A6269KLJTR-T

A6269 Automotive LED Array Driver Features and Benefits Description ▪ AEC-Q100 qualified ▪ Total LED drive current up to 400 mA ▪ Current shared equally up to 200 mA by 2 strings ▪ 6 to 50 V supply ▪ Low dropout voltage ▪ LED output short-to-ground and thermal protection ▪ On/off toggle switch input ▪ Enable input for PWM control ▪ Current slew rate limit during PWM ▪ Current set by reference resistor ▪ Automotive temperature range The A6269 is a linear, programmable current regulator providing up to 200 mA from each of two outputs to drive arrays of high brightness LEDs. The regulated LED current from each output, accurate to 5%, is set by a single reference resistor. Current matching in each string is better than 10% without the use of ballast resistors. Driving LEDs with constant current ensures safe operation with maximum possible light output. Output control is provided by an enable input, giving direct control for PWM applications, and by a debounced switch input, proving an on/off toggle action. ▪ Dome light, map light, space lighting, mood lighting Optimum performance is achieved driving 1 to 3 LEDs in each string: up to 2 strings at 200 mA each. Outputs can be connected in parallel or left unused as required. Package: 8-pin SOICN with exposed thermal pad (suffix LJ) Short detection is provided to protect the LEDs and the A6269 during a short-to-ground at any LED output pin. The output will automatically resume the regulated current when the short is removed. Applications: A temperature monitor is included to reduce the LED drive current if the chip temperature exceeds an adjustable thermal threshold. The device package is an 8-pin SOICN (LJ) with exposed pad for enhanced thermal dissipation. It is lead (Pb) free, with 100% matte tin leadframe plating. Not to scale Typical Application Diagram + Automotive 12 V power net VIN PWM dimming input from LCU A6269 EN On/Off SW LA1 IREF LA2 THTH PAD GND – A6269-DS, Rev. 7 200 mA 200 mA A6269 Automotive LED Array Driver Selection Guide LED Outputs Ambient Operating Temperature, TA (°C) 2 at 200 mA each –40 to 125 Part Number A6269KLJTR-T Packing 3000 pieces per 13-in. reel Package 8-pin SOICN with exposed thermal pad, 3.9 × 4.9 mm case Absolute Maximum Ratings1 Characteristic Rating Unit –0.3 to 50 V –0.3 to 50 V Pins LA1, LA2 –0.3 to 50 V Pins IREF, THTH, SW –0.3 to 6.5 V –40 to 125 °C 150 °C 175 °C –55 to 150 °C Load Supply Voltage Symbol Notes VIN Pin EN Ambient Operating Temperature Range2 TA Maximum Continuous Junction Temperature TJ(max) Transient Junction Temperature TtJ Storage Temperature Range Tstg K temperature range Over temperature event not exceeding 10 s, lifetime duration not exceeding 10 h, guaranteed by design characterization 1With respect to GND. 2Limited by power dissipation. Thermal Characteristics*may require derating at maximum conditions, see application section for optimization Characteristic Symbol Package Thermal Resistance (Junction to Ambient) RθJA Package Thermal Resistance (Junction to Pad) RθJP Test Conditions* Value Unit On 4-layer PCB based on JEDEC standard 35 ºC/W On 2-layer generic test PCB with 0.8 in.2 of copper area each side 62 ºC/W 2 ºC/W *Additional thermal information available on the Allegro™ website. Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 2 A6269 Automotive LED Array Driver Functional Block Diagram VBAT VIN D SW C Deglitch Q R Q Power-On Reset Current Regulators Control Logic EN LA1 THTH IREF Temp Comp Temp Monitor LA2 Slew Limit Current Reference RTH RREF PAD GND Terminal List Table Pin-out Diagram 8 SW Number Name 1 THTH Function 2 IREF Current reference 3 GND Ground reference Thermal threshold THTH 1 IREF 2 GND 3 6 VIN 4 LA1 LED anode (+) connection 1 LA1 4 5 LA2 5 LA2 LED anode (+) connection 2 6 VIN Supply 7 EN Enable 8 SW Switch input – PAD Exposed thermal pad PAD 7 EN LJ Package Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 3 A6269 Automotive LED Array Driver ELECTRICAL CHARACTERISTICS1 Valid at TJ = –40°C to 150°C, VIN = 7 to 40 V; unless otherwise noted Characteristics Symbol Test Conditions Min. Typ. Max. Unit Supply and Reference VIN Functional Operating Range2 6 – 50 V VIN Quiescent Current IINQ LA1, LA2 connected to VIN – – 10 mA VIN Sleep Current IINS EN = GND, VIN = 16 V – – 15 μA Startup Time tON VIN > 7 V to ILA1 < –5 mA, RREF = 125 Ω 5 15 30 μs Current Regulation Reference Voltage Reference Current Ratio Current Accuracy3 Current Matching4 Output Current VIREF GH EILAx EIMLAx ILAx 0.7 mA < IREF < 8.8 mA 1.15 1.2 1.25 V ILAx / IREF – 25 – – –20 mA > ILAx > –200 mA –5 ±4 5 % –40 mA > ILAx > –200 mA, VLAx match to within 1 V – 5 10 % EN = high – GH × IREF – – IREF = 8 mA, EN = high Maximum Output Current Minimum Drop-out Voltage ILAxmax VDO Current Slew Time –210 –200 –190 mA IREF = 9.2 mA, EN = high – – –220 mA VIN – VLAx , ILAx = –200 mA – – 800 mV VIN – VLAx , ILAx = –80 mA – – 660 mV Current rising or falling between 10% and 90% 50 80 110 μs Logic Inputs EN and SW Input Low Voltage VIL – – 0.8 V Input High Voltage VIH 2 – – V Input Hysteresis (EN pin) VIhys 150 350 – mV Pull-Down Resistor (EN pin) RPD – 50 – kΩ Pull-Up Current (SW pin) IPU – 100 – μA SW Input Debounce Time tSW 10 – 50 ms Protection Short Detect Voltage VSCD Measured at LAx 1.2 – 1.8 V Short Circuit Source Current ISCS Short present LAx to GND –4 –1.6 –1 mA VSCR Measured at LAx – – 1.9 V 200 – 500 mV Short Release Voltage Short Release Voltage Hysteresis Thermal Monitor Activation Temperature Thermal Monitor Slope VSChys TJM dISEN/dTJ VSCR – VSCD TJ with ISEN = 90%, THTH open 95 115 130 °C ISEN = 50%, THTH open –3.5 –2.5 –1.5 %/°C 120 135 150 °C Thermal Monitor Low Current Temperature TJL TJ at ISEN = 25%, THTH open Overtemperature Shutdown TJF Temperature increasing – 170 – °C Overtemperature Hysteresis TJhys Recovery = TJF – TJhys – 15 – °C 1For input and output current specifications, negative current is defined as coming out of (sourcing) the specified device pin. 2Function is correct but parameters are not guaranteed outside the general limits (7 to 40 V). 3When EN = high, E ILAx = 100 × [( | ILAx | × RREF / 30 ) –1], with ILAx in mA and RREF in kΩ. 4E IMLA = 100 × [ max ( | ILAx– ILA(AV) | ) / ILA(AV) ] , where ILA(AV) is the average current of all active outputs. Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 4 A6269 Automotive LED Array Driver Functional Description The A6269 is a linear current regulator that is designed to provide drive current and protection for parallel strings of seriesconnected high brightness LEDs in automotive applications. It provides up to two matched programmable current outputs at up to 200 mA, with low minimum dropout voltages below the main supply voltage. For 12 V power net applications, optimum performance is achieved when driving 2 strings of 1 to 3 LEDs, at current up to 200 mA per string. The A6269 is specifically designed for use in internal illumination applications where the LED activity is controlled by a PWM signal, by a logic signal, or by a push-to-make, ground-connected switch. Current regulation is maintained and the LEDs protected during a short to ground at any point in the LED string. A short to ground on any regulator output terminal will disable that output until the short is removed. Open load on any output will be ignored. Integrated thermal management reduces the regulated current level at high internal junction temperatures to limit power dissipation. Pin Functions VIN Supply to the control circuit and current regulators. A small value ceramic bypass capacitor, typically 100 nF, should be connected from close to this pin to the GND pin. GND Ground reference connection. Should be connected directly to the negative supply. EN Logic input to enable LED current output. This provides a direct on/off action and can be used for direct PWM control. Note that PWM dimming can only be applied when the LED is initially in the off state. If the LED is already turned on using SW input, it will remain on regardless of EN. SW Logic input to toggle LED current output on and off. A single push-to-make switch between SW and GND will provide push-to-make/push-to-break, on/off toggle action. The SW input is debounced by typically 30 ms and is internally pulled to typically 3 V, with approximately 100 μA. IREF 1.2 V reference to set current reference. Connect resistor, RREF , to GND to set reference current. THTH Sets the thermal monitor threshold, TJM , where the output current starts to reduce with increasing temperature. Connecting THTH directly to GND will disable the thermal monitor function. LA1, LA2 Current source connected to the anode of the first LED in each string. Connect directly to VIN to disable the respective output. In this document “LAx” indicates any one of the outputs. LED Current Level The LED current is controlled by a matching linear current regulator between the VIN pin and each of the LAx outputs. The basic equation that determines the nominal output current at each LAx pin is: Given EN = high, ILAx = K (1) RREF where ILAx is in mA and RREF is in kΩ; K is 30. The output current may be reduced from the set level by the thermal monitor circuit. Conversely the reference resistors may be calculated from: K ILAx where ILAx is in mA and RREF is in kΩ. RREF = (2) For example, where the required current is 180 mA for both channels the resistor value will be: RREF = 30 = 167 Ω 180 It is important to note that because the A6269 is a linear regulator, the maximum regulated current is limited by the power dissipation and the thermal management in the application. All current calculations assume adequate heatsinking for the dissipated power. Thermal management is at least as important as the electrical design in all applications. In high current high ambient temperature applications the thermal management is the most important aspect of the systems design. The application section below provides further detail on thermal management and the associated limitations. Operation with Fewer LED Strings or Higher Currents The A6269 may be configured to use fewer than the maximum quantity of LED strings: by connecting outputs together for higher currents, by leaving the outputs open, or by connecting the output directly to VIN to disable the regulator for that output. Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 5 A6269 Automotive LED Array Driver VIN Sleep Mode When EN is held low the A6269 will be in shutdown mode and all sections will be in a low power sleep mode. The input current will be typically less than 10 μA. This means that the complete circuit, including LEDs, may remain connected to the power supply under all conditions. Safety Features The circuit includes several features to ensure safe operation and to protect the LEDs and the A6269: • The current regulators between VIN and each LAx output provide a natural current limit due to the regulation. • Each LAx output includes a short-to-ground detector that will disable the output to limit the dissipation. • The thermal monitor reduces the regulated current as the temperature rises. • Thermal shutdown completely disables the outputs under extreme overtemperature conditions. Short Circuit Detection A short to ground on any LED cathode (figure 1A) will not result in a short fault condition. The current through the remaining LEDs will remain in regulation and the LEDs will be protected. Due to the difference in the voltage drop across the LEDs, as a result of the short, the current matching in the A6269 may exceed the specified limits. Any LAx output that is pulled below the short detect voltage (figure 1B) will disable the regulator on that output. A small current will be sourced from the disabled output to monitor the short and detect when it is removed. When the voltage at LAx rises above the short detect voltage, the regulator will be re-enabled. A shorted LED (figure 1C) will not result in a short fault condition. The current through the remaining LEDs will remain in regulation and the LEDs will be protected. Due to the difference in the voltage drop across the LEDs, as a result of the short, the current matching in the A6269 may exceed the specified limits. A short between LEDs in different strings (figure 1D) will not result in a short fault condition. The current through the remaining LEDs will remain in regulation and the LEDs will be protected. The current will be summed and shared by the affected strings. Current matching in the strings will then depend on the LED forward voltage differences. A. Any LED cathode short to ground. Current remains regulated in non-shorted LEDs. Matching may be affected. A6269 LA1 LA2 GND VIN A6269 B. Any LAx output short to ground. Shorted output is disabled. Other outputs remain active. LA1 LA2 GND VIN A6269 C. Current remains regulated. Matching may be affected. Only the shorted LED is inactive. LA1 LA2 GND VIN D. Short between LEDs in different strings. Current remains regulated. Current is summed and shared by affected strings. Intensity match dependent on voltage binning. A6269 LA1 LA2 GND Figure 1. Short circuit conditions. Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 6 A6269 The temperature at which the current reduction begins can be adjusted by changing the voltage on the THTH pin. When THTH is left open the temperature at which the current reduction begins is defined as the thermal monitor activation temperature, TJM, and is specified, in the characteristics table, at the 90% current level. 100 Relative Sense Current (%) Temperature Monitor A temperature monitor function, included in the A6269, reduces the LED current as the silicon junction temperature of the A6269 increases (see figure 2). By mounting the A6269 on the same thermal substrate as the LEDs, this feature can also be used to limit the dissipation of the LEDs. As the junction temperature of the A6269 increases, the regulated current level is reduced, reducing the dissipated power in the A6269 and in the LEDs. The current is reduced from the 100% level at typically 4% per degree Celsius until the point at which the current drops to 25% of the full value, defined at TJL . Above this temperature the current will continue to reduce at a lower rate until the temperature reaches the overtemperature shutdown threshold temperature, TJF. Automotive LED Array Driver 90 80 60 TJM 40 25 20 TJF TJL 0 70 130 90 110 Junction Temperature, TJ (°C) 150 170 Figure 2. Temperature monitor current reduction. TJM will increase as the voltage at the THTH pin, VTHTH , is reduced and is defined as approximately: TJM = 1.46 –VTHTH (°C) (3) 0.0039 A resistor connected between THTH and GND will reduce VTHTII and increase TJM. A resistor connected between THTH and a reference supply greater than 1 V will increase VTHTH and reduce TJM. In extreme cases, if the chip temperature exceeds the overtemperature limit, TJF , all regulators will be disabled. The temperature will continue to be monitored and the regulators re-activated when the temperature drops below the threshold provided by the specified hysteresis. Note that it is possible for the A6269 to transition rapidly between thermal shutdown and normal operation. This can happen if the thermal mass attached to the exposed thermal pad is small and TJM is increased to close to the shutdown temperature. The period of oscillation will depend on TJM , the dissipated power, the thermal mass of any heatsink present, and the ambient temperature. 1.2 200 1.1 150 RTH pull-down to GND 100 50 0 70 1.0 VTHTH 0.9 RTH pull-up to 3 V 80 VTHTH (V) RTH pull-up to 5 V RTH (kΩ) Figure 3 shows how the nominal value of the thermal monitor activation temperature varies with the voltage at THTH and with either a pull-down resistor, RTH, to GND or with a pull-up resistor, RTH , to 3 V and to 5 V. 1.3 250 90 100 110 120 130 140 Thermal Monitor Activation Temperature, TJM (°C) 0.8 150 Figure 3. TJM versus a pull-up or pull-down resistor, RTH, and VTHTH. Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 7 A6269 Automotive LED Array Driver Application Information Power Dissipation The most critical design considerations when using a linear regulator such as the A6269 are the power produced internally as heat and the rate at which that heat can be dissipated. There are three sources of power dissipation in the A6269: Note that the voltage drop across the regulator, VREG , is always greater than the specified minimum drop-out voltage, VDO . The output current is regulated by making this voltage large enough to provide the voltage drop from the supply voltage to the total forward voltage of all LEDs in series, VLED . The total power dissipated in the A6269 is the sum of the quiescent power, the reference power, and the power in each of the regulators: • The quiescent power to run the control circuits • The power in the reference circuit • The power due to the regulator voltage drop PDIS = PQ + PREF + PREGA + PREGB + PREGC + PREGD The elements relating to these dissipation sources are illustrated in figure 4. Quiescent Power The quiescent power is the product of the quiescent current, IINQ , and the supply voltage, VIN , and is not related to the regulated current. The quiescent power, PQ, is therefore defined as: PQ = VIN × IINQ (4) The power that is dissipated in each string of LEDs is: PLEDx = VLEDx × ILEDx (VIN – VREF) × VREF VIN A6269 VREG ILAx LAx (5) RREF Regulator Power In most application circuits the largest dissipation will be produced by the output current regulators. The power dissipated in each current regulator is simply the product of the output current and the voltage drop across the regulator. The total current regulator dissipation is the sum of the dissipation in each output regulator. The regulator power for each output is defined as: PREGx = (VIN – VLEDx ) × ILEDx where x is 1 or 2. (8) where x is A, B, C, or D, and VLEDx is the voltage across all LEDs in the string. Reference Power The reference circuit draws the reference current from the supply and passes it through the reference resistor to ground. The reference current is 8% of the output current on any one active output. The reference circuit power is the product of the reference current and the difference between the supply voltage and the reference voltage, typically 1.2 V. The reference power, PREF , is therefore defined as: PREF = (7) VIN IREF IINQ VLED IREF VREF RREF GND (6) Figure 4. Internal power dissipation sources. Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 8 A6269 Automotive LED Array Driver Dissipation Limits There are two features limiting the power that can be dissipated by the A6269: thermal shutdown and thermal foldback. Thermal Shutdown If the thermal foldback feature is disabled by connecting the THTH pin to GND, or if the thermal resistance from the A6269 to the ambient environment is high, then the silicon temperature will rise to the thermal shutdown threshold and the current will be disabled. After the current is disabled the power dissipated will drop and the temperature will fall. When the temperature falls by the hysteresis of the thermal shutdown circuit, then the current will be re-enabled and the temperature will start to rise again. This cycle will repeat continuously until the ambient temperature drops or the A6269 is switched off. The period of this thermal shutdown cycle will depend on several electrical, mechanical, and thermal parameters, and could be from a few milliseconds to a few seconds. Thermal Foldback If there is a good thermal connection to the A6269, then the thermal foldback feature will have time to act. This will limit the silicon temperature by reducing the regulated current and therefore the dissipation. operation of the A6269 with 2 strings of 3 red LEDs, each string running at 100 mA. The forward voltage of each LED is 2.3 V and the graph shows the current as the supply voltage increases from 14 to 17 V. As the supply voltage increases, without the thermal foldback feature, the current would remain at 100 mA, as shown by the dashed line. The solid line shows the resulting current decrease as the thermal foldback feature acts. If the thermal foldback feature did not affect LED current, the current would increase the power dissipation and therefore the silicon temperature. The thermal foldback feature reduces power in the A6269 in order to limit the temperature increase, as shown in figure 7. The figure shows the operation of the A6269 under the same conditions as figure 6. That is, 2 strings of 3 red LEDs, each string running at 100 mA with each LED forward voltage 54 52 Without thermal monitor 50 ILED (mA) From these equations (and as illustrated in figure 5) it can be seen that, if the power in the A6269 is not limited, then it will increase as the supply voltage increases but the power in the LEDs will remain constant. 48 46 44 The thermal monitor will reduce the LED current as the temperature of the A6269 increases above the thermal monitor activation temperature, TJM , as shown in figure 6. The figure shows the With thermal monitor 2 Strings VLED = 6.9 V ILED = 100 mA TA = 50°C 42 40 14.0 14.5 15.0 15.5 16.0 Supply Voltage, VIN (V) 16.5 17.0 Figure 6. LED current versus Supply Voltage 3.0 130 125 2.0 120 TJ (°C) Power Dissipation, PD (W) 2.5 1.5 LED Power 1.0 A6269 Power 0.5 0 8 9 10 Figure 5. Power Dissipation versus Supply Voltage 14 15 115 Without thermal monitor With thermal monitor 110 2 Strings VLED = 6.9 V ILED = 100 mA 11 12 13 Supply Voltage, VIN (V) 2 Strings VLED = 6.9 V ILED = 100 mA TA = 50°C 105 16 100 14.0 14.5 15.0 15.5 16.0 Supply Voltage, VIN (V) 16.5 17.0 Figure 7. Junction Temperature versus Supply Voltage Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 9 A6269 at 2.3 V. The graph shows the temperature as the supply voltage increases from 14 to 17 V. Without the thermal foldback feature the temperature would continue to increase up to the thermal shutdown temperature as shown by the dashed line. The solid line shows the effect of the thermal foldback function in limiting the temperature rise. Figures 6 and 7 show the thermal effects where the thermal resistance from the silicon to the ambient temperature is 40°C/W. Thermal performance can be enhanced further by using a significant amount of thermal vias as described below. Supply Voltage Limits In many applications, especially in automotive systems, the available supply voltage can vary over a two-to-one range, or greater when double battery or load dump conditions are taken into consideration. In such systems is it necessary to design the application circuit such that the system meets the required performance targets over a specified voltage range. To determine this range when using the A6269 there are two limiting conditions: • For maximum supply voltage the limiting factor is the power that can be dissipated from the regulator without exceeding the temperature at which the thermal foldback starts to reduce the output current below an acceptable level. • For minimum supply voltage the limiting factor is the maximum drop-out voltage of the regulator, where the difference between the load voltage and the supply is insufficient for the regulator to maintain control over the output current. Minimum Supply Limit: Regulator Saturation Voltage The supply voltage, VIN , is always the sum of the voltage drop across the high-side regulator, VREG , and the forward voltage of the LEDs in the string, VLED, as shown in figure 4. VLED is constant for a given current and does not vary with supply voltage. Therefore VREG provides the variable difference between VLED and VIN . VREG has a minimum value below which the regulator can no longer be guaranteed to maintain the output current within the specified accuracy. This level is defined as the regulator drop-out voltage, VDO. The minimum supply voltage, below which the LED current does not meet the specified accuracy, is therefore determined by the Automotive LED Array Driver sum of the minimum drop-out voltage, VDO , and the forward voltage of the LEDs in the string, VLED . The supply voltage must always be greater than this value and the minimum specified supply voltage, that is: VIN > VDO + VLED, and VIN > VIN (min) (9) As an example, consider the configuration used in figures 6 and 7 above, namely 2 strings of 3 red LEDs, each string running at 100 mA, with each LED forward voltage at 2.3 V. The minimum supply voltage will be approximately: VIN(min) = 0.55 + (3 × 2.3) = 7.45 V Maximum Supply Limit: Thermal Limitation As described above, when the thermal monitor reaches the activation temperature, TJM (due to increased power dissipation as the supply voltage rises), the thermal foldback feature causes the output current to decrease. The maximum supply voltage is therefore defined as the voltage above which the LED current drops below the acceptable minimum. This can be estimated by determining the maximum power that can be dissipated before the internal (junction) temperature of the A6269 reaches TJM. Note that, if the thermal monitor circuit is disabled (by connecting the THTH pin to GND), then the maximum supply limit will be the specified maximum continuous operating temperature, 150°C. The maximum power dissipation is therefore defined as: PD(max) = ∆T(max) RθJA (10) where ΔT(max) is difference between the thermal monitor activation temperature, TJM , of the A6269 and the maximum ambient temperature, TA(max), and RθJA is the thermal resistance from the internal junctions in the silicon to the ambient environment. If minimum LED current is not a critical factor, then the maximum voltage is simply the absolute maximum specified in the parameter tables above. Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 10 A6269 Automotive LED Array Driver Thermal Dissipation The amount of heat that can pass from the silicon of the A6269 to the surrounding ambient environment depends on the thermal resistance of the structures connected to the A6269. The thermal resistance, RθJA , is a measure of the temperature rise created by power dissipation and is usually measured in degrees Celsius per watt (°C/W). The temperature rise, ΔT, is calculated from the power dissipated, PD , and the thermal resistance, RθJA , as: ΔT = PD × RθJA (11) A thermal resistance from silicon to ambient, RθJA , of approximately 35°C/W can be achieved by mounting the A6269 on a standard FR4 double-sided printed circuit board (PCB) with a copper area of a few square inches on each side of the board under the A6269. Additional improvements in the range of 20% may be achieved by optimizing the PCB design. Optimizing Thermal Layout The features of the printed circuit board, including heat conduction and adjacent thermal sources such as other components, have a very significant effect on the thermal performance of the device. To optimize thermal performance, the following should be taken into account: • The device exposed thermal pad should be connected to as much copper area as is available. • Copper thickness should be as high as possible (for example, 2 oz. or greater for higher power applications). • The greater the quantity of thermal vias, the better the dissipation. If the expense of vias is a concern, studies have shown that concentrating the vias directly under the device in a tight pattern, as shown in figure 8, has the greatest effect. • Additional exposed copper area on the opposite side of the board should be connected by means of the thermal vias. The copper should cover as much area as possible. • Other thermal sources should be placed as remote from the device as possible Signal traces LJ package footprint 0.7 mm 0.7 mm LJ package exposed thermal pad Top-layer exposed copper Ø0.3 mm via Figure 8. Suggested PCB layout for thermal optimization (maximum available bottom-layer copper recommended) Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 11 A6269 Application Examples Operation with High-Side PWM Supply In some filament bulb replacement applications the supply may be provided by a PWM-driven high-side switch. The A6269 can be used in this application by simply connecting EN to VIN. The toggle action of the SW input will be reset to off at each power-up. From this stage, applying an EN = high signal turns the LED on, and an EN = low turns the LED off. When power is applied (with EN connected to VIN), there will be a short startup delay, tON , before the current starts to rise. The rise time of the current will be limited by the internal current slew rate control. Figures 9a to 9c show application circuit options, including a higher voltage supply, and combinations of outputs tied together and disabled. Operation with both EN and SW In some applications it may be required to utilize the functionality of both the EN input and the SW input. For example in dome lighting (see figure 10), a manual switch may be used to toggle the light on or off. While Automotive LED Array Driver the light is in the off state, the central lighting control unit may send a PWM signal to dim the light gradually before turning off completely. The interaction of the two control inputs is explained below: • Internal flip-flop (hence LED light) starts from off state, ensured by power-on reset. • The light can be turned on by either EN = high or by a momentary toggle (high→low→high) at the SW input. • If the light is initially turned on by EN = high, it can be turned off by EN = low. This allows PWM dimming of the light. • If the light is initially turned on by SW input, it stays on regardless of the state of EN. The light goes off only when another momentary toggle is received at the SW input, or when the power is removed. The behavior above is graphically represented by the state diagram in figure 11. Note that the manual SW input always take precedence over the EN/PWM dimming input. Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 12 A6269 Automotive LED Array Driver + + 12 V PWM high-side drive Automotive 24 V power net VIN VIN A6269 EN A6269 LA1 LA1 On/Off EN SW IREF SW LA2 IREF LA2 THTH THTH GND GND – – A. High brightness (HB) LED incandescent lamp replacement B. Higher voltage operation + Automotive 12 V power net VIN A6269 LA1 EN On/Off SW IREF LA2 THTH GND – C. Mix of output combinations Figure 9. Typical applications with various supply and output options. + Automotive 24 V power net SW = momentarily shorted to GND to toggle VIN PWM dimming input from LCU EN = L SW = H EN = H A6269 EN EN = H LA1 On/Off Start LED = Off LED = On SW IREF EN = L LED = Off PWM Dimming LA2 THTH SW = GND – Figure 10. Typical applications using SW and EN together SW = SW = LED = On Figure 11. State diagram when both SW and EN are used Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 13 A6269 Automotive LED Array Driver Package LJ, 8-Pin SOICN with Exposed Thermal Pad 4.90 ±0.10 0.65 8° 0° 8 0.25 0.17 B 2.41 NOM A 1 3.90 ±0.10 6.00 ±0.20 SEATING PLANE GAUGE PLANE Branded Face 1.27 BSC 1 1.27 0.40 0.25 BSC 0.51 0.31 2.41 2 SEATING PLANE 0.10 C C 5.60 2 3.30 C PCB Layout Reference View For Reference Only; not for tooling use (reference MS-012BA) Dimensions in millimeters Dimensions exclusive of mold flash, gate burrs, and dambar protrusions Exact case and lead configuration at supplier discretion within limits shown 1.70 MAX 0.15 0.00 1.27 1.04 REF 3.30 NOM 8X 8 1.75 A Terminal #1 mark area B Exposed thermal pad (bottom surface) C Reference land pattern layout (reference IPC7351 SOIC127P600X175-9AM); all pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary to meet application process requirements and PCB layout tolerances; when mounting on a multilayer PCB, thermal vias at the exposed thermal pad land can improve thermal dissipation (reference EIA/JEDEC Standard JESD51-5) Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 14 A6269 Automotive LED Array Driver Revision History Revision Revision Date Rev. 7 June 24, 2013 Description of Revision Update Features List, fig. 5 Copyright ©2009-2013, Allegro MicroSystems, LLC Allegro MicroSystems, LLC reserves the right to make, from time to time, such departures from the detail specifications as may be required to permit improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the information being relied upon is current. Allegro’s products are not to be used in life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the failure of that life support device or system, or to affect the safety or effectiveness of that device or system. The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, LLC assumes no responsibility for its use; nor for any infringement of patents or other rights of third parties which may result from its use. For the latest version of this document, visit our website: www.allegromicro.com Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 15