A6260 High Brightness LED Current Regulator Features and Benefits Description ▪ AEC Q-100 qualified ▪ LED drive current up to 350 mA ▪ 6 to 40 V supply ▪ Reverse battery protection ▪ Low drop-out voltage ▪ LED short circuit and thermal protection ▪ 10 μA maximum shutdown current ▪ PWM dimming control input ▪ Current slew rate limiting The A6260 is a linear, programmable current regulator providing up to 350 mA for driving high-brightness LEDs. The LED current, accurate to 4%, is set by a single low-power sense resistor. Driving LEDs with constant current ensures safe operation with maximum possible light output. For automotive applications, optimum performance is achieved when driving between 1 and 3 LEDs at currents up to 350 mA. The low dropout voltage of the A6260 allows a single white LED to be driven safely, at full current, with a supply voltage down to 6 V. An enable input allows PWM dimming and can be used to enable low-current sleep mode. The rate of change of current during PWM switching is limited to reduce EMI. Overcurrent detection is provided to protect the LEDs and the A6260 during short-to-supply or short-to-ground at any LED terminal. The integrated temperature monitor can be used to reduce the LED drive current if the chip temperature exceeds the thermal limit. The device is available in an 8-pin SOIC package with exposed thermal pad (suffix LJ). The device is lead (Pb) free with 100% matte-tin leadframe plating. Package: 8-pin SOICN with exposed thermal pad (suffix LJ) Not to scale Not to scale Typical Application 7 to 20 V (–14 V min, 40 V max) VIN PWM Dimming and On-Off Control LA EN A6260 Automotive 12 V Power Net THTH LC LSS SENSE GND 6260-DS, Rev. 7 DRAFT sept10 2013 A6260 High Brightness LED Current Regulator Selection Guide Part Number A6260KLJTR-T A6260SLJTR-T Ambient Temperature, TA (°C) Packing 3000 pieces per reel 3000 pieces per reel –40 to 125 –20 to 85 Absolute Maximum Ratings* Characteristic Symbol Notes Rating Units Load Supply Voltage VIN –14 to 40 V EN Pin Voltage VEN –14 to 40 V LA and LC Pins Voltage VLx –0.3 to 40 V VLSS –0.3 to 0.3 V SENSE Pin Voltage VSENSE –0.3 to 0.3 V THTH Pin Voltage VTHTH –0.3 to 7 V Range K –40 to 125 ºC Range S –20 to 85 ºC –40 to 150 ºC LSS Pin Voltage Ambient Operating Temperature Range TA Junction Operating Temperature Range TJ Storage Temperature Range Tstg –55 to 150 ºC ESD Rating, Human Body Model AEC-Q100-002, all pins 2000 V ESD Rating, Charged Device Model AEC-Q100-011, all pins 1050 V *With respect to GND. 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 Value Unit On 4-layer PCB based on JEDEC standard Test Conditions* 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 A6260 High Brightness LED Current Regulator Functional Block Diagram VBATT VIN Current Limited Reg EN THTH Control Output Logic Monitor Temp Temp Comp Monitor LC Current Slew Reference R LA Switch Regulator Limit Generator LSS SENSE TH Pad GND RS Pin-out Diagram 8 LSS SENSE 1 GND 2 THTH 3 6 LA EN 4 5 VIN Pad 7 LC Terminal List Table Number Name Description 1 SENSE 2 GND 3 THTH 4 EN Enable input 5 VIN Main supply Current sense input Ground reference Thermal threshold input 6 LA LED anode (+) connection 7 LC LED cathode (-) connection 8 LSS Low-side sense connection 9 Pad Exposed pad for enhanced thermal dissipation Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 3 A6260 High Brightness LED Current Regulator ELECTRICAL CHARACTERISTICS valid at TJ = –40°C to 150°C, VIN = 7 to 40 V, unless noted otherwise Characteristics Symbol Test Conditions Min. Typ. Max. Units Supply and Reference VIN Functional Operating Range1 VIN 6 – 40 V VIN Quiescent Current IINQ LA, LC unconnected – – 4 mA VIN Shutdown Current IINS EN < 400 mV – 1 10 μA Startup Time tON EN 2 V to 35 mA ILC 9 18 27 μs Current Regulation Maximum Current Sink Current Sink Current Sink Accuracy SENSE Reference Voltage ILCmax RS = 250 mΩ, VIN – VLA > 2 V 350 – – mA ILC RS = 286 mΩ, VIN – VLA > 2 V 333 350 367 mA 100 mA < ILC < 350 mA –5 ±4 5 % 97 102 107 mV VIN – VLA , ILOAD = 350 mA – 2.25 2.35 V VIN – VLA , ILOAD = 150 mA – 1.35 1.4 V VLC – VSENSE, ILOAD = 350 mA – 500 550 mV VLC – VSENSE, ILOAD = 150 mA – 250 275 mV errILC VSENREF 260 mΩ < RS < 1Ω Switch Dropout Voltage VDO Regulator Saturation Voltage VSAT Output Current Slew Time tr Current rising from 10% to 90% 50 80 120 μs tf Current falling from 90% to 10% 60 100 150 μs Logic Input Input Low Voltage VIL – – 0.8 V Input High Voltage VIH 2 – – V VIhys 150 350 – mV –600 –500 –400 mA – 3 – μs – 1.5× ILAOC – mA Measured at VLC, when rising 1.0 1.2 1.4 V mA Input Hysteresis Protection Switch Overcurrent Trip Level ILAOC Overcurrent Detection Time2 tOCD Switch Current Limit ILALIM LC Short Circuit Release Voltage Short Circuit Source Current2 VSCCR From detection to ISCU > –1.2 mA ISCU When short is detected –1.5 –1.1 –0.7 Thermal Monitor Activation Temperature TJM TJ at ILC = 90%, THTH open 90 105 120 ºC Thermal Monitor Low Current Temperature TJL TJ at ILC = 25%, THTH open 110 130 150 ºC TJF Temperature increasing – 165 – ºC TJhys Recovery = TJF – TJhys – 15 – ºC Overtemperature Shutdown Threshold Overtemperature Hysteresis 1Functions 2For correctly, but parameters are not guaranteed, below the general limit (7 V). input and output current specifications, negative current is defined as coming out of (sourcing) the specified device pin. Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 4 A6260 High Brightness LED Current Regulator Functional Description The A6260 is a linear current regulator that is designed to provide drive current and protection for series-connected, high brightness LEDs in automotive applications. It provides programmable current output at load voltages up to 3 V below the main supply voltage. For automotive applications optimum performance is achieved when driving 1 to 3 LEDs at currents up to 350 mA. The LED current is set by a single low-power sense resistor and the LED brightness can be further controlled by a PWM input to the EN pin. The EN input can also be used as an on/off switched input and the A6260 will enter a low current (<10 μA) sleep mode if EN is held low. For incandescent replacement configurations, the EN input can be connected directly to the VIN pin with the supply to VIN controlled by a simple on/off switch. The LEDs and the regulator are protected from excessive currents caused by short circuits to ground or supply or by reversal of the power supply connections. Integrated thermal management circuits can be used to reduce the regulated current level at high temperatures to limit power dissipation. LA Pin Switched and protected current source connected to the anode of the LEDs. LC Pin Controlled current sink connected to the cathode of the LEDs. LSS Pin Low-side current sink connection from the current regu- lator to power ground via a sense resistor. A current sense resistor (240 mΩ to 3 Ω) is connected between LSS and power ground. SENSE Pin LED current sense input. The high impedance SENSE input should have an independent connection to the top (LSS connection side) of the sense resistor. LED Current Level The LED current is controlled by the internal current regulator between the LC and LSS pins. This current, defined as the current into the LC pin, ILC, is set by the value, RS , of the sense resistor. The voltage across the sense resistor, measured between the SENSE pin and the GND pin, is compared to a reference voltage, nominally 102 mV, allowing the use of a low-value sense resistor with low power dissipation. The LED current is thus defined as: ILC = VSENREF / RS conversely: RS = VSENREF / ILC Pin Functions VIN Pin Supply to the control circuit. A small-value ceramic bypass capacitor (typically 100 nF) should be connected from close to this pin to the GND pin. GND Pin Ground reference connection. Should be connected directly to the negative supply as close as possible to the bottom (ground connection) of the sense resistor. EN Pin Logic input to enable operation. Can be used as a direct PWM input. Chip enters a low-power sleep mode when this pin is held low. (1) The nominal output current settings, ILC, versus the current setting resistor values, RS, are given in the following table. The current level defined here is the 100% current level before any current reduction effects due to the temperature monitor, described later in this document. Sense Resistor Selection ILC (mA) RS (mΩ) PD(RS) (mW) ILC (mA) RS (mΩ) PD(RS) (mW) 350 286 35 125 800 13 300 333 30 100 1000 10 250 400 25 70 1429 7 THTH Pin Sets the thermal monitor threshold, TJM, where the 200 500 20 50 2000 5 output current starts to be reduced with increasing temperature. When this pin is left open, the threshold temperature will typically be the specified default value. A resistor connected between THTH and GND can be used to increase the threshold temperature. A resistor connected between THTH and VIN can be used to decrease the threshold temperature. Connecting THTH directly to GND disables the thermal monitor function. 150 667 15 35 2857 4 Parallel operation The A6260 is a constant current controller, that is, it controls the output current irrespective of output voltage (within the compliance range). This allows the outputs of two or more A6260s to be connected in parallel (see figure 7, in the Applications Information section). In this configuration, each A6260 must have a Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 5 A6260 High Brightness LED Current Regulator dedicated sense resistor, which determines its share of the current provided to the LED. that the complete circuit, including LEDs, may remain connected to the power supply under all conditions. LED Brightness Safety Features Although the LED brightness can be controlled by changing the current (intensity) this may slightly affect the color or the color temperature of the light from the LED. When multiple LEDs are used, it is usually more desirable to control the brightness by switching the fixed LED current with a pulse width modulated signal. This allows the LED brightness to be set using a digital control input with little effect on the LED color. The circuit includes several features to ensure safe operation and to protect the LEDs and the A6260: In the A6260, the brightness level can be controlled by a PWM signal applied to the EN input. This controls both the low-side linear regulator and the high-side switch. When EN is switched from high to low, the low-side regulator reduces the current to zero before allowing the high-side switch to turn off. ▪ The high-side switch between VIN and LA has overcurrent detection and a current limiter. It assumes that a short circuit is present if the current exceeds the trip value, ILAOC , for longer than the overcurrent detection time, tOCD. ▪ The current regulator between LC and LSS provides a natural current limit due to the regulation. ▪ 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 total of five short circuit conditions can exist as illustrated in figure 1. When EN is switched from low to high, the high-side switch is turned on before the low-side regulator increases the current to the full operating level. LA Short to Supply (figure 1a) This condition is permitted To assist EMC, the rate of change of the LED current is limited and the current will rise and fall within the limits (tr, tf) defined in the Electrical Characteristics table. because the current remains regulated by the current sink. This configuration may also be used in applications with low supply voltages (see figure 4d in the Applications Information section). Note that EN can be used for PWM dimming even when the high-side switch is bypassed. (See figure 7(d)). LA Short to Ground (figure 1b) This condition is detected when Sleep Mode When EN is held low, the A6260 will be in shutdown mode and all internal circuits will be in a low-power sleep mode. In this mode, the input current, IINS , will be less than 10 μA. This means VIN LA A6260 VIN LA A6260 LC GND VIN LA A6260 LC GND the high-side switch current exceeds the trip value, ILAOC , for longer than the overcurrent detection time, tOCD (3 μs typical). When a short is detected, the switch and the regulator are both disabled. When the voltage at LC drops below the short release voltage, VSCCR, a low value current, ISCU (1.1 mA typical), is then sourced from LA to provide a short circuit monitor. When VIN LC GND VIN LA A6260 LA A6260 LC LC GND GND (a) LA Short to Supply (b) LA Short to Ground (c) LC Short to Supply (d) LC Short to Ground (e) LA Short to LC Permitted because current remains regulated Detected when switch current exceeds trip value for longer than 3 μs, released when VLC >VSCCR Current remains regulated, thermal shutdown provides protection Detected when switch current exceeds trip value for longer than 3 μs, released when VLC >VSCCR Current remains regulated, thermal shutdown provides protection Figure 1. Short circuit conditions detected Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 6 A6260 High Brightness LED Current Regulator the short circuit is removed the short circuit source current, ISCU , pulls the voltage at the LC pin above VSCCR, and the switch and regulator are re-enabled. LC Short to Supply (figure 1c) In this condition, the current into the LC pin remains regulated but the power dissipated in the A6260 increases. This higher dissipation causes the thermal monitor to reduce the current to protect the regulator. In extreme cases, or in cases where the thermal monitor is disabled, the increased dissipation may cause temperature to reach the thermal shutdown level, at which point the regulator will be disabled. LC Short to Ground (figure 1d) This condition is detected when the high-side switch current exceeds the trip value, ILAOC , for longer than the overcurrent detection time, tOCD (3 μs typical). When a short is detected, the switch and the regulator are both disabled. When the voltage at LC drops below the short release voltage, VSCCR, a low value current, ISCU (1.1 mA typical), is then sourced from LA to provide a short circuit monitor. When the short circuit is removed, ISCU pulls the voltage at the LC pin above VSCCR, and the switch and regulator are re-enabled. LA Short to LC (figure 1e) This condition is effectively the same per degree Celsius typically, until the point at which the current drops to 25% of the full level. The junction temperature at the 25% current level is defined as TJL. If the temperature continues to rise above TJL, the temperature monitor would continue to reduce current, but at a slower rate, until the temperature reaches the overtemperature shutdown temperature, TJF. 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 typically 98°C. The thermal monitor activation temperature, TJM, is defined in the Electrical Characteristics table at the 90% current level. TJM can be increased by reducing the voltage at the THTH pin, VTHTH, and is defined as approximately: 1.503 − V THTH TJM = (2) 0.00363 where TJM is in °C. A resistor connected between THTH and a reference supply greater than 2 V will increase VTHTH and reduce TJM. as the LC Short-to-Supply condition. In this condition, the current into the LC pin remains regulated but the power dissipated in the A6260 increases. This higher dissipation causes the thermal monitor to reduce the current to protect the regulator. In extreme cases, or in cases where the thermal monitor is disabled, the increased dissipation may cause temperature to reach the thermal shutdown level, at which point the regulator will be disabled. The primary function of the temperature monitor included in the A6260 is to limit the power dissipation of the A6260 and maintain the junction temperature below the maximum. However, it can also be used to reduce LED current as LED temperature increases. This can be achieved by mounting the A6260 on the same thermal substrate as the LEDs, so that temperature rise in the LEDs would also affect the A6260. As the junction temperature of the A6260 increases, the integrated temperature monitor lowers the regulated current level, reducing the dissipated power in the A6260 and in the LEDs. As shown in figure 2, from the full 100% current level (see the LED Current Level section), current is reduced at a rate of 4% 90 Relative LED Current, ILC (%) Temperature Monitor 100 80 60 40 25 20 0 70 90 TJM 110 TJL 130 150 170 Junction Temperature, TJ (°C) Figure 2. Temperature monitor current reduction Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 7 High Brightness LED Current Regulator LED Current, Power Loss, and Junction Temperature Calculations 1.40 900 1.35 800 1.30 700 TH 500 RTH pull-up to 5 V 400 1.10 1.05 1.00 100 0.95 0.90 60 80 Figure 4 shows LED current versus input voltage and figure 5 shows junction temperature versus input voltage. Test conditions were: 120 140 Figure 3. TJM versus RTH (pull-up or –down), and VTHTH 400 380 Without thermal monitor ILED 360 340 320 With thermal monitor ILEDM 300 280 260 then the RθJA for the device, when mounted on a typical application board, 30 °C/W. If thermal derating is used, ILED current is reduced at a rate of 4% per °C (typ) from TJM. 100 TJM (°C) I LED(mA) (4) 1.15 200 40 if VSENREF = 0.102 V, IINQ = 3 mA (typ), and given 1.20 300 Power loss across IC, PD = (VIN – VLED – VSENREF) × ILED + VIN × IINQ (3) VLED=7V I LED=350mA TA=50°C 240 220 RθJA= 30 °C/W 200 8 10 12 VIN (V) 14 16 Figure 4. LED current, ILED, versus input voltage, VIN, both with and without thermal monitor • VLED = 7 V, 150 • ILED = 350 mA, 140 Without thermal monitor TJ 130 • TA = 50°C, 120 TJ(°C) • RθJA = 30 °C/W, and • The THTH pin open for thermal monitor testing RTH pull-down to GND TH 0 The maximum LED current the A6260 can deliver depends on voltage drop across the IC ( VIN – VLED ), ambient temperature ( TA ), and thermal resistance ( RθJA ) from the IC junction to ambient. RθJA depends on board construction, and air flow, and can be calculated as follows: Junction temperature, TJ = PD × RθJA 1.25 V 600 RTH (kΩ) In extreme cases, if the chip temperature exceeds the overtemperature limit, TJF, both the sink regulator and the source switch will be disabled. The temperature will continue to be monitored and the output re-activated when the temperature drops below the threshold provided by the specified hysteresis, TJhys. 1000 (V) Figure 3 shows how the nominal value of the thermal monitor activation temperature varies with the voltage at THTH and with a pull-down resistor, RTH, to GND or with a pull-up resistor, RTH, to 5 V. V A6260 110 100 With thermal monitor, TJM 90 80 VLED=7V I LED=350mA TA=50°C RθJA= 30 °C/W 70 60 50 8 10 12 VIN (V) 14 16 Figure 5. Junction temperature, TJ, versus input voltage, VIN, both with and without thermal monitor Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 8 A6260 High Brightness LED Current Regulator Thermal Dissipation Optimizing Thermal Layout The amount of heat that can pass from the silicon of the A6260 to the surrounding ambient environment depends on the thermal resistance of the structures connected to the A6260. 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 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 temperature rise, ΔT, is calculated from the power dissipated, PD , and the thermal resistance, RθJA , as: ΔT = PD × RθJA (5) A thermal resistance from silicon to ambient, RθJA , of approximately 35°C/W can be achieved by mounting the A6260 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 A6260. Additional improvements in the range of 20% may be achieved by optimizing the PCB design. • 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 6, 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 6. 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 9 A6260 High Brightness LED Current Regulator Applications Information Automotive 12V Power Net Automotive 12V Power Net VIN LA VIN LA A6260 PWM Dimming and On-Off Control A6260 PWM Dimming and On-Off Control EN EN LC THTH GND LC THTH LSS SENSE LSS GND Ground SENSE Ground (a) Basic circuit with PWM Automotive 12 V Power Net (b) Switched supply plus high-side PWM source Low Voltage (>6V) Supply VIN VIN LA LA A6260 A6260 PWM Dimming and On-Off Control EN THTH GND EN LC THTH LSS SENSE GND Ground LC LSS SENSE Ground (c) Simple switched supply (lamp replacement) Automotive 12 V Power Net (d) Low voltage operation VIN VIN LA LA A6260 PWM Dimming and On-Off Control A6260 EN THTH GND EN LC LSS SENSE LC LSS SENSE THTH GND Ground (e) Parallel operation for higher LED current Figure 7. Typical applications circuits Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 10 A6260 High Brightness LED Current Regulator Package LJ 8-Pin SOICN with Exposed Thermal Pad 4.90 ±0.10 0.65 8° 0° 8 B A 1 3.90 ±0.10 6.00 ±0.20 2 SEATING PLANE GAUGE PLANE Branded Face SEATING PLANE 0.10 C 1.27 BSC 1 1.27 0.40 0.25 BSC 0.51 0.31 2.41 1.04 REF 3.30 NOM 8X 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 1.75 0.25 0.17 2.41 NOM 8 A Terminal #1 mark area B Exposed thermal pad (bottom surface); dimensions may vary with device 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 11 A6260 High Brightness LED Current Regulator Revision History Revision Revision Date Rev. 7 September 12, 2013 Description of Revision Update functional description Copyright ©2007-2013, 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 12