MC34845

Document Number: MC34845 Rev. 3.0, 2/2010 Freescale Semiconductor Advance Information * This document contains certain information on a new product. Specifications and information herein are subject to change without notice. © Freescale Semiconductor, Inc., 2010. All rights reserved. Low Cost 6 Channel LED Backlight Driver with Integrated Power Supply The 34845 series represents high efficiency LED drivers for use in backlighting LCD displays from 10” to 17” +. Operating from supplies of 5.0 to 21V, the 34845 series is capable of driving up to 16 LEDs in series in 6 separate strings. The LED current tolerance in the 6 strings is within ±2% maximum and is set using a resistor to GND. PWM dimming is performed by applying a PWM input signal to the PWM pin which modulates the LED channels directly. An Enable Pin (EN) provides for low power standby. Alternatively, a single wire scheme selects power down when PWM is connected to the Wake Pin and held low. The integrated boost converter uses dynamic headroom control to automatically set the output voltage. There are three device versions for boost frequency; 34845/C is 600 kHz, 34845A is 1.2 MHz and the 34845B/D is 300 kHz. External compensation allows the use of different inductor/ capacitor combinations. The 34845 includes fault protection modes for LED short and open, over temperature, over current and over voltage errors. It features an internally fixed OVP value of 60V (typical) which protects the device in the event of a failure in the externally programmed OVP. The OVP level can be set by using an external resistor divider. Features • Input voltage of 5.0 to 21V • Boost output voltage up to 60V • 2.0 A integrated boost FET • Fixed boost frequency - 300 kHz, 600 kHz or 1.2 MHz • OTP, OCP, UVLO fault detection • LED short/open protection • Programmable LED current between 3.0 mA and 30 mA • 24-Ld 4x4x0.65mm μQFN Package Figure 1. 34845 Simplified Application Diagram 34845 34845A/B/C/D LED DRIVER 98ASA00087D 24-PIN QFN-EP ORDERING INFORMATION Device Temperature Range (TA) Package MC34845EP/R2 -40° to 85°C 24 QFN-EP MC34845AEP/R2 MC34845BEP/R2 MC34845CEP/R2 MC34845DEP/R2 12V FAIL PGNDB 34845 SWA SWB VOUT PGNDA CH1 CH2 CH3 CH4 CH5 CH6 EP EN PWM ISET VIN VDC1 VDC2 COMP WAKE ~~ ~~ ~~ ~~ ~~ ~~ OVP GND GND CONTROL UNIT 5V Typical Applications • PC Notebooks • Netbooks • Picture Frames • Portable DVD Players • Small Screen Televisions • Industrial Displays • Medical Displays Document Number: MC34845 Rev. 3.0, 2/2010 Freescale Semiconductor Advance Information * This document contains certain information on a new product. Specifications and information herein are subject to change without notice. © Freescale Semiconductor, Inc., 2010. All rights reserved. DEVICE VARIATIONS Table 1. Device Variations Characteristic Symbol Min Typ Max Unit Boost Switch Current Limit 34845, 34845A, 34845C 34845B, 34845D IBOOST_LIMIT 1.9 2.1 2.1 2.35 2.3 2.6 A Switching Frequency 34845, 34845C 34845A 34845B, 34845D fS 540 1080 270 600 1200 300 660 1320 330 kHz Slope Compensation 34845, 34845C 34845A 34845B, 34845D VSLOPE - - - 0.52 0.73 0.22 - - - V/μs Document Number: MC34845 Rev. 3.0, 2/2010 Freescale Semiconductor Advance Information * This document contains certain information on a new product. Specifications and information herein are subject to change without notice. © Freescale Semiconductor, Inc., 2010. All rights reserved. INTERNAL BLOCK DIAGRAM Figure 2. 34845 Simplified Internal Block Diagram VIN VDC1 COMP EN PWM ISET SWA SWB PGNDB FAIL CH1 CH2 CH3 CH4 CH5 CH6 6 CHANNEL BOOST LOGIC CONTROLLER CURRENT MIRROR V SENSE GND PGNDA LDO VDC2 VOUT BANDGAP CIRCUIT WAKE LOW POWER MODE Document Number: MC34845 Rev. 3.0, 2/2010 Freescale Semiconductor Advance Information * This document contains certain information on a new product. Specifications and information herein are subject to change without notice. © Freescale Semiconductor, Inc., 2010. All rights reserved. ELECTRICAL CHARACTERISTICS ABSOLUTE MAXIMUM RATINGS Table 2. Absolute Maximum Ratings All voltages are with respect to ground unless otherwise noted. Exceeding these ratings may cause a malfunction or permanent damage to the device. Ratings Symbol Value Unit ELECTRICAL RATINGS Maximum Pin Voltages SWA, SWB, VOUT CH1, CH2, CH3, CH4, CH5, CH6 (Off state) CH1, CH2, CH3, CH4, CH5, CH6 (On state) FAIL, OVP COMP, ISET PWM, WAKE EN, VIN VMAX -0.3 to 65 -0.3 to 45 -0.3 to 20 -0.3 to 7.0 -0.3 to 2.7 -0.3 to 5.5 -0.3 to 24 V Maximum LED Current per Channel ILED_MAX 33 mA ESD Voltage(1) Human Body Model (HBM) Machine Model (MM) VESD ±2000 ±200 V THERMAL RATINGS Operating Ambient Temperature Range TA -40 to 85 °C Maximum Junction Temperature TJ 150 °C Storage Temperature Range TS -40 to 150 °C Peak Package Reflow Temperature During Reflow(2), (3) TPPRT Note 3 °C Thermal Resistance Junction to Ambient(4) TθJA 36 °C/W Thermal Resistance Junction to Case(5) TθJC 3.1 °C/W Power Dissipation(4) TA = 25°C TA = 85°C PD 3.4 1.8 W Notes 1. ESD testing is performed in accordance with the Human Body Model (HBM) (AEC-Q100-2) (CZAP = 100 pF, RZAP = 1500 Ω), and the Machine Model (MM) (CZAP = 200 pF, RZAP = 0 Ω. 2. Pin soldering temperature limit is for 10 seconds maximum duration. Not designed for immersion soldering. Exceeding these limits may cause malfunction or permanent damage to the device. 3. Freescale’s Package Reflow capability meets Pb-free requirements for JEDEC standard J-STD-020C. For Peak Package Reflow Temperature and Moisture Sensitivity Levels (MSL), Go to www.freescale.com, search by part number [e.g. remove prefixes/suffixes and enter the core ID to view all orderable parts. (i.e. MC33xxxD enter 33xxx), and review parametrics. 4. Per JEDEC51-8 Standard for Multilayer PCB 5. Theoretical thermal resistance is from the die junction to the exposed pad. Document Number: MC34845 Rev. 3.0, 2/2010 Freescale Semiconductor Advance Information * This document contains certain information on a new product. Specifications and information herein are subject to change without notice. © Freescale Semiconductor, Inc., 2010. All rights reserved. STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS Table 3. Static and Dynamic Electrical Characteristics Characteristics noted under conditions VIN = 12 V, VOUT = 35 V, ILED = 30 mA, fS = 600 kHz, fPWM = 600 Hz - 40°C ≤ TA ≤ 85°C, unless otherwise noted. Typical values noted reflect the approximate parameter means at TA = 25°C under nominal conditions, unless otherwise noted. Characteristic Symbol Min Typ Max Unit SUPPLY Supply Voltage VIN 5.0 10 21 V Supply Current when in Shutdown Mode EN = Low, PWM = Low ISHUTDOWN - 2.0 10 μA Supply Current when Operational Mode Boost = Pulse Skipping, Channels = 1% of Duty Cycle EN = High, PWM = Low IOPERATIONAL - 5.0 6.5 mA Under-voltage Lockout VIN Rising UVLO 4.0 - 4.4 V Under-voltage Hysteresis VIN Falling UVLOHYST - 0.25 - V VDC1 Voltage(6) CVDC1 = 2.2 μF VDC1 2.4 2.5 2.6 V VDC2 Voltage(6) (VIN between 7.0 and 21 V) CVD2C = 2.2 μF VDC2 5.7 6.0 6.3 V BOOST Output Voltage Range(7) VIN = 5.0 V VIN = 21 V VOUT1 VOUT2 8.0 24 - - 43 60 V Boost Switch Current Limit 34845, 34845A, 34845C 34845B, 34845D IBOOST_LIMIT 1.9 2.1 2.1 2.35 2.3 2.6 A Boost Switch Current Limit Timeout tBOOST_TIME - 10 - ms RDSON of Internal FET IDRAIN= 1.0 A RDSON - 300 520 mΩ Boost Switch Off state Leakage Current VSWA,SWB = 60 V IBOOST_LEAK - - 1.0 μA Feedback pin Off-state Leakage Current VOUT = 60 V VOUTLEAK - - 500 μA Peak Boost Efficiency(8) VOUT = 33 V, RL = 330 Ω EFFBOOST - 90 - % Notes 6. This output is for internal use only and not to be used for other purposes 7. Minimum and maximum output voltages are dependent on Min/Max duty cycle condition. 8. Boost efficiency test is performed under the following conditions: fSW = 600 kHz, VIN = 12 V, VOUT = 33 V and RL = 330 Ω. The following external components are used: L = 10 μH DCR = 0.1 Ω, COUT = 3x1 μF (ceramic), Schottky diode VF = 0.35 V. Document Number: MC34845 Rev. 3.0, 2/2010 Freescale Semiconductor Advance Information * This document contains certain information on a new product. Specifications and information herein are subject to change without notice. © Freescale Semiconductor, Inc., 2010. All rights reserved. BOOST (CONTINUED) Line Regulation VIN = 7.0 V to 21 V, ICH = 30 mA ILED/VIN -0.2 - 0.2 %/V Load Regulation VLED = 24 V to 40 V (all Channels), ICH = 30 mA ILED/VLED -0.2 - 0.2 %/V Minimum Duty Cycle DMIN - 10 15 % Maximum Duty Cycle DMAX 88 90 - % OVP Internally Fixed Value (no external voltage resistor divider) VOVP_INT 56 60 64 V OVP Programming Range(9) (set through an external resistor divider) VOVP_EXT 15 - 60 V OVP Reference Voltage VREF_OVP 6.3 6.9 7.5 V OVP Sink Current ISINK_OVP - 0.2 - μA Switching Frequency 34845, 34845C 34845A 34845B, 34845D fS 540 1080 270 600 1200 300 660 1320 330 kHz Soft Start Time (Fs=600 kHz, 100% PWM duty) tSS - 3.0 - ms Soft Start VOUT Overshoot (Fs=600 kHz, 100% PWM duty) SS_VOUT - - OVP V Boost Switch Rise Time BOOST_tR - 8.0 - ns Boost Switch Fall Time BOOST_tF - 6.0 - ns Current sense Amplifier Gain ACSA - 9.0 - OTA Transconductance GM - 200 - μS Transconductance Sink and Source Current Capability ISS - 100 - μA Slope Compensation 34845, 34845C 34845A 34945B, 34845D VSLOPE - - - 0.52 0.73 0.22 - - - V/μs LED DRIVER LED Driver Sink Current RISET = 51 kΩ 0.1%, PWM = 3.3 V RISET = 5.1 kΩ 0.1%, PWM = 3.3 V ILED 2.88 29.4 3.0 30 3.12 30.6 mA ISET Pin Voltage RISET = 5.1 kΩ 0.1% VISET 2.011 2.043 2.074 V Regulated Minimum Voltage Across LED Drivers Pulse Width > 400ns VMIN 0.675 0.75 0.825 V LED Current Channel to Channel Tolerance 10 mA ≤ ILED ≤ 30 mA 3.0 mA ≤ ILED < 10 mA ITOLERANCE -2.0 -4.0 - - 2.0 4.0 % Notes 9. The OVP level must be set 5.0 V above the worst-case LED string voltage. Table 3. Static and Dynamic Electrical Characteristics (continued) Characteristics noted under conditions VIN = 12 V, VOUT = 35 V, ILED = 30 mA, fS = 600 kHz, fPWM = 600 Hz - 40°C ≤ TA ≤ 85°C, unless otherwise noted. Typical values noted reflect the approximate parameter means at TA = 25°C under nominal conditions, unless otherwise noted. Characteristic Symbol Min Typ Max Unit Document Number: MC34845 Rev. 3.0, 2/2010 Freescale Semiconductor Advance Information * This document contains certain information on a new product. Specifications and information herein are subject to change without notice. © Freescale Semiconductor, Inc., 2010. All rights reserved. LED DRIVER (CONTINUED) Off State leakage Current, All Channels VCH = 45 V ICH_LEAK - - 1.0 μA LED Channels Rise and Fall Time tR/tF - 50 75 ns LED Open Protection, Channel Disabled if VCH ≤ OFDV OFDV - - 0.55 V LED Short Protection Voltage, Channel Disabled if VCH ≥ SFDV (channel on time ≥ 10 μs) SFDV 6.5 7.0 7.5 V FAIL PIN Off State Leakage Current VFAIL = 5.5 V IFAIL_LEAK - - 5.0 μA On State Voltage Drop ISINK = 4.0 mA VOL - - 0.4 V OVER-TEMPERATURE SHUTDOWN Over-temperature Threshold (shutdown mode) Rising Hysteresis OTTSHUTDOWN 150 - 165 25 - - °C PWM INPUT PWM Dimming Mode LED Current Control PWM = 3.3 V, fPWM = 600 Hz 10% duty; PWM = 3.3 V, fPWM = 600 Hz 50% duty PWM = 3.3 V, fPWM = 600 Hz 100% duty PWMCONTROL 9.9 49.5 - 10 50 100 10.1 50.5 - % Input Minimum Pulse PWM Pin (VPWM=3.3 V) Start-up (Wake Mode) Operational (Wake Mode) Start-up (Enable Mode) Operational (Enable Mode) tPWM_IN 1.6 - 0.4 - - 0.2 - 0.2 - - - - μs Input Frequency Range for PWM Pin fPWM DC - 100 kHz WAKE Shutdown Mode Timeout tSHUTDOWN 27 30 33 ms LOGIC INPUTS (PWM) Input Low Voltage VILL -0.3 - 0.5 V Input High Voltage VIHL 1.5 - 5.5 V Input Current ISINK -1.0 - 1.0 μA LOGIC INPUTS (EN) Input Low Voltage VILL -0.3 - 0.5 V Input High Voltage VIHL 2.1 - 21 V Input Current (VEN = 12 V) ISINK - 6.0 10 μA LOGIC INPUTS (WAKE) Input Low Voltage VILL -0.3 - 0.5 V Input High Voltage VIHL 2.1 - 5.5 V Input Current ISINK -1.0 - 1.0 μA Table 3. Static and Dynamic Electrical Characteristics (continued) Characteristics noted under conditions VIN = 12 V, VOUT = 35 V, ILED = 30 mA, fS = 600 kHz, fPWM = 600 Hz - 40°C ≤ TA ≤ 85°C, unless otherwise noted. Typical values noted reflect the approximate parameter means at TA = 25°C under nominal conditions, unless otherwise noted. Characteristic Symbol Min Typ Max Unit Document Number: MC34845 Rev. 3.0, 2/2010 Freescale Semiconductor Advance Information * This document contains certain information on a new product. Specifications and information herein are subject to change without notice. © Freescale Semiconductor, Inc., 2010. All rights reserved. PIN CONNECTIONS Figure 3. 34845 Pin Connections Table 4. 34845 Pin Definitions Pin Number Pin Name Definition 1 VIN Main voltage supply Input. IC Power input supply voltage, is used internally to produce internal voltage regulation for logic functioning, and also as an input voltage for the boost regulator. 2 PGNDB Power ground. This is the ground terminal for the internal Boost FET. 3 SWB Boost switch node connection B. Switching node of boost converter. 4 SWA Boost switch node connection A. Switching node of boost converter. 5 PGNDA Power ground. This is the ground terminal for the internal Boost FET. 6 EN Enable pin (active high, internal pull-down). 7 - 12 CH1 - CH6 LED string connections 1 to 6. LED current drivers. Each line has the capability of driving up to 30 mA. 13, 19, 21 GND Ground Reference for all internal circuits other than the Boost FET. The Exposed Pad (EP) should be used for thermal heat dissipation. 14 FAIL Fault detected pin (open drain): No Failure = Low-impedance pull-down Failure = High-impedance When a fault situation is detected, this pin goes into high impedance. 15 ISET LED current setting. The maximum current is set using a resistor from this pin to GND. 16 PWM External PWM control signal. 17 COMP Boost compensation component connection. This passive terminal is used to compensate the boost converter. Add a capacitor and a resistor in series to GND to stabilize the system as well as a shunt capacitor. 18 WAKE Low power consumption mode for single wire control. This is achieved by connecting the WAKE and PWM pins together and grounding the ENABLE (EN) pin. 20 VDC1 2.5 V internal voltage decoupling. This pin is for internal use only, and not to be used for other purposes. A capacitor of 2.2 μF should be connected between this pin and ground. 22 OVP External boost over-voltage setting. Requires a resistor divider from VOUT to GND. If no external OVP setting is desired, this pin should be grounded. 23 VDC2 6.0 V internal voltage decoupling. This pin is for internal use only, and not to be used for other purposes. A capacitor of 2.2 μF should be connected between this pin and ground. 24 VOUT Boost voltage output feedback. EP EP Ground and thermal enhancement pad VIN PGNDB SWB SWA PGNDA GNDEN WAKE ISET FAIL VO U T VD C 2 O V P COMP VD C 1 G N D G N D PWM C H 1 C H 2 C H 3 C H 4 C H 5 C H 6 24 17 18 1920212223 1 87 6 5 4 3 2 16 9 10 11 12 13 14 15 EP GND TRANSPARENT TOP VIEW Document Number: MC34845 Rev. 3.0, 2/2010 Freescale Semiconductor Advance Information * This document contains certain information on a new product. Specifications and information herein are subject to change without notice. © Freescale Semiconductor, Inc., 2010. All rights reserved. FUNCTIONAL DESCRIPTION INTRODUCTION LED backlighting has been popular for use in small LCD displays for many years. This technology is now rapidly replacing the incumbent Cold Cathode Fluorescent Lamp (CCFL) in mid-size displays such as those used use in notebooks, monitors and industrial/ consumer displays. LEDs offer a number of advantages compared to the CCFL, including lower power, thinner, longer lifetime, low voltage drive, accurate wide-range dimming control and advanced architectures for improved image quality. LEDs are also void of hazardous materials such as mercury which is used in CCFL. LED backlights use different architecture depending on the size of the display and features required. For displays in the 10” to 17” + range such as those used in notebooks, edge-lit backlights offer very thin designs down to 2mm or less. The efficiency of the LED backlight also extends battery life in portable equipment compared to CCFL. In large size panels, direct backlights support advanced architectures such as local dimming, in which power consumption and contrast ratio are drastically improved. Edge lighting can also be used in large displays when low cost is the driving factor. The 34845 targets mid size panel applications in the 10” to 17” + range with edge-lit backlights. The device supports LED currents up to 30mA and supports up to 6 strings of LEDs. This enables backlights up to 10W to be driven from a single device. The device includes a boost converter to deliver the required LED voltage from either a 2 or 3 cell Li-ion battery, or a direct 12V input supply. The current drivers match the current between devices to provide superior uniformity across the display. The 34845 provides for a wide range of PWM dimming from a direct PWM control input. FUNCTIONAL DEVICE OPERATION POWER SUPPLY The 34845 supports 5.0V to 21V at the VIN input pin. Two internal regulators generate internal rails for internal operation. Both rails are de-coupled using capacitors on the VDC1 and VDC2 pins. The VIN, VDC1, and VDC2 supplies each have their own UVLO mechanisms. When any voltage is below the UVLO threshold, the device stops operating. All UVLO comparators have hysteresis to ensure constant on/off cycling does not occur. The power up sequence for applying VIN respect to the ENABLE and PWM signals is important since the 34845 device will behave differently depending on how the sequence of these signals is applied. For the case where VIN is applied before the ENABLE and PWM signals, the device will have no limitation in terms of how fast the VIN ramp should be. However for the case where the PWM and ENABLE signals are applied before VIN, the ramp up time of VIN between 0V and 5V should be no longer than 2ms. Figures 4 and 5 illustrate the two different power up conditions. Figure 4. Power up sequence case 1, VIN applied before the ENABLE and PWM signals. No limitation for VIN ramp up time. VIN EN PWM VOUT Boost Soft Star t Document Number: MC34845 Rev. 3.0, 2/2010 Freescale Semiconductor Advance Information * This document contains certain information on a new product. Specifications and information herein are subject to change without notice. © Freescale Semiconductor, Inc., 2010. All rights reserved. Figure 5. Power up sequence case 2, VIN applied after the ENABLE and PWM signals. VIN ramp up time between 0V and 5V should be not higher than 2ms BOOST CONVERTER The boost converter uses a Dynamic Headroom Control (DHC) loop to automatically set the output voltage needed to drive the LED strings. The DHC is designed to operate under specific pulse width conditions in the LED drivers. It operates for pulse widths higher than 400 ns. If the pulse widths are shorter than specified, the DHC circuit will not operate and the voltage across the LED drivers will increase to a value given by the OVP, minus the total LED voltage in the LED string. It is therefore imperative to select the proper OVP level to avoid exceeding the max off state voltage of the LED drivers (45V). The boost operates in current mode and is compensated externally through a type 2 network on the COMP pin. A modification of the compensation network is suggested to mi