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| A6260 High Brightness LED Current Regulator Features and Benefits Automotive grade 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 A maximum shutdown current PWM dimming control input Current slew rate limiting Description 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 SOIC with exposed thermal pad (suffix LJ) Not to scale Typical Application 7 to 20 V (-14 V min, 40 V max) VIN PWM Dimming and On-Off Control Automotive 12 V Power Net THTH LC LSS SENSE GND LA EN A6260 6260-DS A6260 High Brightness LED Current Regulator Selection Guide Part Number A6260KLJTR-T Packing 3000 pieces per reel Absolute Maximum Ratings* Characteristic Load Supply Voltage EN Pin Voltage LA and LC Pins Voltage LSS Pin Voltage SENSE Pin Voltage THTH Pin Voltage Ambient Operating Temperature Range Junction Operating Temperature Range Storage Temperature Range ESD Rating, Human Body Model ESD Rating, Charged Device Model *With respect to GND. Symbol VIN VEN VLx VLSS VSENSE VTHTH TA TJ Tstg AEC-Q100-002, all pins AEC-Q100-011, all pins Range K Notes Rating -14 to 40 -14 to 40 -0.3 to 40 -0.3 to 0.3 -0.3 to 0.3 -0.3 to 7 -40 to 125 -40 to 150 -55 to 150 2000 1050 Units V V V V V V C C C V V THERMAL CHARACTERISTICS may require derating at maximum conditions Characteristic Symbol RJA RJP *Additional thermal information available on Allegro website. Test Conditions* 4-layer PCB based on JEDEC standard Package Thermal Resistance 2-layer PCB with 0.8 each side in.2 of copper area Value 35 62 2 Units C/W C/W C/W Allegro MicroSystems, Inc. 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 Reg Current Limited Switch LA EN Control Logic Output Monitor THTH Temp Comp Reference Temp Monitor Current Slew Limit Regulator LC LSS SENSE RS R Generator TH GND Pin-out Diagram SENSE GND THTH EN 1 2 3 4 8 LSS 7 LC 6 LA 5 VIN Terminal List Table Number 1 2 3 4 5 6 7 8 Name SENSE GND THTH EN VIN LA LC LSS Description Current sense input Ground reference Thermal threshold input Enable input Main supply LED anode (+) connection LED cathode (-) connection Low-side sense connection Allegro MicroSystems, Inc. 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 = -40C to 150C, VIN = 7 to 40 V, unless noted otherwise Characteristics Supply and Reference VIN Functional Operating Range1 VIN Quiescent Current VIN Shutdown Current Startup Time Current Regulation Maximum Current Sink Current Sink Current Sink Accuracy SENSE Reference Voltage Switch Dropout Voltage Regulator Saturation Voltage Output Current Slew Time Logic Input Input Low Voltage Input High Voltage Input Hysteresis Protection Switch Overcurrent Trip Level Overcurrent Detection Time2 Switch Current Limit LC Short Circuit Release Voltage Short Circuit Source Current2 Thermal Monitor Activation Temperature Thermal Monitor Low Current Temperature Overtemperature Shutdown Threshold Overtemperature Hysteresis 1Functions 2For Symbol VIN IINQ IINS tON ILCmax ILC errILC Test Conditions Min. 6 Typ. - - 1 18 - 350 4 102 2.25 1.35 500 250 80 100 - - 350 -500 3 1.5x ILAOC 1.2 -1.1 105 130 165 15 Max. 40 4 10 27 - 367 5 107 2.35 1.4 550 275 120 150 0.8 - - -400 - - 1.4 -0.7 120 150 - - Units V mA A s mA mA % mV V V mV mV s s V V mV mA s mA V mA C C C C LA, LC unconnected EN < 400 mV EN 2 V to 35 mA ILC RS = 250 mW, VIN - VLA > 2 V RS = 286 mW, VIN - VLA > 2 V 100 mA < ILC < 350 mA VIN - VLA , ILOAD = 350 mA VIN - VLA , ILOAD = 150 mA VLC - VSENSE, ILOAD = 350 mA VLC - VSENSE, ILOAD = 150 mA Current rising from 10% to 90% Current falling from 90% to 10% - - 9 350 333 -5 97 - - - - 50 60 - 2 150 -600 VSENREF 260 m < RS < 1 VDO VSAT tr tf VIL VIH VIhys ILAOC tOCD ILALIM VSCCR ISCU TJM TJL TJF TJhys Measured at VLC, when rising When short is detected TJ at ILC = 90%, THTH open TJ at ILC = 25%, THTH open Temperature increasing Recovery = TJF - TJhys From detection to ISCU > -1.2 mA - - 1.0 -1.5 90 110 - - 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, Inc. 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 A) 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. Pin Functions VIN Pin Supply to the control circuit. A small-value ceramic 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 m to 3 ) 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: conversely: ILC = VSENREF / RS RS = VSENREF / ILC 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) 350 300 250 200 150 RS (m) 286 333 400 500 667 PD(RS) (mW) 35 30 25 20 15 ILC (mA) 125 100 70 50 35 RS (m) 800 1000 1429 2000 2857 PD(RS) (mW) 13 10 7 5 4 (1) 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. THTH Pin Sets the thermal monitor threshold, TJM, where the 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. 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 4e, in the Applications Information section). In this configuration, each A6260 must have a 5 Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com A6260 High Brightness LED Current Regulator 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 A6260: 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. LA Short to Supply (figure 1a) This condition is permitted dedicated sense resistor, which determines its share of the current provided to the LED. LED Brightness 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. 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. 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. 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. Note that EN can be used for PWM dimming even when the high-side switch is bypassed. (See figure 4(d)). 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 A. This means 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). LA Short to Ground (figure 1b) This condition is detected when the high-side switch current exceeds the trip value, ILAOC , for longer than the overcurrent detection time, tOCD (3 s 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 LA A6260 LC GND VIN LA A6260 LC GND VIN LA A6260 LC GND VIN LA A6260 LC GND VIN LA A6260 LC GND VIN (a) LA Short to Supply Permitted because current remains regulated (b) LA Short to Ground Detected when switch current exceeds trip value for longer than 3 s, released when VLC >VSCCR (c) LC Short to Supply Current remains regulated, thermal shutdown provides protection (d) LC Short to Ground Detected when switch current exceeds trip value for longer than 3 s, released when VLC >VSCCR (e) LA Short to LC Current remains regulated, thermal shutdown provides protection Figure 1. Short circuit conditions detected Allegro MicroSystems, Inc. 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 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 98C. 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. The equivalent circuit of the THTH pin is a 1.124 V source with a series 5 k resistor. A resistor connected between THTH and GND will reduce VTHTH and increase TJM , according to the following formula: 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 s 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 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. VTHTH = 1.124 x RTH 5 + RTH (3) where RTH, in k, is the resistor between THTH and GND. A resistor connected between THTH and a reference supply greater than 2 V will increase VTHTH and reduce TJM. For Temperature Monitor 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% 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 Relative LED Current, ILC (%) 100 90 80 60 40 25 20 0 TJM 70 90 110 TJL 130 TJF 150 170 Junction Temperature, TJ (C) Figure 2. Temperature monitor current reduction Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 7 A6260 High Brightness LED Current Regulator example, with RTH connected to 5 V, VTHTH will be: 300 1.4 V THTH = 1.124 + (V R - 1.124) x 5 5 + R TH 250 1.3 (4) 200 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 5V. 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. RTH (k) 150 1.1 100 RTH pull-up to 5 V 1.0 50 0.9 RTH pull-down to GND 0 50 70 90 110 130 0.8 150 TJM (C) Figure 3. TJM versus RTH (pull-up or -down), and VTHTH Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com VTHTH (V) VT HT 1.2 H 8 A6260 High Brightness LED Current Regulator Applications Information Automotive 12V Power Net Automotive 12V Power Net VIN LA VIN LA PWM Dimming and On-Off Control High-Side EN PWM Source LC LSS SENSE Ground EN THTH THTH LC LSS SENSE GND Ground GND (a) Basic circuit with PWM (b) Switched supply plus high-side PWM source Automotive 12 V Power Net VIN LA Low Voltage (>6V) Supply VIN LA EN EN THTH LC LSS SENSE Ground THTH LC LSS SENSE GND Ground GND (c) Simple switched supply (lamp replacement) (d) Low voltage operation Automotive 12 V Power Net VIN LA LA VIN PWM Dimming and On-Off Control EN EN THTH LC LSS SENSE LC LSS SENSE THTH GND GND Ground (e) Parallel operation for higher LED current Figure 4. Typical applications circuits Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 9 A6260 High Brightness LED Current Regulator Package LJ 8-Pin SOICN with Exposed Thermal Pad 4.90 8 4 0.21 B 2.41 3.90 A 6.00 0.84 1 2 3.30 0.25 SEATING PLANE GAUGE PLANE All dimensions nominal, not for tooling use (reference JEDEC MS-012 AA) Dimensions in millimeters A B 8X 0.10 C 0.41 1.27 0.18 SEATING PLANE 1.75 MAX C Terminal #1 mark area Exposed thermal pad (mounting side) Copyright (c)2007, Allegro MicroSystems, Inc. The products described here are manufactured under one or more U.S. patents or U.S. patents pending. Allegro MicroSystems, Inc. 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, Inc. 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, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 10 |
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