ELM915BA 50V 1A switching LED driver ■General description ELM915BA is constant current LED driver with fixed off time, which consists of internal switching that can drive 1A peak current and capable of driving single or multiple LEDs in series connection efficiently. ELM915BA consists of switch NMOS transistor (Max.1A current) can operate from 6V to 50V. The low-side current detection circuit which is able to set the average current of output by output NMOS switch and external resistors is also included in ELM915BA. ELM915BA can be used as buck type and buck-boost type as well. Through input of external control signal to LD/PWM pin, ELM915BA is capable of adjusting the value of output current. The LD/PWM is able to control the continuous output current which is from DC level input and the digital one which is from PWM input. The LD/PWM is also equipped with soft start function to prevent inrush current. The SOT-26 small package makes ELM915BA suitable for LED MR-16 bulb applications. ■Features ■Application • • • • • • • • • • • • • • • • • Linear or PWM dimming Soft-start function Cycle by cycle current limit Constant off time control Off time period programmable Thermal shutdown protection Over voltage protection Internal NMOS switch High efficiency Wide input voltage range Package : 155±30°C : 53V±5% : 54V, 1A : Max.90% : 6V to 50V : SOT-26 MR16 and general lighting Automotive lighting Low voltage Industrial lighting Battery charging LED back lighting Illuminated signs ■Maximum absolute ratings Parameter Power supply voltage SW output peak current I/O pin voltage Power dissipation Operating ambient temperature Storage temperature Symbol Vdd Isw Vio Pd Top Tstg Limit 50 1 GND-0.3 to Vdd+0.3 450 -40 to +125 -55 to +150 Caution:Permanent damage to the device may occur when ratings above maximum absolute ones are used. Unit V A V mW °C °C ■Selection guide ELM915BA-S Symbol a b c Package Product version Taping direction B: SOT-26 A S: Refer to PKG file ELM915BA - S ↑↑ ↑ ab c * Taping direction is one way. 6-1 Rev.1.2 ELM915BA 50V 1A switching LED driver ■Pin configuration SOT-26(TOP VIEW) 6 5 4 1 2 3 Pin No. 1 2 3 4 5 6 Pin name CS GND RT LD/PWM VDD SW Pin description Current sense Ground Constant off time setting Linear dim/PWM dim Power input Internal switch drain ■Marking SOT-26 a to e : Assembly lot No. A to Z (I, O, X excepted) and 0 to 9 abcde ■Standard circuit ● ● ● ● 8 to 24Vac C ● ● ▲ SBD LED1 ● LED2 Dimming L ● LD/ PWM VDD SW ELM915BA RT GND CS Rs Rt 6-2 Rev.1.2 ELM915BA 50V 1A switching LED driver ■Block diagram VDD Regulator 5 5V Toff time modulation 5V 3 RT Vd(mV) LD/PWM 4 ● 250 25 0.25 2.5 Vin OTP/OVP 6 SW 250mV + S R ● Q + 250mV ● + 1 CS 2 GND ■Electrical characteristics Vin=6V Parameter Symbol Condition Input DC supply voltage range Vdd DC supply voltage Shut-down mode Iin_SD LD/PWM to GND, Vin=6V supply current VDD under voltage lockout UVLO Vdd rising threshold UVLO hysteresis ΔUVLO Vdd falling LD/PWM low disable voltage Vsd LD/PWM voltage falling LD/PWM linear dimming Vld voltage range Current sense pull-in Vcs-th Vin=6V, Top=25°C threshold voltage Constant off time(100kΩ) Toff Rt=100kΩ, Vin=6V, Vcs=0.4V Constant off time(500kΩ) Toff Rt=500kΩ, Vin=6V, Vcs=0.4V SW switch resistance Rsw(on) Vin=6V, Vcs=0V Current sense blanking time Tblank Vld/pwm=Vdd, Vcs=0.4V Voltage overvoltage protection OVP Overheat protection temperature OTP 6-3 Min. 6 180 Typ. Top=25°C Max. Unit 50 V 600 μA 5.4 V 300 mV mV 0.25 238 250 50 125 1.22 4.92 0.5 300 53 155 2.50 V 262 mV 56 185 μs μs Ω ns V °C Rev.1.2 ELM915BA 50V 1A switching LED driver ■Application notes 1) Setting peak current with external resistor Rs ELM915BA uses open loop peak current mode driver with internal power switch; peak current is determined by the value of Rs which is connected between CS and GND. Ipk = 0.25/Rs (A) 2) Setting constant off time period Toff RT is used to set the fixed off time of internal NMOS switch . The fixed off time is determined by the value of the resistor which is connected to RT and GND. The connection between Rt and ToffIt is shown as following chart. When RT is set to be 100kΩ, Toff becomes 1.22μs. Toff-Rt characteristic Rt (k�) 1000 100 10 0.1 1 10 Toff (�S) 3) Dimming function ELM915BA provides two types of dimming function: linear dimming and PWM one. Linear dimming activates when DC voltage added to LD/PWM is within the range from 0.25V to 2.5V; the luminance would be 0% under 0.25V, and 100% under 2.5V. For PWM dimming function, ELM915BA is able to adjust the luminance by digital signal when voltage of LD/PWM is under 0.25V. LD/PWM(V) LD/PWM-Luminance 120 5 Luminance (%) 100 PWM 80 60 0 40 T 20 0 0 0.5 1 1.5 2 2.5 3 LD/PWM (V) 4) Over voltage protection When VDD is above OVP. OVP function start to stop internal NMOS operation. OVP function is released when VDD is down below UVLO voltage. 6-4 Rev.1.2 ELM915BA 50V 1A switching LED driver 5) Buck topology application Vin(dc) 12V C LED SBD 350mA LEDx1 Open LD/ VDD PWM L 30μH SW ELM915.BA RT CS GND Rs 0.6Ω Rt 100kΩ The above diagram shows buck topology circuit. a) Vin = 12Vdc. b) Vled = 3.5V LED average forward current is 350mA and ripple current range is 20%(280mA~420mA). If constant off time is 1.22μs, then Rt is required to be 100kΩ. Toff=1.22μs 420mA ±20% 350mA 280mA D = Vled / Vin = 3.5 / 12 = 0.292, ΔI = 140mA = Vled / L × Toff = 3.5 / L × 1.22μ, Rs = 0.25 / Imax. = 0.25 / 420mA = 0.595 Ω L = 3.5 × 1.22μ / 0.14 = 30.5μH The duty would be changed by Vin voltage. 6) Buck-boost topology application Vin 12Vdc C1 10μF 25V LED LED L 100μH C2 10μF 25V Dimming Vld/PWM LD VDD PWM SBD SW LED LED LED LED LEDx6 ELM915BA RT Rt 100kΩ GND CS Rs 0.6Ω 6-5 Rev.1.2 ELM915BA 50V 1A switching LED driver ■1 LED buck topology application characteristics Iin→ Vin Iled ↓ 220μF 60V 100V 1A LED 500mA Max. Vf=3.8V L Open LD/ VDD PWM SW ELM915.BA RT GND 1 CS 1 2 2 Rt=100kΩ, L=15μH, Rs=0.5Ω Rt=470kΩ, L=100μH, Rs=0.5Ω Rs Rt Vin vs Iin 250 Iin (mA) 200 150 �Average Iin(mA) �Average Iin(mA) 100 50 0 0 5 10 15 20 25 30 Vin (V) Vin-Average Iled 350 Iled (mA) 300 250 �Average Iled(mA) �Average Iled(mA) 200 150 100 0 10 20 30 Vin (V) 6-6 Rev.1.2