LP8550TLX-A/NOPB

Sample & Buy Product Folder Support & Community Tools & Software Technical Documents LP8550 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 LP8550 High-Efficiency LED Backlight Driver for Notebooks 1 Features 3 Description • The LP8550 is a white-LED driver with integrated boost converter. It has six adjustable current sinks which can be controlled by PWM input or with I2Ccompatible serial interface. The boost converter has adaptive output voltage control based on the LED driver voltages. This feature minimizes the power consumption by adjusting the voltage to lowest sufficient level in all conditions. High-Voltage DC/DC Boost Converter with Integrated FET with Four Switching Frequency Options: 156/312/625/1250 kHz 2.7-V to 22-V Input Voltage Range to Support 1x to 5x Cell Li-Ion Batteries Programmable PWM Resolution – 8 to 13 True Bits (Steady State) – Additional 1 to 3 Bits Using Dithering During Brightness Changes 2 I C and PWM Brightness Control Automatic PWM & Current Dimming for Improved Efficiency PWM output frequency and LED Current set through Resistors Optional Synchronization to Display VSYNC Signal Six LED Outputs with LED Fault (Short/Open) Detection Low Input Voltage, Overtemperature, Overcurrent Detection, and Shutdown Minimum Number of External Components 1 • • • • • • • • • 2 Applications • Notebook and Netbook LCD Display LED Backlight LED Lighting • LED outputs have 8-bit current resolution and up to 13-bit PWM resolution with additional 1- to 3-bit dithering to achieve smooth and precise brightness control. Proprietary Phase Shift PWM control is used for LED outputs to reduce peak current from the boost converter, thus making the boost capacitors smaller. The Phase Shifting scheme also eliminates audible noise. Automatic PWM dimming at lower brightness values and current dimming at higher brightness values can be used to improve the optical efficiency. Internal EEPROM is used for storing the configuration data. This makes it possible to have minimum external component count and make the solution very small. The LP8550 has safety features which make it possible to detect LED outputs with open or short fault — low input voltage and boost overcurrent conditions are monitored, and chip is turned off in case of these events. Thermal de-rating function prevents overheating of the device by reducing backlight brightness when set temperature has been reached. Device Information(1) PART NUMBER PACKAGE LP8550 DSBGA (25) BODY SIZE (MAX) 2.49 x 2.49 mm (1) For all available packages, see the orderable addendum at the end of the datasheet. Simplified Schematic L1 5.5V ± 22V CVLDO D1 CIN 15 éH 5V VSYNC signal 100 nF VDDIO VLDO FB VSYNC OUT1 FILTER 1 éF 120 k5 RISET OUT2 ISET RFSET LP8550 FSET OUT5 SCLK SDA OUT6 FAULT VIN = 12V 90 85 VIN = 9V 80 75 70 65 60 0 10 20 30 40 50 60 70 80 90 100 DUTY CYCLE (%) PWM EN Can be left floating if not used OUT3 OUT4 MCU 95 4.7 éF SW VIN 100 COUT 39 pF 10 éF 1 éF VDDIO reference voltage 10V ± 40V 210 mA ± 400 mA EFFICIENCY (%) VBATT LED Efficiency GNDs 1 An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications, intellectual property matters and other important disclaimers. PRODUCTION DATA. LP8550 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 www.ti.com Table of Contents 1 2 3 4 5 6 7 Features .................................................................. Applications ........................................................... Description ............................................................. Revision History..................................................... Device Default Values ........................................... Pin Configuration and Functions ......................... Specifications......................................................... 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10 7.11 7.12 1 1 1 2 3 4 5 Absolute Maximum Ratings ...................................... 5 Handling Ratings ...................................................... 5 Recommended Operating Conditions....................... 5 Thermal Information .................................................. 6 Electrical Characteristics.......................................... 6 Boost Converter Electrical Characteristics ............. 6 LED Driver Electrical Characteristics ....................... 7 PWM Interface Characteristics ................................ 7 Undervoltage Protection .......................................... 8 Logic Interface Characteristics............................... 8 I2C Serial Bus Timing Parameters (SDA, SCLK) .. 8 Typical Characteristics ............................................ 9 8 Detailed Description ............................................ 11 8.1 8.2 8.3 8.4 8.5 8.6 9 Overview ................................................................. Functional Block Diagram ....................................... Feature Description................................................. Device Functional Modes........................................ Programming .......................................................... Register Maps ......................................................... 11 12 12 21 22 26 Application and Implementation ........................ 36 9.1 Application Information............................................ 36 9.2 Typical Applications ............................................... 36 10 Power Supply Recommendations ..................... 40 11 Layout................................................................... 40 11.1 Layout Guidelines ................................................. 40 11.2 Layout Examples................................................... 41 12 Device and Documentation Support ................. 43 12.1 Trademarks ........................................................... 43 12.2 Electrostatic Discharge Caution ............................ 43 12.3 Glossary ................................................................ 43 13 Mechanical, Packaging, and Orderable Information ........................................................... 43 4 Revision History NOTE: Page numbers for previous revisions may differ from page numbers in the current version. Changes from Revision D (November 2013) to Revision E • Page Changed formatting to match new TI datasheet guidelines; added Device Information and Handling Ratings tables, Power Supply Recommendations, Layout, and Device and Documentation Support sections; moved some curves to Application Curves section, reformatted Detailed Description and Application and Implementation sections, adding additional content. ................................................................................................................................................................. 1 Changes from Revision C (May 2013) to Revision D Page • Added note re EEPROM ...................................................................................................................................................... 25 • Added note re: EEPROM ..................................................................................................................................................... 30 2 Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 LP8550 www.ti.com SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 5 Device Default Values ADDR EEPROM DEFAULT VALUE A0h 1010 0001 A1h 0110 0000 A2h 1001 1111 A3h 0011 1111 A4h 0000 1000 A5h 1000 1010 A6h 0110 0100 A7h 0010 1001 Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 3 LP8550 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 www.ti.com 6 Pin Configuration and Functions 25 DSBGA (YZR) Top View 25 DSBGA (YZR) Bottom View 1 2 3 4 5 5 A GND SW GND SW EN PWM FB FB B SW SW ISET FSET GND_S C VIN FILTER FAULT VDDIO D VLDO VSYNC SCLK E OUT6 OUT5 OUT4 4 3 2 1 PWM EN GND SW GND SW A GND_S FSET ISET SW SW B OUT3 OUT3 VDDIO FAULT FILTER VIN C SDA OUT2 OUT2 SDA SCLK VSYNC VLDO D GND_L OUT1 OUT1 GND_L OUT4 OUT5 OUT6 E Pin Functions PIN DESCRIPTION NAME A1 GND_SW G Boost switch ground A2 GND_SW G Boost switch ground A3 EN I Enable input pin A4 PWM A PWM dimming input. This pin must be connected to GND if not used. A5 FB A Boost feedback input B1 SW A Boost switch B2 SW A Boost switch B3 ISET A Set resistor for LED current. This pin can be left floating if not used. (1) 4 TYPE (1) NUMBER B4 FSET A PWM frequency set resistor. This pin can be left floating if not used. B5 GND_S G Signal ground C1 VIN P Input power supply up to 22 V. If 2.7 V ≤ VBATT < 5.5 V (Figure 31) then external 5-V rail must be used for VLDO and VIN. C2 FILTER A Low pass filter for PLL. This pin can be left floating if not used. C3 FAULT OD C4 VDDIO P Digital IO reference voltage (1.65 V to 5 V) for I2C interface. If brightness is controlled with PWM input pin then this pin can be connected to GND. C5 OUT3 A Current sink output D1 VLDO P LDO output voltage. External 5-V rail can be connected to this pin in low voltage application. D2 VSYNC I VSYNC input. This pin must be connected to GND if not used. D3 SCLK I Serial clock. This pin must be connected to GND if not used. D4 SDA I/O Serial data. This pin must be connected to GND if not used. D5 OUT2 A Current sink output E1 OUT6 A Current sink output E2 OUT5 A Current sink output Fault indication output. If not used, can be left floating. E3 OUT4 A Current sink output E4 GND_L G LED ground E5 OUT1 A Current sink output A: Analog Pin, G: Ground Pin, P: Power Pin, I: Input Pin, I/O: Input/Output Pin, O: Output Pin, OD: Open Drain Pin Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 LP8550 www.ti.com SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 7 Specifications 7.1 Absolute Maximum Ratings over operating free-air temperature range (unless otherwise noted) (1) (2) MIN MAX VIN –0.3 24 VLDO –0.3 6 Voltage on logic pins (VSYNC, PWM, EN, SCLK, SDA) –0.3 6 –0.3 VVDDIO + 0.3 Voltage on logic pin (FAULT) Voltage on analog pins (FILTER, VDDIO, ISET, FSET) –0.3 6 V (OUT1...OUT6, SW, FB) –0.3 44 Continuous power dissipation (3) V Internally Limited Junction temperature (TJ-MAX) 125 Maximum lead temperature (soldering) (1) UNIT See °C (4) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability. If Military/Aerospace specified devices are required, please contact the TI Sales Office/Distributors for availability and specifications. Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ = 150°C (typ.) and disengages at TJ = 130°C (typ.). For detailed soldering specifications and information, please refer to Application Report AN-1112 DSBGA Wafer Level Chip Scale Package (SNVA009). (2) (3) (4) 7.2 Handling Ratings Tstg Storage temperature range Human body model (HBM), per ANSI/ESDA/JEDEC JS-001, all pins V(ESD) Electrostatic discharge (1) Charged device model (CDM), per JEDEC spec. JESD22-C101, all pins (2) Machine model (1) (2) MIN MAX UNIT –65 150 °C kV -2 2 –200 200 V –1 1 kV JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process. JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process. 7.3 Recommended Operating Conditions over operating free-air temperature range (unless otherwise noted) (1) (2) MIN VIN (Figure 27) VIN + VLDO (Figure 31) Input voltage range VDDIO V(OUT1...OUT6, SW, FB) TJ TA (1) (2) (3) (3) NOM MAX 5.5 22 4.5 5.5 1.65 5 0 40 Junction temperature –30 125 Ambient temperature –30 85 UNIT V °C Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability. All voltages are with respect to the potential at the GND pins. 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 = 125°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 (RθJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (RθJA × PD-MAX). Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 5 LP8550 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 www.ti.com 7.4 Thermal Information DSBGA THERMAL METRIC (1) RθJA (1) (2) Junction-to-ambient thermal resistance UNIT 25 PINS (2) 40 - 73 °C/W For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953. Junction-to-ambient thermal resistance is highly application and board-layout dependent. In applications where high maximum power dissipation exists, special care must be paid to thermal dissipation issues in board design. Electrical Characteristics (1) (2) 7.5 Limits are for TA = 25°C (unless otherwise specified); VIN = 12 V, VDDIO = 2.8 V, CVLDO = 1 μF, L1 = 15 μH, CIN = 10 μF, COUT = 10 μF. RISET = 16 kΩ, unless otherwise specified. (3) PARAMETER Standby supply current Normal mode supply current fOSC Internal oscillator frequency accuracy VLDO Internal LDO voltage ILDO Internal LDO external loading (3) (4) Internal LDO disabled EN=L and PWM=L MAX 1 (4) UNIT μA 3 10-MHz PLL Clock 3.7 20-MHz PLL Clock 4.7 40-MHz PLL Clock 6.7 –4% –7% (4) 4.5 mA 4% 7% (4) (4) 5 5.5 (4) V 5 mA Boost Converter Electrical Characteristics PARAMETER RDSON Switch ON resistance VMAX Boost maximum output voltage ILOAD Maximum continuous load current VOUT/VIN TEST CONDITIONS ISW = 0.5 A TYP Ω V 300 3 V ≤ VBATT, VOUT = 25 V 180 fSW Switching frequency VOV Overvoltage protection voltage tPULSE Switch pulse minimum width no load tSTARTUP Start-up time Note SW pin current limit BOOST_IMAX = 0 BOOST_IMAX = 1 UNIT 40 450 BOOST_FREQ BOOST_FREQ BOOST_FREQ BOOST_FREQ MAX 0.12 6 V ≤ VBATT, VOUT = 35 V fSW = 1.25 MHz IMAX MIN 9 V ≤ VBATT, VOUT = 35 V Conversion ratio 6 TYP All voltages are with respect to the potential at the GND pins. Minimum (MIN) and Maximum (MAX) limits are specified by design, test, or statistical analysis. Typical numbers represent the most likely norm. Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics. Limits apply over the full operating ambient temperature range (–30°C ≤ TA ≤ 85°C). 7.6 (1) MIN LDO enabled, boost enabled, no current going through LED outputs 5-MHz PLL Clock IIN (1) (2) TEST CONDITIONS mA 10 = 00 = 01 = 10 = 11 156 312 625 1250 kHz VBOOST + 1.6V V 50 ns 6 ms (1) 1.4 2.5 A Start-up time is measured from the moment boost is activated until the VOUT crosses 90% of its target value. Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 LP8550 www.ti.com 7.7 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 LED Driver Electrical Characteristics TYP MAX Leakage current PARAMETER Outputs OUT1 to OUT6, VOUT = 40 V 0.1 1 IMAX Maximum source current OUT1 to OUT6 EN_I_RES = 0, CURRENT[7:0] = FFh 30 EN_I_RES = 1, CURRENT[7:0] = FFh 50 IOUT Output current accuracy (1) Output current set to 23 mA, EN_I_RES =1 IMATCH Matching (1) Output current set to 23 mA, EN_I_RES =1 ILEAKAGE PWMRES fLED (2) (3) (4) (5) PWM output resolution (3) LED switching frequency (3) Saturation voltage (4) VSAT (1) TEST CONDITIONS MIN –3% -4% (2) UNIT μA mA 3% 4% (2) 0.5% fLED = 5 kHz, fPLL = 5 MHz 10 fLED = 10 kHz, fPLL = 5 MHz 9 fLED = 20 kHz, fPLL = 5 MHz 8 fLED = 5 kHz, fPLL = 40 MHz 13 fLED = 10 kHz, fPLL = 40 MHz 12 fLED = 20 kHz, fPLL = 40 MHz 11 bits PWM_FREQ[4:0] = 00000b PLL clock 5 MHz 600 PWM_FREQ[4:0] = 11111b PLL clock 5 MHz 19.2k Output current set to 20 mA 105 220 (5) Output current set to 30 mA 160 290 (5) Hz mV Output Current Accuracy is the difference between the actual value of the output current and programmed value of this current. Matching is the maximum difference from the average. For the constant current sinks on the part (OUT1 to OUT6), the following are determined: the maximum output current (MAX), the minimum output current (MIN), and the average output current of all outputs (AVG). 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. The typical specification provided is the most likely norm of the matching figure for all parts. Note that some manufacturers have different definitions in use. Limits apply over the full operating ambient temperature range (–30°C ≤ TA ≤ 85°C). PWM output resolution and frequency depend on the PLL settings. Please see section PWM Frequency Setting for full description. Saturation voltage is defined as the voltage when the LED current has dropped 10% from the value measured at 1 V. Limits apply over the full operating ambient temperature range (–30°C ≤ TA ≤ 85°C). 7.8 PWM Interface Characteristics PARAMETER TEST CONDITIONS MIN TYP fPWM PWM frequency range tMIN_ON Minimum pulse ON time 0.1 1 tMIN_OFF Minimum pulse OFF time 1 tSTARTUP Turnon delay from standby to backlight on PWM input active, EN pin rise from low to high TSTBY Turn off delay PWMRES PWM input resolution MAX 25 UNIT kHz μs 6 ms PWM input low time for turn off, slope disabled 50 ms fIN fIN fIN fIN 10 11 12 13 bits < 9 kHz < 4.5 kHz < 2.2 kHz < 1.1 kHz Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 7 LP8550 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 7.9 www.ti.com Undervoltage Protection PARAMETER TEST CONDITIONS MIN UVLO[1:0] = 00 VUVLO 7.10 VIN UVLO threshold voltage TYP MAX UNIT Disabled UVLO[1:0] = 01, falling 2.55 2.70 2.94 UVLO[1:0] = 01, rising 2.62 2.76 3.00 UVLO[1:0] = 10, falling 5.11 5.40 5.68 UVLO[1:0] = 10, rising 5.38 5.70 5.98 UVLO[1:0] = 11, falling 7.75 8.10 8.45 UVLO[1:0] = 11, rising 8.36 8.73 9.20 V Logic Interface Characteristics PARAMETER TEST CONDITIONS MIN TYP MAX UNIT 0.4 (1) V LOGIC INPUT EN VIL Input low level VIH Input high level II 1.2 (1) Input current -1 (1) (1) V 1 (1) μA LOGIC INPUT VSYNC VIL 0.4 (1) V 1 (1) μA 55000 Hz 0.4 (1) V 1 (1) μA 0.2xVDDIO (1) V Input low level VIH Input high level 2.2 II Input current –1 (1) fVSYNC Frequency range 58 V 60 LOGIC INPUT PWM VIL Input low level (1) VIH Input high level 2.2 II Input current –1 (1) V LOGIC INPUTS SCL, SDA VIL Input low level VIH Input high level II 0.8xVDDIO (1) Input current –1 V (1) 1 (1) μA LOGIC OUTPUTS SDA, FAULT VOL Output low level IL (1) Output leakage current IOUT = 3 mA (pull-up current) 0.5 (1) 0.3 VOUT = 2.8 V –1 (1) 1 V (1) μA Limits apply over the full operating ambient temperature range (–30°C ≤ TA ≤ 85°C). 7.11 I2C Serial Bus Timing Parameters (SDA, SCLK) (1) MIN fCLK Clock frequency 1 Hold time (repeated) START condition 2 3 MAX UNIT 400 kHz 0.6 μs Clock low time 1.3 μs Clock high time 600 ns 4 Setup time for a repeated START condition 600 ns 5 Data hold time 50 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 9 Setup time for STOP condition 600 ns 10 Bus free time between a STOP and a START condition 1.3 μs (1) 8 ns Specified by design. Not production tested. VDDIO = 1.65 V to 5.5 V. Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 LP8550 www.ti.com SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 I2C Serial Bus Timing Parameters (SDA, SCLK) (1) (continued) MIN MAX UNIT 10 200 ns Capacitive load parameter for each bus line Load of 1 pF corresponds to 1 ns. Cb Figure 1. I2C Timing Diagram 7.12 Typical Characteristics Unless otherwise specified: VBATT = 12 V, CVLDO = 1 μF, L1 = 33 μH, CIN = 10 μF, COUT = 10 μF 100 100 95 VIN = 12V 90 85 EFFICIENCY (%) EFFICIENCY (%) 95 VIN = 9V 80 75 85 VIN = 12V 80 75 70 70 65 65 60 VIN = 9V 90 60 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 DUTY CYCLE (%) DUTY CYCLE (%) fLED = 9.6 kHz fLED = 9.6 kHz Figure 2. LED Drive Efficiency L1 = 15 µH Figure 3. LED Drive Efficiency 100 1,200 98 1,000 VBOOST = 35V 94 92 IBATT (mA) EFFICIENCY (%) 96 VBOOST = 40V 90 88 800 VBOOST = 40V VBOOST = 35V 600 400 86 VBOOST = 30V 84 200 82 VBOOST = 30V 80 LOAD = 150 mA 0 0 50 100 150 200 250 300 IOUT (mA) 6 8 10 12 14 16 18 20 VBATT (V) Figure 4. Boost Converter Efficiency Figure 5. Battery Current Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 9 LP8550 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 www.ti.com Typical Characteristics (continued) Unless otherwise specified: VBATT = 12 V, CVLDO = 1 μF, L1 = 33 μH, CIN = 10 μF, COUT = 10 μF 50 ILED (mA) 40 CURRENT[7:0] = FFh 30 20 10 0 CURRENT[7:0] = 7Fh 0 10 20 30 40 50 60 70 80 90 100 RISET (k ) Figure 6. ILED vs. RISET Figure 7. Boost Line Transient Response 6 130 120 15 inch panel, 23 mA current PWM AND CURR 25% MODE 5 PWM AND CURR 50% MODE INPUT POWER (W) OPTICAL EFFICIENCY (Nits/W) 140 110 100 90 PWM 80 4 3 PWM 2 1 70 PWM AND CURRENT 50% MODE 15 inch panel, 23 mA current 60 PWM AND CURRENT 25% MODE 0 0 10 20 30 40 50 60 70 80 90 100 0 PWM INPUT (%) 100 200 Figure 8. Optical Efficiency With 15-inch Panel PWM AND CURR 50% MODE POWER SAVED (%) LUMINANCE (Nits) 500 35 30 300 PWM 200 100 25% MODE 25 20 15 50% MODE 10 5 0 PWM AND CURR 25% MODE 0 -5 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 PWM INPUT (%) PWM INPUT (%) Figure 10. Luminance vs. PWM Input 10 400 Figure 9. Input Power vs. Luminance 500 400 300 LUMINANCE (Nits) Figure 11. Power Saved with PWM & Current Mode Compared to PWM Mode Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 LP8550 www.ti.com SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 8 Detailed Description 8.1 Overview LP8550 is a high voltage LED driver for medium-sized LCD backlight applications. It includes high voltage boost converter. Boost voltage automatically sets to the correct level needed to drive the LED strings. This is done by monitoring LED output voltage drop in real time. Six LED outputs are driven either with constant current sinks with PWM control or by controlling both PWM and current. Constant current value is set with EEPROM bits and with RISET resistor. Brightness (PWM) is controlled either with I2C register or with PWM input. PWM frequencies are set with EEPROM bits and with RFSET resistor. Special Phase-Shift PWM mode can be used to reduce boost output current peak, thus reducing output ripple, capacitor size and audible noise. With LP8550 it is possible to synchronize the PWM output frequency to VSYNC signal received from video processor. Internal PLL ensures that the PWM output clock is always synchronized to the VSYNC signal. Special dithering mode makes it possible to increase output resolution during fading between two brightness values and by this making the transition look very smooth with virtually no stepping. Transition slope time can be adjusted with EEPROM bits. Safety features include LED fault detection with open and short detection. LED fault detection prevents system overheating in case of open in some of the LED strings. Chip internal temperature is constantly monitored and based on this LP8550 can reduce the brightness of the backlight to reduce thermal loading once certain trip point is reached. Threshold is programmable in EEPROM. If chip internal temperature reaches too high, the boost converter and LED outputs are completely turned off until the internal temperature has reached acceptable level. Boost converter is protected against too high load current and over-voltage. LP8550 notifies the system about the fault through I2C register and with FAULT pin. EEPROM programmable functions include: • PWM frequencies • Phase shift PWM mode • LED constant current • Boost output frequency • Temperature thresholds • Slope for brightness changes • Dithering options • PWM output resolution • Boost control bits External components RISET and RFSET can also be used for selecting the output current and PWM frequencies. Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 11 LP8550 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 www.ti.com 8.2 Functional Block Diagram VIN VLDO VIN SW LDO OSC TSD VSYNC TEMP SENSOR FB BOOST GND_SW OUT1 VSYNC FILTER PLL OUT2 OUT3 VDDIO PWM PWM DETECTOR OUT4 LED DRIVERS OUT5 OUT6 MCU SCLK SDA LOGIC 2 I C/ INTERFACE ISET RISET FSET GND_LED FAULT RFSET EN EEPROM GND 8.3 Feature Description 8.3.1 Clock Generation LP8550 has internal 5-MHz oscillator which is used for clocking the boost converter, state machine, PWM input duty cycle measurement, internal timings such as slope time for output brightness changes. Internal clock can be used for generating the PWM output frequency. In this case the 5-MHz clock can be multiplied with the internal PLL to achieve higher resolution. The higher the clock frequency for PWM generation block, the higher the resolution but the tradeoff is higher IQ of the part. Clock multiplication is set with EEPROM Bits. The PLL can also be used for generating the required PWM generation clock from the VSYNC signal. This makes sure that the LED output PWM is always synchronized to the VSYNC signal and there is no clock variation between LCD display video update and the LED backlight output frequency. Also HSYNC signal up to 55 kHz can be used. PLL has internal counter which has 13-bit control to achieve correct output clock frequency based on the VSYNC frequency. It can take a couple of seconds for the PLL to synchronize to 60-Hz VSYNC signal in start-up and before this correct PWM clock frequency is generated from internal oscillator. FILTER pin component selection affects the time it takes from the PLL to lock to VSYNC signal. Special logic is implemented for allowing steady clock frequency even if there are missing VSYNC pulses. In case pulses are randomly left out, the LP8550 can generate the pulses internally while keeping the same PWM output frequency. When VSYNC pulses are available again, the internal logic automatically switches to the external VSYNC clock without glitch. 12 Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 LP8550 www.ti.com SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 Feature Description (continued) PWM_FREQ[4:0] or External VSYNC 60 Hz EN_VSYNC VBOOST set resistor RFSET PSPWM 0/1 PLL 5 MHz...40 MHz Phase Detector 5MHz internal oscillator Filter VCO PWM generation LED Drivers 1-6 PLL[12:0] BOOST_FREQ N = 4, 8, 16, 32 Divider 1/N Counter 1/N State machine, PWM input, internal timings, Slope etc. Boost PWM_RESOLUTION[1:0] Figure 12. Principle Of The Clock Generation 8.3.2 Brightness Control Methods LP8550 controls the brightness of the backlight with PWM. PWM control is received either from PWM input pin or from I2C register bits. The PWM source selection is done with bits as follows: BRT_MODE[1] BRT_MODE[0] PWM SOURCE 0 0 PWM input pin duty cycle control. Default. 0 1 PWM input pin duty cycle control. 1 0 Brightness register 1 1 PWM direct control (PWM in = PWM out) 8.3.2.1 PWM Input Duty Cycle With PWM input pin duty cycle control the output PWM is controlled by PWM input duty cycle. PWM detector block measures the duty cycle in the PWM pin and uses this 13-bit value to generate the output PWM. Output PWM can have different frequency than input in this mode and also phase shift PWM mode can be used. Slope and dither are effective in this mode. PWM input resolution is defined by the input PWM clock frequency. 8.3.2.2 Brightness Register Control With brightness register control the output PWM is controlled with 8-bit resolution register bits. Phase shift scheme can be used with this and the output PWM frequency can be freely selected. Slope and dither are effective in this mode. 8.3.2.3 PWM Direct Control With PWM direct control the output PWM directly follows the input PWM. Due to the internal logic structure the input is anyway clocked with the 5 MHz clock or the PLL clock. PSPWM mode is not possible in this mode. Slope and dither are not effective in this mode. 8.3.2.4 PWM Calculation Data Flow Figure 13 shows a flow chart of the PWM calculation data flow. In PWM direct control mode most of the blocks are bypassed and this flow chart does not apply. Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 13 LP8550 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 HYSTERESIS 5 MHz [1:0] clock PWM input signal PWM detector BRT_MODE [1:0] 13-bit Temperature sensor Brightness register Brightness control www.ti.com PWM_FREQ[4:0] 13-bit Resolution selector SLOPE[3:0] 8...13-bit 12-bit I_SLOPE[1:0] 16-bit Sloper PWM & Current Control DITHER[1:0] 8...16-bit 16-bit Dither 13-bit EN_PWM_&_I_CTRL PWM_RESOLUTION [1:0] 0/1 ... LED Drive 1-6 PWM Counter MODE_25/50%_SEL 8-bit PWM comparator PLL clock 5...40 MHz Figure 13. PWM Calculation Data Flow 8.3.2.5 PWM Detector The PWM detector block measures the duty cycle of the input PWM signal. Resolution depends on the input signal frequency. Hysteresis selection sets the minimum allowable change to the input. If smaller change is detected, it is ignored. With hysteresis the constant changing between two brightness values is avoided if there is small jitter in the input signal. 8.3.2.6 Brightness Control Brightness control block gets 13-bit value from the PWM detector, 12-bit value from the temperature sensor and also 8-bit value from the brightness register. selects whether to use PWM input duty cycle value or the brightness register value as described earlier. Based on the temperature sensor value the duty cycle is reduced if the temperature has reached the temperature limit set to the EEPROM bits. 8.3.2.7 Resolution Selector Resolution selector takes the necessary MSB bits from the input data to match the output resolution. For example if 11-bit resolution is used for output, then 11 MSB bits are selected from the input. Dither bits are not taken into account for the output resolution. This is to make sure that in steady state condition, there is no dithering used for the output. 8.3.2.8 Sloper Sloper makes the smooth transition from one brightness value to another. Slope time can be adjusted from 0 to 500 ms with EEPROM bits. The sloper output is 16-bit value. 8.3.2.9 PWM & Current Control Automatic PWM & current control improves the optical efficiency of the LEDs by using PWM control with small brightness values and current control with bigger values. EEPROM bit selects whether the PWM & current control is used instead of PWM control or not. PWM to current dimming switch point can be set to 25% or 50% of the brightness range with EEPROM bit. Current slope can be adjusted by using the EEPROM bits. 8.3.2.10 Dither With dithering the output resolution can be “artificially” increased during sloping from one brightness value to another. This way the brightness change steps are not visible to eye. Dithering can be from 0 to 3 bits, and is selected with EEPROM bits. 8.3.2.11 PWM Comparator The PWM counter clocks the PWM comparator based on the duty cycle value received from Dither block. Output of the PWM comparator controls directly the LED drivers. If PSPWM mode is used, then the signal to each LED output is delayed certain amount. 14 Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 LP8550 www.ti.com SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 8.3.2.12 Current Setting Maximum current of the LED outputs is controlled with CURRENT[7:0] EEPROM register bits linearly from 0 to 30 mA. If = 1 the maximum LED output current can be scaled also with external resistor, RISET. RISET controls the LED current as shown in Equation 1: (1) Default value for CURRENT[7:0] = 7Fh (127d). Therefore, the output current can be calculated as shown in Equation 2: (2) For example, if a 16-kΩ RISET resistor is used, then the LED maximum current is 23 mA. Please note: formula is only approximation for the actual current. 8.3.2.13 PWM Frequency Setting PWM frequency is selected with PWM_FREQ[4:0] EEPROM register. If PLL clock frequency multiplication is used, the output PWM frequency is also affected. EEPROM bits select the PLL output frequency and hence the PWM frequency and resolution. Table 1 lists PWM frequencies with = 0. PWM resolution setting effects the PLL clock frequency (5 MHz to 40 MHz). Highlighted frequencies with boldface can be selected also with external resistor RFSET. To activate RFSET frequency selection the EEPROM bit must be 1. Table 1. Available PWM Frequencies and Resolutions PWM_RES[1:0] 00 01 10 11 PWM_FREQ[4:0] 5 MHz 10 MHz 20 MHz 40 MHz RESOLUTION (bits) 11111 19232 - - - 8 11110 16828 - - - 8 11101 14424 - - - 8 11100 12020 - - - 8 11011 9616 19232 - - 9 11010 7963 15927 - - 9 11001 6386 12771 - - 9 11000 4808 9616 19232 - 10 10111 4658 9316 18631 - 10 10110 4508 9015 18030 - 10 10101 4357 8715 17429 - 10 10100 4207 8414 16828 - 10 10011 4057 8114 16227 - 10 10010 3907 7813 15626 - 10 10001 3756 7513 15025 - 10 10000 3606 7212 14424 - 10 01111 3456 6912 13823 - 10 01110 3306 6611 13222 - 10 01101 3155 6311 12621 - 10 01100 3005 6010 12020 - 10 01011 2855 5710 11419 - 10 01010 2705 5409 10818 - 10 01001 2554 5109 10217 - 10 01000 2404 4808 9616 19232 11 00111 2179 4357 8715 17429 11 00110 1953 3907 7813 15626 11 Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 15 LP8550 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 www.ti.com Table 1. Available PWM Frequencies and Resolutions (continued) PWM_RES[1:0] 00 01 10 11 PWM_FREQ[4:0] 5 MHz 10 MHz 20 MHz 40 MHz RESOLUTION (bits) 00101 1728 3456 6912 13823 11 00100 1503 3005 6010 12020 11 00011 1202 2404 4808 9616 12 00010 1052 2104 4207 8414 12 00001 826 1653 3306 6611 12 00000 601 1202 2404 4808 13 RFSET resistance values with corresponding PWM frequencies: Table 2. PWM Frequency Selection with Resistor PWM_RES[1:0 ] 00 01 10 11 RFSET (kΩ) 5 MHz CLOCK RESOLUTION 10 MHz CLOCK RESOLUTION 20 MHz CLOCK RESOLUTION 40 MHz CLOCK RESOLUTION 10...15 19232 8 19232 9 19232 10 19232 11 26...29 16828 8 15927 9 16227 10 17429 11 36...41 14424 8 12771 9 14424 10 15626 11 50...60 12020 8 9616 10 12020 10 12020 11 85...100 9616 9 8715 10 9616 11 9616 12 135...150 7963 9 7813 10 7813 11 8414 12 200...300 6386 9 6311 10 6010 11 6811 12 450... 4808 10 4808 11 4808 12 4808 13 8.3.2.14 Phase Shift PWM (PSPWM) Scheme Phase shift PWM scheme allows delaying the time when each LED output is active. When the LED output are not activated simultaneously, the peak load current from the boost output is greatly decreased. This reduces the ripple seen on the boost output and allows smaller output capacitors. Reduced ripple also reduces the output ceramic capacitor audible ringing. PSPWM scheme also increases the load frequency seen on boost output by x6 and therefore transfers the possible audible noise to so high frequency that human ear cannot hear it. Description of the PSPWM mode is seen in Figure 14. PSPWM mode is enabled by setting EEPROM bit to 1. Shift time is the delay between outputs and it is defined as 1 / (fPWM x 6). If the bit is 0, then the delay is 0 and all outputs are active simultaneously. Shift time tSHIFT = 1/(FPWM x 6) Cycle time 1/(FPWM) OUT1 OUT2 OUT3 OUT4 OUT5 OUT6 Figure 14. Phase Shift PWM Mode 16 Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 LP8550 www.ti.com SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 8.3.2.15 Slope and Dithering During transition between two brightness (PWM) values special dithering scheme is used if the slope is enabled. It allows increased resolution and smaller average steps size. Dithering is not used in steady state condition. Slope time can be programmed with EEPROM bits from 0 to 500 ms. Same slope time is used for sloping up and down. Advanced slope makes brightness changes smooth for eye. Dithering can be programmed with EEPROM bits from 0 to 3 bits. Figure 16 below is for 1-bit dithering; for 3-bit dithering, every 8th pulse is made 1 LSB longer to increase the average value by 1/8 of LSB. Brightness (PWM) Sloper Input Brightness (PWM) PWM Output Time Steady state without dithering Normal slope If dither is enabled it will be used during transition to enable smooth effect Advanced slope Time Slope Time Figure 15. Sloper Operation PWM value 510 (10-bit) +1 LSB PWM value 510 1/2 (10-bit) PWM value 511 (10-bit) Figure 16. Example Of The Dithering, 1-Bit Dither, 10-Bit Resolution 8.3.2.16 Driver Headroom Control Driver headroom can be controlled with EEPROM bits. Driver headroom control sets the minimum threshold for the voltage over the LED output which has the smallest driver headroom and controls the boost output voltage accordingly. Boost output voltage step size is 125 mV. The LED output which has the smallest forward voltage is the one which has highest VF across the LEDs. The strings with highest forward voltage is detected automatically. To achieve best possible efficiency smallest possible headroom voltage should be selected. If there is high variation between LED strings, the headroom can be raised slightly to prevent any visual artifacts. Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 17 LP8550 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 www.ti.com 8.3.3 Boost Converter 8.3.3.1 Operation The LP8550 boost DC/DC converter generates a 10-V to 40-V supply voltage for the LEDs from 2.7-V to 22-V input voltage. The output voltage can be controlled either with EEPROM register bits or automatic adaptive voltage control can be used. The converter is a magnetic switching PWM mode DC/DC converter with a current limit. The topology of the magnetic boost converter is called CPM (current programmed mode) control, where the inductor current is measured and controlled with the feedback. Switching frequency is selectable between 156 kHz and 1.25 MHz with EEPROM bit . When EEPROM register bit is set to 1, then boost activates automatically when backlight is enabled. In adaptive mode the boost output voltage is adjusted automatically based on LED driver headroom voltage. Boost output voltage control step size is in this case 125 mV to ensure as small as possible driver headroom and high efficiency. Enabling the adaptive mode is done with EEPROM bit. If boost is started with adaptive mode enabled, then the initial boost output voltage value is defined with the EEPROM register bits in order to eliminate long output voltage iteration time when boost is started for the first time. Figure 17 shows the boost topology with the protection circuitry: FB SW Startup VREF Light Load OVP R R + gm - + R S Boost output voltage adjustment Osc/ ramp R Switch Driver OCP 6 Active Load + - Figure 17. Boost Topology with Protection Circuitry 8.3.3.2 Protection Three different protection schemes are implemented: 1. Overvoltage protection, limits the maximum output voltage. – Overvoltage protection limit changes dynamically based on output voltage setting. – Keeps the output below breakdown voltage. – Prevents boost operation if battery voltage is much higher than desired output. 2. Overcurrent protection, limits the maximum inductor current. 3. Duty cycle limiting. 8.3.3.3 Manual Output Voltage Control User can control the boost output voltage with EEPROM register bits when adaptive mode is disabled. VBOOST[4:0] 18 VOLTAGE (typical) Bin Dec Volts 00000 0 10 00001 1 11 00010 2 12 00011 3 13 00100 4 14 Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 LP8550 www.ti.com SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 VBOOST[4:0] VOLTAGE (typical) ... ... ... 11101 29 39 11110 30 40 11111 31 40 8.3.3.4 Adaptive Boost Control Adaptive boost control function adjusts the boost output voltage to the minimum sufficient voltage for proper LED driver operation. The output with highest VF LED string is detected and boost output voltage adjusted accordingly. Driver headroom can be adjusted with EEPROM bits from approximately 300 mV to 1200 mV. Boost adaptive control voltage step size is 125 mV. Boost adaptive control operates similarly with and without PSPWM. VBOOST Driver headroom OUT1 string VF OUT6 string VF OUT5 string VF OUT4 string VF OUT3 string VF OUT2 string VF OUT1 string VF VBOOST Time Figure 18. Boost Adaptive Control Principle With PSPWM 8.3.4 Fault Detection The LP8550 has fault detection for LED fault, low-battery voltage, overcurrent and thermal shutdown. The open drain output pin (FAULT) can be used to indicate occurred fault. The cause for the fault can be read from status register. Reading the fault register also resets the fault. Setting the EN pin low also resets the faults, even if an external 5-V line is used to power VLDO pin. 8.3.4.1 LED Fault Detection With LED fault detection, the voltages across the LED drivers are constantly monitored. Shorted or open LED string is detected. If LED fault is detected: • The corresponding LED string is taken out of boost adaptive control loop; • Fault bits are set in the fault register to identify whether the fault has been open/short and how many strings are faulty; and • Fault open-drain pin is pulled down. LED fault sensitivity can be adjusted with EEPROM bit which sets the allowable variation between LED output voltage to 3.3 V or 5.3 V. Depending on application and how much variation there can be in normal operation between LED string forward voltages this setting can be adjusted. Fault is cleared by setting EN pin low or by reading the fault register. By default the LED fault detection is active only in automatic PWM & Current Dimming Mode. If LED fault detection is needed in PWM dimming mode, please contact a TI representative for guidance. Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 19 LP8550 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 www.ti.com 8.3.4.2 Undervoltage Detection The LP8550 has detection for too-low VIN voltage. Threshold level for the voltage is set with EEPROM register bits as seen in Table 3: Table 3. Threshold Level for Voltage Set with EEPROM Register Bits UVLO[1:0] THRESHOLD (V) 00 OFF 01 2.7 10 5.4 11 8.1 When undervoltage is detected the LED outputs and boost shut down, FAULT pin is pulled down, and corresponding fault bit is set in fault register. LEDs and boost start again when the voltage has increased above the threshold level. Hysteresis is implemented to threshold level to avoid continuous triggering of fault when threshold is reached. Fault is cleared by setting EN pin low or by reading the fault register. 8.3.4.3 Overcurrent Protection The LP8550 has detection for too-high loading on the boost converter. When overcurrent fault is detected, the LP8550 shuts down. Fault is cleared by setting EN pin low or by reading the fault register. 8.3.4.4 Device Thermal Regulation The LP8550 has an internal temperature sensor which can be used to measure the junction temperature of the device and protect the device from overheating. During thermal regulation, LED PWM is reduced by 2% of full scale per °C whenever the temperature threshold is reached. Temperature regulation is enabled automatically when chip is enabled. 11-bit temperature value can be read from Temp MSB and Temp LSB registers, MSB should be read first. Temperature limit can be programmed in EEPROM as shown in Table 4. Thermal regulation function does not generate fault signal. Table 4. Temperature Limits Programmable in EEPROM TEMP_LIM[1:0] OVER-TEMP LIMIT (°C) 00 OFF 01 110 10 120 11 130 8.3.4.5 Thermal Shutdown If the LP8550 reaches thermal shutdown temperature (150°C ) the LED outputs and boost shuts down to protect it from damage. Also the FAULT pin is pulled down to indicate the fault state. The device activates again when temperature drops below 130°C degrees. Fault is cleared by setting EN pin low or by reading the fault register. 20 Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 LP8550 www.ti.com SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 8.4 Device Functional Modes RESET EN = H (pin) VLDO ok EN = L (VLDO low) or POR = H STANDBY EN = H (pin) and BL_CTL = 1 or PWM = H (pin) BL_CTL = 0 and PWM = L INTERNAL STARTUP SEQUENCE VREF = 95% OK* TSD = H ~2 ms Delay EN_BOOST = 1* EN_BOOST = 0* BOOST STARTUP EN_BOOST rising edge* ~4 ms Delay NORMAL MODE *) TSD = L Figure 19. Modes of Operation RESET: In the RESET mode all the internal registers are reset to the default values. Reset is entered always when VLDO voltage is low. EN pin is enable for the internal LDO. Power On Reset (POR) activates during the chip startup or when the supply voltage VLDO falls below POR level. Once VLDO rises above POR level, POR will inactivate, and the chip will continue to the STANDBY mode. STANDBY: The STANDBY mode is entered if the register bit BL_CTL is LOW and external PWM input is not active and POR is not active. This is the low power consumption mode, when only internal 5V LDO is enabled. Registers can be written in this mode, and the control bits are effective immediately after start-up. START-UP: When BL_CTL bit is written high or PWM signal is high, the INTERNAL START-UP SEQUENCE powers up all the needed internal blocks (VREF, Bias, Oscillator etc.). Internal EPROM and EEPROM are read in this mode. To ensure the correct oscillator initialization, etc., a 2-ms delay is generated by the internal state-machine. If the chip temperature rises too high, the Thermal Shutdown (TSD) disables the chip operation and STARTUP mode is entered until no thermal shutdown event is present. BOOST START-UP: Soft start for boost output is generated in the BOOST START-UP mode. The boost output is raised in low current PWM mode during the 4 ms delay generated by the state-machine. All LED outputs are off during the 4-ms delay to ensure smooth start-up. The Boost start-up is entered from Internal Start-up Sequence if EN_BOOST is HIGH. NORMAL: During NORMAL mode the user controls the chip using the external PWM input or with Control Registers through I2C. The registers can be written in any sequence and any number of bits can be altered in a register in one write. Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 21 LP8550 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 www.ti.com 8.5 Programming 8.5.1 I2C-Compatible Serial Bus Interface 8.5.1.1 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 bidirectional communications between the ICs connected to the bus. The two interface lines are the Serial Data Line (SDA) and the Serial Clock Line (SCLK). 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 SCLK. The LP8550 is always a slave device. 8.5.1.2 Data Transactions One data bit is transferred during each clock pulse. Data is sampled during the high state of the serial clock SCLK. Consequently, throughout the clock’s high period, the data should remain stable. Any changes on the SDA line during the high state of the SCLK and in the middle of a transaction, aborts the current transaction. New data should be sent during the low SCLK state. This protocol permits a single data line to transfer both command/control information and data using the synchronous serial clock. SDA SCL Data Line Stable: Data Valid Change of Data Allowed Figure 20. Bit Transfer Each data transaction is composed of a Start Condition, a number of byte transfers (set by the software) and a Stop Condition to terminate the transaction. Every byte written to the SDA bus must be 8 bits long and is transferred with the most significant bit first. After each byte, an Acknowledge signal must follow as described in below sections. Data Output by Transmitter Transmitter Stays Off the Bus During the Acknowledgment Clock Data Output by Receiver Acknowledgment Signal From Receiver SCL 1 2 3-6 7 8 9 S Start Condition Figure 21. Start and Stop The Master device on the bus always generates the Start and Stop Conditions (control codes). After a Start Condition is generated, the bus is considered busy and it retains this status until a certain time after a Stop Condition is generated. A high-to-low transition of the data line (SDA) while the clock (SCLK) is high indicates a Start Condition. A low-to-high transition of the SDA line while the SCLK is high indicates a Stop Condition. 22 Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 LP8550 www.ti.com SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 Programming (continued) SDA SCL S P Start Condition Stop Condition Figure 22. Start and Stop Conditions In addition to the first Start Condition, a repeated Start Condition can be generated in the middle of a transaction. This allows another device to be accessed, or a register read cycle. 8.5.1.3 Acknowledge Cycle The Acknowledge Cycle consists of two signals: the acknowledge clock pulse the master sends with each byte transferred, and the acknowledge signal sent by the receiving device. The master generates the acknowledge clock pulse on the ninth clock pulse of the byte transfer. The transmitter releases the SDA line (permits it to go high) to allow the receiver to send the acknowledge signal. The receiver must pull down the SDA line during the acknowledge clock pulse and ensure that SDA remains low during the high period of the clock pulse, thus signaling the correct reception of the last data byte and its readiness to receive the next byte. 8.5.1.4 “Acknowledge After Every Byte” Rule The master generates an acknowledge clock pulse after each byte transfer. The receiver sends an acknowledge signal after every byte received. There is one exception to the “acknowledge after every byte” rule. When the master is the receiver, it must indicate to the transmitter an end of data by not-acknowledging (“negative acknowledge”) the last byte clocked out of the slave. This “negative acknowledge” still includes the acknowledge clock pulse (generated by the master), but the SDA line is not pulled down. 8.5.1.5 Addressing Transfer Formats Each device on the bus has a unique slave address. The LP8550 operates as a slave device with 7-bit address combined with data direction bit. Slave address is 2Ch as 7-bit or 58h for write and 59h for read in 8-bit format. Before any data is transmitted, the master transmits the address of the slave being addressed. The slave device should send an acknowledge signal on the SDA line, once it recognizes its address. The slave address is the first seven bits after a Start Condition. The direction of the data transfer (R/W) depends on the bit sent after the slave address — the eighth bit. When the slave address is sent, each device in the system compares this slave address with its own. If there is a match, the device considers itself addressed and sends an acknowledge signal. Depending upon the state of the R/W bit (1:read, 0:write), the device acts as a transmitter or a receiver. MSB LSB ADR6 Bit7 ADR5 bit6 ADR4 bit5 ADR3 bit4 ADR2 bit3 ADR1 bit2 ADR0 bit1 x x x x x x x R/W bit0 2 I C SLAVE address (chip address) Figure 23. I2C Chip Address Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 23 LP8550 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 www.ti.com Programming (continued) 8.5.1.6 Control Register Write Cycle • Master device generates start condition. • Master device sends slave address (7 bits) and the data direction bit (r/w = 0). • Slave device sends acknowledge signal if the slave address is correct. • Master sends control register address (8 bits). • Slave sends acknowledge signal. • Master sends data byte to be written to the addressed register. • Slave sends acknowledge signal. • If master will send further data bytes the control register address will be incremented by one after acknowledge signal. • Write cycle ends when the master creates stop condition. 8.5.1.7 Control Register Read Cycle • Master device generates a start condition. • Master device sends slave address (7 bits) and the data direction bit (r/w = 0). • Slave device sends acknowledge signal if the slave address is correct. • Master sends control register address (8 bits). • Slave sends acknowledge signal. • Master device generates repeated start condition. • Master sends the slave address (7 bits) and the data direction bit (r/w = 1). • Slave sends acknowledge signal if the slave address is correct. • Slave sends data byte from addressed register. • If the master device sends acknowledge signal, the control register address will be incremented by one. Slave device sends data byte from addressed register. • Read cycle ends when the master does not generate acknowledge signal after data byte and generates stop condition. Table 5. Data Read and Write Cycles ADDRESS MODE 24 Data Read [Ack] [Ack] [Ack] [Register Data] … additional reads from subsequent register address possible Data Write [Ack] [Ack] [Ack] … additional writes to subsequent register address possible Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 LP8550 www.ti.com SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 Data from master [ ] Data from slave S Slave Address (7 bits) '0' A Control Register Add. A (8 bits) Register Data (8 bits) A P Data transfered, byte + Ack R/W From Slave to Master A - ACKNOWLEDGE (SDA Low) S - START CONDITION From Master to Slave P - STOP CONDITION Register Write Format Figure 24. Register Write S Slave Address (7 bits) '0' A Control Register Add. A Sr (8 bits) Slave Address (7 bits) R/W '1' A Data- Data (8 bits) A/ P NA Data transfered, byte + Ack/NAck R/W Direction of the transfer will change at this point From Slave to Master From Master to Slave A - ACKNOWLEDGE (SDA Low) NA - ACKNOWLEDGE (SDA High) S - START CONDITION Sr - REPEATED START CONDITION P - STOP CONDITION Register Read Format Figure 25. Register Read 8.5.2 EEPROM EEPROM memory stores various parameters for chip control. The 64-bit EEPROM memory is organized as 8 x 8 bits. The EEPROM structure consists of a register front-end and the non-volatile memory (NVM). Register data can be read and written through the serial interface, and data is effective immediately. To read and program NVM, separate commands need to be sent. Erase and program voltages are generated on-chip charge pump, no other voltages than normal input voltage are required. A complete EEPROM memory map is shown in the EEPROM Register Map. NOTE EEPROM NVM can be programmed or read by customer for bench validation. Programming for production devices should be done in TI production test, where appropriate checks are performed to confirm EEPROM validity. Writing to EEPROM Control register of production devices (for burning or reading EEPROM) is not recommended. If special EEPROM configuration is required, please contact the TI Sales Office for availability. Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 25 LP8550 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 www.ti.com EE_PROG = 1 EEPROM NVM EEPROM REGISTERS Startup or EE_READ=1 Address A0h...A7h I C 8 x 8 bits 2 User Device Control REGISTERS ADDRESS 00h...72h Device Control Figure 26. EEPROM Control Structure 8.6 Register Maps Table 6. Register Map ADDR REGISTER 00H Brightness Control D7 01H Device Control 02H Fault OPEN 03H ID PANEL 04H Direct Control 05H Temp MSB 06H Temp LSB 72H EEPROM_control D6 D5 D4 D3 D2 D1 D0 BRT[7:0] BRT_MODE[1:0] SHORT 2_CHANNELS 1_CHANNEL DEFAULT 0000 0000 BL_FAULT OCP MFG[3:0] TSD BL_CTL 0000 0000 UVLO 0000 0000 REV[2:0] 1111 1100 OUT[6:1] 0000 0000 TEMP[10:3] 0000 0000 TEMP[2:0] 0000 0000 EE_READY EE_INIT EE_PROG EE_READ 0000 0000 8.6.1 Register Bit Explanations 8.6.1.1 Brightness Control Address 00h Reset value 0000 0000b BRIGHTNESS CONTROL REGISTER 7 6 5 4 3 2 1 2 1 0 BRT[7:0] Name Bit Access BRT 7:0 R/W Description Backlight PWM 8-bit linear control. 8.6.1.2 Device Control Address 01h Reset value 0000 0000b DEVICE CONTROL REGISTER 7 6 5 4 3 BRT_MODE[1:0] Name 26 Bit Access 0 BL_CTL Description Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 LP8550 www.ti.com SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 DEVICE CONTROL REGISTER BRT_MODE 2:1 R/W PWM source mode 00b = PWM input pin duty cycle control (default) 01b = PWM input pin duty cycle control 10b = Brightness register 11b = Direct PWM control from PWM input pin BL_CTL 0 R/W Enable backlight 0 = Backlight disabled and chip turned off if BRT_MODE[1:0] = 10. In external PWM pin control the state of the chip is defined with the PWM pin and this bit has no effect. 1 = Backlight enabled and chip turned on if BRT_MODE[1:0] = 10. In external PWM pin control the state of the chip is defined with the PWM pin and this bit has no effect. 8.6.1.3 Fault Address 02h Reset value 0000 0000b FAULT REGISTER 7 6 5 4 3 2 1 0 OPEN SHORT 2_CHANNELS 1_CHANNEL BL_FAULT OCP TSD UVLO Name Bit Access OPEN 7 R Description LED open fault detection 0 = No fault 1 = LED open fault detected. Fault pin is pulled to GND. Fault is cleared by reading the register 02h or setting EN pin low. SHORT 6 R LED short fault detection 0 = No fault 1 = LED short fault detected. Fault pin is pulled to GND. Fault is cleared by reading the register 02h or setting EN pin low. 2_CHANNELS 5 R LED fault detection 0 = No fault 1 = 2 or more channels have generated either short or open fault. Fault pin is pulled to GND. Fault is cleared by reading the register 02h or setting EN pin low. 1_CHANNEL 4 R LED fault detection 0 = No fault 1 = 1 channel has generated either short or open fault. Fault pin is pulled to GND. Fault is cleared by reading the register 02h or setting EN pin low. BL_FAULT 3 R LED fault detection 0 = No fault 1 = LED fault detected. Generated with OR function of all LED faults. Fault pin is pulled to GND. Fault is cleared by reading the register 02h or setting EN pin low. OCP 2 R Overcurrent protection 0 = No fault 1 = Overcurrent detected in boost output. OCP detection block monitors the boost output and if the boost output has been too low for more than 50 ms it generates an OCP fault and disable the boost. Fault pin is pulled to GND. Fault is cleared by reading the register 02h or setting EN pin low. After clearing the fault boost starts up again. TSD 1 R Thermal shutdown 0 = No fault 1 = Thermal fault generated, 150°C reached. Boost converted and LED outputs are disabled until the temperature has dropped down to 130°C. Fault pin is pulled to GND. Fault is cleared by reading the register 02h or setting EN pin low. Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 27 LP8550 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 www.ti.com FAULT REGISTER UVLO 0 R Undervoltage detection 0 = No fault 1 = Undervoltage detected in VIN pin. Boost converted and LED outputs are disabled until VIN voltage is above the threshold voltage. Threshold voltage is set with EEPROM bits from 3 V to 9 V. Fault pin is pulled to GND. Fault is cleared by reading the register 02h or setting EN pin low. 8.6.1.4 Identification Address 03h Reset value 1111 1100b IDENTIFICATION REGISTER 7 6 5 PANEL 28 4 3 MFG[3:0] Name Bit Access PANEL 7 R Panel ID code MFG 6:3 R Manufacturer ID code REV 2:0 R Revision ID code 2 1 0 REV[2:0] Description Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 LP8550 www.ti.com SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 8.6.1.5 Direct Control Address 04h Reset value 0000 0000b DIRECT CONTROL REGISTER 7 6 5 4 3 2 1 0 OUT[6:1] Name Bit Access OUT 5:0 R/W Description Direct control of the LED outputs 0 = Normal operation. LED output are controlled with PWM. 1 = LED output is forced to 100% PWM. 8.6.1.6 Temp MSB Address 05h Reset value 0000 0000b TEMP MSB REGISTER 7 6 5 4 3 2 1 0 TEMP[10:3] Name Bit Access TEMP 7:0 R Description Device internal temperature sensor reading first 8 MSB. MSB must be read before LSB, because reading of MSB register latches the data. 8.6.1.7 Temp LSB Address 06h Reset value 0000 0000b TEMP LSB REGISTER 7 6 5 4 3 2 1 0 TEMP[2:0] Name Bit Access TEMP 7:5 R Description Device internal temperature sensor reading last 3 LSB. MSB must be read before LSB, because reading of MSB register latches the data. 8.6.1.8 EEPROM Control Address 72h Reset value 0000 0000b EEPROM CONTROL REGISTER 7 6 5 4 Name Bit Access Description EE_READY 7 R 3 EE_READY 2 1 0 EE_INIT EE_PROG EE_READ EEPROM ready 0 = EEPROM programming or read in progress 1 = EEPROM ready, not busy EE_INIT 2 R/W EEPROM initialization bit. This bit must be written 1 before EEPROM read or programming. Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 29 LP8550 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 www.ti.com EEPROM CONTROL REGISTER EE_PROG 1 R/W EEPROM programming. 0 = Normal operation 1 = Start the EEPROM programming sequence. EE_INIT must be written 1 before EEPROM programming can be started. Programs data currently in the EEPROM registers to non volatile memory (NVM). Programming sequence takes about 200 ms. Programming voltage is generated inside the chip. EE_READ 0 R/W EEPROM read 0 = Normal operation 1 = Reads the data from NVM to the EEPROM registers. Can be used to restore default values if EEPROM registers are changed during testing. Programming sequence (program data permanently from registers to NVM): 1. Turn on the chip by writing BL_CTL bit to 1 and BRT_MODE[1:0] to 10b (05h to address 01h) 2. Write data to EEPROM registers (address A0h…A7h). 3. Write EE_INIT to 1 in address 72h. (04h to address 72h). 4. Write EE_PROG to 1 and EE_INIT to 0 in address 72h. (02h to address 72h). 5. Wait 200 ms. 6. Write EE_PROG to 0 in address 72h. (00h to address 72h). Read sequence (load data from NVM to registers): 1. Turn on the chip by writing BL_CTL bit to 1 and BRT_MODE[1:0] to 10b (05h to address 01h). 2. Write EE_INIT to 1 in address 72h. (04h to address 72h). 3. Write EE_READ to 1 and EE_INIT to 0 in address 72h. (01h to address 72h). 4. Wait 200 ms. 5. Write EE_READ to 0 in address 72h. (00h to address 72h). Data written to EEPROM registers is effective immediately even if the EEPROM programming sequence has not been done. When power is turned off, the device, however, loses the data if it is not programmed to the NVM. During startup device automatically loads the data from NVM to registers. NOTE EEPROM NVM can be programmed or read by customer for bench validation. Programming for production devices should be done in TI production test, where appropriate checks are performed to confirm EEPROM validity. Writing to EEPROM Control register of production devices (for burning or reading EEPROM) is not recommended. If special EEPROM configuration is required, please contact the TI Sales Office for availability. 8.6.2 EEPROM Bit Explanations 8.6.2.1 EEPROM Register Map 30 ADDR REGISTER A0H eeprom addr 0 D7 D6 D5 A1H eeprom addr 1 BOOST_FREQ[1:0] EN_PWM_&_ I_CTRL A2H eeprom addr 2 ADAPTIVE_SPEED[1:0] ADV_SLOPE A3H eeprom addr 3 UVLO[1:0] EN_PSPWM A4H eeprom addr 4 PWM_RESOLUTION[1:0] EN_I_RES A5H eeprom addr 5 A6H eeprom addr 6 A7H eeprom addr 7 D4 D3 D2 D1 D0 CURRENT[7:0] EN_VSYNC TEMP_LIM[1:0] MODE_25/50% _SEL EN_ADAPT LED_FAULT_T HR I_SLOPE[0] SLOPE[2:0] EN_BOOST BOOST_IMAX I_SLOPE[1] PWM_FREQ[4:0] DITHER[1:0] DRV_HEADR[2:0] VBOOST[4:0] PLL[12:5] PLL[4:0] Submit Documentation Feedback EN_F_RES HYSTERESIS[1:0] Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 LP8550 www.ti.com SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 8.6.2.2 EEPROM Address 0 Address A0h EEPROM ADDRESS 0 REGISTER 7 6 5 4 3 2 1 0 CURRENT[7:0] Name Bit Access CURRENT 7:0 R/W Description Backlight current adjustment. If EN_I_RES = 0 the maximum backlight current is defined only with these bits as described below. If EN_I_RES = 1, then the external resistor connected to ISET pin also scales the LED current. With a 16-kΩ resistor and CURRENT set to 7Fh, the output current is then 23 mA. EN_I_RES = 0 EN_I_RES = 1 0000 0000 0 mA 0 mA 0000 0001 0.12 mA (1/255) x 600 x 1.23V/RISET 0000 0010 0.24 mA (2/255) x 600 x 1.23V/RISET ... ... ... 0111 1111 15.00 mA (127/255) x 600 x 1.23V/RISET ... ... ... 1111 1101 29.76 mA (253/255) x 600 x 1.23V/RISET 1111 1110 29.88 mA (254/255) x 600 x 1.23V/RISET 1111 1111 30.00 mA (255/255) x 600 x 1.23V/RISET 8.6.2.3 EEPROM Address 1 Address A1h EEPROM ADDRESS 1 REGISTER 7 6 BOOST_FREQ[1:0] 5 4 EN_PWM_&_I_CTRL Name Bit Access BOOST_FREQ 7:6 R/W 3 2 1 TEMP_LIM[1:0] 0 SLOPE[2:0] Description Boost Converter Switch Frequency 00 = 156 kHz 01 = 312 kHz 10 = 625 kHz 11 = 1250 kHz EN_PWM_&_I_CTRL 5 R/W Enable PWM & Current Control 0 = PWM control used with constant current 1 = Automatic PWM & Current Control enabled TEMP_LIM 4:3 R/W Thermal deration function temperature threshold 00 = thermal deration function disabled 01 = 110°C 10 = 120°C 11 = 130°C SLOPE 2:0 R/W Slope time for brightness change 000 = Slope function disabled, immediate brightness change 001 = 50 ms 010 = 75 ms 011 = 100 ms 100 = 150 ms 101 = 200 ms 110 = 300 ms 111 = 500 ms Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 31 LP8550 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 www.ti.com 8.6.2.4 EEPROM Address 2 Address A2h EEPROM ADDRESS 2 REGISTER 7 6 ADAPTIVE_SPEED[1:0] 5 4 3 2 1 0 ADV_SLOPE MODE_25/50_S EL EN_ADAPT EN_BOOST BOOST_IMAX I_SLOPE[1] Name Bit Access ADAPTIVE SPEED[1] 7 R/W Description Boost converter adaptive control speed adjustment 0 = Normal mode 1 = Adaptive mode optimized for light loads. Activating this helps the voltage droop with light loads during boost / backlight start-up. ADAPTIVE SPEED[0] 6 ADV_SLOPE 5 R/W Boost converter adaptive control speed adjustment 0 = Adjust boost once for each phase shift cycle or normal PWM cycle 1 = Adjust boost every 16th phase shift cycle or normal PWM cycle R/W Advanced slope 0 = Advanced slope is disabled 1 = Use advanced slope for brightness change to make brightness changes smooth for eye MODE_25/50_SEL 4 R/W 25% or 50% mode selection for PWM & current control 0 = 50% mode selected 1 = 25% mode selected EN_ADAPT 3 R/W Enable boost converter adaptive mode 0 = adaptive mode disabled, boost converter output voltage is set with VBOOST EEPROM register bits 1 = adaptive mode enabled. Boost converter startup voltage is set with VBOOST EEPROM register bits, and after start-up voltage is reached the boost converter adapts to the highest LED string VF. LED driver output headroom is set with DRV_HEADR EEPROM control bits. EN_BOOST 2 R/W Enable boost converter 0 = boost is disabled 1 = boost is enabled and turns on automatically when backlight is enabled BOOST_IMAX 1 R/W Boost converter inductor maximum current 0 = 1.4 A 1 = 2.5 A (recommended) I_SLOPE[1] 0 R/W 8.6.2.5 EEPROM Address 3 Address A3h EEPROM ADDRESS 3 REGISTER 7 6 UVLO[1:0] 5 4 EN_PSPWM Name Bit Access UVLO 7:6 R/W 3 2 1 0 PWM_FREQ[4:0] Description 00 = Disabled 01 = 2.7 V 10 = 5.4 V 11 = 8.1 V EN_PSPWM 5 R/W Enable phase shift PWM scheme 0 = PSPWM disabled, normal PWM mode used 1 = PSPWM enabled 32 Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 LP8550 www.ti.com SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 EEPROM ADDRESS 3 REGISTER PWM_FREQ 4:0 R/W PWM output frequency setting. See PWM Frequency Setting for full description of selectable PWM frequencies. 8.6.2.6 EEPROM Address 4 Address A4h EEPROM ADDRESS 4 REGISTER 7 6 PWM_RESOLUTION[1:0] 5 4 3 EN_I_RES LED_FAULT_THR I_SLOPE[0] Name Bit Access PWM RESOLUTION 7:6 R/W 2 1 0 DRV_HEADR[2:0] Description PWM output resolution selection. Actual resolution depends also on the output frequency. See PWM Frequency Setting for full description. 00 = 8...10 bits (19.2 kHz...4.8 kHz) 01 = 9...11 bits (19.2 kHz... 4.8 kHz) 10 = 10...12 bits (19.2 kHz...4.8 kHz) 11 = 11...13 bits (19.2 kHz...4.8 kHz) EN_I_RES 5 R/W Enable LED current set resistor 0 = Resistor is disabled and current is set only with CURRENT EEPROM register bits 1 = Enable LED current set resistor. LED current is defined by the RISET resistor and the CURRENT EEPROM register bits. LED_FAULT_T HR 4 R/W LED fault detector thresholds. VSAT is the saturation voltage of the driver, typically 200 mV. 0 = 3.3V 1 = 5.3V I_SLOPE[0] 3 R/W DRV_HEADR 2:0 R/W LED output driver headroom control. VSAT is the saturation voltage of the driver, typically 200 mV. 000 = VSAT + 125 mV 001 = VSAT + 250 mV 010 = VSAT + 375 mV 011 = VSAT + 500 mV 100 = VSAT + 625 mV 101 = VSAT + 750 mV 110 = VSAT + 875 mV 111 = VSAT + 1000 mV Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 33 LP8550 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 www.ti.com 8.6.2.7 EEPROM Address 5 Address A5h EEPROM ADDRESS 5 REGISTER 7 6 EN_VSYNC 5 4 3 2 DITHER[1:0] 1 0 VBOOST[4:0] Name Bit Access EN_VSYNC 7 R/W Description Enable VSYNC function 0 = VSYNC input disabled 1 = VSYNC input enabled. VSYNC signal is used by the internal PLL to generate PWM output and boost frequency. DITHER 6:5 R/W Dither function controls 00 = Dither function disabled 01 = 1-bit dither used for output PWM transitions 10 = 2-bit dither used for output PWM transitions 11 = 3-bit dither used for output PWM transitions VBOOST 4:0 R/W Boost voltage control from 10 V to 40 V with 1-V step. If adaptive boost control is enabled, this sets the initial start voltage for the boost converter. If adaptive mode is disabled, the output voltage of the boost converter is directly set. 0 0000 = 10 V 0 0001 = 11 V 0 0010 = 12 V ... 1 1101 = 39 V 1 1110 = 40 V 1 1111 = 40 V 8.6.2.8 EEPROM Address 6 Address A6h EEPROM ADDRESS 6 register 7 6 5 4 Name Bit Access PLL 7:0 R/W 3 2 1 0 PLL[12:5] Description 13-bit counter value for PLL, 8 MSB bits. PLL[12:0] bits are used when en_vsync = 1. See Table 7 for PLL value calculation. 8.6.2.9 EEPROM Address 7 Address A7h EEPROM ADDRESS 7 REGISTER 7 6 5 4 3 PLL[4:0] 2 EN_F_RES 1 0 HYSTERESIS[1:0] Name Bit Access Description PLL 7:3 R/W 13-bit counter value for PLL, 5 LSB bits. PLL[12:0] bits are used when en_vsync = 1. See Table 7 for PLL value calculation. EN_F_RES 2 R/W Enable PWM output frequency set resistor 0 = Resistor is disabled and PWM output frequency is set with PWM_FREQ EEPROM register bits 1 = PWM frequency set resistor is enabled. RFSET defines the output PWM frequency. See PWM Frequency Setting for full description of the PWM frequencies. 34 Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 LP8550 www.ti.com SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 EEPROM ADDRESS 7 REGISTER HYSTERESIS 1:0 R/W PWM input hysteresis function. Defines how small changes in the PWM input are ignored to remove constant switching between two values. 00 = OFF 01 = 1-bit hysteresis with 11-bit resolution 10 = 1-bit hysteresis with 10-bit resolution 11 = 1-bit hysteresis with 8-bit resolution Table 7. PLL Value Calculation en_vsync PLL FREQUENCY [MHz] PLL[12:0] 0 5, 10, 20, 40 not used 1 5 5 MHz / (26 x fVSYNC) 10 10 MHz / (50 x fVSYNC) 20 20 MHz / (98 x fVSYNC) 40 40 MHz / (196 x fVSYNC) PLL frequency is set by PWM_RESOLUTION[1:0] bits. For Example: If fPLL = 5 MHz and fVSYNC = 60 Hz, then PLL[12:0] = 5000000 Hz / (26 * 60 Hz) = 3205d = C85h. If fPLL = 10 MHz and fVSYNC = 75 Hz, then PLL[12:0] = 10000000 Hz / (50 * 75 Hz) = 2667d = A6Bh. Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 35 LP8550 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 www.ti.com 9 Application and Implementation NOTE Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality. 9.1 Application Information The LP8550 is designed for LCD backlighting for portable devices, such as laptops and tablets. 6 LED current sinks allow driving up to 60 LEDs with high efficiency. Boost converter optimizes the system efficiency by adjusting the LED current driver headroom to optimal level in each case. Due to a flexible input voltage configuration, the LP8550 can be used also in various applications since the input voltage supports 1x to 5x series Li-Ion cells. Main limiting factor for output power is inductor current limit, which is calculated in the Detailed Design Procedure. The following design procedure can be used to select component values for the LP8550. 9.2 Typical Applications 9.2.1 Typical Application Using Internal LDO VBATT L1 5.5V ± 22V CVLDO 10V ± 40V 210 mA ± 400 mA D1 CIN 15 éH 5V 39 pF 10 éF COUT 4.7 éF 1 éF VDDIO reference voltage VDDIO VSYNC signal 100 nF VLDO SW VIN FB VSYNC OUT1 FILTER 1 éF 120 k5 RISET OUT2 ISET RFSET LP8550 OUT3 OUT4 FSET OUT5 SCLK SDA OUT6 MCU PWM EN Can be left floating if not used FAULT GNDs Figure 27. LP8550 with Internal LDO 9.2.1.1 Design Requirements DESIGN PARAMETER 36 EXAMPLE VALUE Input voltage range 5.5...22 V Brightness Control PWM input duty cycle (default), I2C can be used as well PWM output frequency With RFSET resistor 85 kΩ to 100 kΩ; 9.8 kHz with PSPWM enabled LED Current With RISET resistor 15 kΩ; 25 mA/channel Brightness slopes 200-ms linear slope + advanced slope External set resistors Enabled Inductor 10 µH to 33 µH, with 2.5-A saturation current Boost SW frequency 625 kHz SW current limit 2.5 A Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 LP8550 www.ti.com SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 9.2.1.2 Detailed Design Procedure 9.2.1.2.1 Inductor Selection There are two main considerations when choosing an inductor; the inductor should not saturate, and the inductor current ripple should be small enough to achieve the desired output voltage ripple. Different saturation current rating specifications are followed by different manufacturers so attention must be given to details. Saturation current ratings are typically specified at 25°C. However, ratings at the maximum ambient temperature of application should be requested from the manufacturer. Shielded inductors radiate less noise and should be preferred. The saturation current should be greater than the sum of the maximum load current and the worst case average to peak inductor current. Equation 3 below shows the worst case conditions. ISAT > IOUTMAX '¶ Where IRIPPLE = Where D = • • • • • • • + IRIPPLE (VOUT ± VIN) (2 x L x f) (VOUT ± VIN) (VOUT) x VIN VOUT DQG'¶= (1 - D) IRIPPLE: Average to peak inductor current IOUTMAX: Maximum load current VIN: Maximum input voltage in application L: Min inductor value including worst case tolerances f: Minimum switching frequency D: Duty cycle for CCM Operation VOUT: Output voltage (3) Example using Equation 3: • VIN = 12 V • VOUT = 38 V • IOUT = 400 mA • L = 15 μH − 20% = 12 μH • f = 1.25 MHz • ISAT = 1.6 A As a result the inductor should be selected according to the ISAT. A more conservative and recommended approach is to choose an inductor that has a saturation current rating greater than the maximum current limit of 2.5 A. A 15-μH inductor with a saturation current rating of 2.5 A is recommended for most applications. The inductor’s resistance should be less than 300 mΩ for good efficiency. For high efficiency choose an inductor with high frequency core material such as ferrite to reduce core losses. To minimize radiated noise, use shielded core inductor. Inductor should be placed as close to the SW pin and the IC as possible. Special care should be used when designing the PCB layout to minimize radiated noise and to get good performance from the boost converter. 9.2.1.2.2 Output Capacitor A ceramic capacitor with 50-V voltage rating or higher is recommended for the output capacitor. The DC-bias effect can reduce the effective capacitance by up to 80%, which needs to be considered in capacitance value selection. For light loads a 4.7-μF capacitor is sufficient. Effectively the capacitance should be 4 μF for < 150 mA loads. For maximum output voltage/current 10-μF capacitor (or two 4.7-μF capacitors) is recommended to minimize the output ripple. 9.2.1.2.3 LDO Capacitor A 1μF ceramic capacitor with 10-V voltage rating is recommended for the LDO capacitor. Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 37 LP8550 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 www.ti.com 9.2.1.2.4 Output Diode A Schottky diode should be used for the output diode. Peak repetitive current should be greater than inductor peak current (2.5 A) to ensure reliable operation. Average current rating should be greater than the maximum output current. Schottky diodes with a low forward drop and fast switching speeds are ideal for increasing efficiency in portable applications. Choose a reverse breakdown voltage of the Schottky diode significantly larger (approximately 60 V) than the output voltage. Do not use ordinary rectifier diodes, since slow switching speeds and long recovery times cause the efficiency and the load regulation to suffer. 9.2.1.2.5 Resistors for Setting the LED Current and PWM Frequency See EEPROM Bit Explanations on how to select values for these resistors. 9.2.1.2.6 Filter Component Values Optimal components for 60-Hz VSYNC frequency and 4-Hz cut-off frequency of the low-pass filter are shown in Figure 27, Figure 28, and Figure 31. If a 2-Hz cut-off frequency, that is, slower response time is desired, filter components are: C1 = 1 μF, C2 = 10 μF and R = 47 kΩ. If different VSYNC frequency or response time is desired, please contact a TI representative for guidance. Figure 28. Filter Components 9.2.1.3 Application Curves Typical Boost and LED Current Waveforms with fLED = 9.6 kHz. fLED = 9.6 kHz fLED = 9.6 kHz Figure 30. Typical Waveforms Figure 29. Typical Waveforms 9.2.2 Typical Application for Low Input Voltage In Single Li-Ion cell powered application the internal circuitry of LP8550 can be powered from external 5-V rail. Boost is powered directly from Li-Ion battery and VLDO and VIN pins are connected to external 5-V rail. Current draw from the 5-V rail is maximum 10 mA. A separate 5-V rail to VIN/VLDO can be used also in higher input voltage application to improve efficiency or add increase input voltage range above 22 V in some cases. There are no power sequencing requirement for VIN/VLDO and VBATT other than VBATT must be available when enabling backlight to prevent a false overcurrent fault. 38 Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 LP8550 www.ti.com SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 2.7V ± 22V VBATT 5.5V ± 22V L1 D1 10 ± 25V, 180 mA 10 ± 40V, 180 ± 400 mA CIN 15 éH +5V input rail 39 pF 10 éF 1 éF 4.7 éF CVLDO VDDIO reference voltage VSYNC signal 100 nF VDDIO VLDO SW VIN COUT FB VSYNC OUT1 FILTER 1 éF 120 k5 RISET OUT2 ISET OUT3 LP8550 OUT4 RFSET FSET OUT5 SCLK SDA OUT6 MCU PWM EN Can be left floating if not used FAULT GNDs Figure 31. Typical Application for Low-Input Voltage 9.2.2.1 Design Requirements DESIGN PARAMETER EXAMPLE VALUE Input voltage range, VBATT 2.7 V to VOUT 5-V input rail, VLDO/VIN 4.5 V to 5.5 V, 10 mA Brightness Control PWM input duty cycle (default), I2C can be used as well PWM output frequency With RFSET resistor 85 kΩ to 100 kΩ; 9.8 kHz with PSPWM enabled LED Current With RISET resistor 15 kΩ; 25 mA/channel Brightness slopes 200-ms linear slope + advanced slope External set resistors Enabled Inductor 10 µH to 33 µH, with 2.5-A saturation current Boost SW frequency 625 kHz SW current limit 2.5 A 9.2.2.2 Detailed Design Procedure Component selection follows Design Requirements above. VLDO capacitor voltage rating can be set based on the 5-V rail voltage specification, which must be < 5.5 V in all cases. Note that UVLO is detected from the VIN pin voltage, not from the VBATT voltage. 9.2.2.3 Application Curves Typical Boost and LED current behavior is seen in the Application Curves section. Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 39 LP8550 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 www.ti.com 10 Power Supply Recommendations The device is designed to operate from an input voltage supply range between 2.7 V and 22 V. This input supply should be well-regulated and able to withstand maximum input current and maintain stable voltage without voltage drop even at load transition condition (start-up or rapid brightness change). The resistance of the input supply rail should be low enough that the input current transient does not cause drop high enough in the LP8550 supply voltage that can cause false UVLO fault triggering. If a separate 5-V power rail is used to power LP8550 VLDO/VIN pins, this voltage must be stable 4.5 V to 5 V. Excessive noise or ripple in this rail can have adverse effect on device performance, so good grounding and sufficient bypass capacitors must be used. If the input supply is located more than a few inches from the LP8550 additional bulk capacitance may be required in addition to the ceramic bypass capacitors. Depending on device EEPROM configuration and usage case the boost converter is configured to operate optimally with certain input voltage range. Examples are seen in the Detailed Design Procedure section. In uncertain cases, it is recommended to contact a TI Sales Representative for confirmation of the compatibility of the use case, EEPROM configuration, and input voltage range. 11 Layout 11.1 Layout Guidelines Figure 33 is a layout recommendation for the LP8550. The figure is used for demonstrating the principle of good layout. This layout can be adapted to the actual application layout if/where possible. It is important that all boost components are close to the chip and the high current traces should be wide enough. By placing the boost component on one side of the chip it is easy to keep the ground plane intact below the high current paths. This way other chip pins can be routed more easily without splitting the ground plane. If the chip is placed in the center of the boost components, the I2C lines, LED lines, etc. cut the ground plane below the high current paths, and it makes the layout design more difficult. VIN and VLDO need to be as noise-free as possible. Place the bypass capacitors near the corresponding pins and ground them to as noise-free ground as possible. Here are some main points to help the PCB layout work: 1. Current loops need to be minimized: (a) For low frequency the minimal current loop can be achieved by placing the boost components as close to the SW and SW_GND pins as possible. Input and output capacitor grounds need to be close to each other. (b) Minimal current loops for high frequencies can be achieved by making sure that the ground plane is intact under the current traces. High frequency return currents try to find route with minimum impedance, which is the route with minimum loop area, not necessarily the shortest path. Minimum loop area is formed when return current flows just under the “positive” current route in the ground plane, if the ground plane is intact under the route. Traces from inner pads of the LP8550 need to be routed from below the part in the second layer so that traces do not split the ground plane under the boost traces or components. 2. GND plane needs to be intact under the high current boost traces to provide shortest possible return path and smallest possible current loops for high frequencies. 3. Current loops when the boost switch is conducting and not conducting needs to be on the same direction in optimal case. 4. Inductor placement should be so that the current flows in the same direction as in the current loops. Rotating inductor 180 degrees changes current direction. 5. Use separate “noisy” and “silent” grounds. Noisy ground is used for boost converter return current and silent ground for more sensitive signals, like VIN and VLDO bypass capacitor grounding. 6. Boost output voltage to LEDs need to be taken out “after” the output capacitors, not straight from the diode cathode. 7. Small (such as 39 pF) bypass capacitor should be placed close to the FB pin. 8. RISET resistor should be grounded to silent ground, since possible ground ripple will show at the LED current. 9. VIN line should be separated from the high current supply path to the boost converter to prevent high 40 Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 LP8550 www.ti.com SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 Layout Guidelines (continued) frequency ripple affecting the chip behavior. Separate 100-nF bypass capacitor is used for VIN line and it is grounded to noise-free ground. 10. Input and output capacitors need strong grounding (wide traces, vias to GND plane). 11. If two output capacitors are used they need symmetrical layout to get both capacitors working ideally. 12. Output capacitors DC-bias effect. If the output capacitance is too low, it can cause boost to become unstable on some loads and this increases EMI. DC bias characteristics need to be obtained from the component manufacturer; it is not taken into account on component tolerance. 50-V 1210-size X5R/X7R capacitors are recommended. 11.2 Layout Examples RED line = keep routes short VBATT CIN 2 x 10 éF 5.5V ± 22V CVLDO L1 10V ± 40V 210 mA ± 400 mA D1 15 éH 5V 39 pF 100 nF 1 éF Sensitive node, quiet ground! VDDIO reference voltage VDDIO COUT 2 x 10 éF SW VLDO VIN FB GND OUT1 OUT2 Sensitive node, quiet ground! 16 k ISET OUT3 LP8550 OUT4 91 k FSET OUT5 SCLK SDA OUT6 MCU PWM EN Can be left floating FAULT GND_S GND_LED GND_SW Sensitive node, quiet ground! Figure 32. LP8550 Application Schematic for Layout Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 41 LP8550 SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 www.ti.com Layout Examples (continued) Figure 33. LP8550 Layout 42 Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 LP8550 www.ti.com SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014 12 Device and Documentation Support 12.1 Trademarks All trademarks are the property of their respective owners. 12.2 Electrostatic Discharge Caution This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. 12.3 Glossary SLYZ022 — TI Glossary. This glossary lists and explains terms, acronyms, and definitions. 13 Mechanical, Packaging, and Orderable Information The following pages include mechanical, packaging, and orderable information. This information is the most current data available for the designated devices. This data is subject to change without notice and revision of this document. For browser-based versions of this data sheet, refer to the left-hand navigation. Submit Documentation Feedback Copyright © 2010–2014, Texas Instruments Incorporated Product Folder Links: LP8550 43 PACKAGE OPTION ADDENDUM www.ti.com 10-Dec-2020 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan (2) Lead finish/ Ball material MSL Peak Temp Op Temp (°C) Device Marking (3) (4/5) (6) LP8550TLE/NOPB ACTIVE DSBGA YZR 25 250 RoHS & Green SNAGCU Level-1-260C-UNLIM LP8550TLX-A/NOPB ACTIVE DSBGA YZR 25 3000 RoHS & Green SNAGCU Level-1-260C-UNLIM LP8550TLX/NOPB ACTIVE DSBGA YZR 25 3000 RoHS & Green SNAGCU Level-1-260C-UNLIM -30 to 85 8550 D71B -30 to 85 8550 (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may reference these types of products as "Pb-Free". RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption. Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of