Atmel LED Drivers MSL2041/MSL2042 Low-cost, Simple 4-string LED Drivers with External Current Sink MOSFETs, 5000:1 Dimming Range and Per String PWM Input Datasheet Brief Atmel LED Drivers-MSL2041/MSL2042 Low-cost, Simple 4-string LED Drivers with External Current Sink MOSFETs, 5000:1 Dimming Range and Per String PWM Input General Description The Atmel® LED DriversMSL2041 and MSL2042 compact, high-power LED string controllers use external current control MOSFETs to sink up to 1A per string, with string current matching of ±0.5%. The MSL2041/2 drive four parallel strings of LEDs and offer fault detection and management of open circuit and short circuit LEDs. The MSL2041 features four PWM inputs that allow independent frequency, dimming and phasing of each string, while the MSL2042 offers one PWM input for frequency and dimming control of all four strings, and automatically phase shifts the string drive signals. Peak string currents are set using current sense (FET source) resistors and adjustable with an internal 8-bit DAC. 2 The MSL2041/2 adaptively control up to two DC-DC converters that power the LED strings, using Atmel's Adaptive SourcePower™ technology. These Efficiency Optimizers minimize power use while maintaining LED current accuracy. Multiple MSL2041/2s cascade to automatically negotiate the optimum power supply voltage when driving more than four strings from a single power supply. The MSL2041/2 features fault control for open-circuit strings, LED shortcircuits and device over-temperature conditions. When a string open-circuit or LED short-circuit condition is detected, the MSL2041/2 turn off the faulty string and pull the open-drain fault output low. The MSL2041/2 feature stand-alone operation, and the basic circuit requires just one to four external PWM dimming inputs. An I2C serial interface is provided to allow optional control and monitoring of the various fault detection and Adaptive SourcePower parameters, but is not required for operation. The MSL2041/2 are offered in the 32-pin, 300mil SOP package, and operate over the -40°C to +85°C temperature range. Applications • LCD-TVs • PC Monitors • Industrial Displays • General Illumination • Street-lighting • Post-regulated or Offline Powered LED Strings Ordering Information PART NO. PWM INPUTS AUTO-PHASE DELAY PACKAGE MSL2041GU 4 NO 32 pin, 300mil SOP MSL2042GU 1 YES 32 pin, 300mil SOP Atmel LED Drivers-MSL2041/2042 Atmel LED Drivers-MSL2041/MSL2042 Low-cost, Simple 4-string LED Drivers with External Current Sink MOSFETs, 5000:1 Dimming Range and Per String PWM Input Key Features • Drives Four Parallel High Power LED Strings • Up to 1A LED String Current with External N-channel MOSFETS • Multiple MSL2041/2s Share a String Supply and Automatically Negotiate the Optimum Supply Voltage • ±0.5% Current Matching Between Strings • Operates Stand-alone, Basic Circuit Needs Only PWM Input(s) • String Open-circuit and LED Short-Circuit Fault Detection and Protection • Four PWM Inputs Allow Individual Frequency, Brightness and Phase Control of each LED String (MSL2041) • External MOSFETs Offer Flexibility of LEDs Used in Each String • One PWM Input Controls the Frequency and Brightness of the Automatically Phase Shifted Strings (MSL2042) • 8-bit Adaptive SourcePower™ Correction Optimizes String Power Supply for Maximum Efficiency • I2C Serial Interface Allows Optional Control of Device Functions and Faults • 32-pin 300mil SOP Package • -40°C To +85°C Operating Temperature Range • Lead-Free, Halogen-free, RoHS Compliant Package Application Circuit Ω Ω Atmel LED Drivers-MSL2041/2042 3 Package and Pinout – SOP • • FBO1 1 32 FBI1 FBO1 1 32 FBI1 EN 2 31 FBO2 EN 2 31 FBO2 PWM3 3 30 FBI2 CGND 3 30 FBI2 PWM2 4 29 GND CGND 4 29 GND PWM1 5 28 VIN CGND 5 28 VIN PWM0 6 27 VCC PWM0 6 27 VCC FLTB 7 26 CVDD FLTB 7 26 CVDD SCL 8 25 VDD SCL 8 SDA 9 24 NC SDA 9 24 NC D0 10 23 D3 D0 10 23 D3 G0 11 22 G3 G0 11 22 G3 S0 12 21 S3 S0 12 21 S3 D1 13 20 S2 D1 13 20 S2 G1 14 19 G2 G1 14 19 G2 S1 15 18 D2 S1 15 18 D2 NC 16 17 NC NC 16 17 NC MSL2041 (TOP VIEW) MSL2042 (TOP VIEW) 25 VDD Package Dimensions: 32 Pin 20.52mm x 7.49mm x 2.49mm SOP (1.27mm pin pitch) 4 Atmel LED Drivers-MSL2041/2042 Atmel LED Drivers-MSL2041/MSL2042 Low-cost, Simple 4-string LED Drivers with External Current Sink MOSFETs, 5000:1 Dimming Range and Per String PWM Input Pin Descriptions PIN MSL2041 MSL2042 NAME DESCRIPTION Efficiency optimizer feedback output 1 Connect FBO1 to the feedback node of the first external string power supply through a diode, or to FBI1 of the next device when operating the devices in a chain configuration. If unused, leave FBO1 unconnected. Enable input (Active high) Drive EN high to turn on the MSL2041/2, drive it low to turn off the MSL2041/2. For automatic startup connect EN to VIN through a 100kΩ resistor. Toggle EN low to release FLTB and to return any and all registers to their power-up default values. 1 1 FBO1 2 2 EN 3 - PWM3 PWM dimming input 3 Drive PWM3 with a pulse-width modulated signal to control the brightness of string three. If unused, connect PWM3 to ground. 4 - PWM2 PWM dimming input 2 Drive PWM2 with a pulse-width modulated signal to control the brightness of string two. If unused, connect PWM2 to ground. 5 - PWM1 PWM dimming input 1 Drive PWM1 with a pulse-width modulated signal to control the brightness of string one. If unused, connect PWM1 to ground. 6 6 PWM0 Pwm dimming input 0 Drive PWM0 with a pulse-width modulated signal to control the brightness of string zero (MSL2041) or all strings (MSL2042). 7 7 FLTB Fault indication output (Open drain, active low) FLTB sinks current to GND whenever the MSL2041/2 detects and verifies a fault condition. Toggle EN low (or read the fault registers) to clear FLTB. 8 8 SCL I²C serial clock input SCL is the I²C serial interface clock input. 9 9 SDA 10 10 D0 11 11 G0 12 12 S0 13 13 D1 Drain sense input 1 Drain Sense Input for External MOSFET 1. Connect D1 through a resistor to the drain of the external MOSFET driving LED string 1. If unused, connect D1 to ground. 14 14 G1 Gate output 1 Gate drive output for external MOSFET 1. Connect G1 to the gate of the external MOSFET driving LED string 1. If unused, connect G1 to ground. I²C serial data I/O SDA is the I²C serial interface bi-directional data line. Drain sense input 0 Drain Sense Input for External MOSFET 0. Connect D0 through a resistor to the drain of the external MOSFET driving LED string 0. If unused, connect D0 to ground. Gate output 0 Gate drive output for external MOSFET 0. Connect G0 to the gate of the external MOSFET driving LED string 0. If unused, connect G0 to ground. Source sense input for string 0 Connect S0 to the source of the external MOSFET, and to the current sense resistor for LED string 0. The full scale LED current is reached when 500mV is across the current sense resistor. If unused, connect S0 to VDD. 15 15 S1 Source sense input for string 1 Connect S1 to the source of the external MOSFET, and to the current sense resistor for LED string 1. The full scale LED current is reached when 500mV is across the current sense resistor. If unused, connect S1 to VDD 16, 17, 24 16, 17, 24 NC No internal connection NC is not internally connected . 18 18 D2 Drain sense input 2 Drain Sense Input for External MOSFET 2. Connect D2 through a resistor to the drain of the external MOSFET driving LED string 2. If unused, connect D2 to ground. Atmel LED Drivers-MSL2041/2042 5 PIN NAME DESCRIPTION MSL2041 MSL2042 19 19 G2 20 20 S2 21 21 S3 22 22 G3 Gate output 3 Gate drive output for external MOSFET 3. Connect G3 to the gate of the external MOSFET driving LED string 3. If unused, connect G3 to ground. 23 23 D3 Drain sense input 3 Drain Sense Input for External MOSFET 3. Connect D3 through a resistor to the drain of the external MOSFET driving LED string 3. If unused, connect D3 to ground. 25 25 VDD 2.5V internal LDO regulator output VDD powers internal logic. Bypass VDD to GND with a 2.2µF ceramic capacitor placed close to VDD. 26 26 CVDD 27 27 VCC 5V internal LDO regulator output VCC powers internal logic. Bypass VCC to GND with a 2.2µF ceramic capacitor placed close to VCC. 28 28 VIN Supply voltage input Connect a 12V ±10% supply to VIN. Bypass VIN to GND with a 1.0µF ceramic capacitor. 29 29 GND Power ground Connect GND to system ground. 30 30 FBI2 Efficiency Optimizer feedback input 2 Connect FBI2 to FBO2 of the previous device when using the devices in a chain configuration. If unused, connect FBI2 to ground. 31 31 FBO2 Efficiency Optimizer feedback output 2 Connect FBO2 to the feedback node of the second external string power supply through a diode, or to FBI2 of the next device when operating the devices in a chain configuration. If unused, leave FBO2 unconnected. 32 32 FBI1 Efficiency Optimizer feedback input 1 Connect FBI1 to FBO1 of the previous device when using the devices in a chain configuration. If unused, connect FBI1 to ground. - 3, 4, 5 CGND 6 Gate output 2 Gate drive output for external MOSFET 2. Connect G2 to the gate of the external MOSFET driving LED string 2. If unused, connect G2 to ground. Source sense input for string 2 Connect S2 to the source of the external MOSFET, and to the current sense resistor for LED string 2. The full scale LED current is reached when 500mV is across the current sense resistor. If unused, connect S2 to VDD. Source sense input for string 3 Connect S3 to the source of the external MOSFET, and to the current sense resistor for LED string 3. The full scale LED current is reached when 500mV is across the current sense resistor. If unused, connect S3 to VDD. Connect to VDD Connect CVDD to VDD. Connect to ground Connect all CGND pins to GND as close to the MSL2042 as possible. Atmel LED Drivers-MSL2041/2042 Atmel LED Drivers-MSL2041/MSL2042 Low-cost, Simple 4-string LED Drivers with External Current Sink MOSFETs, 5000:1 Dimming Range and Per String PWM Input Absolute Maximum Ratings Voltage - With Respect to GND (SOP), EP/GND (TQFN) VIN, EN, G0 - G3................................................................................................................................................................................ -0.3V to +16V D0 - D3....................................................................................................................................................................................................... -0.3V to +24V VDD, CVDD............................................................................................................................................................................................-0.3V to +2.75V VCC..................................................................................................................................................................................................................-0.3V to +5.5V SDA, SCL, PWM0 - PWM3........................................................................................................................................................-0.3V to +5.5V FBI1, FBI2, FBO1, FBO2, FLTB.......................................................................................................................... -0.3V to (VCC + 0.3V) Current - (Into Pin) VIN........................................................................................................................................................................................................................................ 50mA GND...................................................................................................................................................................................................................................500mA D0 - D3.................................................................................................................................................................................................................................1mA All other pins..................................................................................................................................................................................................................20mA Continuous Power Dissipation at 70°C 32-Pin SOP (derate 28.7mW/°C above TA = +70°C)...................................................................................................1576mW Ambient Operating Temperature Range TA = TMIN to TMAX................................................................... -40°C to +85°C Junction Temperature ..................................................................................................................................................................................... +125°C Storage Temperature Range............................................................................................................................................. -65°C to +125°C Lead Soldering Temperature, 10s........................................................................................................................................................+300°C Atmel LED Drivers-MSL2041/2042 7 Electrical Characteristics VIN = 12V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VIN = 12V, TA = +25°C. PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNIT 10.8 DC ELECTRICAL CHARACTERISTICS VIN Operating Supply Voltage VIN Operating Supply Current All drivers driven, I²C serial interface idle 12.0 19.2 13.2 31.5 V mA VIN Sleep Supply Current I²C serial interface idle, SLEEP = 1 2.9 4.2 mA VIN Shutdown Supply Current EN = 0, all digital inputs = VDD or GND 0.1 2 μA 2.5 2.75 V VDD Regulation Voltage Input High Voltage PWM0 - PWM3, SCL, SDA Input Low Voltage PWM0 - PWM3, SCL, SDA EN Input High Voltage 2.25 0.7 x VDD V 0.3 x VDD 1.9 EN Input Low Voltage 1.0 EN Input Hysteresis 150 SDA, FLTB Output Low Voltage Open Circuit String Fault Detect Voltage OCREF Short Circuit String Fault Detect Voltage SCREF Sinking 3mA 6 9.0 G0 - G3 Gate Drive Current PWMn = VDD; Sn = GND; Gn = GND G0 - G3 Gate Sink Current PWMn = GND; Gn = 9.6V Current Sense Regulation Voltage String-to-String Current Matching Thermal Cut-Off temperature FBIn to FBOn Current Transfer Error FBOn Current Step-Size FBOn Feedback Output Current Maximum V 6 V μA 9.6 5 μA 10.2 V 109 mA -18 ISTR0 = 0xFF; TA = 25°C 465 ISTR0 = 0xFF; TA = 85°C 455.7 ISTR0 = 0x7F; TA = 25°C 242.5 ISTR0 = 0x7F; TA = 85°C 235 V 0.1 Voltage between 9V to 16V G0 - G3 Maximum Gate Drive Voltage V mV 0.5 Voltage under 9V D0 - D3 Leakage Current PARAMETER V 490 mA 498.75 mV 524.3 mV 250 257.5 mV 265 mV ISTR0 = 0x7F; TA = 25°C 0.50 ±2.2 ISTR0 = 0x7F; TA = -40°C to +85°C 0.75 ±3.2 FBIn = 100uA 135 ±2 1.1 Compliance voltage 3.5V minimum SYMBOL CONDITIONS °C % μA 210 MIN % μA TYP MAX UNIT AC ELECTRICAL CHARACTERISTICS PWM Frequency PWM Duty Cycle 8 fPWM (Note 7) 0 50,000 Hz (Note 7) 0 100 % Atmel LED Drivers-MSL2041/2042 Atmel LED Drivers-MSL2041/MSL2042 Low-cost, Simple 4-string LED Drivers with External Current Sink MOSFETs, 5000:1 Dimming Range and Per String PWM Input PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNIT 1,000 kHz I²C SWITCHING CHARACTERISTICS SCL Clock Frequency STOP to START Condition Bus Free Time 1/tSCL Bus timeout disabled (Note 1) 0 tBUF 0.5 µs tHD:STA 0.26 µs Repeated START Condition Setup Time tSU:STA 0.26 µs STOP Condition Setup Time tSU:STOP 0.26 µs SDA Data Hold Time tHD:DAT 5 ns Repeated START Condition Hold Time SDA Data Valid Acknowledge Time tVD:ACK (Note 2) 0.05 0.55 µs SDA Data Valid Time tVD:DAT (Note 3) 0.05 0.55 µs SDA Data Set-Up Time tSU:DAT 100 ns SCL Clock Low Period tLOW 0.5 µs SCL Clock High Period tHIGH SDA, SCL Fall Time tF SDA, SCL Rise Time tR SDA, SCL Input Suppression Filter Period tSP 0.26 µs (Note 4, Note 5) (Note 6) 50 120 ns 120 ns ns Note 1. Minimum SCL clock frequency is limited by the bus timeout feature, which resets the serial bus interface if either SDA or SCL is held low for tTIMEOUT. Note 2. tVD:ACK = SCL LOW to SDA (out) LOW acknowledge time. Note 3. tVD:DAT = minimum SDA output data-valid time following SCL LOW transition. Note 4. A master device must internally provide an SDA hold time of at least 300ns to ensure an SCL low state. Note 5. The maximum SDA and SCL rise times is 300ns. The maximum SDA fall time is 250ns. This allows series protection resistors to be connected between SDA and SCL inputs and the SDA/SCL bus lines without exceeding the maximum allowable rise time. Note 6. MSL2041/2 includes input filters on SDA and SCL that suppress noise less than 50ns. Note 7. Parameter is guaranteed by design and not production tested. Atmel LED Drivers-MSL2041/2042 9 Block Diagram Figure 1. Atmel LED Drivers-MSL2041/2 Block Diagram 10 Atmel LED Drivers-MSL2041/2042 Atmel LED Drivers-MSL2041/MSL2042 Low-cost, Simple 4-string LED Drivers with External Current Sink MOSFETs, 5000:1 Dimming Range and Per String PWM Input Ω Ω Ω Ω Ω Ω Ω Ω Ω Typical Application Circuit Figure 2. Atmel LED Drivers-MSL2042 driving four LED strings at 350mA peak current per string, controlling a single power supply Atmel LED Drivers-MSL2041/2042 11 Detailed Description The MSL2041 and MSL2042 are highly integrated, flexible, four-string LED drivers that use external MOSFETs to allow high string currents, and include power supply control to maximize efficiency of up to two external string power supplies. Optimized for stand-alone operation they require only external PWM signal(s), a few external components (including the string drive N-Channel MOSFETs) and an external string power supply. The MSL2041/2s four MOSFET gate drive outputs, G0 - G3, are optimized to drive FETs with a maximum gate voltage threshold of 3V. The MSL2041/2 LED drivers provide simple control of LED brightness through both peak current and external PWM drive controls. Peak current control, set by external FET source resisters, offers excellent color consistency, while pulse width control allows simple brightness management. Multiple devices easily connect together to drive more than four LED strings while maintaining optimum system efficiency. An active low fault output activates when either a string open circuit or an LED short circuit condition is detected and verified. The MSL2041/2 are intended for stand-alone operation but offer additional string control and monitoring through a 1MHz I2C/SMBus compatible serial interface. Use of the serial interface is not required for operation. The MSL2041 offers four PWM inputs that directly control the four string drive outputs, while the MSL2042 requires only a single PWM input signal and features automatic, progressive phase spreading of the four string drive signals. With phase spreading a ¼ PWM frame time delay is calculated and applied progressively to the string drive signals. Phase spreading helps reduce both the transient load on the LED power supply, and the power supply output capacitor size requirement. The Adaptive SourcePower Efficiency Optimizer (EO) outputs control a wide range of different architectures of external DC/DC and AC/DC converters. Multiple drivers in a system communicate with each other in real time to select an optimized operating voltage for the LEDs. The EO allows design of the power supply for the worst case Forward Voltage (Vf) of the LEDs without worrying about excessive power dissipation issues, while ensuring that the LED drive system is operating at optimum 12 efficiency. During start-up the EO automatically reduces the string power supply voltage to the minimum value required to keep the LEDs in current regulation. The EO periodically performs re-optimization to compensate for changes of the LED’s forward voltage, and to assure continued optimum power savings. Additionally, all string drivers are continually monitored for proper operation, and if any of the LED strings become starved for current the Efficiency Optimizer automatically increases the string power supply voltage to bring the string back in to current regulation. Setting the Maximum LED String Current with the FET Source Resistor RS The maximum string current, ILED, for each string is set by a shunt resistor, RS, connected to ground from the source terminal of the string drive MOSFET (Figure 1, page 6). Determine the resistor value using 127 0.50196 Ω RS = ∗ 255 I LED (where 127 is the default value of ISTR, String Current Control register 0x0E). For example, a full-scale LED current of 350mA returns RS = 0.715Ω (to the nearest 1% resistor value). LED String Fault Response The MSL2041/2 monitor the LED strings to detect LED short-circuit and string open-circuit faults (Figure 3). When verified, all string faults force the open drain fault output FLTB low. After power-up, when shorted LEDs are verified in a string the string is disabled and no longer monitored by the Efficiency Optimizer. The short circuit threshold is 6V (typical) and the additive voltage drop lost from the shorted LEDs, plus the headroom required for the external FET, must be equal to or greater than the 6V threshold to generate a fault. Typically, two LEDs in a string must be shorted to cause a short circuit fault, Atmel LED Drivers-MSL2041/2042 Atmel LED Drivers-MSL2041/MSL2042 Low-cost, Simple 4-string LED Drivers with External Current Sink MOSFETs, 5000:1 Dimming Range and Per String PWM Input but because LEDs differ, the number of shorted LEDs required to generate a fault varies. The current fold-back option, available through the serial interface, slightly changes the fault response when an LED short circuit event is suspected. A string with an open circuit LED is off by default, and when this situation is verified the faulty string is disabled and no longer monitored by the Efficiency Optimizer. Toggling EN low and then high clears all faults and the MSL2041/2 begin to control and monitor all strings as if experiencing an initial power-up. Fault conditions that persist re-establish fault responses. Faulty strings are flagged in the fault registers. When using the serial interface, fault conditions are typically read in response to FLTB pulling low. Over Temperature Shutdown The MSL2041/2 includes an automatic overtemperature shutdown. If the die temperature exceeds 135°C, the device turns off, just as if the enable input EN is forced low. When the die temperature drops below 120°C the device wakes up again and turns on as if experiencing an initial power-up. Connecting the Efficiency Optimizer to an LED String Power Supply and Selecting Resistors The MSL2041/2 are designed to control LED string power supplies that use a voltage divider (RTOP and RBOTTOM in Figure 4) to set output voltage, and whose regulation feedback voltage is not more than 3.5V - VF. The Efficiency Optimizer improves power efficiency by injecting a current of between 0µA and 280.5µA into the voltage divider of the external power supply, dynamically adjusting the power supply’s output to the minimum voltage required by the LED strings. Each of the two EOs monitors two LED strings. Strings zero and one are assigned to FBO1, and strings two and three are assigned to FBO2 (Table 1). When a single supply is used for all four strings connect FBO2 to FBI1 (Figure 4), as explained in the next section “Using Multiple EOs/Devices to Control a Common Power Supply”. The MSL2041/2 then automatically maximizes efficiency for all strings. When two supplies are used, connect FBO1 to the supply powering strings zero and one, and connect FBO2 to the supply powering strings two and three (Figure 5). For clarity, Figure 4 and Figure 5 do not show the Source and Drain connections between the devices and the MOSFETs. Figure 3. Open-Circuit and Short-Circuit Detection Block Diagram Figure 3. Open-circuit and Short-circuit Detection Block Diagram Atmel LED Drivers-MSL2041/2042 13 Table 1. String EO Assignments Figure 4. EO Configuration When Using a Single String Power Supply 14 Atmel LED Drivers-MSL2041/2042 Atmel LED Drivers-MSL2041/MSL2042 Low-cost, Simple 4-string LED Drivers with External Current Sink MOSFETs, 5000:1 Dimming Range and Per String PWM Input Figure 5. EO Configuration When Using Two String Power Supplies Atmel LED Drivers-MSL2041/2042 15 To select RTOP and RBOTTOM first determine VOUT(MIN) and VOUT(MAX), the minimum and maximum string supply voltage limits, using: Assure that the power supply settling time for a voltage step size of 1.1µA * RTOP is less than the 4ms EO Step-hold duration time. VOUT(MIN) = (Vf (MIN) *[#ofLEDs])+ 0.5 , Using Multiple EOs/Devices to Control a Common Power Supply and VOUT(MAX) = (Vf (MAX) *[#ofLEDs])+ 0.5 , where Vf(MIN) and Vf(MAX) are the LED’s minimum and maximum forward voltage drops at the peak current set by RS. For example, if the LED data are Vf(MIN) = 3.5V and Vf(MAX) = 3.8V, and ten LEDs are used in a string, then the total minimum and maximum voltage drop across a string is 35V and 38V. Adding an allowance of 0.5V for the string drive MOSFET headroom brings VOUT(MIN) to 35.5V and VOUT(MAX) to 38.5V. Then determine RTOP using: RTOP = VOUT ( MAX ) − VOUT ( MIN ) I FBOn ( MAX ) IFBO(MAX / MIN) = 280.5µA* (0.98)N-1 , , where IFBOn(MAX) is the 280.5µA maximum output current of the Efficiency Optimizer outputs FBOn (280.5µA = 1.1µA * 255, the current per LSB of the FBO DAC times the maximum DAC count). Finally, determine RBOTTOM using: RBOTTOM = RTOP * VFB VOUT(MAX) _ VFB , where VFB is the regulation feedback voltage of the power supply. Place a diode (1N4148 or similar) between FBOn and the supply’s feedback node to protect the MSL2041/2 against current flow into FBOn. Once configured, determine the change in power supply output voltage in response to a change in FBOn output current using: ∆VOUT = ∆I FBOn ∗ RTOP 16 Cascade multiple Efficiency Optimizers (EOs), either within the same device or across multiple devices, into a chain configuration (Figure 6), with the FBIn of one EO connected to the FBOn of the next. Connect the first FBOn to the power supply feedback resistor node through a diode (1N4148 or similar) placed close to the power supply feedback node, and unused FBIn inputs to ground as close to the MSL2041/2 as possible. The chained EOs work together to ensure that the system operates at optimum efficiency. Note that the accuracy of the feedback chain may degrade through each link of the FBIn/FBOn chain by 2% (typical). Derate the maximum FBOn current using: where N is the number of EOs connected in series. Use IFBOn(MAX/MIN) in the above RTOP resistor equation for the term IFBOn(MAX) instead of using 280.5µA. Take care in laying out the traces for the Efficiency Optimizer connections. Minimize the FBIn/FBOn trace lengths as much as possible. Do not route the signals close to traces with large variations in voltage or current, because noise may couple into FBIn. If these traces must be routed near noisy signals, shield them from noise by using ground planes or guard traces. For clarity, Figure 6 shows Source and Drain connections only for unused outputs 2 and 3 of device two. Note that because of the interplay between EOs and the automatic fault response behavior, when both strings monitored by a single EO fault and turn off, that the string supply is forced to its maximum value and all remaining active strings typically detect short circuit faults and also turn off. . Atmel LED Drivers-MSL2041/2042 Atmel LED Drivers-MSL2041/MSL2042 Low-cost, Simple 4-string LED Drivers with External Current Sink MOSFETs, 5000:1 Dimming Range and Per String PWM Input Figure 6. EO Chain Configuration of Two Devices, Six Strings and a Single String Power Supply Atmel LED Drivers-MSL2041/2042 17 Choosing the Drain Resistor RD Table 2. Some Typical IDARK and VF(DARK) Values Determined Using Figure 7 The drain resistor RD connects the MSL2041/2 to the Drain of the external MOSFET. Choose RD using: Ω, where VOUT(MAX) is the value calculated above in the section “Connecting the Efficiency Optimizer to an LED String Power Supply and Selecting Resistors” beginning on page12, N is the number of LEDs in the string, IDARK is the maximum allowable string off current and VF(DARK) is the LED forward voltage drop at IDARK. When the value calculated for RD < 0 use 0Ω. LED manufacturers typically do not publish IDARK and VF(DARK) information. One way to determine these numbers is to use the following method. Set up the test circuit of Figure 7. Adjust R1 until the current meter indicates IDARK (choose IDARK < 1mA). Use a volt meter to measure the voltage at the anode of the LED (A), and then at the cathode of the LED (B). Subtract the voltage measured at B from that measured at A to determine VF(DARK). Some typical values determined using this method are listed in Table 2. LED TYPE LED PART # LOW POWER LW Y1SG 1.72 2.285 MEDIUM POWER LW G6SP 1.67 2.276 HIGH POWER LXLW-PWC1 1.72 2.195 IDARK (µA) VF(DARK) (V) Large values of RD may cause false LED short circuit faults. Discharge of the parasitic capacitance at the Dn node through a large RD holds the node above the string fault threshold for longer than the LED short circuit verification time. The addition of a feed-forward capacitor, CFF in Figure 8, mitigates this issue. The value for CFF depends upon the amount of parasitic capacitance at the Dn node and the size of RD, but CFF = 15pF is an appropriate first approximation. Ω Figure 8. Feed Forward Capacitor Figure 7. Test Circuit for Determining Figure 8. Feed Forward Capacitor Figure 7. Test Circuit for Determining VF(DARK) 18 Atmel LED Drivers-MSL2041/2042 Atmel LED Drivers-MSL2041/MSL2042 Low-cost, Simple 4-string LED Drivers with External Current Sink MOSFETs, 5000:1 Dimming Range and Per String PWM Input Direct PWM Control of the LED Strings An external PWM signal applied to the inputs PWM0 - PWM3 (MSL2041) or PWM0 (MSL2042) allows direct control over the strings frequency and duty cycle. The PWM inputs recognize signals of DC to 50kHz, and 0% to 100% duty cycle. The MSL2042, which allows only a single PWM input, calculates and applies a progressive delay of 1/4th the PWM frame successively to strings one - three, while string zero follows the PWM input directly. Register Map Summary Control the MSL2041/2 using the registers in the range 0x00 - 0x18. Register bit values always revert to their default values (Table 4) when EN is taken high. Do not write to registers not listed in Table 3. Table 3. Register Map ADDRESS AND REGISTER NAME 0x00 FUNCTION LED String Enable STRINGEN REGISTER DATA D7 D6 D5 D4 D3 D2 D1 D0 - - - - STR3EN STR2EN STR1EN STR0EN 0x01 UNUSED 0x02 CONFIG 0x03 FLTSTATUS* Configuration FLDBKEN I2CTOEN Fault Status - - - - STRSCFEN STROCFEN FBOEN SLEEP - - STRSCDET STROCDET - FLTBDRV 0x04 - 0x07 UNUSED 0x08 FLTMASK String Fault Enable - - - - FLTMASK3 0x09 SCSTAT* LED Short Circuit Fault - - - - SC3 SC2 SC1 SC0 0x0A OCSTAT* String Open Circuit Fault - - - - OC3 OC2 OC1 OC0 0 1 0 0 - - ACALEN ICHKDIS - - - 0x0B - 0x0D 0x0E ISTR UNUSED 8-Bit Global String Current ISTR[7:0] 0x0F 0x10 0x11 UNUSED RESERVED Must Be 0x04 Efficiency Optimizer Control FBOCTRL 0 0 FBOSTEP[1:0] 0x12 - 0x13 0x14 0x15 Efficiency Optimizer DAC FBODAC2* Readback FBODAC1* FBOSTAT* 0 0 HDRMSTEP[1:0] UNUSED FBODAC1[7:0] FBODAC2[7:0] 0x16 - 0x17 0x18 FLTMASK2 FLTMASK1 FLTMASK0 UNUSED FBO Status - - FBIGNDSTAT[1:0] - * Read Only Registers Atmel LED Drivers-MSL2041/2042 19 Register Power-up Defaults Register power-up default values are shown in Table 4. Table 4. Register Power-up Defaults REGISTER NAME AND ADDRESS 0x00 STRINGEN 0x02 CONFIG 0x08 FLTMASK 0x0E ISTR 0x10 RESERVED 0x11 FBOCTRL Atmel Corporation 2325 Orchard Parkway San Jose, CA 95131 USA Tel: (+1)(408) 441-0311 Fax:(+1)(408) 487-2600 www.atmel.com POWER-UP CONDITION REGISTERS INITIALIZED FROM E²PROM REGISTER DATA D7 D6 D5 D4 D3 D2 D1 D0 HEX All Four LED String Drive Outputs Enabled 0 0 0 0 1 1 1 1 0F Device Awake Efficiency Optimizer Outputs Enabled String Open Circuit Detection Enabled LED Short Circuit Detection Enabled I2C Timeout Enabled String Current Fold-Back Disabled 0 1 0 0 1 1 1 0 4E All Four Strings Monitored for Faults 0 0 0 0 1 1 1 1 0F Global String Peak Current is ½ its Programmable Value 0 1 1 1 1 1 1 1 7F 0x04 0 0 0 0 0 1 0 0 04 MOSFET Current Sink Error Detection Enabled Efficiency Optimizer Auto-Recalibration Enabled Efficiency Optimizer Initial Calibration Step Size = 1 LSBs Efficiency Optimizer Headroom Correction Step Size = 1 LSBs 0 0 0 1 0 0 1 0 1A Atmel Asia Limited Unit 01-5 & 16, 19F BEA Tower, Millennium City 5 418 Kwun Tong Road Kwun Tong, Kowloon HONG KONG Tel: (+852) 2245-6100 Fax:(+852) 2722-1369 Atmel Munich GmbH Business Campus Parkring 4 D-85748 Garching b. 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