ALT80800KLPATR

ALT80800 ALLEGRO

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Technical content

DESCRIPTION

The ALT80800 is a synchronous buck switching regulator that provides constant-current output to drive high-power LEDs. It integrates both high-side and low-side N-channel DMOS switches for DC-to-DC step-down conversion. A true average current is output using a cycle-by-cycle, controlled on-time method. Output current is user-selectable by an external current sense resistor. Output voltage is automatically adjusted to drive various numbers of LEDs in a single string. This ensures the optimal system efficiency. LED dimming is accomplished by a direct logic input pulse- width modulation (PWM) signal at the PWM pin while EN is enabled. Alternatively, applying a PWM signal at the EN pin while PWM pin is high can enable “chopped battery” PWM dimming for legacy control modules. Furthermore, an Analog Dimming input (ADIM pin) can be used, for example, to calibrate the LED current or implement thermal foldback in conjunction with external NTC thermistor. The ALT80800 is provided in a 16-pin TSSOP (suffix LP), with exposed pad for enhanced thermal dissipation. ALT80800-DS, Rev. 1 MCO-0000344 FEATURES AND BENEFITS

• AEC-Q100 qualified
• Supply voltage 4.5 to 55 V
• 2.0 A maximum output over operating temperature range
• Integrated high-side and low-side MOSFETs: 200 mΩ / 150 mΩTYP
• True average output current control
• Internal control loop compensation
• Integrated 5 V , 14 mA LDO regulator for peripheral circuits
• Dimming via PWM pin or EN pin down to 0.1% at 200 Hz
• Analog dimming (ADIM pin) for brightness calibration and thermal foldback
• Low-power shutdown (1 µA typical)
• Cycle-by-cycle current limit
• Active low fault flag output
• LED open fault mask setting for low VIN operation
• Undervoltage lockout (UVLO) and thermal shutdown protection
• Switching frequency dithering for improved EMC
• Robust protection against: □ Adjacent pin-to-pin short □ Pin-to-ground short □ Component open/short faults Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED Driver PACKAGE: Not to scale ALT80800 Figure 1: ALT80800 Typical Application Circuit APPLICATIONS: Automotive lighting
• Daytime runni ng lights
• Front and rear fog lights
• T urn/stop lights
• Map light
• Dimmable inte rior lights 16-Pin eTSSOP (suffix LP) November 13, 2018 LED+ GND VIN CIN PWM GND ADIM VCC FFn External PWM dimming signal External analog dimming signal FDSET BOOT CSH CSL SGND EN VCCIN TON PWM ALT80800 ADIM VCC FFn SWVIN RON CBIAS CBOOT CLED RSENSE PGND VIN GND VCC

Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED DriverALT80800 Allegro MicroSystems, LLC

955 Perimeter Road

Manchester, NH 03103-3353 U.S.A. www.allegromicro.com SELECTION GUIDE Part Number Package Packing ALT80800KLPATR 16-pin TSSOP with exposed thermal pad 4000 pieces per 13-inch reel ABSOLUTE MAXIMUM RATINGS Characteristic Symbol Notes Rating Unit Supply Voltage VIN, VVCCIN –0.3 to 60 V Bootstrap Drive Voltage VBOOT –0.3 to VIN + 8 V Switching Voltage VSW Continuous –0.3 to VIN + 0.3 V Pulsed, t < 50 ns –1 to VIN + 3 V EN Voltage VEN –0.3 to VIN + 0.3 V Current Sense Voltages VCSH, VCSL V Linear Regulator Terminal VCC –0.3 to 7 V ADIM pin, TON pin VADIM, VTON V FDSET Voltages VFDSET V FFn and PWM Voltages VFFn, VPWM V Maximum Junction Temperature TJ(max) 150 °C Storage Temperature Tstg –55 to 150 °C THERMAL CHARACTERISTICS* : May require derating at maximum conditions; see application section for optimization Characteristic Symbol Test Conditions* Value Unit Package Thermal Resistance (Junction to Ambient) RθJA On 4-layer PCB based on JEDEC standard 34 °C/W Package Thermal Resistance (Junction to Pad) RθJP 2 °C/W *Additional thermal information available on the Allegro™ website. SPECIFICATIONS Table of Contents Features and Benefits 1 Description 1 Applications 1 Package 1 Typical Application Circuit 1 Selection Guide 2 Specifications 2 Absolute Maximum Ratings 2 Thermal Characteristics 2 Pinout Diagrams and Terminal List Tables 3 Functional Block Diagrams 4 Electrical Characteristics 5 Functional Description 7 Application Circuit Diagrams 20

Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED DriverALT80800 Allegro MicroSystems, LLC Manchester, NH 03103-3353 U.S.A. www.allegromicro.com TSSOP-16 (LP) Pinout Diagram PGND PGND VIN EN PWM FDSET ADIM TON SW BOOT VCCIN FFn VCC SGND CSL CSH PAD Terminal List Table Number Name Function 1, 2 PGND Power ground terminal. 3 VIN Supply input voltage for power stage. 4 EN Enable pin for internal LDO regulator and whole IC. EN pin can also be used as PWM dimming when keeping PWM pin High.

5 PWM Logic input for PWM dimming: when PWM = LOW, LED is off; if

PWM = High and at the same time EN is enabled, LED is ON.

6 FDSET

FDSET pin to set the LED Open fault mask threshold. Connect to a voltage divider formed between VIN and PGND. When VIN is low, resulting in FDSET below the internal reference, LED Open Fault detection will be masked.

7 ADIM

Analog dimming control voltage input. If not used for analog dimming, tie ADIM to 5 V or VCC; if used for analog dimming, keep ADIM less than 2.5 V. 8 TON Regulator on-time setting resistor terminal. Connect a resistor between TON pin and SGND to set the switching frequency. 9 CSH Current Sense (positive end) feedback input for LED current. 10 CSL Current Sense (negative end) feedback input for LED current. 11 SGND Signal ground terminal.

12 VCC

Internal IC bias regulator output. Connect at least 1 µF MLCC to PGND. Can be used to supply up to 14 mA for external load. 13 FFn Open-drain output which is pulled low in case of fault. Connect through an external pull-up resistor to the desired logic level.

14 VCCIN It is recommended to connect VCCIN to VIN to bias the internal

LDO regulator. 15 BOOT High-side gate driver bootstrap terminal; a 0.47uF capacitor is recommended between BOOT and SW. 16 SW Switched output terminal. The output inductor should be connected to this pin. – PAD Exposed pad for enhanced thermal dissipation; connect to ground. PINOUT DIAGRAM AND TERMINAL LIST TABLE

Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED DriverALT80800 Allegro MicroSystems, LLC Manchester, NH 03103-3353 U.S.A. www.allegromicro.com Figure 2: Functional Block Diagram LED+ VIN CIN PWM CBOOT RON CBIAS RSENSE SW BOOT PGND CSH CSL VIN TON PWM VCC CLED VIN On-Time Select Buck Converter Duty Cycle Control VOUT VOUT LDO Internal 5.0 V bias VREF (0 – 200 mV)i_LED reference ADIMADIM On-Time VIN Fault Handling FFn FFn VCC LED Current Gate Driver Differential Amp RADJ FDSET VCCIN SGND Up to 14 mA external load REF1 VCSREG EN UVLO VIN LED Open Fault LED Short Fault VOUT Other Faults 17 ms Boot Charger ALT80800 VCC CBIAS

Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED DriverALT80800 Allegro MicroSystems, LLC Manchester, NH 03103-3353 U.S.A. www.allegromicro.com ELECTRICAL CHARACTERISTICS: Valid at VIN = 12 V, VOUT = 6 V, TJ = –40°C to 125°C, typical values at TJ = 25°C, unless otherwise noted Characteristics Symbol Test Conditions Min. Typ. Max. Unit Input Supply Voltage VIN 4.5 – 55 V VIN Undervoltage Lockout Threshold VUVLO(ON) VIN increasing, VIN = VVCCIN, ICC = 0 mA – – 4.3 V VIN Undervoltage Lockout Hysteresis VUVLO(HYS) VIN decreasing, VIN = VVCCIN, ICC = 0 mA 100 – 300 mV VIN Pin Supply Current IIN VCSH – VCSL = 0.5 V, VEN = VIH_EN, VPWM = VIH_PWM, RON = 402 kΩ – 5 – mA VIN Pin Shutdown Current IINSD VEN = VIL_EN – 1 10 µA Output Current Sense Common Mode Voltage (measured at CSL pin) [1] VOUT VIN = 55 V, fSW = 500 kHz, iLED = 0.5 A 2.65 – 50 V Buck Switch Current Limit Threshold ISWLIM 2.5 3.25 4.0 A Buck High-Side Switch On-Resistance RDSON(HS) VBOOT = VIN + 4.3 V, TJ = 25°C, ISW = 0.5 A – 0.2 0.32 Ω Buck Low-Side Switch On-Resistance RDSON(LS) TJ = 25°C, ISW = 0.5 A – 0.15 0.24 Ω BOOT Undervoltage Lockout Threshold VBOOTUV VBOOT to VSW increasing 3.1 3.4 3.7 V BOOT Undervoltage Lockout Hysteresis VBOTUVHYS VBOOT to VSW decreasing – 750 – mV Switching Minimum Off-Time tOFFmin VCSH – VCSL = 0 V – 100 125 ns Switching Minimum On-Time tONmin – 65 90 ns Selected On-Time tON VIN = 12 V, VOUT = 6 V, RON = 42.2 kΩ 200 – 300 ns Low-Side Switching Minimum On-Time [2] tLS_ONmin – 60 90 ns tON Dithering Range fSW_DITH RON = 42.2 kΩ – ±5% – – Dithering Modulation Frequency fSW_MOD RON = 42.2 kΩ – 12.5 – kHz REGULATION COMPARATOR AND ERROR AMPLIFIER Load Current Sense Regulation Threshold at 100% [3] VCSREG VCSH – VCSL decreasing, SW turns on, ADIM tied to VCC 194 200 206 mV CSH Input Sense Current [4] ICSH VCSH – VCSL = 0.2 V – –250 – µA CSL Input Sense Current ICSL VCSH – VCSL = 0.2 V 50 75 100 µA INTERNAL LINEAR REGULATOR VCC Regulated Output VCC 0 mA < ICC < 14 mA, VVCCIN > 6 V 4.85 5.0 5.15 V VCC Dropout Voltage VLDO Measure VVCCIN – VCC: VVCCIN = 4.8 V, ICC = 14 mA – 0.3 0.55 V VCC Current Limit iVCCLIM VCC ≥ 4.35 V 20 – – mA VCC Undervoltage Lockout VCCUVLO Rising 3.65 3.9 4.05 V VCCUVLOHYS Hysteresis 175 225 275 mV PWM INPUT Logic High Voltage VIH_PWM VEN increasing 1.8 – – V Logic Low Voltage VIL_PWM VEN decreasing – – 1.2 V PWM Pin Pull-Up Resistance RPWMPU VCC = 5 V – 100 – kΩ EN INPUT Maximum IC Turn Off Delay tOFFDelay Measured while PWM dimming signal applied at EN keeping low and exceeding tOFFDelay results in shutdown 10 17 – ms Logic High Voltage VIH_EN EN increasing 1.8 – – V Logic Low Voltage VIL_EN EN decreasing – – 0.4 V Continued on the next page…

Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED DriverALT80800 Allegro MicroSystems, LLC Manchester, NH 03103-3353 U.S.A. www.allegromicro.com Characteristics Symbol Test Conditions Min. Typ. Max. Unit ANALOG DIMMING INPUT Input Voltage for 100% LED Current VADIMH VCSH – VCSL = VCSREG 2.1 – – V Regulation Threshold at 50% Analog Dimming VCSREG50 VADIM = 1.0 V – 100 – mV Regulaton Threshold at 20% Analog Dimming VCSREG20 VADIM = 0.4 V 38.4 40 41.4 mV FAULT LED Open/Short Detect Condition ADIM Range VADIM rising 244 264 284 mV LED Short Fault Output Voltage Low Threshold VOUT falling 1.3 1.5 1.7 V LED Open-Fault Enable Reference VREF1 2.352 2.4 2.448 V LED Open Fault Current Threshold VCS_OPEN VCSREG = 200 mV start falling (PWM duty = max), VADIM = VCC, VFDSET = VCC (20 mV) 10% (50 mV) 25% (80 mV) 40% – LED Open Fault Current Hysteresis [1] VCS_OPEN_HYS VCSREG = 200 mV start falling (PWM duty = max), VADIM = VCC, VFDSET = VCC (6 mV) (12 mV) (18 mV) 9% – Fault Deglitch Timer tFDG 35 50 65 µs Fault Mask Timer tMASK 70 100 130 µs FFn Pull-Down Voltage VFAULT(PD) Fault condition asserted, pull-up current = 1 mA – – 0.4 V FFn Pin Leakage Current IFAULT(LKG) Fault condition cleared, pull-up to 5 V – – 1 µA FFn Rising Time [1] tRISE The transition time FFn pin takes from Low to High – – 10 µs FFn Falling Time [1] tFALL The transition time FFn pin takes from High to Low – – 10 µs Cool Down Timer for Fault Retry t RETRY – 1 – ms THERMAL SHUTDOWN Thermal Shutdown Threshold [1] TSD 150 165 180 °C Thermal Shutdown Hysteresis TSDHYS – 25 – °C [1] Determined by design and characterization. Not production tested. [2] Guaranteed by design, HS and LS switches are interlocked, as illustrated below: tdead tLS_ONmin SW Low Side VGS tdead tOFFmin tdead ≈ (tOFFMIN – tLS_ONmin) / 2 [3] In test mode, a ramp signal is applied between CSH and CSL pins to determine the VCSH – VCSL regulation threshold voltage. In actual application, the average VCSH – VCSL voltage is regulated at VCSREG regardless of ripple voltage. [4] Negative current is defined as coming out of (sourcing) the specified device pin or node. ELECTRICAL CHARACTERISTICS (continued): Valid at VIN = 12 V, VOUT = 6 V, TJ = –40°C to 125°C, typical values at TJ = 25°C, unless otherwise noted

Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED DriverALT80800 Allegro MicroSystems, LLC Manchester, NH 03103-3353 U.S.A. www.allegromicro.com The ALT80800 is a synchronous buck regulator designed for driving a high-current LED string. It uses average current mode control to maintain constant LED current and consistent bright- ness. The LED current level is easily programmable by selection of an external sense resistor, with a value determined as follows: i LED = VCSREG / RSENSE where VCSREG = VCSH – VCSL = 0.2 V typical. If necessary, a resistor can be inserted in series with the CSL pin to fine-tune the LED current, as shown below: CSH CSL Radj RSENSEVCSREG +VSENSE iLED iCSH iCSL – + iCSL × Radj VCSREG = iLED × RSENSE + iCSL × Radj Therefore iLED = (VCSREG – iCSL × Radj) / RSENSE Figure 3: How To Fine-Tune LED Current Using Radj For example, with a desired LED current of 1.4 A, the required RSENSE = 0.2 V / 1.4 A = 0.143 Ω. But the closest power resistor available is 0.13 Ω. Therefore, the difference is Radj × iCSL = 0.2 V – 1.4 A × 0.13 Ω = 0.018 V where iCSL = 75 µA typical Radj = 0.018 V / 75 µA = 240 Ω The LED current is further modulated by the ADIM (Analog Dimming) pin voltage. This feature can be used for LED bright- ness calibration, or for thermal foldback protection. See Analog Dimming section for details. Synchronous Regulation The ALT80800 integrates an N-channel DMOS as the low-side switch to implement synchronous regulation for LED drivers, as shown in Figure 4. CBOOT SW BOOT GND VIN Floating Gate Driver Integrated Switch SW L i_L Rsc CLED VOUT Boot Charger ALT80800 Figure 4: Synchronous Buck LED Driver The Synchronous configuration can effectively pull down SW to ground by forcing the low-side synchronous switch on even with small inductor current, as shown in Figure 5. Therefore, the BOOT capacitor can be charged normally every switch cycle to ensure the normal operation of buck LED drivers. Figure 5: Normal SW waveform with SR configuration when VIN ≈ VOUT: VIN = 5.4 V, VOUT = 5.14 V (2 white LEDs) FUNCTIONAL DESCRIPTION

Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED DriverALT80800 Allegro MicroSystems, LLC Manchester, NH 03103-3353 U.S.A. www.allegromicro.com Switching Frequency The ALT80800 operates in fixed on-time mode during switching. The on-time (and hence switching frequency) is programmed using an external resistor connected between the TON pin and ground, as given by the following equation: t ON = k × (RON + RINT ) × ( VOUT / VIN ) fSW = 1 / [ k × (RON + RINT )] where k = 0.0127, with fSW in MHz, tON in µs, and RON and RINT (internal resistance, 3 kΩ) in kΩ. 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 0 100 200 300 400 500 600 700 800 900 1000 fSW (MHz) RON (kΩ) 2.4 Figure 6: Switching Frequency vs. TON resistance To minimize the peaks of switching frequency harmonics in EMC measurement, a dithering feature is implemented. The dithering range is internally set at ±5%. The actual switching frequency is swept linearly between 0.95 × f SW and 1.05 × fSW, where fSW is the programmed switching frequency. The rate of modulation for f SW is fixed internally at 12.5 kHz. ENABLE AND DIMMING The ALT80800 is activated when a logic high signal is applied to the EN (enable) pin and V IN = VVCCIN is above UVLO threshold 4.3 V. The buck converter ramps up the LED current to a target level set by RSENSE when PWM pin = High. The EN pin is high-voltage tolerant and can be directly connected to a power supply. However, if V EN is higher than the VIN voltage at any time, a series resistor (10 kΩ) is required to limit the current flowing into the EN pin. This resistor is helpful in preventing EN from damage in case of reverse-battery connection. This series resistor is not necessary if EN is driven from a logic input. The PWM pin is a logic input pin and is internally pulled up to VCC through a resistor. EN pin and PWM pin function as illustrated below: EN pin PWM pin VCC LED High Low ON OFF High High/Open ON ON Low x Shutdown When the EN pin is forced from high to low, the LED current is turned off, but the IC remains in standby mode for up to at least 10 ms. If EN goes high again within this period, the LED current is turned on immediately if PWM pin is high. If EN pin is low for more than t OFFDelay, the IC enters shutdown mode to reduce power consumption. The next high signal on EN will initialize a full startup sequence, which includes a startup delay of approximately 150 μs. This startup delay is not present during PWM operation. Active dimming of the LED is achieved with 2 options: by send- ing a PWM (pulse-width modulation) signal to the EN pin (while PWM = High), or by sending a dimming PWM signal to the PWM pin (while EN is enabled) as illustrated in the table above. The resulting LED brightness is proportional to the duty cycle of the applied PWM signal. A practical range for PWM dimming frequency is between 100 Hz (period = 10 ms) and 2 kHz. If the PWM dimming signal at PWM pin is low when the EN pin is high, the LED will be off immediately and IC is alive waiting for next PWM pulse. The internal LDO is still on and can provide bias to the internal and external circuits. In PWM dimming operation and when V IN is above 40 V , a 10 kΩ resistor is needed to be in parallel with a 0.047 µF output capacitor across the LED string to facilitate BOOT charging dur- ing PWM dimming OFF period.

Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED DriverALT80800 Allegro MicroSystems, LLC Manchester, NH 03103-3353 U.S.A. www.allegromicro.com PWM DIMMING RATIO The brightness of the LED string can be changed by adjusting the PWM duty cycle at the EN pin as follows: Dimming ratio = PWM on-time / PWM period For example, by selecting a PWM period of 5 ms (200 Hz PWM fre- quency) and a PWM on-time of 5 µs, a dimming ratio of 0.1% can be achieved. This is sometimes referred to as “1000:1 dimming.” In an actual application, the minimum dimming ratio is deter- mined by various system parameters, including: VIN , VOUT , inductance, LED current, switching frequency, PWM frequency, and fault flag usage. The device is easily capable of PWM on- time as short as 5 µs; however, if fault flag for open/short LED detection is required, it should be above 130 µs due to the fault mask timer. ANALOG DIMMING In addition to PWM dimming, the ALT80800 also provides an analog dimming feature. When V ADIM is over 2.0 V , the LED cur- rent is at 100% level (as defined by the SENSE resistor). When V ADIM is below 2 V , the LED current decreases linearly down to 20% at VADIM = 0.4 V . This is shown in the following figure: ADIM pin voltage 2 V 200 mV ±6 mV (100%) 0.4 V 40 mV 100 mV 1 V VCSREG Figure 7: ADIM Pin Voltage Controls SENSE Reference Voltage (hence LED current) It is possible to pull ADIM pin below 0.4 V to achieve lower than 20% analog dimming. However, if the average LED cur- rent determined by ADIM becomes too low and is below half the inductor current ripple, negative current will flow through the inductor. To prevent such cases from happening, it is suggested that ADIM voltage should meet the condition below: ADIM > R SENSE / 0.2 × (VIN – VOUT) / L × D × T where D is duty cycle, D ≈ VOUT / VIN, T is switching period, T = 1 / fSW, L is the inductance. For example, when RSENSE = 0.2 Ω, RON = 178 kΩ, L = 33 µH, VIN = 12 V , VOUT = 5.2 V , ADIM voltage should be above 0.21 V , i.e. 11% level, to avoid negative inductor current. ADIM pin can be used in conjunction with PWM dimming to provide wider LED dimming range over 1000:1. In addition, the IC can provide thermal foldback protection by using an external NTC (negative temperature coefficient) thermistor, as shown below: NTC RP RS VCC ADIM Figure 8: Using an External NTC Thermistor to Implement Thermal Foldback ADIM is tied to 5 V (or VCC) if never used for analog dimming, or always less than 2.5 V when used for analog dimming. For long term reliability, or extended period with extreme temperature condition, it is better to keep ADIM always less than 2.5 V .

Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED DriverALT80800 Allegro MicroSystems, LLC Manchester, NH 03103-3353 U.S.A. www.allegromicro.com OUTPUT VOLTAGE AND DUTY CYCLE The figure below provides simplified equations for approximat- ing output voltage. The output voltage of a buck converter is approximately given as: VOUT ≈ VIN × D , D = tON / (tON + tOFF) where D is the duty cycle. VIN VOUT SW GND MOSCIN L iL RSENSE VSW iL t t VIN tON Period, t –VD tOFF iRIPPLE D Figure 9: Simplified Waveforms for a Buck Converter During SW on-time: iRIPPLE = (VIN – VOUT) / L × tON = (VIN – VOUT) / L × t × D where D = tON / t. During SW off-time: iRIPPLE = VOUT / L × tOFF = VOUT / L × t × (1 – D) Simplified equation for output voltage: VOUT = VIN × D More precisely: VOUT = (VIN – iAVG × RDSON(HS)) × D – (1 – D) × RDSON(LS) × iAVG – (DCR + RSENSE) × iAVG where DCR is the internal resistance of the inductor, RSENSE is the current sensing resistance, RDSON(HS) is the on-resistance of high-side switch, RDSON(LS) is the on-resistance of low-side switch, iAV G is the average current through inductor and equal to LED current.

Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED DriverALT80800 Allegro MicroSystems, LLC Manchester, NH 03103-3353 U.S.A. www.allegromicro.com MINIMUM AND MAXIMUM OUTPUT VOLTAGES For a given input voltage, the maximum output voltage depends on the switching frequency and minimum tOFF . For example, if tOFF(min) = 100 ns and fSW = 1 MHz, then the maximum duty cycle is 90%. So for an 18 V input, the maximum output is approximately 16.2 V (based on the simplified equation of VOUT = VIN × D). This means up to 5 LEDs can be operated in series, assuming Vf = 3.3 V or less for each LED. The minimum output voltage depends on minimum tON and switching frequency. For example, if the minimum tON = 65 ns and fSW = 1 MHz, then the minimum duty cycle is 6.5%. That means with VIN = 18 V , the theoretical minimum V OUT is just 1.2 V . However, the internal current sense amplifier is designed to guarantee the current accuracy down to VOUT = 2.65 V . When the output voltage is lower than 2.65 V , the regulator keeps switch- ing to regulate, but the current accuracy will suffer and not be guaranteed. To a lesser degree, the output voltage is also affected by other factors such as LED current, on-resistance of the high-side switch, and DCR of the inductor. As a general rule, switching at lower frequencies allows a wider range of V OUT , and hence more flexible LED configurations. VOUT (V) Frequency (MHz) VOUT(max) (V) VOUT(min) (V) Figure 10: Minimum and Maximum Output Voltage vs. Switching Freqency (VIN = 18 V, minimum tON = 90 ns and tOFF = 100 ns) If the required output voltage is lower than that permitted by the minimum tON , the controller will automatically extend the tOFF to maintain the correct duty cycle. This means that the switching frequency will drop lower when necessary to keep the LED cur- rent in regulation. If the LED string is completely shorted (V OUT = 0 V), the con- troller will continue to switch at minimum tON and will not enter into Hiccup mode. THERMAL BUDGETING The ALT80800 is capable of supplying a 2 A current through its high-side switch. However, depending on the duty cycle, the conduction loss in the high-side switch may cause the package to overheat. Therefore care must be taken to ensure the total power loss of package is within budget. For example, if the maximum temperature rise allowed is ∆T = 60°C at the device case surface, then the maximum power dissipation of the IC is 1.75 W . Assum- ing the maximum RDSON(HS) = 0.32 Ω, RDSON(LS) = 0.24 Ω, and a duty cycle of 70%, then the maximum LED current is limited to 2 A approximately.

Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED DriverALT80800 Allegro MicroSystems, LLC Manchester, NH 03103-3353 U.S.A. www.allegromicro.com FAULT HANDLING The ALT80800 is designed to handle the following faults:

• Pin-to-ground short
• Pin-to-neighboring pin short
• Pin open
• External component open or short
• Output short to ground LED OPEN/OUTPUT SHORT FAULTS Referring to Fault Function block diagram below, LED Open Fault is masked when VIN is below the pre-set adjustable threshold at FDSET pin or ADIM is below 264 mV . When FDSET is below REF1 or ADIM is below 264 mV with asserting fault flag (FFn = Low), the fault flag keeps asserted if open LED fault exists. Only when FDSET is above REF1 and ADIM is above 264 mV , then the Open fault will be detected by checking current sensing volt- age VCSREG and duty cycle. LED Open fault will force regulator into Hiccup mode and assert fault flag, and then fault flag remains asserted during the remaining hiccup mode periods. Once LED open fault disappears, fault flag goes high after hiccup mode period when PWM is high. (refer to Figure 11 and Table 1). 1 ms Hiccup Mode FFn FFn VCC FDSET SGND LED Open LED Short VIN REF1 Duty MaxDuty TON Resistor Open /Short, RSENSE Open/Short, Inductor Open/Short, Overcurrent 1.5 V -VOUT 25% iLED -VCSREG ADIM 0.264 V Figure 11a: Simplified Faults Block Diagram FDSET PWM VCSREG REF1 (or ADIM @ 264 mV) 25% × iLED FFn Flag LED OPEN FAULT LED OPEN FAULT Figure 11b: LED Open Fault Timing Diagram

Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED DriverALT80800 Allegro MicroSystems, LLC Manchester, NH 03103-3353 U.S.A. www.allegromicro.com Table 1: LED Open Fault Truth Table FDSET ADIM FFnn LED Open Fault Event? PWM FFnn+1 VCSREG < 25% × iLED Max Duty High High x No Open Fault 1 High High x Yes, Open Fault 0 Low x 1 x x 1 x Low 1 x x 1 Low x 0 Yes, Open Fault x 0 x Low 0 Yes, Open Fault x 0 Low x 0 No Open Fault 1 x Low 0 No Open Fault 1 FDSET High means FDSET > REF1; FDSET Low means FDSET < REF1; ADIM High means ADIM > 264 mV; ADIM Low means ADIM < 264 mV When output Short fault (such as LED shorted to ground or out- put capacitor shorted to ground) occurs, FFn will be flagged as VOUT drops below 1.5 V and ADIM voltage is above 264 mV; but regulator will not enter into Hiccup mode and will work continu- ously. When short is removed, ALT80800 will return to normal operation. When an LED Open/Short fault occurs, the Fault pin will be flagged if the fault remains active after a deglitch period (tFDG). A mask timer (tMASK) is also introduced whenever PWM signal goes from Low to High. During this mask time, faults will not be detected, so the fault will not be detected when the PWM pulse width is less than this mask time. When PWM goes low, fault flag is latched. Fault flag will keep prior state when PWM is Low.

Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED DriverALT80800 Allegro MicroSystems, LLC Manchester, NH 03103-3353 U.S.A. www.allegromicro.com The Fault deglitch time is fixed; and the Fault mask time is also fixed (refer to Electrical Characteristics table). The LED Open/ Short Fault timing diagrams are illustrated below: tMASK Short Fault Short Removed Short Fault Short Removed Short Fault tFDG tMASK PWM FFn Figure 12a: LED Short Fault Timing Diagram Overview tMASK Open Fault Open Removed Open Fault Open Removed Open Fault tFDG tMASK PWM FFn SW ~1 ms Hiccup period ~1 ms Hiccup Current to regulation timer ~1 ms Hiccup ~1 ms Hiccup Current to regulation timer Figure 12b: LED Open Fault Timing Diagram Overview

Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED DriverALT80800 Allegro MicroSystems, LLC Manchester, NH 03103-3353 U.S.A. www.allegromicro.com Case 1: LED Open/Short Event is outside Mask Timer at PWM = H Case 2: LED Open/Short Event is within Mask Timer at PWM = H Mask Timer Fault Event Deglitch Timer PWM Fault Event Fault Flag LED Open/Short No LED Fault Mask Timer Fault Event Mask Timer PWM Fault Event Fault Flag LED Open/Short Case 3: LED Open/Short Event is close to PWM ↓ at PWM = H Case 4: LED Open/Short Event is at PWM = L Mask Timer Fault Event PWM Fault Flag Mask Timer Fault Event LED Open/Short Mask Timer No LED Fault Mask Timer Fault Event PWM Fault Flag Fault Event Mask Timer LED Open/Short Case 5: LED Open/Short Removed at PWM = L a) LED Short Removed at PWM = L b) LED Open Removed at PWM = L Mask Timer Fault Removed PWM Fault Flag Short Event Mask Timer No LED Short Mask Timer Fault Removed Fault Flag Open Event Current to regulation timer : * PWM No LED Open Case 6: LED Open/Short Removed outside Mask Timer at PWM = H a) LED Short Removed outside Mask Timer at PWM = H b) LED Open Removed outside Mask Timer at PWM = H Mask Timer Fault Removed PWM Fault Flag Short Event No LED Short LED Short Mask Timer Fault Removed Current to regulation timer * PWM Fault Flag Open Event LED Open Hiccup period : ~1 ms No LED Open Case 7: LED Open/Short Removed within Mask Timer at PWM = H a) LED Short Removed within Mask Timer at PWM = H b) LED Open Removed within Mask Timer at PWM=H Mask Timer Fault Removed PWM Fault Flag Short Event No LED Short LED Short Mask Timer Fault Removed Current to regulation Timer * PWM Fault Flag Open Event LED Open No LED Open * Current to regulation timer is 256 switching cycles. The basic timing configurations are detailed below for LED Open/Short faults:

Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED DriverALT80800 Allegro MicroSystems, LLC Manchester, NH 03103-3353 U.S.A. www.allegromicro.com SYSTEM FAILURE DETECTION AND PROTECTION DEMONSTRATION IC-Level Failure Modes Protected against - Any pin open - Any pin shorted to ground - Adjacent pin-to-pin short C4 open or short R1 = open or short L1 = open or short C5 = open or short RSENSE open or short C3 open or short LED string open or short to GND C1,C2 = open or short System-Level Failure Modes Protected against open/short fault for all external components, including: - LED string - Sense resistor - Inductor - Input/output caps, etc. V IN LED+ GND EN GND SW BOOT GND CSH CSL VIN TON EN PWM VCC ALT80800 PWM C1 C2 RSENSE SGND PGND Figure 13: Demonstration of various possible fault cases in an application circuit Table 2: System Failure Mode Table (partial) Failure Mode Symptom Observed FAULT flag asserted? ALT80800 Response Inductor open Dim light from LED Yes [1] When VIN is below preset FDSET setting, regulator switches at maximum duty cycle; when VIN is above FDSET setting, enters into Hiccup mode with 1 ms retry period. Inductor shorted Dim light from LED Yes Current spike trips SW OCP and turns off switching, entering into Hiccup mode with about 1 ms retry period. Sense resistor open Dim light from LED Yes High differential sense voltage causes IC to shut off switching, entering into Hiccup mode with about 1 ms retry period. Sense resistor shorted Dim light from LED Yes Triggers SW OCP fault, entering into Hiccup mode with about 1 ms retry period. LED string open [1] No light from LED Yes [1] Enter into Hiccup mode with about 1 ms retry period. LED Strings shorted [2] (Either LED shorted to GND or Output cap shorted to GND) < 1.5 V Dim light from LED Yes Continues switching at minimum TON; regulator will not enter into Hiccup mode. Output cap open Normal light from LED No Normal operation (since IC only monitors inductor current) Boot capacitor open Dim light from LED Yes IC attempts to switch but can’t fully turn on SW. Boot capacitor shorted No light from LED No IC detects undervoltage fault across BOOT capacitor and will not start switching. TON resistor open Dim light from LED Yes Enter into Hiccup mode with about 1 ms retry period. TON resistor shorted Dim light from LED Yes Enter into Hiccup mode with about 1 ms retry period. [1] For LED Open Fault, fault flag will not be asserted when VIN is below preset mask threshold, ADIM is below 0.264 V or PWM dimming pulse width is below fault mask timer. [2] For LED Short Fault, fault flag will not be asserted when ADIM is below 0.264 V or PWM dimming pulse width is below fault mask timer.

Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED DriverALT80800 Allegro MicroSystems, LLC Manchester, NH 03103-3353 U.S.A. www.allegromicro.com CLAMP DIODES FOR LED OPEN/SHORT PROTECTION Refer to Figure 14. It is recommended to add clamp diode D1 to provide LED short protection when VIN is above 40 V ; if VIN is below 40 V , D1 is not needed. Diode D2 is needed to clamp the overshoot from L-C resonance due to LED Open fault when VIN is above 45 V ; when VIN is below 45 V , D2 is not required. L1 RSENSE CSH SW VIN CLED VOUT Figure 14: Clamp Diode D1 for LED Short Protection when VIN is above 40 V. Clamp Diode D2 for LED Open Protection when VIN is above 45 V.

Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED DriverALT80800 Allegro MicroSystems, LLC Manchester, NH 03103-3353 U.S.A. www.allegromicro.com COMPONENT SELECTIONS The inductor is often the most critical component in a buck con- verter. Follow the procedure below to derive the correct param- eters for the inductor: 1. Determine the saturation current of the inductor. This can be done by simply adding 20% to the average LED current: iSAT ≥ iLED × 1.2. 2. Determine the ripple current amplitude (peak-to-peak value). As a general rule, ripple current should be kept between 10% and 30% of the average LED current: 0.1 < iRIPPLE(pk-pk) / iLED < 0.3. 3. Calculate the inductance based on the following equations: L = (VIN – VOUT ) × D × t / iRIPPLE , and D = VOUT / VIN , where D is the duty cycle, and t is the period 1/ fSW. OUTPUT FILTER CAPACITOR The ALT80800 is designed to operate in current regulation mode. Therefore it does not require a large output capacitor to stabilize the output voltage. This results in lower cost and smaller PCB area. In fact, having a large output capacitor is not recommended. In most applications, however, it is beneficial to add a small filter capacitor (around 0.1 μF) across the LED string. This capacitor serves as a filter to eliminate switching spikes seen by the LED string. This is very important in reducing EMI noises, and may also help in ESD testing. In PWM dimming operation and when V IN is above 40 V , it is suggested to use a 0.047 µF output capacitor, as described in Enable and Dimming section. ADDITIONAL NOTES ON RIPPLE CURRENT

• For consistent switching frequency, it is recommended to choose the inductor and switching frequency to ensure the induc- tor ripple current percentage is at least 10% over normal operat- ing voltage range (ripple current is lowest at lowest VIN).
• If ripple current is less than 10%, the switching frequency may jitter due to insufficient ripple voltage across CSH and CSL pins. However, the average LED current is still regulated.
• For best accuracy in LED current regulation, a low current ripple of less than 20% is required.
• There is no hard limit on the highest ripple current percentage allowed. A 40% ripple current is still acceptable, as long as both the inductor and LEDs can handle the peak current (average cur- rent × 1.2 in this case). However, higher ripple current percentage affects the accuracy of LED current, and limits the minimum current that can be regulated when using ADIM.
• In general, allowing a higher ripple current percentage enables lower-inductance inductors to be used, which results in smaller size and lower cost.
• If lower ripple current is required for the LED string, one solution is to add a small capacitor (such as 1 to 2.2 μF) across the LED string from LED+ to ground. In this case, the induc- tor ripple current remains high while the LED ripple current is greatly reduced.
• The effectiveness of this filter capacitor depends on many fac- tors, such as: switching frequency, inductors used, PCB layout, LED voltage and current, and so forth.
• The addition of this capacitor introduces a longer delay in LED current during PWM dimming operation. Therefore the accuracy of average LED current is reduced at short PWM on-time. INDUCTOR SELECTION CHART The chart in the figure below summarizes the relationship between LED current, switching frequency, and inductor value. Based on this chart: assuming LED current = 1 A and L = 22 μH, then minimum fSW = 0.68 MHz in order to keep the ripple current at 20% or lower. If the switching frequency is lower, then a larger inductance must be used to meet the same ripple current require- ment. Figure 15: Minimum switching frequency vs. LED current, given different inductance used (VIN = 12 V, VOUT = 6 V, ripple current = 20%)

Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED DriverALT80800 Allegro MicroSystems, LLC Manchester, NH 03103-3353 U.S.A. www.allegromicro.com VIN GND RSENSE LED+ iRIPPLE VIN GND RSENSE LED+ iRIPPLE iRIPPLE Without output capacitor: The same inductor ripple current flows through sense resistor and LED string. With a small capacitor across LED string: Ripple current through LED string is reducted, while ripple voltage across R SENSE remains high. Figure 16: Using an Output Filter Capacitor to Reduce Ripple Current in LED String Effects of Output Capacitor on LED Ripple Current

Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED DriverALT80800 Allegro MicroSystems, LLC Manchester, NH 03103-3353 U.S.A. www.allegromicro.com APPLICATION CIRCUIT DIAGRAMS Figure 17: Application Circuit Example for ALT80800 (LED current = 1 A, 500 kHz) LED+ VIN PWM CBOOTRON 2.2 µF RSENSE ADIM CLEDExternal PWM dimming signal BOOT FFn CSH CSL TON PWM ADIM VCC ALT80800 GND SWVIN VCCIN EN VIN FDSET VIN FFn 0.2 Ω 178 kΩ 33 µH 0.47 µF 0.1 µF 187 kΩ 187 kΩ 100 kΩ 10 kΩ 0.1 µF +33 µF 4.7 µF SGND PGND VCC VCC

Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED DriverALT80800 Allegro MicroSystems, LLC Manchester, NH 03103-3353 U.S.A. www.allegromicro.com APPLICATION CIRCUIT DIAGRAMS (continued) Figure 18: Using 2 (or more) ALT80800 in parallel to drive the same LED string. Total LED current is the sum of currents from each LED driver. (Note: each LED driver shares the same VIN and ADIM as illustrated). CBOOT SW BOOT GND VIN SW i_L2 Rsc2 CLED2 VOUT CBOOT SW BOOT GND VIN SW i_L1 Rsc1 CLED1 ADIM ADIM Input Voltage ADIM Voltage CSH1 CSL1 CSH2 CSL2 ALT80800 ALT80800 FFn FFn 5 V

Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED DriverALT80800 Allegro MicroSystems, LLC Manchester, NH 03103-3353 U.S.A. www.allegromicro.com Package LP, 16-Pin TSSOP with Exposed Thermal Pad A

1.20 MAX

0.15 0.00 0.30 0.19 0.20 0.09 0.60 ±0.15

1.00 REF

C SEATING PLANE C0.10 16X

0.65 BSC

0.25 BSC

5.00 ±0.10 GAUGE PLANE SEATING PLANE A B B C D Exposed thermal pad (bottom surface); dimensions may vary with device 6.10 0.650.45 1.70 3.00 3.00 2 1 C D Branded Face

3 NOM

For Reference Only – Not for Tooling Use (Reference MO-153 ABT) 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 PCB Layout Reference View Terminal #1 mark area Reference land pattern layout (reference IPC7351 SOP65P640X110-17M); 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) Branding scale and appearance at supplier discretion Standard Branding Reference View YYWW NNNNNNN LLLL = Device part number = Supplier emblem = Last two digits of year of manufacture = Week of manufacture = Characters 5-8 of lot number N Y W L PACKAGE OUTLINE DRAWINGS

Automotive-Grade, Constant-Current 2.0 A PWM Dimmable Synchronous Buck LED DriverALT80800 Allegro MicroSystems, LLC Manchester, NH 03103-3353 U.S.A. www.allegromicro.com For the latest version of this document, visit our website: www.allegromicro.com

Revision History

– December 7, 2017 Initial release 1 November 13, 2018 Updated Enable and Dimming section (page 8) and Output Filter Capacitor section (page 18). Copyright ©2018, 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.