchronous serial clock. I2C DATA VALIDITY The data on SDA line must be stable during the HIGH period of the clock signal (SCL). In other words, state of the data line can only be changed when CLK is LOW. 12 Copyright © 1999-2012, Texas Instruments Incorporated LM3435 30162515 I2C Signals : Data Validity I2C START and STOP CONDITIONS START and STOP bits classify the beginning and the end of the I2C session. START condition is defined as SDA signal transitioning from HIGH to LOW while SCL line is HIGH. STOP condition is defined as the SDA transitioning from LOW to HIGH while SCL is HIGH. The I2C master always generates START and STOP bits. The I2C bus is considered to be busy after START condition and free after STOP condition. During data transmission, I2C master can generate repeated START conditions. First START and repeated START conditions are equivalent, function-wise. 30162516 I2C Start and Stop Conditions I2C ADDRESSES AND TRANSFERRING DATA Every byte put on the SDA line must be eight bits long, with the most significant bit (MSB) being transferred first. Each byte of data has to be followed by an acknowledge bit. The acknowledge bit related clock pulse is generated by the master. The transmitter releases the SDA line (HIGH) during the acknowledge clock pulse. The receiver must pull down the SDA line during the 9th clock pulse, signifying an acknowledgement. A receiver which has been addressed must generate an acknowledge bit after each byte has been received. After the START condition, the I2C master sends a chip address. This address is seven bits long followed by an eighth bit which is a data direction bit (R/W). The LM3435 address is 50h or 51H which is determined by the R/W bit. I2C address (7 bits) for LM3435 is 28H. For the eighth bit, a “0” indicates a WRITE and a “1” indicates a READ. The second byte selects the register to which the data will be written. The third byte contains data to write to the selected register. 30162517 I2C Chip Address Register changes take an effect at the SCL rising edge during the last ACK from slave. 30162532 Copyright © 1999-2012, Texas Instruments Incorporated 13 LM3435 w = write (SDA = “0”) r = read (SDA = “1”) ack = acknowledge (SDA pulled down by either master or slave) rs = repeated start id = 7-bit chip address, 50H (ADDR_SEL=0) or 51H (ADDR_SEL=1) for LM3435. I2C Write Cycle When a READ function is to be accomplished, a WRITE function must precede the READ function, as shown in the Read Cycle waveform. 30162533 I2C Read Cycle I2C TIMING PARAMETERS (VIN = 2.7V to 5.5V, SVDD = 1.7V to VIN) 30162534 I2C Timing Diagram Symbol Parameter Limit 1 Hold Time (repeated) START Condition 0.6 µs 2 Clock Low Time 1.3 µs 3 Clock High Time 600 ns 4 Setup Time for a Repeated START Condition 600 ns 5 Data Hold Time (Output direction) 300 ns 5 Data Hold Time (Input direction) 0 ns 6 Data Setup Time 100 7 Rise Time of SDA and SCL 20+0.1Cb 300 ns 8 Fall Time of SDA and SCL 15+0.1Cb 300 ns Min Units Max ns 9 Set-up Time for STOP condition 600 ns 10 Bus Free Time between a STOP and a START Condition 1.3 µs Cb Capacitive Load for Each Bus Line 10 200 pF Note: Data guaranteed by design. 14 Copyright © 1999-2012, Texas Instruments Incorporated LM3435 I2C REGISTER DETAILS The I2C bus interacts with the LM3435 to realize the features of LED current program inter-color delay time program and Fault reporting function. The operation of these functions requires the writing and reading of the internal registers of the LM3435. In below is the master register map of the device. Master Register Map ADDR REGISTER D7 D6 00h LEDLO 0 0 01h GLEDH GLED[9:2] 1111 1111 02h BLEDH BLED[9:2] 1111 1111 03h RLEDH RLED[9:2] 1111 1111 05h FLT_RPT 06h DELAY 07h FAULT 0 D5 0 0 RDLY[1:0] 1 GO GS D4 D3 RLED[1:0] 0 0 D1 BO 1 BS D0 GLED[1:0] 0 BDLY[1:0] 0 D2 BLED[1:0] 0 0 DEFAULT 0011 1111 FLT_RPT 0000 0001 GDLY[1:0] RO RS 1111 1111 0000 0000 LED Current Register Definitions The LED currents for each color can be accurately adjusted by 10 bits resolution (1024 steps) independently. By writing control bytes into the LM3435 LED current Registers, the LED currents can be precisely set to any value in the range of IMIN to IREF. In below is the LED Current Low register bit definition: ADDR REGISTER D7 D6 00h LEDLO 0 0 Bits 7:6 5:4 D5 D4 D3 RLED[1:0] D2 D1 BLED[1:0] D0 GLED[1:0] DEFAULT 0011 1111 Description Reserved. These bits always read zeros. The least significant bits of the 10-bit RLED register. This register is for programming the level of current for the Red LED. The least significant bits of the 10-bit BLED register. This register is for programming the level of current for the Blue LED. The least significant bits of the 10-bit GLED register. This register is for programming the level of current for the Green LED. 3:2 1:0 In below is the LED Current High register bit definition: ADDR REGISTER 01h GLEDH D7 D6 D5 D4 D3 D2 D1 D0 DEFAULT GLED[9:2] 1111 1111 02h BLEDH BLED[9:2] 1111 1111 03h RLEDH RLED[9:2] 1111 1111 Bits 7:0 Description The most 8 significant bits of the 10-bit GLED, BLED and RLED registers respectively. These registers are for programming the level of current of the Green LED, Blue LED and Red LED independently. Fault Reporting Register Definition The fault reporting feature of the LM3435 can be selected by the system designer according to their application needs. To select or de-select this feature is realized by writing one bit into the FLT_RPT register. ADDR REGISTER D7 D6 D5 D4 D3 D2 D1 05h FLT_RPT 0 0 0 0 0 0 0 Bits 7:1 0 D0 DEFAULT FLT_RPT 0000 0001 Description Reserved. These bits always read zeros. This bit defines the mode of fault report feature. Writing a “ 1 “ into this bit enables the fault reporting feature, otherwise no Fault signal output at Pin 27. Color Transition Delay Register Definition The transition of one color into next color is not executed immediately. Certain delay is inserted in between to guarantee the LED rail voltage stabilized before turning the next LED on. This delay is user programmable by writing control bits into the DELAY register Copyright © 1999-2012, Texas Instruments Incorporated 15 LM3435 for each color individually. The power up default delay time is 35µs and this delay can be programmed from 5 µs to 35 µs maximum in step of 10 µs. ADDR REGISTER 06h DELAY Bits 7:6 5 4:3 2 1:0 D7 D6 RDLY[1:0] D5 1 D4 D3 BDLY[1:0] D2 1 D1 D0 GDLY[1:0] DEFAULT 1111 1111 Description These two bits are for programming the Red transition delay. Reserved. This bit always read “ 1“. These two bits are for programming the Blue transition delay. Reserved. This bit always read “ 1“. These two bits are for programming the Green transition delay. Fault Register Definition The LM3435 features LED fault detection capability. Whenever a LED fault is detected (open or short), the FAULT output (pin 27) will go high to indicate a LED fault is detected. The details of the fault can be investigated by reading the FAULT register. The FAULT register is read only. The fault status can be cleared by clearing and then re-enabling the FLT_RPT register or power up reset of the device. ADDR REGISTER D7 D6 D5 D4 D3 D2 D1 D0 DEFAULT 07h FAULT GO GS 0 BO BS 0 RO RS 0000 0000 Bits 7 6 5 4 3 2 1 0 16 Description GO – Green Open. This read only register bit indicates the presence of an OPEN fault of the GREEN LED. GS – Green Short. This read only register bit indicates the presence of an SHORT fault of the GREEN LED. Reserved. This bit always read “ 0 “. BO – Blue Open. This read only register bit indicates the presence of an OPEN fault of the BLUE LED. BS – Blue Short. This read only register bit indicates the presence of an SHORT fault of the BLUE LED. Reserved. This bit always read “ 0 “. RO – Red Open. This read only register bit indicates the presence of an OPEN fault of the RED LED. RS – Red Short. This read only register bit indicates the presence of an SHORT fault of the RED LED. Copyright © 1999-2012, Texas Instruments Incorporated LM3435 Design Procedures This section presents a design example of a typical pico projector application. By using LM3435, the system requires only single DC-DC converter to drive three color LEDs instead of using three DC-DC converters with conventional design. The suggested approach not only saves components cost, but also releases invaluable PCB space to the system and enhances system reliability. The handy projector is powered by a single lithium battery cell or a 5Vdc wall mount adaptor. The key specifications of the design are as in below: Supply voltage range, VIN = 2.7V to 5.5V Preset LED current per channel, ILED = 1.5A Minimum LED current per channel, ILED(MIN) = 600mA Maximum LED forward voltage drop, VLED = 3.5V @ 1.5A Flyback converter switching Frequency, FSW = ~500kHz SETTING THE FLYBACK CONVERTER SWITCHING FREQUENCY, FSW The LM3435 employs a proprietary Projected On-Time (POT) control scheme, the switching frequency, FSW of the converter is simply set by an external resistor, RRT across RT pin of LM3435 and VOUT of the converter. The flyback converter under POT control can maintain a fairly constant switching frequency that depends mainly on the value of RRT. The relationship between the flyback converter switching frequency, FSW and RRT is approximated by the following relationship: RRT in Ω and FSW in kHz In order to set the flyback converter switching frequency, FSW to 500kHz, the value of RRT can be calculated as in below: A standard resistor value of 499kΩ can be used in place and the period of switching, TSW is about 2µs. SETTING THE NOMINAL LED CURRENT The nominal LED current of the LEDs are set by resistors connected to IREFR, IREFG and IREFB pins. The current for each channel can be set individually and it is not mandatory that all channel currents are the same. Just for simplicity, we assume all channels are set to 1.5A in this example. The LED current and the value of RIREFR, RIREFG and RIREFB is governed by the following equation. RIREFx in Ω and ILEDx in Ampere The resistance value for the current setting resistors is calculated as in below: In order to achieve the required LED current accuracy, high quality resistors with tolerance not higher than +/-1% are recommended. INDUCTOR SELECTION Selecting the correct inductor is one of the major task in application design of a LED driver system. The most critical inductor parameters are inductance, current rating, DC resistance and size. As an rule of thumb, for same physical size inductor, higher the inductance means higher the DC resistance, consequently more power loss with the inductor and lower the DC-DC conversion efficiency. With LM3435, the inductor governs the inductor ripple current and limits the minimum LED current that can be supported. However for the POT control in LM3435, a minimum inductor ripple current of about 300mApk-pk is required for proper operation. The relationship of the ON-Duty, D and the input/output voltages can be derived by applying the Volt-Second Balance equation across the inductor. The waveforms of the inductor current and voltage are shown in below. Copyright © 1999-2012, Texas Instruments Incorporated 17 LM3435 30162547 Inductor Switching Waveforms Applying the Volt-Second Balance equation with the inductor voltage waveform, Referring to the inductor current waveform, the average inductor current, IL(AVG) can be derived as in below: The minimum LED current, ILED(MIN) happens when the inductor current just entered the Critical Conduction Mode operation, i.e. ILripple(MIN)=0. Applying this condition to the last equation: The relationship of the LED current, ILED and the average inductor current, IL(AVG) is shown in below: By combining last two equations, the minimum LED current, ILED(MIN) can be calculated as in below: 18 Copyright © 1999-2012, Texas Instruments Incorporated LM3435 By rearranging the terms, the inductance, L required for any specific minimum LED current, ILED(MIN) can be found with the equation in below: From the equation, it can be noted that for lower minimum LED current, the inductance required will be higher. As mentioned in before, higher the inductance means higher DC resistance in same size inductor. Additionally, the POT control in LM3435, a minimum inductor ripple current is required to maintain proper operation. The restrictions limit the lowest current can be programed by I2C control. In this example, the ILED(MIN)=600mA and the highest ripple will happen when the input voltage is maximum, i.e. VIN=5.5V. The ON Duty, D with average LED forward voltage of 3.5V is calculated in below: The required inductance for this case is: A standard inductance value of 2.2µH is suggested and the minimum LED current, ILED(MIN) is about 595mA @ VIN=5.5V. Other than the inductance, the worst case inductor current, IL(MAX) must be calculated so that an inductor with appropriate saturation current level can be specified. The maximum inductor current, IL(MAX) can be calculated with the equation in below: The highest inductor current occurs when the input voltage is minimum, i.e. VIN=2.7V. The ON Duty, D for this condition can be calculated as in below: The maximum inductor current, IL(MAX) is calculated in below: The calculated maximum inductor current is 4.1A, however the inductance can drop as temperature rise. In order to accommodate all possible variations, an inductor with saturation current specification not less than 5A is suggested. INPUT CAPACITORS SELECTION Input capacitors are required for all supply input pins to ensure that VIN does not drop excessively during high current switching transients. LM3435 have supply input pins located in different sides of the device. Individual capacitors are needed for the supply input pins locally. All capacitors must be placed as close as possible to the supply input pins and have low impedance return ground path to the device grounds and back to supply ground. Capacitors CIN1 and CIN2 are the main input capacitors and additionally, CIN3 is added to de-couple high frequency interference. The capacitance for CIN1 and CIN2 is recommended in the range of 22μF to 47µF and CIN3 is 0.1µF. Compact applications normally have stringent space limitations, small size surface mount capacitors are usually preferred. Low ESR Multi-Layer Ceramic Capacitors (MLCC) are the best choices. MLCC capacitors with X5R and X7R dielectrics are recommended for its low leakage and low capacitance variation against temperature and frequency. Copyright © 1999-2012, Texas Instruments Incorporated 19 LM3435 OUTPUT CAPACITORS SELECTION Two output capacitors are required with LM3435 configuration, one for VOUT to Ground, COUT2 and one for de-coupling the LED current ripple, COUT1. The LM3435 operates at frequencies high enough to allow the use of MLCC capacitors without compromising transient response. Low ESR characteristic of the MLCC allow higher inductor ripple without significant increase of the output ripple. The capacitance recommended for COUT1 is 10µF and COUT2 is 22µF. Again, high quality MLCC capacitors with X5R and X7R dielectrics are recommended. For certain conditions, acoustic problem may be encountered with using MLCC, Low Acoustic Noise Type capacitors are strongly recommended for all output capacitors. Alternatively, the acoustic noise can also be lowered by using smaller size capacitors in parallel to achieve the required capacitance. OTHER CAPACITORS SELECTION Three small startup capacitors connected to CG, CB and CR pins are needed for proper operation. The suggested capacitance for CCR, CCG and CCB is 1nF. Also three capacitors connected to GLED, BLED and RLED pins to protect the device from high transient stress due to the inductance of the connecting wires for the LEDs. The suggested capacitance for CG, CB and CR is 0.47µH. MLCC capacitors with X5R and X7R dielectrics are recommended. All capacitors must be placed as close as possible to the device pins. DIODE SELECTION A schottky barrier diode is added across the SW and VOUT pins, equivalently, its across the internal P-channel MOSFET of the synchronous converter, that can help to improve the conversion efficiency by few percents. A very low forward voltage and 1A rated forward current part is suggested in the schematic diagram. The key selection criteria are the forward voltage and the rated forward current. PCB LAYOUT CONSIDERATIONS The performance of any switching converters depends as much upon the layout of the PCB as the component selection. PCB layout considerations are therefore critical for optimum performance. The layout must be as neat and compact as possible, and all external components must be as close as possible to their associated pins. The PGND connection to CIN and VOUT connection to COUT should be as short and direct as possible with thick traces. The inductor should connect close to the SW pin with short and thick trace to reduce the potential electro-magnetic interference. It is expected that the internal power elements of the LM3435 will produce certain amount of heat during normal operation, good use of the PC board's ground plane can help considerably to dissipate heat. The exposed pad on the bottom of the IC package can be soldered to a copper pad with thermal vias that can help to conduct the heat to the bottom side ground plane. The bottom side ground plane should be as large as possible. 20 Copyright © 1999-2012, Texas Instruments Incorporated LM3435 Schematic of the Example Application for Pico Projector 30162535 Copyright © 1999-2012, Texas Instruments Incorporated 21 LM3435 Physical Dimensions inches (millimeters) unless otherwise noted LLP-40 Pin Package (SQF) For Ordering, Refer to Ordering Information Table NS Package Number SQF40A 22 Copyright © 1999-2012, Texas Instruments Incorporated LM3435 Notes Copyright © 1999-2012, Texas Instruments Incorporated 23 Notes Copyright © 1999-2012, Texas Instruments Incorporated IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46C and to discontinue any product or service per JESD48B. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment. TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms and conditions of sale of semiconductor products. Testing and other quality control techniques are used to the extent TI deems necessary to support this warranty. Except where mandated by applicable law, testing of all parameters of each component is not necessarily performed. TI assumes no liability for applications assistance or the design of Buyers’ products. Buyers are responsible for their products and applications using TI components. To minimize the risks associated with Buyers’ products and applications, Buyers should provide adequate design and operating safeguards. TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other intellectual property right relating to any combination, machine, or process in which TI components or services are used. Information published by TI regarding third-party products or services does not constitute a license to use such products or services or a warranty or endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual property of the third party, or a license from TI under the patents or other intellectual property of TI. Reproduction of significant portions of TI information in TI data books or data sheets is permissible only if reproduction is without alteration and is accompanied by all associated warranties, conditions, limitations, and notices. TI is not responsible or liable for such altered documentation. Information of third parties may be subject to additional restrictions. Resale of TI components or services with statements different from or beyond the parameters stated by TI for that component or service voids all express and any implied warranties for the associated TI component or service and is an unfair and deceptive business practice. TI is not responsible or liable for any such statements. Buyer acknowledges and agrees that it is solely responsible for compliance with all legal, regulatory and safety-related requirements concerning its products, and any use of TI components in its applications, notwithstanding any applications-related information or support that may be provided by TI. Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards which anticipate dangerous consequences of failures, monitor failures and their consequences, lessen the likelihood of failures that might cause harm and take appropriate remedial actions. Buyer will fully indemnify TI and its representatives against any damages arising out of the use of any TI components in safety-critical applications. In some cases, TI components may be promoted specifically to facilitate safety-related applications. With such components, TI’s goal is to help enable customers to design and create their own end-product solutions that meet applicable functional safety standards and requirements. Nonetheless, such components are subject to these terms. No TI components are authorized for use in FDA Class III (or similar life-critical medical equipment) unless authorized officers of the parties have executed a special agreement specifically governing such use. Only those TI components which TI has specifically designated as military grade or “enhanced plastic” are designed and intended for use in military/aerospace applications or environments. Buyer acknowledges and agrees that any military or aerospace use of TI components which have not been so designated is solely at the Buyer's risk, and that Buyer is solely responsible for compliance with all legal and regulatory requirements in connection with such use. TI has specifically designated certain components which meet ISO/TS16949 requirements, mainly for automotive use. Components which have not been so designated are neither designed nor intended for automotive use; and TI will not be responsible for any failure of such components to meet such requirements. Products Applications Audio www.ti.com/audio Automotive and Transportation www.ti.com/automotive Amplifiers amplifier.ti.com Communications and Telecom www.ti.com/communications Data Converters dataconverter.ti.com Computers and Peripherals www.ti.com/computers DLP® Products www.dlp.com Consumer Electronics www.ti.com/consumer-apps DSP dsp.ti.com Energy and Lighting www.ti.com/energy Clocks and Timers www.ti.com/clocks Industrial www.ti.com/industrial Interface interface.ti.com Medical www.ti.com/medical Logic logic.ti.com Security www.ti.com/security Power Mgmt power.ti.com Space, Avionics and Defense www.ti.com/space-avionics-defense Microcontrollers microcontroller.ti.com Video and Imaging www.ti.com/video RFID www.ti-rfid.com OMAP Mobile Processors www.ti.com/omap TI E2E Community e2e.ti.com Wireless Connectivity www.ti.com/wirelessconnectivity Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265 Copyright © 2012, Texas Instruments Incorporated