- SP7616 High Accuracy 4-Channel Low Side LED Driver for CCFL Replacement FEATURES Wide 4.5V to 30V operating range 60mA LED current per channel 1.5% channel to channel current matching Analog Dimming control PWM operation up to 5kHz with 10% Duty Cycle Low dropout: 150mV @ 20mA Built-in Over Temperature Protection Lead Free, RoHS Compliant Packaging: Small 2X3mm DFN Connect heat sink pad to GND DESCRIPTION The SP7616 is a 30V 4-Channel linear low side LED driver. It is capable of powering up to four LED strings of nine LEDs @ 60mA per string for a total of 36 LEDs with 1.5% typical current matching between channels. The desired LED current can be adjusted with an external resistor, and the precision string-to-string current matching ensures consistent color temperature across the whole display. The device also features very low dropout voltage to maximize system efficiency and avoid difficult thermal design constraints. Dimming can be achieved by feeding a PWM signal to the PWM pin, or use an analog signal to control the ISET current, this allows brightness control without unwanted color shifts. Fast LED current turn-on/off time allows up to 5 kHz PWM dimming frequencies with as low as 10% duty cycle, completely eliminating flicker. The built-in thermal protection prevents damage to the device under fault conditions. TYPICAL APPLICATION CIRCUIT RSET Mar 22-07 RevD SP7616: Low Side LED Driver - - 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 of time may affect reliability. VIN……….…………………………………….…-0.3V to 32V LED1, LED2, LED3, LED4 ……………..…... -0.3V to 32V ISET, PWM …..…………………..………….. -0.3V to 6.0V Storage Temperature..…………………… -65 °C to 150 °C Junction Temperature.............................. -40°C to +150°C* Lead Temperature (Soldering, 10 sec)....……………300°C * Internally protected ELECTRICAL SPECIFICATIONS Unless otherwise specified: VIN = 4.5V - 30V, CIN = 1µF, -40°C < TA < 85°C, - 40°C <TJ< 125°C. Bold values apply over the full operating temperature range. PARAMETER Operating Input Voltage Range MIN TYP MAX UNITS 30 V 4.5 CONDITIONS Shutdown Supply Current 30 40 µA Quiescent Supply Current 350 500 µA Quiescent Supply Current 1 1.5 mA Voltage at ISET is pulled to 3V; VIN 30V No LED connected, VLED pins are tied to GND. RSET=1MΩ ILED = 30mA Quiescent Supply Current 1.5 3 mA ILED = 60mA 1.5 3 % LED Current Matching -3 LED Current Line Regulation 0.5 1 %/V Line Regulation Maximum LED Current per channel LED Leakage Current Dropout Voltage Output/ISET Current Multiplication Ratio Thermal Shutdown Die Temperature 0.05 0.1 60 2 0.3 %/V mA µA V 0.2 950 PWM Pin Logic LOW PWM Pin Logic HIGH PWM pin Hysteresis ISET Voltage °C 15 °C 0.8 5.5 2.4 0.985 400 1.00 Turn-on time from Shutdown V V mV ILED = 0mA. LED current will self recover when temperature drops below the trip point, minus thermal shut down hysteresis. Driver is disabled Driver is active 1.015 ISET Shutdown Threshold ISET Shutdown Threshold Hysteresis PWM Dimming Frequency Range PWM Dimming Duty Cycle Range -40°C < TA < 85°C VLED = 0.5V to 25V , VIN = 28V, 2 RSET =50kΏ 3 VIN = 4.5V to 25V, VLED=0.5V RSET = 15.38KΏ, PWM pin LOW’ VLED 1V; VIN 5V Note 4 +/- 4 Percent -40°C < TA < 85°C 150 Thermal Shutdown Hysteresis To reference channel (channel 2) 3 V 5 90 V kHz % 300 µs 20 µs 0.3 0.1 10 100 Turn-off time into Shutdown If ISET is pulled above this threshold the device goes into full shutdown Applied to PWM pin Applied to PWM pin VMOD from 5V to 0.0V, RSET = 50kΩ VMOD from 0.0V to 5V, RSET = 50kΩ Note 1. 2. 3. 4. Reference channel ILED Variations from specified by RSET value ILED Variations from specified by RSET value at VLED changing from 0.5 to 25V ILED Variations from specified by RSET value at VIN changing from 4.5 to 25V RSET = 31.6KΏ: Dropout voltage is measured as the VLED voltage where LED current drops 5% from nominal value Mar 22-07 RevD SP7616: Low Side LED Driver - - 2 2007 Sipex Corporation PIN DESCRIPTION PIN NAME VIN PWM ISET GND LED1LED4 DESCRIPTION PIN # Input voltage for the IC. Connect a 1uF decoupling capacitor between this pin and ground. This pin must be held high to enable the output drivers. It can be used for PWM dimming up to 5 kHz. Connect resistor RSET from this pin to ground to set output current. Pulling this pin above the shutdown threshold stated in the Electrical Specifications puts the IC into shutdown mode Ground return for LED currents and circuitry of the SP7616 Connect an LED between each pin and VIN. Current value is controlled by RSET. The current level through each pin is internally matched within 3%. Connect unused channel (s) to GND to save current consumption. 1 2 3 4 5-8 BLOCK DIAGRAM Mar 22-07 RevD SP7616: Low Side LED Driver - - 3 2007 Sipex Corporation TYPICAL PERFORMANCE CHARACTERISTICS VIN VIN ILED 20mA/Div ILED 20mA/Div Turn on Maximum VIN Channel 1 VIN; Channel 4 ILED Typical Turn on Characteristics Channel 1 VIN; Channel 4 ILED PWM Signal PWM Signal VLED(Cathode Voltage) VLED(Cathode Voltage) LED current 20mA/Div LEDcurrent 20mA/Div PWM Function 1kHz 50% Duty Cycle PWM Function 1 kHz 10% Duty Cycle PWM Signal PWM Signal VLED (Cathode Voltage) VLED (Cathode Voltage) LED current 20mA/Div LED current 20mA/Div PWM Function 1 kHz 90% Duty Cycle Mar 22-07 RevD PWM Function 5 kHz 50% Duty Cycle SP7616: Low Side LED Driver - - 4 2007 Sipex Corporation - TYPICAL PERFORMANCE CHARACTERISTICS LED Current vs. LED voltage (cathode voltage) VIN tied to Anode of LED chain Shutdown current vs. input voltage Voltage on ISET pin = 3V Mar 22-07 RevD SP7616: Low Side LED Driver - - 5 2007 Sipex Corporation THEORY OF OPERATION Introduction The SP7616 is a four-channel constant current source LED driver with programmable output current level. The design consists of a regulator reference voltage source, current amplifier, and output driver. The precision reference voltage ensures good performance over voltage and temperature. The four outputs are tightly coupled allowing for excellent LED current matching. VMOD is an adjustment voltage applied to the bottom side of RSET, 950 is a typical current multiplication ratio IMULT, and ILED is a required LED current in mA/channel. Figure 1 shows the location of the external VMOD source. Setting LED current The LED current is set through the Iset resistor. The SP7616 provides an internal reference voltage that is set to 1V at the Iset Pin (Pin3). RSET is then determined by using equation 1. RSET = VISET *IMULT/ILED (kΩ), (1) Where VISET is the internal reference (1V) IMULT ISET Current Multiplication Figure 1 If adjustment voltage VMOD is not used, RSET resistor should be connected to ground. Shutdown using ISET pin In normal operation, the voltage at ISET pin is around 1V. To ensure fast turn on at low duty cycle and high PWM frequency, only the output drivers are switching in PWM mode. However, the whole chip can be shutdown by pulling the voltage at ISET up to 3V minimum. Ratio ILED is the desired Led current. In example 1: For a 20mA LED current, the current set resistor should be RSET=1V*950/20mA (kΩ), VCC pin Considerations RSET=47.5KΩ VIN of the SP7616 (Pin 1) needs to be connected to the anode of the LED for proper operation PWM Dimming The LED dimming control is done through the PWM pin. The acceptable frequency range of this signal is 100Hz to 5kHz. The acceptable duty cycle range of the signal is 10% to 90% at 1KHZ. When the PWM pin is driven low, only the LED current sources are disabled while the rest of the chip is still enabled. . Unused Channels and LED 2 Channel (pin 7) Analog dimming control Shorted LEDs Besides digital PWM control, the LED current can be controlled continuously (from high to low LED current) by raising the voltage at the bottom of RSET from 0.0V to 1V maximum. RSET value may be determined from equation 1. Equation 2 shows the effect of using a VMOD in the circuit on the Led current ILED = (1V – VMOD)*IMULT/RSET mA (2) Where 1V typical ISET pin voltage IMULT ISET Current Multiplication If all LEDs on a string are shorted, the LED cathode voltage will be VIN. It is still a working condition for this device but it significantly increases the dissipated power. At 20mA LED current and VIN = 30V additional power dissipated in the package is equal to 600mW 0 that will increase die temperature to 59 C/W x 0.6W 0 0 = 35.4 C, where 59 C/W is 2x3 mm DFN package thermal resistance. Assuming that all other channels are working at VLED =1.5V the die 0 temperature will be approximately 41 C above ambient temperature and that decreases operating temperature range. Also to protect the part if too Ratio ILED is the desired Led current. VMOD is the adjustment voltage Mar 22-07 RevD LED 2 channel should never be grounded or left unconnected it should always be used during operation. Other unused channels can be tied to the ground to save on power consumption. SP7616: Low Side LED Driver - - 6 2007 Sipex Corporation - THEORY OF OPERATION many LEDs are shorted, and the VLED voltage becomes to high, making the part dissipates too much power, the over temperature protection will shut the part off when the die temperature reaches 0 150 C. For further information refer to the overtemperature protection section. Over-temperature protection The SP7616 offers Over-temperature protection. 0 When the die temperature rises above 150 C the output drivers are shut off. The output current will self recover when the temperature drops below the 0 trip point with the preset hysteresis of 15 C. Thus a 0 part that shut off at 150 C will not try to restart 0 unless the die temperature is below 135 C TYPICAL APPLICATION CIRCUITS Figure 2 Typical Application: CCFL Replacement powered from 3 Li-ion batteries. Figure 3 Using the SP7616 from a fixed source. Mar 22-07 RevD SP7616: Low Side LED Driver - - 7 2007 Sipex Corporation PACKAGE: 2mmx3mm 8–Pin DFN Mar 22-07 RevD SP7616: Low Side LED Driver - - 8 2007 Sipex Corporation - ORDERING INFORMATION Temperature Range Part Number SP7616ER-L/TR -40°C to +85°C SP7616ER-L -40°C to +85°C Package Type Lead Free 6 Pin TSOT Lead Free 6 Pin TSOT Pack Type/ Quantity Tape & Reel / 2500 Bulk For further assistance: Email: WWW Support page: Sipex Application Notes: [email protected] http://www.sipex.com/content.aspx?p=support http://www.sipex.com/applicationNotes.aspx Sipex Corporation Solved by TM Headquarters and Sales Office 233 South Hillview Drive Milpitas, CA95035 tel: (408) 934-7500 FAX: (408) 935-7600 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. Mar 22-07 RevD SP7616: Low Side LED Driver - - 9 2007 Sipex Corporation