ELM915BA 50V 1A switching LED driver http://www.elm-tech.com ■General description ELM915BA is capable of driving single or multiple series connected LEDs efficiently from a voltage source higher than the LED voltage. ELM915BA is Buck and Buck-Boost controller with internal switching which can stress 1A peak current stress. The controller operating wide input voltage range from 6V to 50V. ELM915BA consists of an output switch and a high-side output current sensing circuit that uses an external resistor to set the nominal average output current. Through applying an external control signal to the LD/PWM pin, it can adjust the output current to above or below the set value. The LD/PWM pin will accept either a DC voltage or a PWM waveform to provide a continuous or a gated output current. The LD/PWM also provide 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 Over temperature protection Over voltage protection Internal NMOS switch NMOS with peak current Low quiescent current High efficiency Wide input voltage range Package : 155±30°C : 53V±5% : 54V : 1A : <250μA : 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 Input voltage SW output peak current Other I/O pin voltage Junction temperature Power dissipation Operating ambient temperature Storage temperature Symbol Vdd Isw Vio Tj Pd Top Tstg Limit 60 1 7 +150 450 -40 to +85 -55 to +150 Caution:Permanent damage to the device may occur when ratings above maximum absolute ones are used. Unit V A V °C 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. Rev.1.4 5-1 ELM915BA 50V 1A switching LED driver http://www.elm-tech.com ■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 Rev.1.4 5-2 ELM915BA 50V 1A switching LED driver http://www.elm-tech.com ■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=6.0V Parameter Input DC supply voltage range LD/PWM Pull-up current Symbol Condition Vin Input voltage Min. 6 Ild Typ. Top=25°C Max. Unit 50 V 4.5 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(200kΩ) Toff Rt=200kΩ, Vin=6V, Vcs=0.4V Toff Rt=820kΩ, Vin=6V, Vcs=0.4V Constant off time(820kΩ) SW switch on resistor Rsw(on) Vin=6V, Vcs=0V Current sense blanking time Tblank Vld/pwm=Vdd, Vcs=0.4V OVP Voltage overvoltage protection Overheat protection temperature OTP μA 450 600 750 μA 4.86 5.40 5.94 V 180 300 0.25 238 250 2.5 9.0 50 125 53 155 mV mV 2.50 V 262 mV 0.5 500 56 185 μs μs Ω ns V °C Rev.1.4 5-3 ELM915BA 50V 1A switching LED driver http://www.elm-tech.com ■Application notes 1) Setting peak current with external resistor Rs ELM915BA is open loop peak current mode driver with internal power switch; Which peak current setting by external resistor Rs connected between CS and GND. Ipk = 0.25/Rs (A) 2) Setting constant off time value (Toff) The RT pin can set internal power switch of time with period. The time with period is constant when resistor value between RT to GND is fixed. Following diagram is the reference data for setting the off-time. ���������������������� ������� ���� ��� �� ��� � �� ��������� 3) Dimming function ELM915BA is capable of two types of dimming function-linear and PWM dimming. The linear dimming function works by setting the LD/PWM voltage between 0.25V to 2.5V. ELM915BA shutdowns once the LD/ PWM voltage is bellow 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) Rev.1.4 5-4 ELM915BA 50V 1A switching LED driver http://www.elm-tech.com 4) Buck topology application ● ● ● Vin(dc) ▲ LED1 LED2 Dimming L ● LD/ PWM SW VDD ELM915BA RT CS GND Rs Rt The above diagram is buck topology circuit. The input and output specifications as following. Vin = 12Vdc. Vled = Vo = 3.5V LED average current is 350mA, and the current ripple is ±20%. If constant off time is 1.2μs, then set Rt to 100kΩ. Toff=1.2μs 420mA ±20% 350mA 280mA D = Vled / Vin = 3.5 / 12 = 0.292, ΔI = Vled / L × Toff ⇒ 140mA = 3.5 / L × 1.2μs, Rs = 0.25 / Imax. = 0.25 / 420mA = 0.595 Ω L = 3.5 × 1.2μs / 0.14 = 30μH The duty will change when Vin voltage varies. 5) 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 Rev.1.4 5-5