MP1521 High Efficiency White LED Driver

Transcription

1 General Description The is a constant-current Boost Regulator. This IC has three individual current-sensing feedbacks, which are ideal for driving multiple strings of series connected LEDs. The OLS pin is designed for detecting loose or open LED connections. The IC uses a peak current, constant minimum off-time architecture. The feedback pins measure voltage across sense resistors in series with the LED strings. When supplying a bias current of ma, the voltage drop across the sense resistor is only 0.V to minimize power loss. Either a DC voltage or a PWM signal at the /PWM input can control the LED brightness. The has an on board power MOSFET switch that is protected by current limit, open load shutdown, thermal shutdown, and under voltage lockout. Ordering Information Part Number Package Temperature EK MSOP0 - to +5 C EQ QFN (x) - to +5 C EV0005 EV00 EK Evaluation Board EQ Evaluation Board For Tape & Reel use suffix - Z (i.e., EK-Z) Features On board power MOSFET Drive 9 white LEDs from.v input Drive 5 white LEDs from 5V input Up to 90% efficiency Over 0mA output current capacity Open Load shutdown Low current sensing feedback voltage Up to string current sensing feedback Analog and Digital PWM brightness control UVLO, Thermal shutdown Soft Start Internal current limit Available in Compact MSOP0 and Tiny mm x mm QFN package Evaluation Boards Available Applications Handheld Computers, Cell phones, PDAs, Digital and Video Cameras, Small LCD Displays Li Ion and NiMH Battery Applications Figure : Typical Application Circuit (One String of Six () LEDs) / PWM /PWM SW 0 9 OLS 5 FB D L C V Efficiency vs LED current, string of Using Toko DCB µh Inductor LED Current (ma) V = 5V V = V V = V Rev._0/0/0

2 Absolute Maximum Ratings Supply Voltage (V ) V Switch Voltage to -0.5V to V V, V, V, V, V, V FB 0.V to V Storage Temperature -55 C to +50 C Electrical Characteristics (V = 5.0V, T A = 5 C unless specified otherwise) Recommended Operating Conditions Supply Voltage (V ).V to 5V Operating Temperature - C to +5 C Switch Voltage to -0.5V to 5V Package Thermal Characteristics Thermal Resistance, Θ JA (MSOP0) 50 C/W Thermal Resistance, Θ JA (QFN) 0 C/W Parameters Symbol Condition Min Typ Max Units Supply Current (shutdown) I () V <0.V µa Supply Current (quiescent) I () V >.5V, V =0V, V FB =0V µa Minimum Off Time, normal V >.5V, V =0.V ns operation Minimum Off Time, start-up (Note ) UVLO t (NORMAL) t (START) V FB =0 V >.5V, V =0.V, V FB =0V.5. µs Under Voltage Lockout V RISG.. V V FALLG.9. V Enable Threshold V Hysterisis 0 mv Leakage Current V =V µa Open Load Shutdown Threshold Measured at OLS Pin 9 V V OLS =5V µa Leakage Current V OLS =5V 5 0 µa Reference Output Voltage I =0A..5. V Load Regulation I =0 to 00µA.5 5 mv Line Regulation V = to 5V, I =0A.5 5 mv Feedback Comparator Threshold V =.V 0 00 mv Hysterisis (Note ) V =.V 0 mv FB Input Bias Current V FB =0.V na PWM Mode Output-Off Threshold V Input Bias V =0.V na Full Scale Threshold (Note ). V Output Switch Switch On Resistance (Note ) R V =5.0V Ω Switch Current Limit ma Leakage Current V SW =5V 5 µa Thermal Shutdown (Note ) 0 C Notes: ) First pulses after switches high. ) Guaranteed by design. ) The output current is off when is driven below the output-off threshold and full-scale when driven above the full-scale threshold. To PWM the output drive above and below these thresholds. Rev._0/0/0

3 Pin Description MSOP0 QFN FB SW OLS Top View OLS FB SW Part Marking: EK Part Marking: Axx Table : MSOP0 and QFN Pin Assignments MSOP QFN Pin Pin Function Pin # Pin# Name Input supply pin. It can be connected to the regulator s input supply, or to the output for boot-strapped operation (boot-strapped operation is required for V of less than V). Regulator On/Off control input. Logic high (V >V) turns on IC, logic low puts it into low current shutdown mode. Place a 00KΩ resistor in series with if it is connected to a voltage greater than 0V..V reference used for setting the analog control voltage at input. This reference can supply up to 0µA to an external load. Do not connect any bypass capacitors to this pin. It is internally compensated. 5 Analog or PWM input for controlling LED brightness. When used in analog mode, apply a DC voltage of 0. to.v. This input voltage is attenuated by / to set the voltage across sense resistors at,, and FB. Maximum brightness (ma) occurs with.v applied. To control brightness in PWM mode, apply a PWM square wave with a minimum voltage less the 0.V and a maximum greater than.v. When a voltage less than 0.V 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 00 to 00 Hz. 5 9 FB Feedback input for measuring voltage across current-sense resistor that is in series with LED string. Unused feedback pins must be connected to any used feedback pin. 0 OLS Open Load Shutdown pin senses regulator output voltage to protect IC during open load operation. When this pin s voltage exceeds V, the output switch is shut off. The output switch remains off until the IC is reset by cycling the enable pin () or input supply () pin. 9, Signal and power ground. Connect directly to ground plane. 0 SW Output switch pin, power DMOS low-side switch. -,,,, 5 N/C No Connect Rev._0/0/0

4 Figure : Functional Block Diagram Internal Regulator & Enable Circuit UVLO & Ther mal Shutdown SW OLS V 0K K.V + - Open Load Shutdown Comparator 500nS One-Shot Timer Control Logic & Output Driv er Current Limit Comparator V 0.5 W Power FET Bandgap Reference.V Feedback Comparator FB + - K 0K.V Rev._0/0/0

5 Functional Description Operation The utilizes a constant off-time control scheme (Refer to the Block Diagram). For maximum brightness, the pin is biased at or above.v. Its voltage is routed through the unity gain buffer whose the output of is clamped at.v. A K/0K divider from the Buffer to the non-inverting input of the Feedback comparator divides the voltage by three to set the current sense threshold. If any of the feedback pins,, or FB is lower than this threshold the Power FET is turned on. The Power MOSFET and inductor current increases until the current limit comparator trips at 0.5A turning off the MOSFET for 500ns. At the end of 500ns if any of the Feedback pins are still lower than the current sense threshold. The Power FET is again turned on. This cycle repeats itself until all three of the feedback pins exceed the threshold. PWM/ Brightness Adjust PWM Brightness Adjust is accomplished by driving the pin with a square wave whose low voltage is below 0.V and whose high voltage is greater than.v. A voltage below 0.V forces the Power MOSFET off. A voltage greater than.v will cause all three feedback pins to regulate at or above 0.V Open Load Shut-Off Open Load Shut-Off is implemented by connecting the OLS pin to V OUT. In the fault condition where the connection to the LED s is open, V OUT will rise up, as all the feedback pins are absent of voltage. Once V OUT exceeds V, the part will cease operation until the pin is cycled off and on. To disable the open load shut-off feature, connect the OLS pin to. Analog Brightness Adjust Analog Brightness Adjust is accomplished by applying a voltage between 0.V to.v on the pin. The.V output can be used to bias a potentiometer whose wiper drives the pin. Rev._0/0/0 5

6 Application Circuits Figure : One String of Four () LEDs SW 0 9 OLS D, B0 µf L µh C.µF V Efficiency vs LED current using µh Toko DCB Inductor LED Current ma Line regulation using µh Toko DCB Inductor V = V V = V 5 FB LED Current (ma) V (V) Figure : One String of Six () LEDs (Low inductor height for portables) SW 0 9 OLS D, B0 µf L C.µF V Efficiency vs V using.mm High Sumida CMDD Inductor.µH 0µH 5µH V (V) 5 FB LED Current (ma) Line regulation using.mm High Sumida CMDD Inductor µH 0µH 5µH V (V) Rev._0/0/0

7 Application Circuits Continued Figure 5: Two Strings of Four () LEDs or Eight () LEDs Total L µh V Efficiency vs LED current using µh Toko DCB Inductor SW 0 9 OLS D, B0 uf C.µF Total LED Current (ma) V = 5V V = V V = V 5 FB LED current (ma) 5 5 Line Regulation using µh Toko DCB Inductor V (V) Figure : Three Strings of Three () LEDs or Nine (9) LEDs Total SW 0 9 OLS D, B0 µf L µh C.µF V Efficiency vs LED current using µh Toko DCB Inductor V = 5V V = V V = V LED current (ma) 5 FB LED Current (ma). Line regulation using µh Toko DCB Inductor V (V) Rev._0/0/0

8 Package Information MSOP0 0.09(0.500)TYP 0.00(0.00) 0.00(0.0) P IDT. 0.(.900) 0.(.00) 0.(.00) 0.0(5.00) SEE DETAIL "A" 0.0(0.50)TYP GATE PLANE 0.00(0.50) 0.0(0.50)TYP 0.0(0.00) 0.0(.00) 0.(.900) 0.(.00) 0.00(0.50) 0.0(0.950) 0 o - o DETAIL "A" 0.0(0.00) 0.05(0.00) 0.00(0.0) 0.00(0.050) 0.00(0.50) NOTE: ) Control dimension is in inches. Dimension in bracket is millimeters. QFN ( x ).00 (0.) BSC Pin Identification Pin Identification 0.50 (0.0) 0.50 (0.0) 0. (0.00) 0. (0.0) 5.00 (0.) BSC (0.0) 0.50 (0.0) Bottom View.00 (0.055).00 (0.0) exp. pad 0.90 (0.05).00 (0.09).500 (0.059) Ref (0.00) 0. (0.009) 0.00 (0.000) 0.05 (0.00) NOTE: ) Control dimension is in millimeters. Dimension in bracket is inch. NOTICE: MPS believes the information in this document to be accurate and reliable. However, it is subject to change without notice. Please contact the factory for current specifications. No responsibility is assumed by MPS for its use or fit to any application, nor for infringement of patent or other rights of third parties. Rev. Monolithic Power Systems, Inc. 0/0/0 9 University Ave, Building D, Los Gatos, CA 950 USA 0 MPS, Inc. Tel: Fax: Web: