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SP7612 SP7614
Low Dropout Linear LED Driver
FEATURES
LED Drivers for parallel connected LEDs No EMI, no switching noise Integrated current matching PWM and Analog brightness control Enable/Shutdown control Shutdown current < 0.01A Tiny, RoHS Compliant Lead-Free Packages: SC-70
N/C VLED1 CTRL
3
2
1
SP7614A SP7614
6 Pin SC70
4
GND
5
VLED2
6
ON/OFF
Pin outs for SP7611A and SP7612A on page 3
Part # SP7612 SP7614
Channels 3 2
Maximum Steady State Current per LED
40mA 80mA
APPLICATIONS Ultra low cost Handsets PDA, DSC, MP3 players Handheld Computers LCD Display Modules Keyboard Backlight LCD Backlight DESCRIPTION
The SP7612/4 provides a simple solution for a matched current source for any color LED. The current in the LEDs can be programmed by an external resistor. The SP7612 is capable of driving three LEDs, while the SP7614 can drive two LEDs. LED1 should always be connected to an LED and never left open in order to have the other LEDs driven with a matched current to LED1. The SP7612 and SP7614 feature Enable pins for flexible on/off control and PWM dimming. SP7612/4 has extremely low (0.01uA typical) shutdown current, prolonging the battery life and giving the longest standby period possible in today's modern design. It is available in a small footprint 6-pin SC-70 package.
TYPICAL APPLICATION SCHEMATIC
SP7612 Typical application
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SP7612/7614 Low Dropout Linear LED driver Page 1
(c) 2008 EXAR Corporation
SP7612 SP7614
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 periods of time may affect reliability. VLED1, VLED2, VLED3, VLED4 and ENABLE Voltage to GND............................................................................... -0.3V to 6V CTRL Voltage to GND . ..................................................................................................................................... .-0.5V Output Current (IOUT) (SP7612)...................................................................................................................... 40mA Output Current (IOUT) (SP7614)........................................................................................................................ 80mA Power Dissipation per Package - 6-pin SC-70 at TA =85C.............................................................................. 190mW Junction Temperature ...................................................................................................................................... +150C Storage Temperature.......................................................................................................................... -55C to +150C ESD Level........................................................................................................................................................................................................ 4kV HBM ESD Level........................................................................................................................................................................................................ 1kV CDM
ELECTRICAL SPECIFICATIONS Specifications are at TA=25C, VIN = 3.3 to 5.5, ENABLE =VIN, denotes the specifications which apply over the full operating temperature range, unless otherwise specified. PARAMETER LED Cathode Voltage (VLED) Ambient Temperature Output Current Multiplication Ratio in Linear Region (Note1) Output Current Multiplication Ratio in Saturation (Note1) LED to LED Current Matching Current in OFF Mode Min. ENABLE ""ON Voltage" (Note 2) Max. ENABLE ""OFF Voltage" (Note 2) -40 SP7612 140 SP7614 SP7612 SP7614 365 730 -3 435 870 0.8 0.01 3 0.5 505 1010 3 1 % A V V 200 260 PART # MIN TYP MAX 5.5 85
UNITS
V C
CONDITIONS See graph for LED Current vs. Cathode Voltage ISET = 100A VLED = 300mV ISET = 100A VLED = 150mV ISET = 25A VLED = 0.5V

ISET = 100A VLED = 300mV VENABLE = 0.0V ISET = 150A
Note 1: Output current Multiplication Ratio (ILED/ISET) is not linear. For actual ratio and ILED please refer to typical performance characteristics on pages 4 through 7. Note 2: ENABLE "ON" is VON/OFF where ILED1 > 20mA @ VLED1 = 0.3V. ENABLE "OFF" is V where I < 1A @ V > 0.3V.
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(c) 2008 EXAR Corporation
SP7612 SP7614
PIN DESCRIPTION SC70 Package
Pin #
1 2 3 4 5 6 SP7612 CTRL LED2 LED1 GND LED3 ENABLE
Pin Name
SP7614 CTRL LED1 NC GND LED2 ENABLE
DESCRIPTION
Sets L E D Current Connect to Cathode of L E D Connect to Cathode of L E D Ground Connect to Cathode of L E D Chip ON/ OFF Disable PINOUTS
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SP7612 SP7614
SP7612 TYPICAL PERFORMANCE CHARACTERISTICS
LED current vs Rset for LED voltage (Vcathode)
Vcontrol set to 3V
LED current vs Cathode voltage (VLED)
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SP7612 SP7614
SP7612 TYPICAL PERFORMANCE CHARACTERISTICS Iset vs Control pin voltage
LED current vs Enable voltage
Iset at .5V VLED(cathode voltage)
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(c) 2008 EXAR Corporation
SP7612 SP7614
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(c) 2008 EXAR Corporation
SP7612 SP7614
SP7614 TYPICAL PERFORMANCE CHARACTERISTICS Iset vs Control pin voltage
LED current vs Cathode voltage (VLED)
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SP7612 SP7614
LED current vs Enable voltage
Iset at .5V VLED(cathode voltage)
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(c) 2008 EXAR Corporation
SP7612 SP7614
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SP7612 SP7614
APPLICATION INFORMATION
necessary. Setting the LED Current The LED current is controlled by ICONTROL and RSET according to the following formula: ILED = Gain X (VCONTROL - VCTRL) / RSET Gain depends on mode of operation VCONTROL is the voltage going into RSET VCTRL is the voltage at the pin of the device The voltage VCTRL can be determined using the ISET vs Control voltage graph located in the typical performance characteristics section. As an example, to set the LED current for an SP761x the procedure is: Take the LED current and divide it by the Gain to get ISET = ILED / Gain. Look up the VCTRL pin voltage using ISET on the graph "Ctrl Current vs. Control Voltage". Once VCTRL is known, use the following formula to find RSET. The gain is not linear, the LED current vs. Cathode voltage graph needs to be used to determine gain. Typically, the gain is ~870 for SP7614 and ~435 for SP7612 when the part is operating in the linear region. RSET = (VCONTROL - VCTRL) / ISET RSET Example For an SP7614 with VCONTROL of 3V and LED current of 20mA. ISET = 20mA/870 (870 is the typical gain in linear operation) = 22uA. Using the graph on page 5 in the typical performance section, the VCTRL voltage on the control pin will be about 1.1V, then RSET will be determined by: RSET = (3V - 1.1V) / 22uA RSET = 86K PWM FUNCTION The LED's brightness can also be adjusted by driving either the ENABLE or the CTRL pin with a PWM signal. The driving signal frequency should be greater than 100Hz to avoid flickering, increasing to more than 1MHz, if
Temperature Considerations LEDs are very sensitive to temperature. In most cases the maximum allowed junction temperature is 100C. The case of overtemperature due to power dissipation is de-scribed by the following: TJ = TA + JA x I x VF where TJ is the LED junction temperature, TA is the ambient temperature, JA is the junction to ambient thermal resistance, I is the LED current and VF is the LED forward voltage. When the temperature rises and the cathode voltage increases, SP7612/4 reduces the current through LEDs. Refer to "LED Current vs. LED Cathode Voltage" graph under the Typical Performance Characteristics section. Efficiency The system efficiency, defined as the ratio between the LED's power and the input supplied power can be calculated as follows: Efficiency = (VIN - VCATHODE) / VIN The lower the VCATHODE , the higher the system efficiency. Efficiency can be further improved using a higher VIN with more LEDs as shown in example 3. The SP7612/4 driver's low dropout architecture can significantly improve the efficiency compared to using simple ballast resistors. Application Information The ultra-low voltage drop across the SP7612/4 series of LED drivers allows the devices to drive white, blue, and other color LEDs in a wide range of input voltages. The driver can be used in many applications. Any of the SP7612/4 series of LED drivers can be used in the applications presented in this document, due to their similar operation. Example 1: Drive low VF white or blue LEDs directly from single cell Li-Ion
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SP7612 SP7614
When using white or blue low VF LEDs, and utilizing the driver's low voltage drop, only 3.4V VIN is needed for the full 20mA LED current. At 3.1V, there is still 5mA of typical current available for the LEDs. The single cell Li-Ion battery is utilized in many applications like cell phones or digital still cameras. In most cases, the Li-Ion battery voltage level only goes down to 3.0V, and not down to the full discharge level (2.7V) before requesting the charger. VDROP < 0.3V. This is the dropout voltage for the SP7611A. - VF = 3.1V. Low VF white LED forward voltage drop - VIN (at 20mA) needs to be greater than (VDROP+VF) 3.1V+.3V= 3.4V Key Advantages 1) No boost circuit needed for the LCD or keyboard backlight. 2) Drivers directly connected to a Li-Ion battery. 3) No EMI, no switching noise, no boost converter efficiency loss, 1 capacitor, and no inductor. Example 2: Drive high VF white or blue LEDs from existing bus ~ 4.0V to 5.5V High VF LEDs have a forward voltage drop in the range of 3.2V to 4.0V. In order to drive these LEDs with the maximum current of 20mA, enabling maximum brightness usually requires a boost circuit for a single cell Li-Ion power supply. The SP761X series is capable of driving high VF white or blue LEDs with its ultra-low dropout feature. The VIN needs to be only 300mV higher than the highest VF in the circuit. - VDROP < 0.3V. Dropout voltage of the SP7611A - VF (at 20mA) < 3.3V to 4.0V (High VF) - VIN (at 20mA) = VDROP + VF = 3.6V to 4.3V - VIN (at 5mA typical) ~ 3.3V Where VIN = Existing bus = 3.3V to 4.3V - PWM - Vcontrol -Amplitude of PWM signal sets maximum LED current -Pulse width controls current between 0 and maximum LED Set current PWM using Enable Key Advantages 1) No boost circuit needed for the LCD or keyboard backlight. 2) Drivers utilize existing bus. 3) Ultra-low voltage drop provides the full 20mA LED current at the lowest possible voltage level. LED Brightness Control The SP7612/4 LED Drivers feature analog and PWM controls to give designers flexible brightness control. To determine the value of RSET , use the "ISET vs. VCRTL" graph under the Typical Performance Characteristics. 1. SP7612/4 - Analog using VCONTROL Set VCONTROL and RSET for LED current SETTING THE LED CURRENT - page 8
- Set VCONTROL and RSET for LED current SETTING THE LED CURRENT - page 6 ENABLE = PWM -Amplitude has no effect on current -Pulse width controls current between 0 and maximum LED set current
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(c) 2008 EXAR Corporation
SP7612 SP7614
BLOCK DIAGRAMS
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(c) 2008 EXAR Corporation
SP7612 SP7614
PACKAGE: 6 PIN SC-70
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SP7612 SP7614
ORDERING INFORMATION
Part Number SP7612EC6-L SP7612EC6-L/TR SP7614EC6-L SP7614EC6-L/TR
Temperature Range -40C to +85C -40C to +85C -40C to +85C -40C to +85C
Package 6 Pin SC70 6 Pin SC70 6 Pin SC70 6 Pin SC70
RoHS
Pack Type Canister Tape & Reel Canister Tape & Reel
Pack Quantity
Status Active Active Active Active
Yes Yes Yes Yes
Any 3000 Any 3000
/TR = Tape and Reel Pack quantity is 2500 for SC70
For further assistance: Email: EXAR Technical Documentation: customersupport@exar.com http://www.exar.com/TechDoc/default.aspx?
Exar Corporation Headquarters and Sales Office 48720 Kato Road Fremont, CA 94538 main: 510-668-7000 fax: 510-668-7030
EXAR Corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free of patent infringement. Charts and schedules contained here in are only for illustration purposes and may vary depending upon a user's specific application. While the information in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies. EXAR Corporation does not recommend the use of any of its products in life support applications where the failure or malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes all such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances.
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(c) 2008 EXAR Corporation

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