Supertex inc. HV9918 Hysteretic, Buck, High Brightness LED Driver with High-Side Current Sensing Features ► ► ► ► ► ► ► ► ► ► General Description Hysteretic control with high-side current sensing Integrated 40V 1.0Ω MOSFET >90% Efficiency Wide input voltage range: 4.5 to 40V ±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 The HV9918 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 up to 700mA. The device is well suited for applications requiring a wide input voltage range. The high-side current sensing and an integrated current-setting circuitry minimize the number of external components while delivering an accurate average output. Dedicated pulse-width modulation (PWM) input enables pulsed LED dimming over a wide range of brightness levels. A hysteretic control method ensures excellent input supply rejection and fast response during load transients and PWM dimming. Applications ► ► ► ► The HV9918 offers an analog-controlled PWM dimming feature that reduces the output current by applying an external DC voltage below the internal 2.0V threshold voltage from ADIM to GND. ADIM can also accept input from a resistor divider including a negative temperature coefficient (NTC) thermistor connected between ADIM and GND, or a positive temperature coefficient (PTC) thermistor connected between ADIM and VDD thus providing a PWM thermal-foldback feature that reduces the LED current when the temperature of the LED string exceeds a specified temperature point. Additional features include thermal-shutdown protection. Low voltage industrial and architectural lighting General purpose constant current source Signage and decorative LED lighting Indicator and emergency lighting The high switching frequency up to 2.0MHz permits the use of small inductors and capacitors, minimizing space and cost in the overall system. The HV9918 comes in a small 8-Lead DFN package and is ideal for industrial and general lighting applications. Typical Application Circuit RSENSE L CIN VIN 0 - 2.0V CS RAMP SW ADIM VDD DIM GND HV9918 Supertex inc. ● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com HV9918 Pin Description Ordering Information Package Options Device CS 1 8 SW VIN 2 7 GND RAMP 3 6 VDD ADIM 4 5 DIM 8-Lead DFN 3.00x3.00mm body, 0.80mm height (max), 0.65mm pitch HV9918 HV9918K7-G -G indicates package is RoHS compliant (‘Green’) GND 8-Lead DFN (K7) (top view) Product Marking Parameter Value VIN, CS, SW to GND -0.3 to +45V VDD, RAMP, DIM, ADIM to GND -0.3 to +6.0V CS to VIN -1.0 to +0.3V Continuous power dissipation, (TA = +25°C) Operating temperature range 8-Lead DFN (K7) Thermal Resistance 1.6W -40°C to +125°C Junction temperature +150°C Storage temperature range Y = Last Digit of Year Sealed W = Code for Week Sealed L = Lot Number = “Green” Packaging 9918 YWLL Absolute Maximum Ratings Package θja 8-Lead DFN (K7) 60OC/W Mounted on FR-4 board, 25mm x 25mm x 1.57mm -65°C to +150°C 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. Electrical Characteristics (VIN = 12V, VDIM = VDD, VRAMP = GND, CVDD = 1.0µF, RCS = 0.5Ω, TA = TJ = -40OC to +125OC* unless otherwise noted) Sym Description Min Typ Max Units VIN Input DC supply voltage range 4.5 VDD Internally regulated voltage - 40 V DC input voltage 4.5 - 5.5 V VIN = 6.0 to 40V Supply current - - 1.5 mA SW = GND IIN, SDN Shutdown supply current - - 900 µA DIM < 0.7V IIN, LIM Current limit - 30 - - 8.0 - Switchingr frequency - - 2.0 MHz UVLO VDD Undervoltage lockout threshold - - 4.5 V VDD rising ΔUVLO VDD Undervoltage lockout hysteresis - 500 - mV VDD falling IIN fSW mA Conditions VIN = 4.5V, VDD = 0V VIN = 4.5V, VDD = 4.0V --- * Guaranteed by design and characterization, 100% tested at TA = 25 C. Typical characteristics are given at TA = 25OC. O Supertex inc. ● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com 2 HV9918 Electrical Characteristics (VIN = 12V, VDIM = VDD, VRAMP = GND, CVDD = 1.0µF, RCS = 0.5Ω, TA = TJ = -40OC to +125OC* unless otherwise noted) Sym Description Min Typ Max Units Conditions Sense Comparator VRS(HI) Sense voltage threshold high 213 - 246 mV (VIN - VCS) rising VRS(LO) Sense voltage threshold low 158 - 182 mV (VIN - VCS) falling tDPDL Propagation delay to SW off - 70 - ns Rising edge of (VIN - VCS) = VRS(HI) +70mV to VSW = 0.9 • VIN tDPDH Propagation delay to SW on - 70 - ns Falling edge of (VIN - VCS) = VRS(LO) -70mV to VSW = 0.1 • VIN ICS Current-sense input current - - 1.0 µA (VIN - VCS) = 200mV Current-sense threshold hysteresis - 56 70 mV --- ICS(HYS) 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 VSW = 0.9 • VIN tOFF Turn-off time - 100 - ns DIM falling edge to VSW = 0.1 • VIN Output Switch IDC SW continuous current - - 0.7 A --- RON ON resistance - 1.0 2.0 Ω --- ILEAK SW leakage current - 10 - µA VIN = 40V 128 140 - ºC --- - 60 - ºC --- 130 - 300 550 - 1250 Over-Temperature Protection TOT ∆THYST Over temperature trip limit Temperature hysteresis Analog Control of PWM Dimming Hz CRAMP = 47nF fRAMP Dimming frequency VLOW RAMP threshold, Low - 0.1 - V --- VHiGH RAMP threshold, High 1.8 - 2.1 V --- VOS ADIM offset voltage -35 - 35 mV --- CRAMP = 10nF * Guaranteed by design and characterization, 100% tested at TA = 25OC. Typical characteristics are given at TA = 25OC. Supertex inc. ● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com 3 HV9918 Block Diagram VIN VDD REGULATOR SW + - CS CURRENT SENSE COMPARATOR BANDGAP REF + - DIM UVLO COMPARATOR GND RAMP PWM RAMP 0.1~1.9V ADIM + Application Information General Description The HV9918 is a step-down, constant current, high-brightness LED (HB LED) driver. The device operates from a 4.5 to 40V input voltage range, and includes an internal 40V 1.0Ω 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. PWM dimming can also be achieved by applying 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 current with ±5% accuracy using a 1% sense resistor. HV9918 DIM Input The HV9918 allows dimming with a PWM signal at the DIM input. A logic level below 0.7V at DIM halts SW switching, turning the LED current off. To turn the LED current back 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 applying an analog control signal to ADIM pin. If an analog control signal of 0 ~ 2.0V is applied to ADIM, the device compares this analog input to a voltage ramp to pulse-widthmodulate the LED current. Connecting an external capacitor to RAMP programs the PWM dimming ramp frequency. fPWM = 1 CRAMP • 120kΩ Undervoltage Lockout (UVLO) The HV9918 includes a 3.7V under-voltage lockout (UVLO) with 500mV hysteresis. When VIN falls below 3.7V, switching of SW is disabled. Switching of SW resumes once VIN is 4.5V or higher. DIM and ADIM inputs can be used simultaneously. In such case, fPWM(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 SW signal. 5.0V Regulator VDD is the output of a 5.0V regulator capable of sourcing 8mA. Bypass VDD to GND with a 1.0μF capacitor. When the analog control of the PWM dimming feature is not used, RAMP must be wired to GND, and ADIM should be connected to VDD. Supertex inc. ● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com 4 HV9918 One possible application of the ADIM feature of the HV9918 may include protection of the LED load from over-temperature by connecting an NTC thermistor at ADIM, as shown in Figure 1. VDD HV9918 the inductor ramps up and the voltage across the sense resistor reaches the upper threshold, the internal MOSFET at SW turns off. The MOSFET turns on again when the inductor current ramps down through the freewheeling diode until the voltage across the sense resistor equals the lower threshold. Use the following equation to determine the inductor value for a desired value of operating frequency fS: ADIM L= NTC GND ∆IO = Setting LED Current with External Resistor RSENSE The output current in the LED is determined by the external current sense resistor (RSENSE) connected between VIN and CS. Disregarding the effect of the propagation delays, the sense resistor can be calculated as: RSENSE ≈ 2 • (VRS(HI) + VRS(LO) ) ILED VRS(HI) RSENSE = VRS(HI) - VRS(LO) RSENSE ∆I = ∆IO + ILED TS = tDPDL VRS(LO) RSENSE (VIN - VOUT )tDPDL VOUT tDPDH ∆IO ∆IO and tDPDL, tDPDH are the propagation delays. Note, that the current ripple ∆I in the inductor L is greater than ∆IO. This ripple can be calculated from the following equation: 200mV Selecting Buck Inductor L The HV9918 regulates the LED output current using an input comparator with hysteresis (Figure 2). As the current through ILED fSVIN ∆IO - where: Figure 1 1 (VIN - VOUT )VOUT (VIN - VOUT)tDPDL L + VOUT tDPDH L For the purpose of the proper inductor selection, note that the maximum switching frequency occurs at the highest VIN and VOUT = VIN/2. 1 fS tDPDH ΔI ΔIO t VDIM Figure 2 Supertex inc. ● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com 5 t HV9918 Thermal Shutdown The HV9918 thermal-shutdown feature turns off the SW driver when the junction temperature exceeds +140°C. The SW driver turns back on when the junction temperature drops 60°C below the shutdown temperature threshold. 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 capacitor 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 possible 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 CIN, the free-wheeling diode and the HV9918 switching MOSFET. To minimize noise interaction, this loop area should be as small as possible. Place RSENSE as close as possible to the input filter and VIN. For better noise immunity, a Kelvin connection is strongly recommended between CS and RSENSE. Connect the exposed tab of the IC to a large-area ground plane for improved power dissipation. Pin Description Pin # Pin Description 1 CS Current sense input. Senses LED string current. 2 VIN Input voltage 4.5 to 40V DC. 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 SW TAB GND Open Drain Output of an internal 40V 1.0Ω MOSFET. Must be wired to pin 7 on PCB. Supertex inc. ● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com 6 HV9918 8-Lead DFN Package Outline (K7) 3.00x3.00mm body, 0.80mm height (max), 0.65mm pitch D2 D 8 8 E E2 Note 1 (Index Area D/2 x E/2) Note 1 (Index Area D/2 x E/2) 1 1 Top View Bottom View View B Note 3 θ A A3 e b A1 L Seating Plane L1 Note 2 View B Side View 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. Symbol Dimension (mm) A A1 MIN 0.70 0.00 NOM 0.75 0.02 MAX 0.80 0.05 A3 0.20 REF b D D2 E E2 e 0.25 2.85* 1.60 2.85* 1.35 0.30 3.00 - 3.00 - 0.35 3.15* 2.50 3.15* 1.75 0.65 BSC L L1 θ 0.30 0.00* 0O 0.40 - - 0.50 0.15 14O 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. (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.) Supertex inc. does not recommend the use of its products in life support applications, and will not knowingly sell them for use in such applications 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) Supertex inc. ©2010 Supertex inc. All rights reserved. Unauthorized use or reproduction is prohibited. Doc.# DSFP-HV9918 C092710 1235 Bordeaux Drive, Sunnyvale, CA 94089 Tel: 408-222-8888 www.supertex.com 7