SP6887 EXAR | Alldatasheet
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Technical content
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Rev. C – 10/31/2007 SP6887 4 Channel WLED Driver © 2007 Exar Corporation
FEATURES
Peak Efficiency: 90% Individual Current Regulation 3-bit Digital Output Control 1x and 1.5x Modes of Operation Current Matching with a Max Tolerance of 3% Output Current up to 30mA per LED Fixed Frequency of 1MHz Open LED Protection Pb-Free Thin QFN-16 3mmx3mm Package
APPLICATIONS
Cellular Phones LED backlighting LCD Modules Handheld Devices Digital Cameras PDAs MP3 Players
DESCRIPTION
The SP6887 is a 4-channel charge pump white LED driver, capable of driving up to 4 LEDs connected in parallel. The device operates in ei ther 1x mode or 1.5x fractional mode, and it can switch from 1x mode to 1.5x mode automa tically when the input voltage decreases. Its internal 4 current sink regu lators ensure both LED current matching and brightness uniformity. The LED current can be prog rammed by an external resistor, R SET, connected between the RSET pin and ground. LED currents of up to 30mA are supported by the input supply voltage over a range of 2.7V to 5.5V, making the device optimized for Li-Ion battery applications. The SP6887 has a fixed switching frequency of 1MHz, allowing the use of very small value ceramic capacitors. The enable input pin allows the device to be placed in shutdown mode while reducing current consum ption to less than 1µA. LED dimming can be done by several methods including using a DC voltage to set the RSET pin current, adding a switched resistor in parallel with RSET or applying a PWM signal to CTRx pin or EN pin. TYPICAL APPLICATION CIRCUIT
Rev. C – 10/31/2007 SP6887 4 Channel WLED Driver © 2007 Exar Corporation Control Lines LED Output CTR2 CTR1 CTR0 LED4 LED3 LED2 LED1 0 0 0 - - - ON 0 0 1 - - ON - 0 1 0 - ON - - 0 1 1 ON - - - 1 0 0 - - ON ON 1 0 1 - ON ON ON 1 1 0 ON ON ON ON 1 1 1 - - - - 1 = Logic high (or VIN), 0 = Logic low (or GND), - = LED output off Table 1: LED Enable Logic
Rev. C – 10/31/2007 SP6887 4 Channel WLED Driver © 2007 Exar Corporation Thin QFN-16 3mmx3mm Pin Number Name Description
1 EN Enable Input, Active High
2 CTR0 Digital Control Input 0
3 CTR1 Digital Control Input 1
4 CTR2 Digital Control Input 2
5 RSET Set Resistance
6 VOUT Charge pump output connected to the LED anodes
7 VIN Supply Voltage
8 C1+ Bucket Capacitor 1 Terminal
9 C1- Bucket Capacitor 1 Terminal
10 C2- Bucket Capacitor 2 Terminal
11 C2+ Bucket Capacitor 2 Terminal
12 GND Ground Reference
13 LED4 LED4 Cathode Terminal
14 LED3 LED3 Cathode Terminal
15 LED2 LED2 Cathode Terminal
16 LED1 LED1 Cathode Terminal
These are stress ratings only and functional operation is not implied. Exposure to absolute maximum ratings for prolonged time periods may affect device reliability. All voltages are with respect to ground. Storage Temperature Range .... -65ºC to +160ºC Recommended Operating Conditions Input/Output/Bucket Capacitors...1±20%µF(typ) Thermal Information Parameter Symbol Package Max Unit Thermal Resistance (Junction to Ambient) θJA TQFN-16 34 ºC Power Dissipation PD@TA=25ºC P D TQFN-16 2.9 W
Rev. C – 10/31/2007 SP6887 4 Channel WLED Driver © 2007 Exar Corporation TA=25ºC, VIN=3.5V, CIN=COUT=1µF, unless otherwise noted. Parameter Symbol Conditions Min Typ. Max Unit Input Voltage Range V IN 2.7 5.5 V Shutdown Current I SD VEN=0V Shutdown Mode 0.05 1 µA 1X Mode, No Load 0.6 1.2 mA Quiescent Current I Q 1.5x Mode, No Load 2.5 5 mA RSET Regulated Voltage V RSET 1.19 1.23 1.25 V Programmed LED Current I LED RSET=90kΩ RSET=29.3kΩ RSET=14.7kΩ 5.0 15.0 30.0 mA LED Current Accuracy I LED-ACC ±5 % LED Channel Matching I LED-DEV (I LED-ILEDAVG)/ILEDAVG ±3 % Output Resistance (Open Loop) RO 1x Mode, IO=100mA 1.5x Mode, IO=100mA 1.7 4.3 Ω Charge Pump Frequency f OSC 1.0 MHz VIN at Mode Transition from 1x to 1.5x VIN-Tran ILED=15mA ILED=20mA 3.45 3.60 V 1x to 1.5x Mode Transition Dropout Delay TDROP 0.4 0.6 0.9 ms Input Leakage Current I EN-CTR On Inputs EN, CTR0, 1 & 2 1 µA High Detect Threshold I EN-CTRH On Inputs EN, CTR0, 1 & 2 1.5 V Low Detect Threshold I EN-CTRL On Inputs EN, CTR0, 1 & 2 0.4 V Typical Characteristics VIN=3.6V, EN=VIN, RSET=24kΩ, CIN=1µF, TA=25ºC, unless otherwise noted. 1. Efficiency vs Input Voltage (4 LEDs) 2. Efficiency vs Output Current (4 LEDs)
Rev. C – 10/31/2007 SP6887 4 Channel WLED Driver © 2007 Exar Corporation 3. LED Current vs Input Voltage (4 LEDs) 4. Supply Current vs Input Voltage (4 LEDs) 5. Ground Current vs Input Voltage 6. Oscillator Frequency vs Input Voltage 7. Output Voltage vs Input Voltage 8. Output Resistance vs Input Voltage
Rev. C – 10/31/2007 SP6887 4 Channel WLED Driver © 2007 Exar Corporation 9. LED Current Setting Using RSET 10. LED Current Setting Using a DC Voltage to RSET Pin 11. LED Current Setting Using a PWM Signal to EN Pin 12. LED Current Setting Using a PWM Signal to CTR0 Pin
Rev. C – 10/31/2007 SP6887 4 Channel WLED Driver © 2007 Exar Corporation 13. Output Ripple THEORY OF OPERATION Detailed Description As shown in the block diagram on page 2, the main components within the SP6887 include a fractional charge pump, mode selection circuit, outp ut selection logic, LED current setting detection circuit, and 4 current sense circuits. The fractional charge pump multiplies the input voltage a multiple of 1X and 1.5X times the input voltage. The charge pump switches at a fixed 1MHz when the mode is 1.5X. The charge pump does not switch during 1X mode, saving power and improving efficiency. The mode selection ci rcuit automatically selects the mode as 1X or 1.5X based on circuit conditions such as LED voltage, input voltage and load current. 1X is the more efficient mode than 1.5X mode. Table 1 on page 2 shows the output selection logic control over the LED outputs for on and off functions with 8 different output states. The current set and de tection circuit uses an external resistor and a 1.20V reference to program the LED current. 4 current regulating circuits sink matched currents from the LEDs. LEDs with matched forward voltage will produce the best possible matched currents. For best matching performance it is recommended that the Vf between LEDs be under 250mV. The unused LED channels can be turned off by CTR0, CTR1 and CTR2, and connecting the respective LED pins to VOUT pin, in which case, the corresponding LED driver sink current is only about 20µA. Methods for Setting LED Current There are 4 methods for setting and adjusting the LED current outlined here. The methods are: 1) RSET only 2) Analog Reference VSET 3) PWM Input at CTR0 4) PWM Input at EN Method 1: LED Current Setting Using the External Resistor RSET The most basic means of setting the LED current is with a resi stor connected from RSET to GND, as shown in the application circuit on Page 1. The resistor RSET establishes the reference current needed for a constant LED current. Values of RSET for a fixed LED current are given in Table 2, “RSET
Rev. C – 10/31/2007 SP6887 4 Channel WLED Driver © 2007 Exar Corporation Thin QFN-16 3mm x 3mm Units: mm (angles in degrees) Coplanarity applies to the exposed pads as well as terminals DAP is 1.90mm x 1.90mm
ORDERING INFORMATION
Temperature Range Package Marking Packing Quantity SP6887ER4-L -40ºC to +85ºC Thin QFN-16 6887 ER4 YWWX SP6887ER4-L/TR -40ºC to +85ºC Thin QFN-16 6887 ER4 YWWX 3,000/T&R “Y” = Year, “WW” = Work Week, “X” = first alpha of lot number Exar Corporation Headquarters and Sales Offices
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Fremont, CA 94538 – USA Fax: +1 (510) 668-7030 www.exar.com