1 introduction the ahk1421 evaluation board demonstrates functionality of the ahk1421 and its application as a white led backlight driver under analogictechs s 2 cwire serial digital interface control. the ahk1421 is a high frequency, high efficiency, constant-current boost converter driving six white leds in series configuration. the input voltage is 2.7v to 5.5v, which is ideal for portable devices powered by single-cell lithium-ion/ polymer (li-ion) batteries. the maximum led current is set by an external resistor from 10 to 31ma. the ahk1421 is programmable with the s2cwire interface, using an onboard microcontroller which is capable of brightening and dim - ming the leds in 32 discrete steps. this document describes the evaluation board and its accompanying user interface. a brief getting started section is included to help the user to begin operating the evaluation board. board pictures (a) top (b) bottom figure 1: ahk1421 evaluation board ev -1 84 ahk14 21 ev al : s 2 cwire contr olled, serial led boost driv er ev alua tion board da t asheet ev-184.2011.05.1.0 www.analogictech.com
2 board schematic 2.2 f c in 10h l1 2.2 f c out ds1 dc+ dc- j2 vout lx 0.1 f c1 1k r7 1k r5 51 k r4 v_mc u en/set up down cycle 1k r8 1k r9 pic12f67 5 vd d 1 gp5 2 gp4 3 gp3 4 gp2 5 gp1 6 gp0 7 vss 8 u2 red led1 1 2 3 j1 lx 1 out 5 33 0 r6 d1 d2 d3 d4 d5 d6 fb r fb 12.5 vi n en/set 3 6 4 led2 green u1 ahk1421ica gnd 2 2.7~5.5v ahk1421 white led driver s2cwire microcontroller figure 2: ahk1421 evaluation board schematic ev -1 84 ahk14 21 ev al : s 2 cwire contr olled, serial led boost driv er ev alua tion board da t asheet ev-184.2011.05.1.0 www.analogictech.com
3 getting started setup (figure 3) 1. connect an input power source (to supply between 2.7v and 5.5v) to the board by placing the jumper, j1 on the left (connects dc+ power to ahk1421). 2. connect the dc+ power to the microcontroller vdd by using the jumper v_mcu. 3. connect the en/set jumper to connect the microcontroller gpios to the ahk1421 en/set pins. 4. after all jumpers are in the correct position, apply power between 2.7v and 5.5v to the dc+ and dc- terminals to power on the ahk1421 (u1) and microcontroller (u2). the red led (led1) will illuminate when the microcontroller is powered. the green led (led2) will flicker when the three buttons to transfer s2c wire data for ahk1421 are operated. 5. use the up, down and cycle buttons to vary the brightness of the 6 white leds using the en/set serial data s 2 cwire interface figure 3: ahk1421 evaluation board measurement configuration s 2 cwire control short the en/set jumper to receive s 2 cwire data generated by the microcontroller according to the status of the three buttons. the ahk1421 records the number of rising edges which control output current in en/set pin and change the value of output current from 20ma to 0.4ma when rfb is 12.5 ? up button: the up button increments the number of en/set rise edges from 1 to 32 each time this button is pushed. by holding down the button for more than 0.6 seconds, the microcontroller enters auto-increment mode. the led will dim and wrap back after s 2 c wire data reaches 32. ? down button: the down button decrements the number of en/set rise edges from 32 to 1 each time this button is pushed. by holding down the button for more than 0.6 seconds, the microcontroller enters auto-decrement mode. the led will brighten and wrap back after s 2 cwire data reaches 1. ? cycle button: the button increments or decrements the number of en/set edges automatically and cyclically after a single push according to the previous en edges up or down event. ? up+down+cycle button: en/set is set to 0v and the ahk1421 is shut down. all white leds are turned off. ev -1 84 ahk14 21 ev al : s 2 cwire contr olled, serial led boost driv er ev alua tion board da t asheet ev-184.2011.05.1.0 www.analogictech.com
4 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 1234567891 01 11 21 31 41 51 61 71 81 92 02 12 22 32 42 52 62 72 82 93 03 13 2 s 2 cwire data i led (ma) figure 4: s 2 cwire dimming control at maximum led current (20ma max) user interface functionality button(s) action effect up push/release once increment the number of en/set edge; toggles through the available dimming level settings for the backlighting section. push hold 0.6 sec.+ auto-increment the number of en/set edges up to 32 then wrap back to 1. down push/release once decrement the number of en/set edge; toggles through the available brightness level settings for the backlighting section. push hold 0.6 sec.+ auto-decrement the number of en/set edges down to 1 then wrap back to 32 cycle push/release once or push hold 0.6 sec.+ auto-cycle in direction last set up+down+cycle push all three and hold shut down table 1: user interface functionality ev -1 84 ahk14 21 ev al : s 2 cwire contr olled, serial led boost driv er ev alua tion board da t asheet ev-184.2011.05.1.0 www.analogictech.com
5 functional testing and evaluation operational waveform figure 5 shows the waveform controlled by s 2 cwire at 3.6v v in when the code changes from 32 to 1.the i led changes from 0.4ma (2% i max ) to 20ma (i max ). figure 5: operational waveform under s2cwire control. start up figure 6 shows the ahk1421 startup waveform after adding rising edge on en/set. soft start control makes the input current rise slowly. figure 6: start up waveform. channel signal 1 v out 2 en/set 3 i led 4 i in channel signal 1 sw 2 v out 3 i led 4 i in ev -1 84 ahk14 21 ev al : s 2 cwire contr olled, serial led boost driv er ev alua tion board da t asheet ev-184.2011.05.1.0 www.analogictech.com
6 efficiency curves figure7 shows that the maximum efficiency is about 85% under 4.2v input voltage. consult the ahk1421 product datasheet about the external diode selection. 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 0123456789 10 11 12 13 14 15 16 17 18 19 20 21 v in = 3.6v v in = 4.2v efficiency (% ) i led (ma) figure 7: efficiency curve waveforms. ev -1 84 ahk14 21 ev al : s 2 cwire contr olled, serial led boost driv er ev alua tion board da t asheet ev-184.2011.05.1.0 www.analogictech.com
7 printed circuit board (a) top (b) bottom figure 8: ahk1421 evaluation board (not to scale) ahk1421 eval board component listing component part number description manufacturer u1 ahk1421ica s2c controlled, serial led boost driver ic, tsot23-6 analogictech u2 pic12f675 8-bit cmos, flash-based uc;soic-8 microchip r6 chip res res 330 1/4w 1% 0603 smd yageo r fb res 12.5 1/4w 1% 0603 smd r5, r7, r8, r9 res 1k 1/4w 1% 0603 smd r4 res 51k 1/4w 1% 0603 smd cin grm188r60j225ke01 cap 2.2f 0603 x5r 10v 10% murata cout grm21br61h225ka73l cap 2.2f 0805 x7r 50v 10% c1 grm188r71c104k cap 0.1uf 0603 x7r 16v 10% d1, d2, d3, d4, d5, d6 rs-0805uw 20ma white led 0805 realstar ds1 ss14l 1.0amp.surface mount schottky barrier rectifers tsc l1 cdrh2d14-100 power inductor 10h smd sumida led1 0805krct red led 0805 hb led2 0805kgct green led 0805 cycle, up, down 6*6*5 12v 50ma push button e-lt table 2: ahk1421 evaluation board bill of materials. ev -1 84 ahk14 21 ev al : s 2 cwire contr olled, serial led boost driv er ev alua tion board da t asheet ev-184.2011.05.1.0 www.analogictech.com
8 ev -1 84 ahk14 21 ev al : s 2 cwire contr olled, serial led boost driv er ev alua tion board da t asheet ev-184.2011.05.1.0 www.analogictech.com advanced analogic technologies, i nc. 3230 scott boulevard, santa clara, ca 95054 phone ( 408) 737-4600 fa x ( 408) 737-4611 ? advanced analogic technologies, inc. analogictech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an analogictech product. no circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. analogictech reserves the right to make changes to their products or specifcations or to discontinue any product or service without notice. except as provided in analogictechs terms and conditions of sale, analogictech assumes no liability whatsoever, and analogictech disclaims any express or implied warranty relating to the sale and/or use of analogictech products including liability or warranties relating to ftness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. in order to minimize risks associated with the customers applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. testing and other quality control techniques are utilized to the extent analogictech deems necessary to support this warranty. specifc testing of all parameters of each device is not necessarily performed. analogictech and the analogictech logo are trademarks of advanced analogic technologies incorporated. all other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
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