SP7121EK-LTR

SP7121 2-Channel Adjustable Low Dropout High Side Linear LED Driver FEATURES • • • • • • • • • LED Driver for common cathode parallel connected LEDs Ultra Low Dropout Voltage of 300mV @ 25mA No EMI, no switching noise Integrated current matching PWM brightness control Enable/Shutdown control Shutdown current < 1µA Adjustable Output current up to 30mA per channel Available in RoHS Compliant, Lead Free Package: Small footprint SOT23-6 TYPICAL APPLICATION • Mobile Phones • PDA, DSC, MP3 players • Handheld Computers • Keypads and display backlight GENERAL DESCRIPTION The SP7121 LED driver provides a simple solution for a matched current source for any color common cathode LEDs. The common cathode connection allows the user to increase the LED power dissipation by having the cathodes heat sinked to the ground plane of the circuit board. The SP7121 output current value is set by an external resistor. At shutdown mode (EN pin is LOW), the supply current drops to .04µA typical. The SP7121 driver is available in a small footprint 6-pin SOT23-6 package. TYPICAL APPLICATION Sept 11 - 07 Rev E SP7121 Low Dropout LED Driver Page 1 © 2007 Sipex Corporation ABSOLUTE MAXIMUM RATINGS These are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. Exposure to absolute maximum rating conditions for extended period may affect reliability. Maximum LED current ILED1, ILED2……….30mA Vcc, VLED1, VLED2, and EN to GND -0.3V to 6V Junction Temperature...........................+150° C o Operating Temperature….........….-40 to +85 C Storage Temperature..............-65° to +150° C C Package Thermal resistance θJA ……190° C/W ESD Level..........................................2kV HBM ESD Level Enable pin…….…… ….1.5KV HBM ESD Level ISET pin (4)……...…..….1.5KV HBM ESD Level..........................................200V MM Lead Temperature (Soldering, 10 sec)....300° C RECOMMENDED OPERATING CONDITIONS Ambient operating temperature ……. -40° - +85°C C ELECTRICAL CHARACTERISTICS Specifications are at TA=25° Vcc = 2.7V to 5.5V, ENABLE =Vcc, ILED=15mA unless specified. C, Parameter Vcc Shutdown Current 1 VLED Dropout Voltage, Vd LED to LED Current Matching 2 LED Current Line Regulation LED Current Load Regulation 3 Min 2.7 Typ 0.04 135 0.2 1 Max 5.5 1 200 1 0.3 0.3 Units V µA mV % %/V mA/V %/ C V V µA kHz µs mA V 0 Conditions EN = LOW Vcc = 5.5V, ILED = 20mA Vcc = 5.5V, Vd > 200mV 2.7V < Vcc < 5.5V Vcc=3.7V; 150mV < Vd < 1.0V Vd = 300mV LED Current Thermal Regulation 4 EN ON Voltage (HIGH) EN OFF Voltage (LOW) EN Input Bias Current EN Switching Frequency EN ON Minimum Pulse Width LED current per channel ISET Voltage ISET current multiplication ratio 0.01 2.4 0 2 Vcc 0.8 5 20 15 25 1.26 210 3 VEN = Vcc = 5.5V 10 1.17 200 1.21 205 VEN=Vcc=3.7V VEN=Vcc=3.7V 1) Difference between Vcc voltage and LED anode voltage at which ILED current drops 10% from nominal value 2) ILED Current Variations per Volt Vcc change 3) ILED Current Variations at Vd change from 0.15 to 1.0V 4) EN input voltage should not exceed Vcc voltage at any condition Sept 11 - 07 Rev E SP7121 Low Dropout LED Driver Page 2 © 2007 Sipex Corporation PIN ASSIGNMENTS Pin Name Vcc GND EN ISET LED2 LED1 SP7121 1 2 3 4 5 6 Pin Description Power input pin. Bypass Vcc to GND with 1nF capacitor as close to VIN as possible Ground pin Enable pin. Device is active if EN is logic HIGH Connect external resistor to set LED current Connect anode of LED2 Connect anode of LED1 BLOCK DIAGRAM VLED2 VLED1 Sept 11 - 07 Rev E SP7121 Low Dropout LED Driver Page 3 VCC © 2007 Sipex Corporation APPLICATION INFORMATION ENABLE The SP7121 allows the LED current level to be adjusted by an external resistor connected to the ISET pin. This option lets costumer select LED current amplitude by selecting appropriate external RSET resistor value. The SP7121 circuit consists of enable, bandgap reference, and current amplifier circuit blocks. The Enable circuit block provides the enable and PWM function for the IC. The Bandgap reference provides a stable voltage source from which the output current is derived. Setting the Current in the SP7121 The internal current amplifier provides a current gain function where the RSET resistor is connected from the ISET pin (pin 4) to GND. The current, produced by the RSET resistor is then amplified and delivered to the LED output. The external RSET resistor value for SP7121 is determined by following equation: RSET = 200 x VSET/ILED W here ILED = required LED current value in mA per channel. VSET = 1.22V 200 is the typical gain The SP712X drivers have a low current shutdown function. In shutdown mode, the part draws less than 1µA current maximum. The part can be shut down using the EN pin (EN = LOW). The enable pin cannot be tristated or left floating. There are no predefined internal states, so leaving this pin open will cause the part to operate incorrectly. PWM Dimming The SP7121 driver allows LED-dimming control by applying a PWM signal to the EN pin. The acceptable frequency range of this signal is 100Hz to 20 kHz. The minimum ON time that is required for the ISET pin to set is 15µs from the time the Enable pin goes high. Thus, for a 2kHz PWM signal, the acceptable duty cycle range is 3% to 100%. To find the minimum PWM duty cycle the following steps need to be followed. Step 1: Determine the time period of the PWM frequency. The LED current level can be set anywhere from 10mA to 25mA per each output. Specifications are not guaranteed for current levels that are set outside this range. The SP7121 doesn’t have protection from ISET pin being shorted to ground or the RSET value being too low. With an operational maximum current of 30mA per channel device may be damaged if the ISET pin is shorted to the ground or the RSET value is below 8k . W here PWMf is the PWM frequency Step 2: Obtain the minimum Enable ON time; this is 15µS for the SP7121 part. Sept 11 - 07 Rev E SP7121 Low Dropout LED Driver Page 4 © 2007 Sipex Corporation APPLICATION INFORMATION Thermal Considerations Example For a 2kHz signal, the minimum duty cycle for the PWM signal is The SP7121 does not have overtemperature protection. Special care needs to be taken to ensure that the driver’s junction temperature stays below 125˚C. The thermal resistance of the package is 160˚C per Watt. Under normal operation conditions with about 30mA of current per LED and a voltage drop across the part of 1V, the part will still only dissipate .06 Watts -- giving a temperature rise of only 11.4˚C Example of thermal calculations. %Minimum Duty cycle =3% Fault Operation If one of the LEDs is shorted, the LED voltage at this pin will be VCC but that channel will provide the nominal current value, thereby increasing power dissipation. If all channels are shorted, excessive power dissipation may damage the device. If an LED is open, the LED pin voltage will be pulled up to Vcc, and the LED current will be reduced to 3mA for the other channels. The SP7121 doesn’t have protection from the ISET pin being shorted to ground or the With an RSET value being too low. operational maximum current of 30mA per channel, the device may be damaged if the ISET pin is shorted to the ground or the RSET value is below 8k . W here P is total power dissipation Vd is the voltage drop across the SP7121 IOUT is the total output current W here P is the total power dissipation ΘJA is the thermal resistance of the package per Watt. Above example Temperature Rise = 11.4˚C The part will be able will operate up to 85˚C under these conditions. BOARD LAYOUT AND GROUNDING Although the SP7121 does not require an input capacitor for normal operation, a 1nF capacitor can be used to obtain better overall circuit performance. To obtain the best performance from the SP7121, a printed circuit board with ground plane is required. High quality, low series resistance ceramic 1nF bypass capacitors should be used at the Vcc and GND pins (pins 1 and 2). This capacitor must be located as close to the pins as possible. The traces connecting the pins and the capacitor must be kept short and should be made as wide as possible. Sept 11 - 07 Rev E SP7121 Low Dropout LED Driver Page 5 © 2007 Sipex Corporation APPLICATION CIRCUITS SP7121 Powering 2 LEDs Powering high 1 high power LED with SP7121 IOUT up to 50mA TYPICAL PERFORMANCE CHARACTERISTICS PWM FUNCTION -- 2 LEDs PWM minimum duty cycle 5kHz Channel 1 PWM signal; Channel 2 ISET pin; Channel 3 VLED; Channel 4 ILED 20ma/Div PWM minimum duty cycle 20kHz Channel 1 PWM signal; Channel 2 ISET pin; Channel 3 VLED; Channel 4 ILED 20ma/Div Sept 11 - 07 Rev E SP7121 Low Dropout LED Driver Page 6 © 2007 Sipex Corporation TYPICAL PERFORMANCE CHARACTERISTICS PWM FUNCTION -- 2 LEDs continued Zoom of the startup Channel 1 Enable; Channel 2 ISET pin; Channel 3 VLED; Channel 4 ILED 20ma/Div PWM FUNCTION -- SINGLE HIGH POWER LED PWM minimum duty cycle 20kHz Channel 1 PWM signal; Channel 2 ISET pin; Channel 3 VLED; Channel 4 ILED 50ma/Div PWM minimum duty cycle 20kHz Channel 1 PWM signal; Channel 2 ISET pin; Channel 3 VLED; Channel 4 ILED 50ma/Div Sept 11 - 07 Rev E SP7121 Low Dropout LED Driver Page 7 © 2007 Sipex Corporation TYPICAL PERFORMANCE CHARACTERISTICS Quiescent Current 1.4 1.2 1 ICQ in mA 0.8 0.6 0.4 0.2 0 5 10 15 20 25 30 35 Rset Resistor in K ohms Iq at -40C Iq at 25C Iq at 85C . Dropout Voltage vs Rset at 25oC 250 . 200 Vdropout in mV 150 100 50 0 5 10 15 20 25 30 35 Rset Resistor in K ohms Sept 11 - 07 Rev E SP7121 Low Dropout LED Driver Page 8 © 2007 Sipex Corporation TYPICAL PERFORMANCE CHARACTERISTICS Total Output Current vs Vin @25oC 60 50 40 Iout 30 20 Iout 15 mA 10 0 2 2.5 3 3.5 4 Vin 4.5 5 5.5 6 Iout25mA Iout 10mA Output Current vs Rset Resistor . Output Current in mA 35 30 25 20 15 10 5 0 5 10 15 20 25 30 35 RsetResistor in K ohms Iout -40C Iout at 25C Iout at 85C Sept 11 - 07 Rev E SP7121 Low Dropout LED Driver Page 9 © 2007 Sipex Corporation PACKAGE: SOT23-6 Sept 11 - 07 Rev E SP7121 Low Dropout LED Driver Page 10 © 2007 Sipex Corporation ORDERING INFORMATION Part Number SP7121EK-L SP7121EK-L/TR Temp Range -40° to C +85° C -40° to C +85° C RoHS/ Lead Free Yes Yes Package SOT23-6 SOT23-6 ja 190° C/W 190° C/W Moisture Sensitivity Level L1 @ 260ºC L1 @ 260ºC Pack Type Canister Tape & Reel Pack Quantity Any 2500 For further assistance: Email: WWW Support page: Sipex Application Notes: Sipexsupport@sipex.com http://www.sipex.com/content.aspx?p=support http://www.sipex.com/applicationNotes.aspx Solved by Sipex Corporation Headquarters and Sales Office 233 South Hillview Drive Milpitas, CA95035 tel: (408) 934-7500 FAX: (408) 935-7600 TM Sipex Corporation reserves the right to make changes to any products described herein. Sipex does not assume any liability arising out of the application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others. Sept 11 - 07 Rev E SP7121 Low Dropout LED Driver Page 11 © 2007 Sipex Corporation