MP A, 24V, 1.4MHz Step-Down White LED Driver in a TSOT23-6

Transcription

1 The Future of Analog IC Technology DESCRIPTION The MP70 is a monolithic step-down white LED driver with a built-in power MOSFET. It achieves.a peak output current over a wide input supply range with excellent load and line regulation. Current mode operation provides fast transient response and eases loop stabilization. Fault condition protection includes cycle-by-cycle current limiting and thermal shutdown. The MP70 requires a minimum number of readily available standard external components. The MP70 is available in a TSOT- package. MP70.A, V,.MHz Step-Down White LED Driver in a TSOT- FEATURES.A Peak Output Current 0.Ω Internal Power MOSFET Switch Stable with Low ESR Output Ceramic Capacitors Also Work with Cap-less Configuration Up to 87% Efficiency 0.μA Shutdown Mode Fixed.MHz Frequency Thermal Shutdown Cycle-by-Cycle Over Current Protection Wide.V to V Operating Input Range 0.V Sense Voltage Available in a TSOT- Package APPLICATIONS WLED Drivers Distributed Power Systems Battery Charger Pre-Regulator for Linear Regulators MPS and The Future of Analog IC Technology are Registered Trademarks of Monolithic Power Systems, Inc. TYPICAL APPLICATION Efficiency vs Output Current Circuit as Figure 00 OFF ON EFFICICY (%) V =8V V =0V V =V OUTPUT CURRT (A) MP70 Rev

2 MP70.A, V,.MHz STEP-DOWN WHITE LED DRIVER A TSOT- PACKAGE REFERCE TOP VIEW Part Number* Package Temperature MP70DJ TSOT- 0 C to 8 C * For Tape & Reel, add suffix Z (eg. MP70DJ Z) For RoHS compliant packaging, add suffix LF (eg. MP70DJ LF Z) ABSOLUTE MAXIMUM RATGS () Supply Voltage V... V... 0.V to V 0.V V BS... V All Other Pins... 0.V to V Junction Temperature...0 C Lead Temperature...0 C Storage Temperature... C to 0 C Recommended Operating Conditions () Supply Voltage V....V to V Output Voltage V OUT... 0.V to V Ambient Temperature... 0 C to 8 C Thermal Resistance () θ JA θ JC TSOT C/W Notes: ) Exceeding these ratings may damage the device. ) The device function is not guaranteed outside of the recommended operating conditions. ) Measured on approximately square of oz copper. ELECTRICAL CHARACTERISTICS V = V, T A = C, unless otherwise noted. Parameters Symbol Condition Min Typ Max Units Feedback Voltage V.V V V V Feedback Current I V = 0.V 0. μa Switch-On Resistance () R DS(ON) 0. Ω Switch Leakage V = 0V, = 0V 0 μa Current Limit ().8 A Oscillator Frequency f V = 0.V...7 MHz Fold-back Frequency V = 0V 700 KHz Maximum Duty Cycle V = 0.V 87 % Minimum On-Time () t ON 00 ns Under Voltage Lockout Threshold Rising..8. V Under Voltage Lockout Threshold Hysteresis 0 mv Input Low Voltage 0. V Input High Voltage. V Input Current V = V. V = 0V 0. Supply Current (Shutdown) I S V = 0V 0..0 μa Supply Current (Quiescent) I Q V = V, V = 0.V μa ma Thermal Shutdown () 0 C Note: ) Guaranteed by design. MP70 Rev

3 MP70.A, V,.MHz STEP-DOWN WHITE LED DRIVER A TSOT- P FUNCTIONS Pin # Name Description Bootstrap. A capacitor is connected between and BS pins to form a floating supply across the power switch driver. This capacitor is needed to drive the power switch s gate above the supply voltage. Ground. This pin is the voltage reference for the regulated output voltage. For this reason care must be taken in its layout. This node should be placed outside of the D to C ground path to prevent switching current spikes from inducing voltage noise into the part. Current Sense Feedback Voltage. Its internal threshold is 0.V. On/Off Control Input. Pull above.v to turn the device on. Supply Voltage. The MP70 operates from a.v to V unregulated input. Input Capacitor is needed to prevent large voltage spikes from appearing at the input. Switch Output. MP70 Rev

4 MP70.A, V,.MHz STEP-DOWN WHITE LED DRIVER A TSOT- TYPICAL PERFORMACE CHARACTERISTICS Circuit as Figure, V = V, Load: one Watt White LED, unless otherwise noted. Steady State Operation Enable Start Up Enable Turn Off V OUT(AC) 0mV/div I DUCTOR V V/div V V/div 00nS/div 0us/div 0us/div Output Short Output Short Entry Output Short Recovery I DUCTOR V OUT V/div V OUT V/div Line Regulation VOUT =.V us/div us/div us/div I Current Limit vs Duty Cycle V V/div V OUT V/div Line Regulation VOUT =.V 00us/div OUTPUT CURRT(A) PWM DIMMG DUTY(%) DUCTOR PEAK CURRT(A) DUTY(%) MP70 Rev

5 MP70.A, V,.MHz STEP-DOWN WHITE LED DRIVER A TSOT- OPERATION The MP70 is a current mode buck regulator. That is, the EA output voltage is proportional to the peak inductor current. At the beginning of a cycle, M is off. The EA output voltage is higher than the current sense amplifier output, and the current comparator s output is low. The rising edge of the.mhz CLK signal sets the RS Flip-Flop. Its output turns on M thus connecting the pin and inductor to the input supply. The increasing inductor current is sensed and amplified by the Current Sense Amplifier. Ramp compensation is summed to the Current Sense Amplifier output and compared to the Error Amplifier output by the PWM Comparator. When the sum of the Current Sense Amplifier output and the Slope Compensation signal exceeds the EA output voltage, the RS Flip- Flop is reset and M is turned off. The external Schottky rectifier diode (D) conducts the inductor current. If the sum of the Current Sense Amplifier output and the Slope Compensation signal does not exceed the EA output for a whole cycle, then the falling edge of the CLK resets the Flip-Flop. The output of the Error Amplifier integrates the voltage difference between the feedback and the 0.V bandgap reference. The polarity is such that a pin voltage lower than 0.V increases the EA output voltage. Since the EA output voltage is proportional to the peak inductor current, an increase in its voltage also increases current delivered to the output. x0 CURRT SSE AMPLIFIER -- RAMP GERATOR REGULATOR D REGULATOR OSCILLATOR.MHz/700KHz pf -- CURRT LIMIT COMPARATOR S R R Q DRIVER M REFERCE 7pF 0.V EA -- ERROR AMPLIFIER -- PWM COMPARATOR Figure Functional Block Diagram MP70 Rev

6 MP70.A, V,.MHz STEP-DOWN WHITE LED DRIVER A TSOT- APPLICATION FORMATION Setting LED Current The current sense resistor is inserted between the anode of WLED and. The current sense resistor value is calculated as: 0.V R = For A WLED current, choose R = 0mΩ Selecting the Inductor A µh to 0µH inductor with a DC current rating of at least % percent higher than the maximum load current is recommended for most applications. For highest efficiency, the inductor s DC resistance should be less than 00mΩ. Refer to Table for suggested surface mount inductors. For most designs, the required inductance value can be derived from the following equation. V L = OUT V (V ΔI L V f OUT Where ΔI L is the inductor ripple current. Choose the inductor ripple current to be 0% of the maximum load current. The maximum inductor peak current is calculated from: ΔIL IL(MAX) = ILOAD Under light load conditions below 00mA, a larger inductance is recommended to improve efficiency. See Table for suggested inductors. Also note that the maximum recommended load current is A if the duty cycle exceeds %. ) Selecting the Input Capacitor The input capacitor reduces the surge current drawn from the input supply and the switching noise from the device. The input capacitor impedance at the switching frequency should be less than the output impedance of the input source to prevent high frequency switching current from passing through the input. Ceramic capacitors with XR or X7R dielectrics are highly recommended because of their low ESR and small temperature coefficients. For most applications, a.7µf capacitor is sufficient. Selecting the Output Capacitor The output capacitor keeps the output current ripple small and ensures feedback loop stability. The output capacitor impedance should be low at the switching frequency. Ceramic capacitors with XR or X7R dielectrics are recommended for their low ESR characteristics. For most applications, a.µf ceramic capacitor will be sufficient. The MP70 can also work properly without output capacitor by adding a small capacitor in the feedback loop (see Figure ). The small capacitor is recommended 80pF. PC Board Layout The high current paths (, and ) should be placed very close to the device with short, direct and wide traces. The input capacitor needs to be as close as possible to the and pins. The external feedback resistors should be placed next to the pin. Keep the switch node traces short and away from the feedback network. MP70 Rev

7 MP70.A, V,.MHz STEP-DOWN WHITE LED DRIVER A TSOT- Table Suggested Surface Mount Inductors Manufacturer Part Number Inductance(µH) Max DCR(Ω) Current Dimensions Rating (A) L x W x H (mm ) Toko A9CY-R7M x. x Sumida CDRHD8C/LD x. x Wurth Electronics x.8 x.8 TYPICAL APPLICATION CIRCUITS V BS MP70 L 0.7A Figure White LED Driver without Output Capacitor V V-V U MP70 L A OFF ON Figure White LED Driver with Over-Voltage Clamp Output V V-V C.7uF V MP70 CB 0nF L.7uH/.A D B0A C.uF V LED OFF ON LED LED Figure Driving White LEDs in Series from V- V Input Voltage MP70 Rev

8 MP70.A, V,.MHz STEP-DOWN WHITE LED DRIVER A TSOT- PACKAGE FORMATION TSOT TYP 0.9 BSC.0 TYP See Note 7 EXAMPLE TOP MARK P AAAA TYP TOP VIEW RECOMMDED LAND PATTERN BSC MAX SEATG PLANE SEE DETAIL FRONT VIEW SIDE VIEW GAUGE PLANE 0. BSC 0 o -8 o DETAIL NOTE: ) ALL DIMSIONS ARE MILLIMETERS. ) PACKAGE LGTH DOES NOT CLUDE MOLD FLASH, PROTRUSION OR GATE BURR. ) PACKAGE WIDTH DOES NOT CLUDE TERLEAD FLASH OR PROTRUSION. ) LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMG) SHALL BE 0.0 MILLIMETERS MAX. ) DRAWG CONFORMS TO JEDEC MO-9, VARIATION AB. ) DRAWG IS NOT TO SCALE. 7) P IS LOWER LEFT P WH READG TOP MARK FROM LEFT TO RIGHT, (SEE EXAMPLE TOP MARK) NOTICE: The information in this document is subject to change without notice. Please contact MPS for current specifications. Users should warrant and guarantee that third party Intellectual Property rights are not infringed upon when integrating MPS products into any application. MPS will not assume any legal responsibility for any said applications. MP70 Rev