Freescale Semiconductor Advance Information Document Number: MC34845 Rev. 2.0, 9/2009 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 V to 21 V, 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 is 600 kHz, 34845A is 1.2 MHz and the 34845B 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 60 V (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 21 V • Boost output voltage up to 60 V • 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 4x4x0.65 mm μQFN Package 34845 34845A/B LED DRIVER 98ASA00087D 24-PIN QFN-EP ORDERING INFORMATION Device Temperature Range (TA) Package -40° to 85°C 24 QFN-EP MC34845EP/R2 MC34845AEP/R2 MC34845BEP/R2 Tape and Reel depicted with “R2” Typical Applications • • • • • • • PC Notebooks Netbooks Picture Frames Portable DVD Players Small Screen Televisions Industrial Displays Medical Displays 34845 12V VIN VDC1 SWA SWB VDC2 VOUT PGNDB COMP PGNDA OVP EN CONTROL UNIT 5V ~ FAIL PWM CH1 CH2 CH3 CH4 CH5 CH6 WAKE ISET GND EP GND Figure 1. 34845 Simplified Application Diagram * This document contains certain information on a new product. Specifications and information herein are subject to change without notice. © Freescale Semiconductor, Inc., 2009. All rights reserved. ~ ~ ~ ~ ~ DEVICE VARIATIONS DEVICE VARIATIONS Table 1. Device Variations Characteristic Symbol Min Typ Max 34845, 34845A 1.9 2.1 2.3 34845B 2.1 2.35 2.6 34845 540 600 660 34845A 1080 1200 1320 270 300 330 34845 - 0.52 - 34845A - 0.73 - 34945B - 0.22 - Boost Switch Current Limit IBOOST_LIMIT Switching Frequency A fS 34845B Slope Compensation Unit kHz VSLOPE V/μs 34845 2 Analog Integrated Circuit Device Data Freescale Semiconductor INTERNAL BLOCK DIAGRAM INTERNAL BLOCK DIAGRAM SWA VIN SWB VDC1 LDO VDC2 PGNDB COMP BOOST CONTROLLER PGNDA VOUT LOGIC EN V SENSE LOW POWER MODE WAKE FAIL CH1 CH2 PWM BANDGAP CIRCUIT ISET 6 CHANNEL CURRENT MIRROR CH3 CH4 CH5 CH6 GND Figure 2. 34845 Simplified Internal Block Diagram 34845 Analog Integrated Circuit Device Data Freescale Semiconductor 3 ELECTRICAL CHARACTERISTICS ABSOLUTE MAXIMUM RATINGS 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 VMAX V SWA, SWB, VOUT -0.3 to 65 CH1, CH2, CH3, CH4, CH5, CH6 (Off state) -0.3 to 45 CH1, CH2, CH3, CH4, CH5, CH6 (On state) -0.3 to 20 FAIL, OVP -0.3 to 7.0 COMP, ISET -0.3 to 2.7 PWM, WAKE -0.3 to 5.5 EN, VIN -0.3 to 24 Maximum LED Current per Channel ESD Voltage ILED_MAX (1) 33 VESD mA V Human Body Model (HBM) ±2000 Machine Model (MM) ±200 THERMAL RATINGS Operating Ambient Temperature Range TA -40 to 85 °C Maximum Junction Temperature TJ 150 °C TS -40 to 150 °C TPPRT Note 3 °C TθJA 36 °C/W TθJC 3.1 °C/W Storage Temperature Range Peak Package Reflow Temperature During Thermal Resistance Junction to Ambient(4) Thermal Resistance Junction to Case Power Dissipation(4) (5) Reflow(2), (3) PD W TA = 25°C 3.4 TA = 85°C 1.8 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. 3. 4. 5. 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. 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. Per JEDEC51-8 Standard for Multilayer PCB Theoretical thermal resistance is from the die junction to the exposed pad. 34845 4 Analog Integrated Circuit Device Data Freescale Semiconductor ELECTRICAL CHARACTERISTICS STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS 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 VIN 5.0 10 21 V - 2.0 10 SUPPLY Supply Voltage Supply Current when in Shutdown Mode μA ISHUTDOWN EN = Low, PWM = Low Supply Current when Operational Mode IOPERATIONAL mA Boost = Pulse Skipping, Channels = 1% of Duty Cycle EN = High, PWM = Low - Under-voltage Lockout 5.0 6.5 UVLO VIN Rising V 4.0 Under-voltage Hysteresis - 4.4 UVLOHYST VIN Falling VDC1 Voltage(6) V - 0.25 - 2.4 2.5 2.6 5.7 6.0 6.3 VDC1 CVDC1 = 2.2 μF VDC2 Voltage(6) (VIN between 7.0 and 21 V) V VDC2 CVD2C = 2.2 μF V BOOST Output Voltage Range(7) VIN = 5.0 V VOUT1 8.0 - 43 VIN = 21 V VOUT2 24 - 60 Boost Switch Current Limit Boost Switch Current Limit Timeout RDSON of Internal FET IBOOST_LIMIT 1.9 2.1 2.3 34845B 2.1 2.35 2.6 - 10 - - 300 520 - - 1.0 - - 500 - 90 - RDSON IDRAIN= 1.0 A Boost Switch Off state Leakage Current Peak Boost Efficiency(8) VOUT = 33 V, RL = 330 Ω μA μA VOUTLEAK VOUT = 60 V ms mΩ IBOOST_LEAK VSWA,SWB = 60 V Feedback pin Off-state Leakage Current A 34845, 34845A tBOOST_TIME V EFFBOOST % 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. 34845 Analog Integrated Circuit Device Data Freescale Semiconductor 5 ELECTRICAL CHARACTERISTICS STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS 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 BOOST (CONTINUED) Line Regulation ILED/VIN VIN = 7.0 V to 21 V, ICH = 30 mA Load Regulation %/V -0.2 - 0.2 -0.2 - 0.2 ILED/VLED VLED = 24 V to 40 V (all Channels), ICH = 30 mA %/V Minimum Duty Cycle DMIN - 10 15 % Maximum Duty Cycle DMAX 88 90 - % 56 60 64 OVP Internally Fixed Value VOVP_INT (no external voltage resistor divider) OVP Programming Range(9) V VOVP_EXT (set through an external resistor divider) V 15 - 60 OVP Reference Voltage VREF_OVP 6.3 6.9 7.5 OVP Sink Current ISINK_OVP - 0.2 - Switching Frequency fS 540 600 660 34845A 1080 1200 1320 34845B 270 300 330 tSS - 3.0 - Soft Start VOUT Overshoot (Fs=600 kHz, 100% PWM duty) μA kHz 34845 Soft Start Time (Fs=600 kHz, 100% PWM duty) V ms SS_VOUT - - OVP V Boost Switch Rise Time BOOST_tR - 8.0 - ns Boost Switch Fall Time BOOST_tF - 6.0 - ns ACSA - 9.0 - OTA Transconductance GM - 200 - μS Transconductance Sink and Source Current Capability ISS - 100 - μA 34845 - 0.52 - 34845A - 0.73 - 34945B - 0.22 - RISET = 51 kΩ 0.1%, PWM = 3.3 V 2.88 3.0 3.12 RISET = 5.1 kΩ 0.1%, PWM = 3.3 V 29.4 30 30.6 Current sense Amplifier Gain Slope Compensation VSLOPE V/μs LED DRIVER LED Driver Sink Current ISET Pin Voltage ILED VISET RISET = 5.1 kΩ 0.1% Regulated Minimum Voltage Across LED Drivers mA V 2.011 2.043 2.074 VMIN Pulse Width > 400ns V 0.675 0.75 0.825 10 mA ≤ ILED ≤ 30 mA -2.0 - 2.0 3.0 mA ≤ ILED < 10 mA -4.0 - 4.0 LED Current Channel to Channel Tolerance % ITOLERANCE Notes 9. The OVP level must be set 5.0 V above the worst-case LED string voltage. 34845 6 Analog Integrated Circuit Device Data Freescale Semiconductor ELECTRICAL CHARACTERISTICS STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS 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 - - 1.0 Unit LED DRIVER (CONTINUED) Off State leakage Current, All Channels μA ICH_LEAK VCH = 45 V 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 SFDV 6.5 7.0 7.5 - - 5.0 (channel on time ≥ 10 μs) V FAIL PIN Off State Leakage Current On State Voltage Drop μA IFAIL_LEAK VFAIL = 5.5 V VOL ISINK = 4.0 mA V - - 0.4 150 165 - - 25 - PWM = 3.3 V, fPWM = 600 Hz 10% duty; 9.9 10 10.1 PWM = 3.3 V, fPWM = 600 Hz 50% duty 49.5 50 50.5 PWM = 3.3 V, fPWM = 600 Hz 100% duty - 100 - 1.6 - - - 0.2 - 0.4 - - - 0.2 - fPWM DC - 100 kHz tSHUTDOWN 27 30 33 ms 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 - 0.5 V OVER-TEMPERATURE SHUTDOWN Over-temperature Threshold (shutdown mode) OTTSHUTDOWN Rising Hysteresis °C PWM INPUT PWM Dimming Mode LED Current Control Input Minimum Pulse PWM Pin (VPWM=3.3 V) PWMCONTROL μs tPWM_IN Start-up (Wake Mode) Operational (Wake Mode) Start-up (Enable Mode) Operational (Enable Mode) Input Frequency Range for PWM Pin % WAKE Shutdown Mode Timeout LOGIC INPUTS (PWM) LOGIC INPUTS (EN) Input Low Voltage VILL -0.3 Input High Voltage VIHL 2.1 - 21 V Input Current (VEN = 12 V) ISINK - 6.0 10 μA VILL -0.3 - 0.5 V LOGIC INPUTS (WAKE) Input Low Voltage Input High Voltage VIHL 2.1 - 5.5 V Input Current ISINK -1.0 - 1.0 μA 34845 Analog Integrated Circuit Device Data Freescale Semiconductor 7 PIN CONNECTIONS STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS VDC2 OVP GND VDC1 GND TRANSPARENT TOP VIEW VOUT PIN CONNECTIONS 24 23 22 21 20 19 VIN 1 18 WAKE PGNDB 2 17 COMP SWB 3 16 PWM EP GND EN 6 13 GND 7 8 9 10 11 12 CH6 14 FAIL CH5 5 CH4 PGNDA CH3 15 ISET CH2 4 CH1 SWA 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 7 - 12 CH1 - CH6 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): Enable pin (active high, internal pull-down). LED string connections 1 to 6. LED current drivers. Each line has the capability of driving up to 30 mA. 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. 34845 8 Analog Integrated Circuit Device Data Freescale Semiconductor PIN CONNECTIONS STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS Table 4. 34845 Pin Definitions (continued) Pin Number Pin Name Definition 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 34845 Analog Integrated Circuit Device Data Freescale Semiconductor 9 FUNCTIONAL DESCRIPTION INTRODUCTION 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 7” 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 7” 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 5.0 V to 21 V 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 MC34845 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. VIN EN PWM Boost Soft Star t VOUT Figure 4. Power up sequence case 1, VIN applied before the ENABLE and PWM signals. No limitation for VIN ramp up time. 34845 10 Analog Integrated Circuit Device Data Freescale Semiconductor FUNCTIONAL DEVICE OPERATION INTRODUCTION voltage and ground with its output connected to the OVP pin. The OVP can be set up to 60 V by varying the resistor divider to match the OVP internal reference of 6.9 V (typical). EN LED DRIVER PWM VIN 5V 2 ms Boost Soft Start VOUT UVLO Rising VIN ramp 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 (45 V). 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 minimize the amplitude of the ripple at VOUT. The details of the suggested compensation network are shown in Figures 10 and 11. An integrated 2.0 A minimum FET supplies the required output current. An Over-current Protection circuit limits the output current cycle-by-cycle to IOCP. If the condition exists longer than 10 ms, then the device will shut down. The frequency of the boost converter is internally set to 300 kHz, 600 kHz or 1.2 MHz, depending on the device’s version. The boost also includes a soft start circuit. Each time the IC comes out of shutdown mode, the soft start period lasts for tSS. Over-voltage Protection is also included. The device has an internally fixed OVP value of 60 V (typical) which serves as a secondary fault protection mechanism, in the event the externally programmed OVP fails (i.e. resistor divider opens up). While the internal 60 V OVP detector can be used exclusively without the external OVP network, this is only recommended for applications where the LED string voltage approaches 55 V or more. The OVP level can be set by using an external resistor divider connected between the output The 6 channel LED driver provides current matching for 6 LED strings to within ±2% maximum. The current in the strings is set using a resistor tied to GND from the ISET pin. The LED current level is given by the equation: RSET = 153/ ILED. The accuracy of the RSET resistor should be 0.1% for best performance. LED ERROR DETECT If an LED is open, the output voltage ramps to the OVP level. If there is still no current in the LED string, the LED channel is turned off and the output voltage ramps back down to normal operating level. If LEDs are shorted and the voltage in any of the channels is greater than the SFDV threshold (7.0 V typical), then the device will turn off that channel. However if the on-time of the channels is less than 10 μs, the SFDV circuit will not disable any of the channels, regardless of the voltage across them. All the LED errors can be cleared by recycling the EN pin or applying a complete power-on-reset (POR). WAKE OPERATION The WAKE pin provides the means to set the device for low power consumption (shutdown mode) without the need of an extra logic signal for enable. This is achieved by connecting the WAKE and PWM pins together, and tying the EN pin to ground. In this configuration, the PWM signal is used to control the LED channels, while allowing low power consumption by setting the device into its shutdown mode every time the PWM signal is kept low for longer time than the WAKE time out of 27 ms. OVER-TEMPERATURE SHUTDOWN AND TEMPERATURE CONTROL CIRCUITS The 34845 includes over-temperature protection. If the internal temperature exceeds the over-temp threshold OTTSHUTDOWN, then the device shuts down all functions. Once the temperature falls below the low level threshold, the device is re-enabled. FAIL PIN The FAIL pin is at its low-impedance state when no error is detected. However, if an error such as an LED channel open or boost over-current is detected, the FAIL pin goes into high-impedance. Once a failure is detected, the FAIL pin can be cleared by recycling the EN pin or applying a complete power-on-reset (POR). If the detected failure is an Overcurrent time-out, the EN pin or a POR must be cycled/ executed to restart the part. 34845 Analog Integrated Circuit Device Data Freescale Semiconductor 11 TYPICAL PERFORMANCE CURVES INTRODUCTION TYPICAL PERFORMANCE CURVES 100.0 90.0 80.0 Efficiency (%) 70.0 60.0 Vin=9V Fs = 600kHz L=10uH, 68mOhm (IHLP2525CZER100M01) Schottky 5A, 100V (PDS5100HDICT-ND) COUT = 2x2.2µF FPWM=25kHz Load = 9 LEDs, 20mA/channel VLED = 27.8V, ±0.5V /channel 50.0 40.0 30.0 20.0 10.0 0.0 0 10 20 30 40 50 60 70 80 90 100 Duty Cycle (%) Figure 6. Typical System Efficiency vs Duty Cycle (FPWM=25kHz) Chablis ILED Dimming Linearity (FPWM=25kHz) 2.000% % ILED Channel mismatch 1.500% (-) Mismatch @ 25°C (+) Mismatch @ 25°C 1.000% 0.500% 0.000% -0.500% -1.000% -1.500% -2.000% 1 10 100 % Duty cycle Figure 7. Typical ILED Dimming Linearity (FPWM=25kHz) 34845 12 Analog Integrated Circuit Device Data Freescale Semiconductor TYPICAL PERFORMANCE CURVES INTRODUCTION PWM VOUT (ac coupled) VCH1 ILED1 Figure 8. Typical Operating Waveforms (FPWM=25kHz, 50% duty) PWM VOUT (ac coupled) VCH1 ILED1 Figure 9. Low Duty Dimming Operation Waveforms (FPWM=25 kHz, 1% duty) 34845 Analog Integrated Circuit Device Data Freescale Semiconductor 13 TYPICAL APPLICATIONS INTRODUCTION TYPICAL APPLICATIONS 10 uH VIN LED LEG 1 60 V, 1A 2 .2uF 10uf 25V LED LEG 2 LED LEG 3 LED LEG 4 LED LEG 5 LED LEG 6 2.2 uF 100 pF 100pF 100 pF VIN 1 VD C2 2 .2uF 10 V VOU T 24 20 2. 2uF 10 V 100 pF PGN D 2 23 100 pF the MC 34845 de vice SWB 3 VD C1 Cap s should be l ocated as c lose as poss ible to SWA 4 0. 1uf PGN D 5 kΩ 5.6 M O 100p F OVP 22 kΩ 1 MO 2 .2nF 22 kΩ kO COM P 1 0 kO kΩ MC34845 17 CH1 7 CH2 8 CH3 9 56 pF CH4 10 EN Cont rol Un it PWM WAKE CH5 11 6 CH6 12 16 18 F AIL 14 15 13 kΩ 7.6 5 KO 0.1 % EP 21 GND GND Figure 10. Typical Application Circuit for Single Wire Control, fS = 600 KHz (VIN = 9.0 V, ILED/channel = 20 mA/channel, 12 LEDs/channel, OVP = 45 V, VPWM = 3.3 V) 4 .7uH VIN LED LEG 1 60 V, 1A 2 .2uF 10uf 25V LED LEG 2 LED LEG 3 LED LEG 4 LED LEG 5 LED LEG 6 2.2 uF 100 pF 100pF 100 pF VIN 4 1 0. 1uf 3 VD C1 VD C2 2 .2uF 10 V 20 24 23 2 2. 2uF 10 V 5 22 SWA SWB Cap s should be l ocated as c lose as poss ible to 100 pF the MC 34845 de vice VOU T 100 pF PGN D PGN D kΩO 5.6 M 100p F OVP kΩ 1 MO 2 .2nF 22 kΩ kO 1 0 kΩ kO COM P 17 MC34845A 7 8 9 56 pF 10 EN Cont rol Un it PWM WAKE 11 6 CH2 CH3 CH4 CH5 CH6 16 18 15 7.6 5 KO kΩ 0.1 % 12 CH1 14 13 GND EP F AIL 21 GND Figure 11. Typical Application Circuit for Single Wire Control, fS = 1.2 MHz (VIN = 9.0 V, ILED = 20 mA/channel, 12 LEDs/channel, OVP = 45 V, VPWM = 3.3 V) 34845 14 Analog Integrated Circuit Device Data Freescale Semiconductor TYPICAL APPLICATIONS INTRODUCTION 33uH VIN LED LEG 1 80V, 1A 2.2uF 2. 2uF LED LEG 2 LED LEG 3 LED LEG 4 LED LEG 5 LED LEG 6 2.2uF 10uf 25V 100 pF 100pF 100pF VI N 1 4 0. 1uf 3 VDC1 VDC2 2. 2uF 10V 24 20 2 23 2.2uF 10V 5 22 S WA S WB Caps should be located as cl ose as possi ble to the MC 34845 device V OUT 100 pF 100pF P GND P GND 1 MO 100 pF OVP 162 kO 8.2nF 3.3 kO COMP 17 MC34845 B 7 8 9 150pF 10 EN Cont rol Unit PWM WAKE 11 6 CH2 CH3 CH4 CH5 CH6 16 18 15 7. 65 K O 0. 1% 12 CH1 14 13 GND EP FAIL 21 GND Figure 12. Typical Application Circuit for Single Wire Control, fS = 300 kHz (VIN = 8.0 V, ILED = 20 mA/channel, 14 LEDs/channel, OVP = 49 V, VPWM = 3.3 V) 34845 Analog Integrated Circuit Device Data Freescale Semiconductor 15 TYPICAL APPLICATIONS COMPONENTS CALCULATION COMPONENTS CALCULATION The following formulas are intended for the calculation of all external components related with the boost converter and network compensation. In order to calculate the Duty Cycle, the internal losses of the MOSFET and Diode should be taken into consideration: I RMS – C OUT D = I OUT × -----------1–D V OUT + V D – V IN D = ---------------------------------------------V OUT + V D – V SW The average input current depends directly on the output current when the internal switch is off. I OUT I IN – AVG = -----------1–D Inductor Note that before calculating the network compensation, all boost converter components need to be known. For this type of compensation it is recommended to push out the Right Half Plane Zero to higher frequencies where it will not significantly affect the overall loop. For calculating the Inductor, consider the losses of the internal switch and winding resistance of the inductor: ( V IN – V SW – ( I IN – AVG × R INDUCTOR ) ) × D L = ----------------------------------------------------------------------------------------------------------------I IN – AVG × r × F SW 2 V OUT × ( 1 – D ) f RHPZ = --------------------------------------------I OUT × 2π × L It is important to look for an inductor rated at least for the maximum input current: V IN × ( V OUT – V IN ) I IN – MAX = I IN – AVG + --------------------------------------------------------2 × L × F SW × V OUT Input Capacitor The input capacitor should handle at least the following RMS current. I RMS – C ⎛ V IN × ( V OUT – V IN )⎞ = ⎜ ---------------------------------------------------------⎟ × 0.3 ⎝ 2 × L × F SW × V OUT ⎠ IN Output Capacitor For the output capacitor selection the transconductance should be taken in consideration. R COMP × 5 × G M × I OUT × L C OUT = ------------------------------------------------------------------------------( 1 – D ) × V OUT × 0.35 The output voltage ripple (ΔVOUT) depends on the ESR of the Output capacitor. For a low output voltage ripple, it is recommended to use ceramic capacitors that have a very low ESR. Since ceramic capacitor are costly, electrolytic or tantalum capacitors can be mixed with ceramic capacitors for a less expensive solution. ESR C OUT V OUT × ΔV OUT × F SW × L = --------------------------------------------------------------------------V OUT × ( 1 – D ) The output capacitor should at least handle the following RMS current. Network Compensation The crossover frequency must be set much lower than the location of the Right half plane zero: f RHPZ f CROSS = -------------5 Since our system has a fixed slope compensation, RCOMP should be fixed for all configurations, i.e. RCOMP = 8.2 Kohm CCOMP1 and CCOMP2 should be calculated as follows: 2 C COMP1 = ---------------------------------------------------------------R 2π × f CROSS × COMP GM C COMP2 = ----------------------------6.28 × F SW The recommended values of these capacitors for an acceptable performance of the system in different operating conditions are Ccomp1=2.2nF and Ccomp2=56pF. In order to improve the transient response of the boost a resistor divider has been implemented from the PWM pin to ground with a connection to the compensation network. This configuration should inject a 1V signal to the COMP pin and the equivalent Thevenin resistance of the divider is close to RCOMP, i.e. 10kΩ and 39kΩ. If a faster transient response is needed, a higher voltage (e.g. 1.3V) should be injected to the COMP pin; so the resistor divider should be modified accordingly but keeping the equivalent Thevenin resistance of the divider close to RCOMP. Since this Boost converter is current controlled, a Type II compensation is needed. 34845 16 Analog Integrated Circuit Device Data Freescale Semiconductor TYPICAL APPLICATIONS COMPONENTS CALCULATION Variable definition D = Duty cycle VOUT = Output voltage VD = Diode voltage VIN = Input voltage VSW = Internal switch voltage drop. IRMS-COUT= RMS current for output capacitor L = Inductor. RINDUCTOR= Inductor winding resistor FSW= Boost switching frequency COUT = Output capacitor RCOMP = Compensation resistor ΔVOUT = Output voltage ripple IIN-AVG = Average input current = IL-AVG IOUT = Output current IIN-MAX = Maximum input current r = Current ripple ratio at the inductor = ΔIL/ IL-AVG IRMS-CIN= RMS current for the input capacitor GM= OTA transconductance ESRCOUT= ESR of the output capacitor fRHPZ= Right half plane zero frequency fCROSS= Crossover frequency CCOMP1= Compensation capacitor CCOMP2= Shunt compensation capacitor 34845 Analog Integrated Circuit Device Data Freescale Semiconductor 17 PACKAGING PACKAGE DIMENSIONS PACKAGING PACKAGE DIMENSIONS For the most current package revision, visit www.freescale.com and perform a keyword search using the “98A” listed below. EP SUFFIX 24-PIN 98ASA00087D REVISION A 34845 18 Analog Integrated Circuit Device Data Freescale Semiconductor PACKAGING PACKAGE DIMENSIONS EP SUFFIX 24-PIN 98ASA00087D REVISION A 34845 Analog Integrated Circuit Device Data Freescale Semiconductor 19 PACKAGING EP SUFFIX 24-PIN 98ASA00087D REVISION A 34845 20 Analog Integrated Circuit Device Data Freescale Semiconductor How to Reach Us: Home Page: www.freescale.com Web Support: http://www.freescale.com/support USA/Europe or Locations Not Listed: Freescale Semiconductor, Inc. Technical Information Center, EL516 2100 East Elliot Road Tempe, Arizona 85284 1-800-521-6274 or +1-480-768-2130 www.freescale.com/support Europe, Middle East, and Africa: Freescale Halbleiter Deutschland GmbH Technical Information Center Schatzbogen 7 81829 Muenchen, Germany +44 1296 380 456 (English) +46 8 52200080 (English) +49 89 92103 559 (German) +33 1 69 35 48 48 (French) www.freescale.com/support Japan: Freescale Semiconductor Japan Ltd. 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Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2009. All rights reserved. MC34845 Rev. 2.0 9/2009