AT9919

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Technical content

Features

► Hysteretic control with high-side current sensing ► Wide input voltage range: 4.5 to 40V ► >90% Efficiency ► Typical ±5% LED current accuracy ► Up to 2.0MHz switching frequency ► Adjustable constant LED current ► Analog or PWM control signal for PWM dimming ► Over-temperature protection ► -40ºC to +125ºC operating temperature range ► AEC-Q100 compliant

Applications

► Automotive LED lighting applications General Description The AT9919 is a PWM controller IC designed to drive high brightness LEDs using a buck topology. It operates from an input voltage of 4.5 to 40VDC and employs hysteretic control with a high-side current sense resistor to set the constant output current. The operating frequency range can be set by selecting the proper inductor. Operation at high switching frequency is possible since the hysteretic control maintains accuracy even at high frequencies. This permits the use of small inductors and capacitors minimizing space and cost in the overall system. LED brightness control is achieved with PWM dimming from an analog or PWM input signal. Unique PWM circuitry allows true constant color with a high dimming range. The dimming frequency is programmed using a single external capacitor. The AT9919 comes in a small, 8-Lead DFN package and is qualified for automotive LED lighting applications. Typical Application Circuit Hysteretic, Buck, High Brightness LED Driver with High-Side Current Sensing CIN 0 - 2.0V AT9919 VIN VDD GATE GND CS RAMP ADIM DIM RSENSE L

Supertex inc. www.supertex.com Doc.# DSFP-AT9919 A061212 Absolute Maximum Ratings Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Parameter Value VIN, CS to GND -0.3 to +45V VDD, GATE, RAMP, DIM, ADIM to GND -0.3 to +6.0V CS to VIN -1.0 to +0.3V Continuous power dissipation, (TA = +25°C) 1.6W Operating temperature range -40°C to +125°C Junction temperature +150°C Storage temperature range -65°C to +150°C Sym Description Min Typ Max Units Conditions VIN Input DC supply voltage range 4.5 - 40 V DC input voltage VDD Internally regulated voltage 4.5 - 5.5 V VIN = 6.0 to 40V IIN Supply current - - 1.5 mA GATE open IIN, SDN Shutdown supply current - - 900 µA DIM < 0.7V IIN, LIM Current limit - 30 - mA VIN = 4.5V, VDD = 0V - 8.0 - VIN = 4.5V, VDD = 4.0V fOSC Oscillator frequency - - 2.0 MHz --- UVLO VDD Undervoltage lockout threshold - - 4.5 V VDD rising ΔUVLO VDD Undervoltage lockout hysteresis - 500 - mV VDD falling Pin Description Product Marking 8-Lead DFN (K7) 8-Lead DFN (K7) (top view)

Electrical Characteristics

(VIN = 12V, VDIM = VDD, VRAMP = GND, CVDD = 1.0µF, RCS = 0.5Ω, TA = TJ = -40OC to +125OC* unless otherwise noted) CS VIN RAMP ADIM GATE GND VDD DIM GND 9919 YWLL Y = Last Digit of Year Sealed W = Code for Week Sealed L = Lot Number = “Green” Packaging Mounted on FR-4 board, 25mm x 25mm x 1.57mm * Guaranteed by design and characterization, 100% tested at TA = 25OC. Typical characteristics are given at TA = 25OC. Typical Thermal Resistance Package θja 8-Lead DFN 37OC/W

Ordering Information

Part Number Package Packing AT9919K7-G 8-Lead DFN 3000/Reel -G indicates package is RoHS compliant (‘Green’)

Supertex inc. www.supertex.com Doc.# DSFP-AT9919 A061212 Sym Description Min Typ Max Units Conditions Sense Comparator VCS(HI) Sense voltage threshold high 198 230 257 mV (VIN - VCS) rising VCS(LO) Sense voltage threshold low 147 170 195 mV (VIN - VCS) falling VCS(AVG) Average reference voltage 186 200 214 mV VCS(AVG) = 0.5VCS(HI) + 0.5VCS(LO) tDPDH Propagation delay to output high - 70 - ns Falling edge of IN - VCS) = VRS(LO) - 70mV tDPDL Propagation delay to output low - 70 - ns Rising edge of IN - VCS) = VRS(HI) + 70mV ICS Current-sense input current - - 1.0 µA (VIN - VCS) = 200mV VCS(HYS) Current-sense threshold hysteresis - 56 80 mV --- DIM Input VIH Pin DIM input high voltage 2.2 - - V --- VIL Pin DIM input low voltage - - 0.7 V --- tON Turn-on time - 100 - ns DIM rising edge to V GATE = 0.5 x VDD, CGATE = 2.0nF tOFF Turn-off time - 100 - ns DIM falling edge to V GATE = 0.5 x VDD, CGATE =2.0nF Gate Driver IGATE GATE current, source† 0.3 0.5 - A VGATE = GND GATE current, sink† 0.7 1.0 - A VGATE = VDD TRISE GATE output rise time - 40 55 ns CGATE= 2.0nF TFALL GATE output fall time - 17 25 ns CGATE= 2.0nF VGATE(HI) GATE high output voltage VDD -0.5 - - V IGATE = 10mA VGATE(LO) GATE low output voltage - - 0.5 V IGATE = -10mA Over-Temperature Protection TOT Over temperature trip limit† 128 140 - ºC --- ∆THYST Temperature hysteresis† - 60 - ºC --- Analog Control of PWM Dimming fRAMP Dimming frequency 130 - 300 Hz CRAMP = 47nF 550 - 1250 CRAMP = 10nF VLOW RAMP threshold, Low - 0.1 - V --- VHiGH RAMP threshold, High 1.8 - 2.1 V --- VOS ADIM offset voltage -35 - +35 mV --- * Guaranteed by design and characterization, 100% tested at TA = 25OC. Typical characteristics are given at TA = 25OC. † Guaranteed by design and characterization. (VIN = 12V, VDIM = VDD, VRAMP = GND, CVDD = 1.0µF, RCS = 0.5Ω, TA = TJ = -40OC to +125OC* unless otherwise noted)

Supertex inc. www.supertex.com Doc.# DSFP-AT9919 A061212

Application Information

0.1~1.9V - BANDGAP REF REGULATOR General Description The AT9919 is a step-down, constant current, high-bright - ness LED (HB LED) driver. The device operates from a 4.5 to 40V input voltage range and provides the gate drive out- put to an external N-channel MOSFET. A high-side current sense resistor sets the output current and a dedicated PWM dimming input (DIM) allows for a wide range of diming duty ratios. The PWM dimming could also be achieved by apply- ing a DC voltage between 0 and 2.0V to the analog dimming input (ADIM). In this case, the dimming frequency can be programmed using a single capacitor at the RAMP pin. The high-side current setting and sensing scheme minimizes the number of external components while delivering LED cur- rent with a ±8% accuracy, using a 1% sense resistor. Undervoltage Lockout (UVLO) The AT9919 includes a 3.7V under-voltage lockout (UVLO) with 500mV hysteresis. When V IN falls below 3.7V, GATE goes low, turning off the external n-channel MOSFET. GATE goes high once V IN is 4.5V or higher. 5.0V Regulator VDD is the output of a 5.0V regulator capable of sourcing 8.0mA. Bypass VDD to GND with a 1.0μF capacitor. DIM Input The AT9919 allows dimming with a PWM signal at the DIM input. A logic level below 0.7V at DIM forces the GATE OUTPUT low, turning off the LED current. To turn the LED current on, the logic level at DIM must be at least 2.2V. ADIM and RAMP Inputs The PWM dimming scheme can be also implemented by ap- plying an analog control signal to ADIM pin. If an analog con- trol signal of 0~2.0V is applied to ADIM, the device compares this analog input to a voltage ramp to pulse-width-modulate the LED current. Connecting an external capacitor to RAMP programs the PWM dimming ramp frequency. f PWM = 1 CRAMP • 120kΩ DIM and ADIM inputs can be used simultaneously. In such case, f PWM(MAX) must be selected lower than the frequency of the dimming signal at DIM. The smaller dimming duty cycle of ADIM and DIM will determine the GATE signal. When the analog control of PWM dimming feature is not used, RAMP must be wired to GND, and ADIM should be connected to VDD.

Supertex inc. www.supertex.com Doc.# DSFP-AT9919 A061212 One possible application of the ADIM feature of the AT9919 may include protection of the LED load from over-tempera - ture by connecting an NTC thermistor at ADIM, as shown in Figure 1. Figure 1 Setting LED Current with External Resistor RSENSE The output current in the LED is determined by the external current sense resistor (R SENSE) connected between VIN and CS. Disregarding the effect of the propagation delays, the sense resistor can be calculated as: R SENSE ≈ 1 • (VRS(HI) + VRS(LO) ) = 200mV

2 ILED ILED

The AT9919 regulates the LED output current using an input comparator with hysteresis (Figure 2). As the current through the inductor ramps up and the voltage across the sense re- sistor reaches the upper threshold, the voltage at GATE goes low, turning off the external MOSFET. The MOSFET turns on again when the inductor current ramps down through the freewheeling diode until the voltage across the sense resis- tor equals the lower threshold. Use the following equation to determine the inductor value for a desired value of operating frequency f L = (VIN - VOUT )VOUT (VIN - VOUT )tDPDL VOUT tDPDH fSVIN∆IO ∆IO ∆IO where: ∆IO = VRS(HI) - VRS(LO) RSENSE and tDPDL, tDPDH are the propagation delays. Note, that the cur- rent ripple ∆I in the inductor L is greater than ∆IO. This ripple can be calculated from the following equation: ∆I = ∆IO + (VIN - VOUT)tDPDL VOUTtDPDH L L For the purpose of the proper inductor selection, note that the maximum switching frequency occurs at the highest V IN and VOUT = VIN/2. Figure 2 t t ILED VDIM VRS(HI) RSENSE VRS(LO) RSENSE tDPDL tDPDH TS = 1 fS ΔI ΔIO NTC VDD ADIM GND AT9919

Supertex inc. www.supertex.com Doc.# DSFP-AT9919 A061212 Pin # Pin Description 1 CS Current sense input. Senses LED string current. 2 VIN Input voltage 4.5 to 40VDC. 3 RAMP Analog PWM dimming ramp output. 4 ADIM Analog 0~2.0V signal input for analog control of PWM dimming. 5 DIM PWM signal input. 6 VDD Internally regulated supply voltage. Connect a capacitor from VDD to ground. 7 GND Device ground. 8 GATE Drives gate of external MOSFET. TAB GND Must be wired to pin 7 on PCB. Pin Description MOSFET Selection MOSFET selection is based on the maximum input operat- ing voltage V IN, output current I LED, and operating switching frequency. Choose a MOSFET that has a higher breakdown voltage than the maximum operation voltage, low R DS(ON), and low total charge for better efficiency. MOSFET threshold voltage must be adequate if operated at the low end of the input-voltage operating range. Freewheeling Diode Selection The forward voltage of the freewheeling diode should be as low as possible for better efficiency. A Schottky diode is a good choice as long as the breakdown voltage is high enough to withstand the maximum operating voltage. The forward current rating of the diode must be at least equal to the maximum LED current. LED Current Ripple The LED current ripple is equal to the inductor current ripple. In cases when a lower LED current ripple is needed, a ca- pacitor can be placed across the LED terminals. PCB Layout Guidelines Careful PCB layout is critical to achieve low switching losses and stable operation. Use a multilayer board whenever pos- sible for better noise immunity. Minimize ground noise by connecting high-current ground returns, the input bypass capacitor ground lead, and the output filter ground lead to a single point (star ground configuration). The fast di/dt loop is formed by the input capacitor C IN, the free-wheeling diode and the MOSFET. To minimize noise interaction, this loop area should be as small as possible. Place R SENSE as close as possible to the input filter and VIN. For better noise immu- nity, a Kelvin connection is strongly recommended between CS and R SENSE. Connect the exposed tab of the IC to a large- area ground plane for improved power dissipation.

Supertex inc. does not recommend the use of its products in life support applications, and will not knowingly sell them for use in such appl ications unless it receives an adequate “product liability indemnification insurance agreement.” Supertex inc. does not assume responsibility for use of devices described, and limits its liability to the replacement of the devices determined defective due to workmanship. No responsibility is assumed for possible omissions and inaccuracies. Circuitry and specifications are subject to change without notice. For the latest product specifications refer to the Supertex inc. (website: http//www.supertex.com) ©2012 Supertex inc. All rights reserved. Unauthorized use or reproduction is prohibited. Supertex inc.

1235 Bordeaux Drive, Sunnyvale, CA 94089

Tel: 408-222-8888 www.supertex.com (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to http://www.supertex.com/packaging.html.) AT9919 Doc.# DSFP-AT9919 A061212 8-Lead DFN Package Outline (K7) 3.00x3.00mm body, 0.80mm height (max), 0.65mm pitch Symbol A A1 A3 b D D2 E E2 e L L1 θ Dimension (mm) MIN 0.70 0.00 0.20 REF 0.65 BSC 0.30 0.00* 0O JEDEC Registration MO-229, Variation WEEC-2, Issue C, Aug. 2003. * This dimension is not specified in the JEDEC drawing. Drawings not to scale. Supertex Doc. #: DSPD-8DFNK73X3P065, Version C081109. Seating Plane θ Top View Side View Bottom View A D E eb L V iew B View B Note 1 (Index Area D/2 x E/2) Note 3 Note 2 Note 1 (Index Area D/2 x E/2) 8 8 Notes: 1. A Pin 1 identifier must be located in the index area indicated. The Pin 1 identifier can be: a molded mark/identifier; an embedded metal marker; or a printed indicator. 2. Depending on the method of manufacturing, a maximum of 0.15mm pullback (L1) may be present. 3. The inner tip of the lead may be either rounded or square.