3-Channel Constant Current LED Driver with Programmable ...

1 3 mm x 3 mm footprintDescriptionThe A6281 is a 3-Channel Constant Current LED Driver that has a wide range of output currents. The A6281 controls LED brightness with a Pulse Width Modulation (PWM) scheme that gives the application the capability of displaying a billion colors in an RGB cluster. The maximum Current is set by an external LED brightness is controlled by performing PWM control on the outputs. The brightness data of the PWM signal for each LED is stored in three 10-bit registers. The peak value for each LED can be adjusted (dot-corrected) to compensate for mismatch, aging, and temperature effects. All the internal latched registers are loaded by a 32-bit shift register.

2 One address bit controls whether dot correction/clock divider ratio or brightness data is loaded into the registers. The remaining bits are used for the A6281 is designed to minimize the number of components needed to drive LEDs with large pixel spacing. A large number of A6281s can be daisy chained together and controlled by just four control signals (clock, serial data, latch, and output enable). Each of these inputs is buffered to drive the next chip in the chain. Also, VIN can be tied to the LED voltage supply A6281-DS, Rev. 1 Features and Benefits 3 10-bit PWM brightness settings 3 7-bit dot correction Current settings 5 to 17 V operation Wide output Current range, 10 to 150 mA per channel Internally generated PWM clock Serial port operates at up to 5 MHz Data and clock logic architecture allows single microcontroller control of large quantities of serially-connected A6281s at fast data transfer rate Buffered logic outputs to drive cables Thermal shutdown and UVLO protection Power-On Reset3- channel Constant Current LED Driver with Programmable PWM ControlContinued on the next : 16-terminal QFN (suffix ES)Application DiagramA6281 Figure 1.

3 Functional drawing of daisy chained display application. Additional pixel boards with A6281 ICs can be EnableLatchMicroprocessorControl BoardClock OutData Out Latch OutOE OutClock InData InLatch InOE InVLEDOutBOutGOutRVINP ower Supply BusA6281 Pixel Board #1 REXTVREGC lock OutData OutOE OutClock InData InOE InVLEDOutBOutGOutRVINA6281 Pixel Board #2 REXTVREGP ixel Board #N Latch OutLatch InCat5 UTPCat5 UTPCat5 UTP3- channel Constant Current LED Driver with Programmable PWM ControlA62812 Allegro MicroSystems, Northeast CutoffWorcester, Massachusetts 01615-0036 ; , thus eliminating the need for a separate chip supply bus or an external include: Colored, large-character LED signs Scrolling, colored marquees Architectural lighting High intensity monochrome displays Large video and graphic displaysThe A6281 is supplied in a 3 mm 3 mm 16-terminal QFN (suffix ES ) package, with mm nominal overall height.

4 The package is lead (Pb) free with 100% matte-tin leadframe NumberPacking*MountingA6281 EESTR-T1500 pieces/reel16 terminal QFN*Contact Allegro for additional packing GuideAbsolute Maximum RatingsCharacteristicSymbolNotesRatingUn itsLoad Supply Voltage VIN17 VOutput VoltageVOUTOUT0, OUT1, OUT2 to 17 VOutput CurrentIOUT170mAGround CurrentIGND600mAVREG PinVREG6 VLogic OutputsVOCO, LO, OEO, SDO7 VLogic Input Voltage RangeVICI, LI, OEI, SDI to 7 VOperating Ambient TemperatureTARange E 40 to 85 CMaximum Junction TemperatureTJ(max)150 CStorage TemperatureTstg 55 to 150 CDescription (continued)Thermal Characteristics CharacteristicSymbolTest Conditions*Rating UnitsPackage Thermal ResistanceR JA4-layer PCB based on JEDEC standard47 C/W*For additional information, refer to the Allegro ( C)Power Dissipation, PD (mW)450040003500300025002000150010005000 (RQJA= 47 C/W)4 layer PCBP ower Dissipation versus Ambient Temperature3- channel Constant Current LED Driver with Programmable PWM ControlA62813 Allegro MicroSystems, Northeast CutoffWorcester, Massachusetts 01615-0036.

5 KHz ClockTo PWM CountersTo logicTo PWM CountersCurrentRegulator 0 CurrentRegulator 1 CurrentRegulator 2 Latched RegistersREXTREXTLGNDPGNDOEOOEIVINVREGLI LOS hift RegisterSDICISDOCO100 nsOne-ShotTerminal List TableNumberNameDescription1 REXTAn external resistor at this terminal establishes maximum output current2 VREGR egulator decoupling3 LGNDL ogic ground4 VINChip power supply voltage; connect to VREG externally if V < VIN < V5 CISerial clock input; PWM clock if external clock is selected6 OEIO utput enable input; when low (active), the output drivers are enabled; when high (inactive), all output drivers are turned off (blanked)7 LILatch input terminal; serial data is latched with high-level input8 SDIS erial data input to shift register9 OUT2 Sinking output terminal10 PGNDP ower ground11 OUT1 Sinking output terminal12 OUT0 Sinking output terminal13 SDOB uffered serial data output after shift register14 LOBuffered latch output15 OEOB uffered output enable output16 COBuffered clock output PADE xposed thermal pad, not internally connected.

6 Connect externally to LGND and DrawingsFunctional Block Diagram12111091234567816151413 COOEOLOSDOCIOEILISDIOUT0 OUT1 PGNDOUT2 REXTVREGLGNDVINPAD3- channel Constant Current LED Driver with Programmable PWM ControlA62814 Allegro MicroSystems, Northeast CutoffWorcester, Massachusetts 01615-0036 ; CHARACTERISTICS, valid at TA = 25 C, VIN = to V, unless otherwise notedCharacteristicSymbolTest CHARACTERISTICSQ uiescent Supply CurrentIDDfCLKIN = Hz Supply CurrentIDDfCLKIN = 5 MHz Supply Voltage 17 VUndervoltage LockoutVIN(UV)VIN rising VVREG Voltage Range1 VREGIOUT =15 mA, VIN = 17 Current (any single output)IOUTREXT = 5 k , scalar = 100% = 15 k , scalar = 100%455157mAOutput to Output Matching Error2 ErrOutput to output variation all outputs on, REXT = 5 k 7 7%Output Voltage RangeVDS(min) Regulation (I%Diff / VDS)

7 REXT = 5 k , VDS = 1 to 3 V 1 3%/VOutput Leakage CurrentIDSXVOH = 17 V ALogic Input VVIL Input Voltage HysteresisAll digital inputs 150 mVCI and SDI Pins Logic Input CurrentIINVIN = 0 to 5 V 20 20 AInput ResistanceRIOEI pin, pull-up150300600k LI pin, pull-down100200400k Logic Output VoltageVOLVIN V, IO = 2 mA VOutput Dot Correction ErrorREXT = 5 k ; LSB 1 bitPWM OscillatorfPWM 800 kHzThermal Shutdown TemperatureTJTSDT emperature increasing 165 CThermal Shutdown HysteresisTJhys 15 CSWITCHING CHARACTERISTICSC lock Hold TimetH(CLK)20 nsData Setup TimetSU(D)20 nsData Hold TimetH(D)20 nsLatch Setup Time3tSU(LI)20 nsLatch Hold TimetH(LI)20 nsOutput Enable Set Up TimetSU(OE)40 nsOutput Enable Falling to Outputs Turning On Propagation Delay TimetP(OE) 200 nsClock to Output Propagation Delay TimetP(OUT)External clock selected, VDS = V, IO = 150 mA 200 nsLogic Output Fall TimetBFCOB = 50 pF, to V 50100nsLogic Output Rise TimetBRCOB = 50 pF, to V 3060nsOutput Fall Time (Turn Off)

8 TfCOUT = 10 pF, 90% to 10% of IOUT = 10 mA 10 nsCOUT = 10 pF, 90% to 10% of IOUT = 150 mA 10 nsOutput Rise Time (Turn On)trCOUT = 10 pF, 10% to 90% of IOUT = 10 mA 50 nsCOUT = 10 pF, 10% to 90% of IOUT = 150 mA 100 nsClock Falling Edge to Serial Data Out Propagation Delay TimetP(SDO) 50 nsLogic In to Output Propagation DelaytP(IO)LI LO, CI CO, OEI OEO 50 nsClock Out Pulse Durationtw(CLK)70100130nsMaximum Clock In FrequencyfCI 6 MHz1If VIN is a to V supply, connect VIN to VREG externally2 Err = [IO (min or max) IO(av)] / IO(av), where IO(av) = average of 3 output Current values. 3In daisy-chained applications, tSU(LI) must be increased for the quantity of pixels in the chain (see Application Information section).

9 3-Channel Constant Current LED Driver with Programmable PWM ControlA62815 Allegro MicroSystems, Northeast CutoffWorcester, Massachusetts 01615-0036 ; 1631CI (External Clock)SDI (Serial Data In)SDO (Serial Data Out)LI (Latch In)LO(Latch Out)D31D29D28D27D26D25D24D23D16D15D0D31 Don t Caretw(CLK)tSU (D )tH( D)tP(SD O )tSU (L I )tH(LI)tP(IO)D30 PWM CounterOEI(Output Enable Input)OEO(Output Enable Output)IOUT0 IOUT1 IOUT2 Brightness Data= 0 Brightness Data= 1 Brightness Data = 1022tP(I O )t w(OE)tP(OE)tP(OUT)tP(OUT)tP(OUT)Internal Oscillator orCI (External Clock)012102300XT1T2TN12 Outputs OffOutputs On012345678 Figure 2. Serial Port TimingFigure 3. PWM Counter and Output Timing3- channel Constant Current LED Driver with Programmable PWM ControlA62816 Allegro MicroSystems, Northeast CutoffWorcester, Massachusetts 01615-0036 ; DescriptionFigure 4.

10 Functional DiagramShift RegisterThe A6281 has a 32-bit shift register that loads data through the SDI (serial data in) pin. The shift register operates by a first-in first-out (FIFO) method. The most significant bit (MSB, bit 31) is the first bit shifted in and the least significant bit (LSB, bit 0) is shifted in last. The serial data is clocked by a rising edge of the CI (clock in) pin. The SDO (serial data out) pin is updated to the state of bit 31 on the falling edge of the CI pin. This will prevent any race conditions and erroneous data that might occur while propagating information through multiple A6281s that are daisy chained together. The contents of the shift register will continue to propagate on every rising edge of the CI pin.