MP Lamp, 36V Precision White LED Driver

Transcription

1 MP8 9 Lamp, V Precision White LED Driver The Future of Analog IC Technology DESCRIPTION The MP8 is a step-up converter designed for driving up to nine (9) series White LEDs (LED) from a single cell Lithium-Ion battery. It regulates the LED current and includes an analog input for varying the LED brightness. The MP8 uses current limited, variable frequency architecture to regulate the LED current while maintaining high efficiency. The BIAS pin measures the output voltage and turns off the converter if an over voltage condition is present to prevent damage due to an open circuit condition. The LED current is measured with an external current sense resistor. The low 0.V full-scale regulation threshold and 0.Ω power switch minimize power loss. The MP8 is available in an 8-pin MSOP, an 8-pin mm x mm QFN and a -pin mm x mm QFN packages. EVALUATION BOARD REFERCE Board Number Dimensions EV8DQ-00A.0 x. x 0. FEATURES Drives up to 9 Series White LEDs Integrated 0.Ω Power MOSFET Low 0.V Full-Scale Current Sense Threshold Over 0mA Output Current Capacity Analog and Digital PWM Brightness Control Open Load Shutdown Soft-Start Internal Current Limit Under Voltage Lockout Thermal Shutdown Available in 8-Pin MSOP, 8-pin mm x mm QFN and -Pin mm x mm QFN Packages APPLICATIONS Handheld Computers PDAs PDA Phones Digital and Video Cameras Small LCD Displays MPS and The Future of Analog IC Technology are Registered Trademarks of Monolithic Power Systems, Inc. TYPICAL APPLICATION V IN D B0B LED Efficiency vs LED Current V IN = V LEDs 7 LEDs MP8 BIAS C 0nF LED9 EFFICICY (%) LEDs 8 LEDs MP8_TAC LED CURRT (ma) MP8_EC0 MP8 Rev..9

2 ORDERING INFORMATION Part Number* Package Top Marking Temperature MP8DQ QFN (mm x mm) AYW 0 C to +8 C Part Number** Package Top Marking Temperature MP8DK MSOP8 8D 0 C to +8 C Part Number*** Package Top Marking Temperature MP8DG QFN8 (mm x mm) AY 0 C to +8 C *For Tape & Reel, add suffix Z (e.g. MP8DQ Z). For RoHS compliant packaging, add suffix LF (e.g. MP8DQ LF Z) **For Tape & Reel, add suffix Z (e.g. MP8DK Z). For RoHS compliant packaging, add suffix LF (e.g. MP8DK LF Z) ***For Tape & Reel, add suffix Z (e.g. MP8DG Z). For RoHS compliant packaging, add suffix LF (e.g. MP8DG LF Z) TOP VIEW PACKAGE REFERCE TOP VIEW TOP VIEW N/C 8 N/C BIAS NC 8 7 NC BIAS 7 BIAS EXPOSED PAD ON BACKSIDE EXPOSED PAD ON BACKSIDE QFN MSOP8 QFN8 ABSOLUTE MAXIMUM RATINGS () Supply Voltage V BIAS to... V V to... 0.V to +V V, V, V to... 0.V to +V Continuous Power Dissipation (T A = + C) () QFN (mm x mm)....w QFN8 (mm x mm)....w MSOP W Storage Temperature... C to +0 C Recommended Operating Conditions () Supply Voltage V BIAS...7V to V Operating Temperature... 0 C to +8 C Thermal Resistance () θ JA θ JC QFN (mm x mm) C/W QFN8 (mm x mm) C/W MSOP C/W Notes: ) Exceeding these ratings may damage the device. ) The maximum allowable power dissipation is a function of the maximum junction temperature T J (MAX), the junction-toambient thermal resistance θ JA, and the ambient temperature T A. The maximum allowable continuous power dissipation at any ambient temperature is calculated by P D (MAX)=(T J (MAX)- T A )/ θ JA. Exceeding the maximum allowable power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. Internal thermal shutdown circuitry protects the device from permanent damage. ) The device is not guaranteed to function outside of its operating conditions. ) Measured on JESD-7 -layer board. MP8 Rev..9

3 ELECTRICAL CHARACTERISTICS V BIAS = V =.0V, V =.V, T A = + C, unless otherwise noted. Parameter Symbol Condition Min Typ Max Units Supply Current (Shutdown) V < 0.V µa Supply Current (Quiescent) V >.0V, = µa Minimum Off Time (Normal Operation) 0 ns Minimum Off Time (Startup). µs Under Voltage Lock Out BIAS Under Voltage Lock Out Enable UVLO V BIAS Rising, 00mV Hysteresis.. V High Threshold V Hysteresis 0 mv Input Leakage Current 0 na Open Load Shutdown Threshold Measured at BIAS 0 V Bias Current Feedback Comparator V BIAS = 0V, V < 0.V µa V BIAS = 0V, V < 0.V µa Regulation Threshold V V =.V V Hysteresis 0 mv Input Leakage Current V = 0.V 0 80 na PWM Mode Using Output-Off Threshold V Input Leakage Current V = 0.V 00 na Full-Scale Threshold. V Output Switch On-Resistance R ON V BIAS =.0V 0. Ω Current Limit 90 ma Thermal Shutdown 0 C MP8 Rev..9

4 TYPICAL PERFORMANCE CHARACTERISTICS Circuit on front page, V IN =.V, 9 LEDs, I LED = 0mA, V =.V, T A = + C, unless otherwise noted. VOLTAGE (mv) Feedback Voltage vs Input Voltage INPUT VOLTAGE (V) MP8_TPC0 VOLTAGE (mv) Feedback Voltage vs Voltage 0 VOLTAGE (V) MP8_TPC0 LED CURRT (ma) LED Current vs Duty 00Hz DUTY CYCLE (%) MP8_TPC0 Steady-State Operation Startup Startup into an Open Load V V/div. V V/div. V 0V/div. V BIAS AC 0.V/div. V 0V/div. V 0V/div. I INDUCTOR 0.A/div. V BIAS 0V/div. V BIAS 0V/div. MP8_TPC0 MP8_TPC0 MP8_TPC0 EFFICICY (%) Efficiency vs LED Current ( LEDs) V IN = V 7.V V.V V EFFICICY (%) Efficiency vs LED Current (8 LEDs) V IN = V 7.V V.V V EFFICICY (%) Efficiency vs LED Current (9 LEDs) V IN = V 7.V V.V V LED CURRT (ma) MP8_TPC LED CURRT (ma) MP8_TPC LED CURRT (ma) MP8_TPC09 MP8 Rev..9

5 PIN FUNCTIONS Pin # QFN MSOP8 QFN8 Name Description Ground. BIAS Feedback Input. The MP8 regulates the voltage across the current sense resistor between and. Connect a current sense resistor from the bottom of the LED string to and connect the bottom of the LED string to. The regulation threshold is set at 0.V for V.V. Power Switch Output. is the drain of the internal MOSFET switch. Connect the power inductor and output rectifier to, which can swing between and V. Internal Power Input. BIAS powers the internal circuitry and measures the output voltage for open circuit protection. Connect BIAS to the output at the top of the LED string. If open circuit protection is not required, BIAS may be connected to the input source to reduce power consumption of the MP8. Regulator On/Off Control Input. A high voltage applied to turns on the converter; a low voltage turns it off. When not used, connect to the input source for automatic startup. If is driven over V, place a 00kΩ resistor in series with. Never leave floating. 7 7 Analog or PWM Input for Controlling LED Brightness. When used in analog mode, apply a DC voltage of 0.7V to.v. This input voltage is attenuated by / to set the voltage across the sense resistor at. Maximum brightness (0mA) occurs with an application of.v. To control the brightness in PWM mode, apply a PWM signal with a minimum voltage less than 0.8V and a maximum voltage greater than.v (when a voltage less than 0.8V is applied to this pin, the output switch is turned off). The regulator operates at maximum brightness when more than.v is applied. The frequency of the PWM signal must be between 00Hz to 00Hz., 8, 8 NC No Connect MP8 Rev..9

6 OPERATION BIAS 9V INTERNAL REGULATOR & ABLE CIRCUIT UVLO & THERMAL SHUTDOWN.V + -- OP LOAD SHUTDOWN COMPARATOR CONTROL LOGIC & OUTPUT DRIVER 0ns ONE-SHOT TIMER FEEDBACK COMPARATOR + -- CURRT LIMIT COMPARATOR V + --.V MP8_F0_BD0 Figure Functional Block Diagram The MP8 utilizes a constant off-time control scheme. For maximum brightness, the pin is biased at or above.v. Its voltage is routed through the unity gain buffer whose output is clamped at.v. A resistor divider from the buffer to the inverting input of the feedback comparator divides the voltage by three to set the current sense threshold. If the pin voltage is lower than this threshold the power MOSFET is turned on. The MOSFET and inductor currents increase until the current limit comparator trips at 90mA, turning off the MOSFET for at least 0ns. At the end of the 0ns, if the pin is still lower than the current sense threshold, the MOSFET is turned on again. Analog Brightness Adjust Analog brightness adjustments are accomplished by applying a voltage between 0.7V to.v on the pin. PWM Brightness Adjust PWM brightness adjustments are accomplished by driving the pin with a digital signal whose low voltage is below 0.8V and high voltage is greater than.v. A voltage below 0.8V forces the power MOSFET to turn off. A voltage greater than.v will cause the pin to regulate at 0.V. Open Load Shutdown Open Load Shutdown is implemented by connecting the BIAS pin to the top of the LED string. In the fault condition where the connection to the LED is open, V OUT will rise up, as the pin has no voltage. Once V OUT exceeds 0V, the MP8 will cease operation until the pin is cycled off and on. Connecting the BIAS pin to the input will disable Open Load Shutdown. MP8 Rev..9

7 APPLICATION INFORMATION Setting the LED Current The LED current is set by the voltage at (V ) and the sense resistor (R) at. The V range for adjusting the LED current is 0.7V to.v. Over this range, the LED current can be calculated as: V ILED = R Voltages greater than.v can be applied to. Use.V in the equation if V.V or the pin is left open. For example, the LED current is set to 0mA if V.V (or left open) and R = 0Ω. Capacitor Selection A.7µF to 0µF ceramic input capacitor (C) and a 0.7µF to µf ceramic output capacitor (C) are recommended for most applications. A capacitor (C, typically nf to 0nF) in parallel with the LED string improves stability, input ripple and output ripple, especially when large inductance values (0µH or above) are used. For the best stability over a wide temperature range, use capacitors with a XR or X7R dielectric. Inductor Selection The MP8 has a 90mA inductor current limit and can drive up to 9 LEDs at 0mA. Inductance values (for L) from.7µh to µh will work as well..µh or.8µh is a good choice for high efficiency and small size. To prevent saturation, use an inductor with a saturation current rating that is higher than the device current limit. Diode Selection The MP8 s high switching frequency demands a high speed rectifier (D) for optimum efficiency. A Schottky diode is recommended due to its fast recovery time and low forward voltage drop. Ensure the diode s average and peak current ratings exceed the average output current and peak inductor current. In addition, the diode s reverse breakdown voltage must exceed the output voltage. Layout Careful PC board layout is required due to fast switching. All components must be placed as close to the IC as possible. Keep the path between the inductor L, diode D, and output capacitor C extremely short for minimal noise and ringing. The feedback components such as the sense resistor R must be kept close to the pin to prevent noise injection on the pin trace. The ground return of C and C should be tied close to the pin. See the MP8 demo board layout for reference. V-8V V IN D B0B LED C 0nF 8 LEDs per string MP8 BIAS LED8 Figure Driving Strings of 8 LEDs in Series (0mA Total Current) MP8 Rev

8 PACKAGE INFORMATION MSOP8 MP8 Rev

9 QFN (mm x mm) PIN ID MARKING PIN ID SEE DETAIL A PIN ID INDEX AREA BSC.0.0 TOP VIEW BOTTOM VIEW 0.0 REF PIN ID OPTION A R0.0 TYP. PIN ID OPTION B R0.0 TYP SIDE VIEW DETAIL A.90 NOTE: ) ALL DIMSIONS ARE IN MILLIMETERS. ) EXPOSED PADDLE SIZE DOES NOT INCLUDE MOLD FLASH. ) LEAD COPLANARITY SHALL BE 0.0 MILLIMETER MAX. ) JEDEC REFERCE IS MO-9, VARIATION VEEA-. ) DRAWING IS NOT TO SCALE RECOMMDED LAND PATTERN MP8 Rev

10 QFN8 (mm x mm) PIN ID MARKING PIN ID SEE DETAIL A PIN ID INDEX AREA BSC.0. TOP VIEW BOTTOM VIEW 0.0 REF PIN ID OPTION A 0.0xº TYP. PIN ID OPTION B R0.0 TYP SIDE VIEW DETAIL A.90 NOTE: ) ALL DIMSIONS ARE IN MILLIMETERS. ) EXPOSED PADDLE SIZE DOES NOT INCLUDE MOLD FLASH. ) LEAD COPLANARITY SHALL BE 0.0 MILLIMETER MAX. ) DRAWING CONFORMS TO JEDEC MO-9, VARIATION VCCD-. ) DRAWING IS NOT TO SCALE RECOMMDED LAND PATTERN 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. MP8 Rev