A1569K Automotive LED Driver with Integrated Hall-Effect Switch FEATURES AND BENEFITS DESCRIPTION * Linear LED drive current 150mA set by an external reference resistor * High sensitivity, omnipolar Hall-effect switch for LED on/off control * Low component count for small size and ease of design * Elegant fade-in/fade-out effects with adjustable duration (optional) * Qualified per AEC-Q100 for automotive applications * Low dropout voltage and low supply current * Chopper-stabilized Hall switch Low switchpoint drift over temperature Insensitivity to physical stress * Input pin for external LED driver control * Slew-rate-limited LED output drive for current transient suppression * Ruggedness and reliability Integrated voltage regulator for operation from 7 to 24V Reverse-battery protection Automatic short-circuit and thermal overload protection and recovery -40C to 125C ambient temperature range * Small 8-pin SOIC package with thermal pad The A1569K is a highly integrated solution that combines a Hall-effect switch with a linear, programmable current regulator, providing up to 150mA to drive one or more LEDs. With the addition of only two passive components and one or more LEDs, the A1569K forms a complete, magnetically actuated lighting solution that is small, flexible, elegant, easy to design, rugged, and reliable. It is optimized for automotive interior and auxilliary lighting such as map lights, glove boxes, consoles, vanity mirrors, hood/truck/bed lights, etc. The LED drive current is set by an external resistor; the LED is then activated by the built-in Hall-effect switch and features an adjustable fade-in/fade-out effect. Omnipolar operation (either north or south pole) and high magnetic sensitivity make the A1569K tolerant of large air gaps and mechanical misalignment. System assembly is easier, as the magnet can be oriented with either pole facing the device. Chopper stabilization provides low switchpoint drift over the operating temperature range. The driver can also be activated via an external input for direct control of the LED. In addition to contactless operation and safe, constant-current LED drive, reliability is further enhanced with reverse-battery protection, thermal foldback, and automatic shutdown for thermal overload and shorts to ground. The A1569K will prevent damage to the system by removing LED drive current until the short is removed and/or the chip temperature has reduced below the thermal threshold. The driver output is slew-ratelimited to reduce electrical noise during operation. PACKAGE: 8-Pin SOICN with Exposed Thermal Pad (Suffix LJ) Continued on the next page... Not to scale For standalone operation, SEN_EN is pulled high (e.g., tied to VIN) Optional Control Signals From MCU or Remote Switch RIREF +V CBYPASS VIN SLEEP LA 150 mA SEN_EN LED_ON EXT No Connect or Connect to GND HALL IREF FADE THTH GND CFADE (optional) Typical Application Diagram A1569K-DS, Rev. 1 MCO-0000611 February 22, 2019 Automotive LED Driver with Integrated Hall-Effect Switch A1569K Description (continued) The device is packaged in an 8-pin SOICN (LJ) with an exposed pad for enhanced thermal dissipation. It is RoHS compliant, with 100% matte-tin leadframe plating. Selection Guide* Part Number Packing A1569KLJTR-T 3000 pieces per 13-in. reel * For non-automotive applications, see A1569E datasheet. The A1569K is intented for automotive applications that require extremely wide operating temperature ranges (up to 125C) and qualification per AEC-Q100. For other applications, refer to the A1569E. Package 8-pin SOICN surface mount Temperature Range, TA (C) -40 to 125 RoHS COMPLIANT SPECIFICATIONS Absolute Maximum Ratings Characteristic Symbol Notes Rating Unit Forward Supply Voltage VIN (VDD) 30 V Reverse Supply Voltage VRDD -18 V VSEN_EN -18 to 30 V VLA -0.3 to 30 V Pin EXT VEXT -0.3 to 6.5 V Pin IREF VIREF -0.3 to 6.5 V Pin THTH VTHTH -0.3 to 6.5 V Pin FADE VFADE Pin SEN_EN Pin LA -0.3 to 6.5 V -40 to 125 C Operating Ambient Temperature TA Maximum Junction Temperature TJ(MAX) 165 C Tstg -65 to 170 C Storage Temperature Range K Allegro MicroSystems, LLC 955 Perimeter Road Manchester, NH 03103-3353 U.S.A. www.allegromicro.com 2 Automotive LED Driver with Integrated Hall-Effect Switch Current Reference Sample & Hold Dynamic Offset Cancellation A1569K Slew Limit GND LA Temp Monitor Control Logic Clock/Logic Regulator Thermal Shutdown Current Regulator Wake Up RPD VIN SEN_EN RPD EXT FADE IREF THTH + CFADE RIREF (optional) Functional Block Diagram Pinout Drawing and Terminal List Terminal List VIN 1 8 GND SEN_EN 2 7 THTH EXT 3 6 IREF LA 4 5 FADE PAD Package LJ, 8-Pin SOICN Pinout Drawing Pin Number Pin Name Description 1 VIN 2 SEN_EN 3 EXT 4 LA LED anode (+) connection 5 FADE Fade-in/fade-out dimming 6 IREF Current reference 7 THTH Thermal threshold 8 GND Ground reference - PAD Exposed thermal pad (may be left floating or tied to ground) Supply Hall sensor enable External override input Allegro MicroSystems, LLC 955 Perimeter Road Manchester, NH 03103-3353 U.S.A. www.allegromicro.com 3 Automotive LED Driver with Integrated Hall-Effect Switch A1569K ELECTRICAL CHARACTERISTICS: Valid at TA = -40C to 125C, VIN = 7 to 24V (unless otherwise specified) Characteristic Symbol Test Conditions Min. Typ.1 Max. Units Electrical Characteristics VIN Functional Operating Range Operating, TJ < 165C 7 - 24 V VIN Quiescent Current VIN (VDD) IINQ LA connected to VIN, LED off - 6 10 mA VIN Sleep Current IINS SEN_EN and EXT = GND - 10 25 A Startup Time tON SEN_EN = VIN, |B| < |BRPx| - 5gauss, RIREF = 600, CFADE = 100 pF, measured from VIN > 7V to ILA source > 90% ILAmax - - 1 ms External Response Time tEXT SEN_EN = GND, VIN > 7V RIREF = 600, CFADE = 100 pF, measured from EXT > VIH(MIN) to ILA source > 5% ILAmax - - 1 ms Current Regulation Reference Voltage VIREF 267A < IREF < 2 mA - 1.2 - V Reference Current Ratio GH (ILA + 0.5) / IREF - 75 - - Current Accuracy2 EILA 20mA > ILA > 150mA -5 4 5 % SEN_EN = high, BFIELD < BRP - GH x IREF - - RIREF = 600, SEN_EN = high and BFIELD < BRP, or EXT = high - 150 170 mA VIN - VLA , ILA = 150mA - - 2.4 V VIN - VLA , ILA = 50mA - 800 - mV Current rising or falling between 10% and 90%, CFADE = 100pF - 80 - s Output Source Current Dropout Voltage Current Slew Time ILA VDO tFADE(MIN) Logic Inputs Input Low Voltage VIL SEN_EN, EXT - - 0.8 V Input High Voltage VIH SEN_EN, EXT 2 - - V Pull-Down Resistor RPD SEN_EN, EXT Input Voltage Range VLOGIC - 50 - k EXT, IREF, THTH, FADE -0.3 - 5.5 V SEN_EN -0.3 - 24 V Continued on next page... 1 2 Typical data is at TA = 25C and VIN = 12V and it is for design information only. When SEN_EN or EXT = high, EILA = 100 x {[( | ILA | + 0.5 ) x RIREF / 90 ] - 1}, with ILA in mA and RIREF in k. Allegro MicroSystems, LLC 955 Perimeter Road Manchester, NH 03103-3353 U.S.A. www.allegromicro.com 4 Automotive LED Driver with Integrated Hall-Effect Switch A1569K ELECTRICAL CHARACTERISTICS (continued): Valid at TA = -40C to 125C, VIN = 7 to 24V (unless otherwise specified) Characteristic Symbol Test Conditions Min. Typ.1 Max. Units 1.2 - 1.8 V - 1 - mA 200 - 500 mV Protection Short Detect Voltage VSCD Measured at LA Short-Circuit Source Current ISCS Short present LA to GND Short Release Voltage Hysteresis Thermal Monitor Activation2 Thermal Monitor Slope2 VSCR - VSCD, measured with 0.1F cap between ILA and GN VSChys TJM dISEN/dTJ TJ with ISEN = 90%, THTH open 110 130 145 C ISEN = 50%, THTH open -3.5 -2.5 -1.5 %/C 135 150 165 C Thermal Monitor Low Current Temperature TJL TJ at ISEN = 25%, THTH open Overtemperature Shutdown TJF Temperature increasing - 170 - C Overtemperature Hysteresis TJhys Recovery occurs at TJF - TJhys - 15 - C BOPS SEN_EN = high and BFIELD > BOP, LED is off (EXT = low) - 40 70 G -70 -40 - G Magnetic Characteristics3 Operate Point Release Point Hysteresis BOPN BRPS SEN_EN = high and BFIELD < BRP, LED is on (EXT = low) 5 25 - G BRPN - -25 -5 G BHYS | BOPX - BRPX | 5 15 25 G BHYS BOP Decreasing BFIELD Magnitude BRP Decreasing Magnitude Field LED Turns On LED Off Increasing Magnitude Field LED Turns Off LED On Increasing BFIELD Magnitude Figure 1: Hall Switch Control of LED State Typical data is at TA = 25C and VIN = 12V; for design information only. Guaranteed by design. 3 Magnetic flux density, B, is indicated as a negative value for north-polarity magnetic fields, and is a positive value for south-polarity magnetic fields. 1 2 Allegro MicroSystems, LLC 955 Perimeter Road Manchester, NH 03103-3353 U.S.A. www.allegromicro.com 5 Automotive LED Driver with Integrated Hall-Effect Switch A1569K THERMAL CHARACTERISTICS Characteristic Symbol Min. Typ. Max. Units RJA (High-K) JEDEC Package MS-012 BA. Test is performed using a high thermal conductivity, multilayer printed circuit board that closely approximates those specified in the JEDEC standards JESD51-7. Thermal vias are included per JESD51-5. Test Conditions - 35 - C/W RJA (Usual-K) JEDEC Package MS-012 BA. Multiple measurement points on both single- and dual-layer printed circuit boards with minimal exposed copper (2-oz) area. See Figure 2 for more detail. - 62-147 - C/W Thermal Resistance (Junction to Ambient) Package Thermal Resistance (C/W) 200 One-sided board Two-sided board 150 * All copper is 2 oz. thickness * Area of copper refers to individual test locations on PCB 100 50 0 0.2 0.4 0.6 2 Area of Copper, One Side (in ) 0.8 Figure 2: Thermal Resistance (RJA) versus Copper Area on Printed Circuit Board (PCB) Allegro MicroSystems, LLC 955 Perimeter Road Manchester, NH 03103-3353 U.S.A. www.allegromicro.com 6 Automotive LED Driver with Integrated Hall-Effect Switch A1569K CHARACTERISTIC PERFORMANCE BHYSS vs. TA 25 20 15 10 TA (C) -40 25 125 5 0 0 5 10 15 20 25 30 Magnetic Hysteresis, BHYSS (gauss) Magnetic Hysteresis, BHYSS (gauss) BHYSS vs. VIN 25 23 21 19 17 15 13 11 9 7 5 VIN (V) 7 12 18 24 -50 Supply Voltage, VIN (V) 0 50 40 30 TA (C) 20 -40 25 125 10 0 15 20 25 30 Magnetic Hysteresis, BOPS (gauss) Magnetic Hysteresis, BOPS (gauss) 60 10 70 60 50 40 VIN (V) 30 7 12 18 24 20 10 0 -50 Supply Voltage, VIN (V) 0 60 -40 25 125 50 40 30 20 10 0 15 20 Supply Voltage, VIN (V) 25 30 Magnetic Hysteresis, BRPS (gauss) Magnetic Hysteresis, BRPS (gauss) TA (C) 10 100 150 BRPS vs. TA 70 5 50 Ambient Temperature, TA (C) BRPS vs. VIN 0 150 BOPS vs. TA 70 5 100 Ambient Temperature, TA (C) BOPS vs. VIN 0 50 70 VIN (V) 60 7 12 18 24 50 40 30 20 10 0 -50 0 50 100 150 Ambient Temperature, TA (C) Allegro MicroSystems, LLC 955 Perimeter Road Manchester, NH 03103-3353 U.S.A. www.allegromicro.com 7 Automotive LED Driver with Integrated Hall-Effect Switch A1569K BHYSN vs. TA -5 -7 -9 -11 -13 -15 -17 -19 -21 -23 -25 TA (C) -40 25 125 0 5 10 15 20 25 30 Magnetic Hysteresis, BHYSN (gauss) Magnetic Hysteresis, BHYSN (gauss) BHYSN vs. VIN -5 -7 -9 -11 -13 -15 -17 -19 -21 -23 -25 VIN (V) 7 12 18 24 -50 Supply Voltage, VIN (V) 0 -20 -30 -40 TA (C) -50 -40 25 125 -60 -70 15 20 25 30 Magnetic Hysteresis, BOPN (gauss) Magnetic Hysteresis, BOPN (gauss) -10 10 0 -10 -20 -30 VIN (V) -40 7 12 18 24 -50 -60 -70 -50 Supply Voltage, VIN (V) 0 -20 -30 -40 TA (C) -50 -40 25 125 -60 -70 15 20 Supply Voltage, VIN (V) 25 30 Magnetic Hysteresis, BRPN (gauss) Magnetic Hysteresis, BRPN (gauss) -10 10 100 150 BRPN vs. TA 0 5 50 Ambient Temperature, TA (C) BRPN vs. VIN 0 150 BOPN vs. TA 0 5 100 Ambient Temperature, TA (C) BOPN vs. VIN 0 50 0 -10 -20 -30 VIN (V) -40 7 12 18 24 -50 -60 -70 -50 0 50 100 150 Ambient Temperature, TA (C) Allegro MicroSystems, LLC 955 Perimeter Road Manchester, NH 03103-3353 U.S.A. www.allegromicro.com 8 Automotive LED Driver with Integrated Hall-Effect Switch A1569K IINQ vs. TA 10 9 8 7 6 5 4 3 2 1 0 TA (C) -40 25 125 0 5 10 15 20 25 Quiescent Current, IINQ (mA) Quiescent Current, IINQ (mA) IINQ vs. VIN 10 9 8 7 6 5 4 3 2 1 0 30 VIN (V) 7 12 18 24 -50 Supply Voltage, VIN (V) 0 IINS vs. VIN 25 TA (C) 20 -40 25 125 15 10 5 Sleep Current, IINS (A) Sleep Current, IINS (A) 100 150 IINS vs. TA 25 0 VIN (V) 7 12 18 24 20 15 10 5 0 0 5 10 15 20 25 30 -50 Supply Voltage, VIN (V) 80 75 70 65 60 10 15 20 Supply Voltage, VIN (V) 25 30 Reference Current Ratio, GH -40 25 125 5 100 90 TA (C) 0 50 150 GH vs. TA (IREF = 2 mA) 90 85 0 Ambient Temperature, TA (C) GH vs. VIN (IREF = 2 mA) Reference Current Ratio, GH 50 Ambient Temperature, TA (C) VIN (V) 85 7 12 18 24 80 75 70 65 60 -50 0 50 100 150 Ambient Temperature, TA (C) Allegro MicroSystems, LLC 955 Perimeter Road Manchester, NH 03103-3353 U.S.A. www.allegromicro.com 9 Automotive LED Driver with Integrated Hall-Effect Switch A1569K ILA vs. TA 180 170 160 150 140 130 TA (C) -40 25 125 120 110 100 0 5 10 15 20 Supply Voltage, VIN (V) 25 30 Output Source Current, ILA (mA) Output Source Current, ILA (mA) ILA vs. VIN 180 170 160 150 140 VIN (V) 7 12 18 24 130 120 110 100 -50 0 50 100 150 Ambient Temperature, TA (C) Allegro MicroSystems, LLC 955 Perimeter Road Manchester, NH 03103-3353 U.S.A. www.allegromicro.com 10 Automotive LED Driver with Integrated Hall-Effect Switch A1569K Function Truth Table EXT SEN_EN Magnetic Field B LED 0 0 X OFF 0 1 B > BOP OFF 0 1 B < BRP ON 1 X X ON Example Function Diagrams BFIELD B > BOP B < BRP SEN_EN High Low EXT High Low ILED Max 0 mA Fade in Fade out Figure 3: Hall-Activated Operation With EXT low and SEN_EN high, the switching of the LED is controlled by the BFIELD as detected by the Hall sensor. BFIELD B > BOP B < BRP SEN_EN High Low EXT High Low ILED Max 0 mA Figure 4: Disabling the Hall Sensor with SEN_EN The Hall sensor can be disabled by driving SEN_EN low. This will force the LED off even if the BFIELD is below BOP. Allegro MicroSystems, LLC 955 Perimeter Road Manchester, NH 03103-3353 U.S.A. www.allegromicro.com 11 Automotive LED Driver with Integrated Hall-Effect Switch A1569K BFIELD B > BOP B < BRP SEN_EN High Low EXT High Low ILED Max 0 mA Don't Care Don't Care Don't Care Figure 5: Overriding the Hall Sensor with EXT When EXT is driven high, it doesn't matter what the state of the SEN_EN input or the BFIELD are, the LED will be on. Allegro MicroSystems, LLC 955 Perimeter Road Manchester, NH 03103-3353 U.S.A. www.allegromicro.com 12 Automotive LED Driver with Integrated Hall-Effect Switch A1569K FUNCTIONAL DESCRIPTION The A1569K is a linear current regulator with an integrated Halleffect switch designed to provide drive current and protection for a string of series-connected high brightness LEDs in automotive applications. It provides a single programmable current output at up to 150mA, with low minimum dropout voltages below the main supply voltage. The A1569K is specifically designed for use in illumination applications where the LED activity is controlled by the integrated Hall-effect switch or an external logic signal, or both. Current regulation is maintained and the LEDs are protected during a short to ground at any point in the LED string. A short to ground on the output terminal will disable the output until the short is removed. 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 regulator. A small value ceramic bypass capacitor, typically 100nF, should be connected from close to this pin to the GND pin. GND Ground reference connection. This pin should be connected directly to the negative supply. SEN_EN Logic input to enable the Hall-effect switch. When this pin is enabled (logic high), the output current can be controlled by the state of the magnetic field on the Hall sensor. If the magnetic field is below BRP, then the LED current will be on, and if the magnetic field is above BOP, then the LED current will be off. EXT Logic input to enable LED current output which provides a direct on/off action. Note, if the LED is on because the SEN_IN pin is enabled and the magnetic field is below BRP, then it will remain on regardless of EXT. FADE A capacitor between this pin and GND controls the turn-on and turn-off times of the LED current. Note: For best performance, it is important that the ground return for CFADE is as short as possible, that it is made directly to the ground pin of the IC, and that it is not shared with other circuitry or carry other ground return currents (Kelvin connection). IREF A 1.2V reference used to set the LED current drive. Connect resistor RIREF to GND to set the reference current. Note: Do not place any capacitance across the RIREF resistor. THTH When floating, the thermal monitor threshold TJM is enabled and the output current will start to reduce with increasing temperature above 130C. Connecting the THTH pin directly to GND will disable the thermal monitor function; however, the thermal shutdown feature will continue to function--it cannot be disabled. Refer to the Temperature Monitor section below for more detail. LA Current source connected to the anode of the first LED in the string. PAD This is an isolated pad for thermal dissipation only. This pad is isolated and can be connected to ground or left floating. LED Current Level The LED current is controlled by a linear current regulator between the VIN pin and the LA output. The basic equation that determines the nominal output current at this pin is: Given SEN_EN = high and BFIELD < BRP, or EXT = high, VREF x GH ILA = RIREF (1) where ILA is in A, RIREF is in , VREF = 1.2V, and GH = 75. Note: the output current may be reduced from the set level by the thermal monitor circuit. Allegro MicroSystems, LLC 955 Perimeter Road Manchester, NH 03103-3353 U.S.A. www.allegromicro.com 13 Automotive LED Driver with Integrated Hall-Effect Switch A1569K Conversely, the reference resistor may be calculated from: VREF x GH RIREF = ILA + 0.5 Safety Features (2) where ILA is in A, RIREF is in , VREF = 1.2V, and GH = 75. For example, where the required current is 75mA, the resistor value will be: RIREF = 90 = 1192 or 1.19 k 0.075 + 0.0005 (3) It is important to note that because the A1569K 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 an adequate heat sink, or airflow, or both, for the power dissipated. 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. The circuit includes several features to ensure safe operation and to protect the LEDs and the A1569K: * The current regulator between VIN and LA output provide a natural current limit due to the regulation. * The LA 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 When SEN_EN and EXT are held low, the A1569K will be in shutdown mode and all sections will be in a low power sleep mode. The input current will be typically less than 10A. A short to ground on any LED cathode as in Figure 6 will not result in a short fault condition. The current through the remaining LEDs will remain in regulation and the LEDs will be protected. If the LA output is pulled below the short detect voltage as in Figure 7, it will disable the regulator on the 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 LA rises above the short detect voltage, the regulator will be re-enabled. A shorted LED or LEDs, as in Figure 8, will not result in a short fault condition. The current through the remaining LEDs will remain in regulation and the LEDs will be protected. Fade-In/Fade-Out Temperature Monitor and Thermal Protection Sleep Mode Fade timing is controlled by external capacitor CFADE on the FADE pin. A larger capacitor will result in a longer fade time. The 10%-90% fade time is approximated by the equation: tFADE = CFADE x 0.8 x 106(4) where tFADE is in seconds and CFADE is in farads. Therefore, CFADE of 1F will result in tFADE of approximately 1second (tFADE = 0.000001F x 0.8 x 106 = 0.8 seconds). The temperature monitor function, included in the A1569K, reduces the LED current as the silicon junction temperature of the A1569K increases (see Figure 9). By mounting the A1569K on the same thermal substrate as the LEDs, this feature can also be VIN Current remains regulated in non-shorted LEDs. Fade-in is triggered when: * EXT goes high, or * SEN_EN is high and BFIELD goes below BRP, or * BFIELD is below BRP and SEN_EN goes high. LA A1569K Fade-out is triggered when: * SEN_EN is low or BFIELD is above BOP and EXT goes low, or * EXT is low and BFIELD is above BOP and SEN_EN goes low, or * EXT is low and SEN_EN is high and BFIELD goes above BOP. GND Figure 6: Any Cathode Short to Ground Allegro MicroSystems, LLC 955 Perimeter Road Manchester, NH 03103-3353 U.S.A. www.allegromicro.com 14 Automotive LED Driver with Integrated Hall-Effect Switch A1569K perature will continue to be monitored and the regulator will be re-activated when the temperature drops below the threshold provided by the specified hysteresis. Note that it is possible for the A1569K 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 too close to the shutdown temperature. The period of oscillation will depend on TJM, the dissipated power, the thermal mass of any heat sink present, and the ambient temperature. In extreme cases, if the chip temperature exceeds the overtemperature limit (TJF), the regulator will be disabled. The tem- 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. VIN LA Shorted output is disabled. Low current is sourced to detect when short is cleared. A1569K GND Figure 7: Output Short to Ground Relative Sense Current (%) used to limit the dissipation of the LEDs. As the junction temperature of the A1569K increases, the regulated current level is reduced, reducing the dissipated power in the A1569K and in the LEDs. The current is reduced from the 100% level at typically 2.5% 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). 100 90 80 TJM 60 40 TJF 25 20 0 70 TJL 90 110 130 150 170 Junction Temperature, TJ (C) Figure 9: Temperature Monitor Current Reduction VIN LA A1569K Only shorted LED(s) is(are) inactive. Current remains regulated in non-shorted LED(s). When THTH is tied to ground, the thermal monitor function is disabled; however, the overtemperature thermal protection will continue to function--it cannot be disabled. GND Figure 8: Shorted LED(s) Allegro MicroSystems, LLC 955 Perimeter Road Manchester, NH 03103-3353 U.S.A. www.allegromicro.com 15 Automotive LED Driver with Integrated Hall-Effect Switch A1569K APPLICATION INFORMATION Power Dissipation The most critical design consideration when using a linear regulator such as the A1569K is 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 A1569K: * The quiescent power to run the control circuits * The power in the reference circuit * The power due to the regulator voltage drop The quiescent power is the product of the quiescent current (IINQ) and the supply voltage (VIN), and it is not related to the regulated current. The quiescent power (PQ) is therefore defined as: PQ = VIN x IINQ (5) REFERENCE POWER The reference circuit draws the reference current from the supply and passes it through the reference resistor to ground. The reference circuit power is the product of the reference current and the difference between the supply voltage and the reference voltage, typically 1.2V. The reference power (PREF) is therefore defined as: (V - VREF ) x VREF (6) PREF = IN RIREF REGULATOR POWER In most application circuits, the largest dissipation will be produced by the output current regulator. The power dissipated the current regulator is simply the product of the output current and the voltage drop across the regulator. The regulator power the output is defined as: PREG = (VIN - VLED) x ILED (7) Note that the voltage drop across the regulator (VREG) is always greater than the specified minimum dropout 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 A1569K is the sum of the quiescent power, the reference power, and the power in the regulator: PD = PQ + PREG - PREF (8) The power that is dissipated in the LEDs is: PLED = VLED x ILED(9) where VLED is the voltage across all LEDs in the string. Dissipation Limits There are two features limiting the power that can be dissipated by the A1569K: thermal shutdown and thermal foldback. THERMAL SHUTDOWN QUIESCENT POWER From these equations (and as illustrated in Figure 10), it can be seen that, if the power in the A1569K is not limited, then it will increase as the supply voltage increases while the power in the LEDs will remain constant. If the thermal foldback feature is disabled by connecting the THTH pin to GND, or if the thermal resistance from the A1569K 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, 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 A1569K is switched off. The period of this thermal shutdown cycle will depend on several electrical, mechanical, and thermal parameters. THERMAL FOLDBACK If RJA is low enough, 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. The thermal monitor will reduce the LED current as the temperature of the A1569K increases above the thermal monitor activation temperature (TJM), as shown in Figure 11. The figure shows the operation of the A1569K with a string of two white LEDs running at 150mA. The forward voltage of each LED is 3.15V, and the graph shows the current as the supply voltage increases from 15 to 18V. As the supply voltage increases, without the thermal foldback feature, the current would remain at 150mA, 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 A1569K in order to limit the temperature increase, as shown in Figure 12. The figure shows the operation of the A1569K under the same conditions as Figure 11, that is, a string of two white LEDs running at 150mA, with each LED forward voltage at 3.15V. The graph shows the temperature as the supply voltage increases from 15 to 18V. Without the thermal foldback Allegro MicroSystems, LLC 955 Perimeter Road Manchester, NH 03103-3353 U.S.A. www.allegromicro.com 16 Automotive LED Driver with Integrated Hall-Effect Switch A1569K Figure 11 and Figure 12 show the thermal effects where the thermal resistance from the silicon to the ambient temperature is 40C/W. Thermal performance can be enhanced further by using a significant amount of thermal vias as described below. Power Dissipation, PD (W) 2.5 2.0 2 LED in series: VLED = 6.3 V ILED = 150 mA 11 12 13 14 15 16 17 18 Supply Voltage, VIN (V) Figure 10: Power Dissipation versus Supply Voltage 154 LED Current, ILA (mA) 130 2 LED in series: VLED = 6.3 V ILED = 150 mA TA = 50C 125 120 18.5 19.0 19.5 20.0 20.5 21.0 Supply Voltage Limits 0.5 152 Without Thermal Monitor 150 148 146 140 18.0 135 Figure 12: Junction Temperature versus Supply Voltage LED Power 142 m her tT hou t i W o al M Supply Voltage, VIN (V) 1.0 144 or nit 140 115 18.0 1.5 0 10 145 Junction Temperature, TJ (C) 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. 19.0 To determine this range when using the A1569K, 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 dropout 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 2 LED in series: VLED = 6.3 V ILED = 150 mA TA = 50C 18.5 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. 19.5 20.0 20.5 Supply Voltage, VIN (V) Figure 11: LED Current versus Supply Voltage 21.0 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). 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 Allegro MicroSystems, LLC 955 Perimeter Road Manchester, NH 03103-3353 U.S.A. www.allegromicro.com 17 Automotive LED Driver with Integrated Hall-Effect Switch A1569K the regulator can no longer be guaranteed to maintain the output current within the specified accuracy. This level is defined as the regulator dropout voltage (VDO). The minimum supply voltage, below which the LED current does not meet the specified accuracy, is therefore determined by the sum of the minimum dropout 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) (10) As an example, consider the configuration used in Figure 11, namely a string of two white LEDs, running at 150mA, with each LED forward voltage at 3.15V. The minimum supply voltage will be approximately: VIN(MIN) = 0.8 + (2 x 3.15) = 7.1 V (11) 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 A1569K 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, 150C. The maximum power dissipation is therefore defined as: T(MAX) PD(MAX) = RJA (12) where T(MAX) is the difference between the thermal monitor activation temperature (TJM) of the A1569K and the maximum ambient temperature (TA(max)), and RJA 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 maximum specified in the parameter tables above. Thermal Dissipation The amount of heat that can pass from the silicon of the A1569K to the surrounding ambient environment depends on the thermal resistance of the structures connected to the A1569K. The thermal resistance (RJA) 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 (T) is calculated from the power dissipated (PD) and the thermal resistance (RJA) as: T = PD x RJA (13) A thermal resistance from silicon to ambient (RJA) of approximately 35C/W can be achieved by using a high thermal conductivity, multilayer printed circuit board as specified in the JEDEC standards JESD51-7 for JEDEC Package MS-012 BA (including thermal vias as called out in JESD51-5). Additional improvements 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 significant effect on the thermal performance of the device. To optimize thermal performance, the following should be taken into account: * Maximizing the forward voltage of the LEDs relative to the VIN of the A1569K will greatly reduce the power dissipated in the A1569K by reducing the voltage drop across the A1569K. * The A1569K exposed thermal pad should be connected to as much copper area as is available. This copper area may be left floating or connected to ground if desired. * Copper thickness should be as high as possible (for example, 2oz. 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 13, has the greatest effect. * Additional exposed copper area on the opposite side of the board should be connected by means of thermal vias. The copper should cover as much area as possible. * Other thermal sources should be placed as far away from the device as possible. Allegro MicroSystems, LLC 955 Perimeter Road Manchester, NH 03103-3353 U.S.A. www.allegromicro.com 18 Automotive LED Driver with Integrated Hall-Effect Switch A1569K Signal Traces LJ Package Outline LJ Package Exposed Thermal Pad Top Layer Exposed Copper 0.7 mm O 0.3 mm Via 0.7 mm Figure 13: Suggested PCB Layout for Thermal Optimization (Maximum available bottom-layer copper recommended) Allegro MicroSystems, LLC 955 Perimeter Road Manchester, NH 03103-3353 U.S.A. www.allegromicro.com 19 Automotive LED Driver with Integrated Hall-Effect Switch A1569K Package Outline Drawing For Reference Only - Not for Tooling Use (Reference MS-012BA) Dimensions in millimeters - NOT TO SCALE Dimensions exclusive of mold flash, gate burrs, and dambar protrusions Exact case and lead configuration at supplier discretion within limits shown 4.90 0.10 1.27 0.65 8 0 3.30 NOM 8 8 1.75 0.25 0.17 D E1 B 2.41 NOM 3.90 0.10 6.00 0.20 2.41 5.60 A 1.04 REF 1 2 1 1.27 0.40 0.25 BSC Branded Face C 8X 0.10 C 0.51 0.31 1.27 BSC 1.70 MAX 0.15 0.00 SEATING PLANE 2 3.30 C PCB Layout Reference View SEATING PLANE GAUGE PLANE 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) D Hall element (E1) centered in package (not to scale). Figure 14: Package LJ, 8-Pin SOICN with Exposed Thermal Pad Allegro MicroSystems, LLC 955 Perimeter Road Manchester, NH 03103-3353 U.S.A. www.allegromicro.com 20 Automotive LED Driver with Integrated Hall-Effect Switch A1569K Revision History Revision Revision Date Description of Revision - December 11, 2015 Initial release 1 February 22, 2019 Minor editorial updates Copyright (c)2019, 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 any devices or systems, including but not limited to life support devices or systems, in which a failure of Allegro's product can reasonably be expected to cause bodily harm. 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. Copies of this document are considered uncontrolled documents. For the latest version of this document, visit our website: www.allegromicro.com Allegro MicroSystems, LLC 955 Perimeter Road Manchester, NH 03103-3353 U.S.A. www.allegromicro.com 21