ZXSC400EV2 ZXSC400EV2 issue 8 - november 2005 1 ZXSC400EV2 user guide description the zxsc400 is voltage mode boost converter in sot23-6 package. its low feedback voltage allows th e current in a chain of leds to be set and accurately monitored with a single resistor with minimal losse s. the ZXSC400EV2 is configured for 25w led driver applications using the zxsc400 boost converter. features drives strings of 23 serially connected r,g & b leds at 350ma typical efficiency of 85% over-voltage protection applications lcd tv rgb backlight high power led driving ordering information order number ZXSC400EV2 please note evaluation boards are subject to availability and qualified leads. typical application circuit vcc gnd sense drive st dn vfb u1 zxsc400 u2 zxt d6717e6 r1 10m ohm r2 0.75 ohm pwm vcc vin led cathode led anode d1 10bq100 l1 68uh/3.5a q1 zxmn10a09k c3 100nf/100v r3 20k d2 bzx84c47 + c1 100uf/25v + c2 47uf/100v d3 bzx84c47 r4 1kohms d4 bzx84c7v5 c4 1uf/10v r5 10k
ZXSC400EV2 ZXSC400EV2 issue 8 - november 2005 2 reference design ZXSC400EV2 is configured to the reference design be low. the target application is a 25w led driver typ ically white or rgb led driver for lcd tv backlighting. the supply voltage is: vin=24v and vcc=12v for the ZXSC400EV2. for other reference designs or further applications information please refer to the zxsc400 datasheet. schematic diagram vcc gnd sense drive st dn vfb u1 zxsc400 u2 zxt d6717e6 r1 10m ohm r2 0.75 ohm pwm vcc vin led cathode led anode d1 10bq100 l1 68uh/3.5a q1 zxmn10a09k c3 100nf/100v r3 20k d2 bzx84c47 + c1 100uf/25v + c2 47uf/100v d3 bzx84c47 r4 1kohms d4 bzx84c7v5 c4 1uf/10v r5 10k materials list ref value package part number manufacturer notes u1 n/a sot23-6 zxsc400e6 zetex boost converter u2 n/a sot23-6 zxtd6717e6 zetex mosfet gate driver q1 n/a dpak zxmn10a09k zetex n-channel mosfet 100v d1 100v/1a smb 10bq100 ir 100v/1a schottky diode d2 47v sot23 bzx84c47 philips 47v zener diode d3 47v sot23 bzx84c47 philips 47v zener diode d4 7v5 sot23 bzx84c7v5 philips 7v5 zener diode l1 68uh/3.5a n/a do5022p-683 coilcraft 68uh/3.5a sm t inductor r1 10m ? 1206 generic 1206 5% tolerance r2 0.75 ? 1206 generic 1205 1% tolerance r3 20k ? 0805 generic 0805 5% tolerance r4 1k ? 0805 generic 0805 5% tolerance r5 10k ? 0805 generic 0805 5% tolerance c1 100 f/25v e eevfk1e101p panasonic smt electrolytic capa citor c2 47 f/100v h13 eevfk2a470q panasonic smt electrolytic c apacitor c3 100nf/100v 1206 generic 100nf/100v/1206/y5v ceramic capacitor c4 1 f/10v 0805 generic 1 f/10v/0805/y5v ceramic capacitor
ZXSC400EV2 ZXSC400EV2 issue 8 - november 2005 3 ZXSC400EV2 operation connection diagram l1 vin q1 u2 u1 r1 vcc pwm d1 + c1 led anode led cathode gnd ZXSC400EV2 25w led driver board zdb246r2 c3 r2 d2 + c2 lk1 d3 r3 d4 r4 c4 copyright zetex plc 2005 r5 ZXSC400EV2 set-up and test 1. connect v in and gnd to positive and zero volts of psu1 supply respectively. 2. connect v cc and gnd to positive and zero volts of psu2 supply respectively. 3. connect led chain to led anode and led cathode o utputs on ZXSC400EV2 4. set the psu1 to 24v and psu2 to 12v. 5. turn on psu1 and psu2. 6. the led chain should illuminate and be regulated at 350ma - this is a functional eval board.
ZXSC400EV2 ZXSC400EV2 issue 8 - november 2005 4 led dimming using the pwm input. by injecting a pwm signal on the pwm input and vary ing the duty cycle, led current and hence led brigh tness can be adjusted. to implement this method of brightness control on t he zxld1100ev2: 1. connect a 10k ? resistor between the drive pin of the zxsc400 and gnd (see diagram below). 2. apply pwm signal with amplitude of between 0.7v and vcc at a frequency of 100hz to 1khz (to eliminate led flicker). the led current and hence l ed brightness is linearly proportional to the duty cycle ratio, so for brightness control adjust duty cycle ratio as necessary. for example, a 10% duty c ycle equates to 10% of full led brightness. vcc gnd sense drive st dn vfb u1 zxsc400 u2 zxt d6717e6 r1 10m ohm r2 0.75 ohm pwm vcc vin led cathode led anode d1 10bq100 l1 68uh/3.5a q1 zxmn10a09k c3 100nf/100v r3 20k d2 bzx84c47 + c1 100uf/25v + c2 47uf/100v d3 bzx84c47 r4 1kohms d4 bzx84c7v5 c4 1uf/10v r5 10k note: it may be necessary to reduce to value of the outp ut capacitor, c2, to optimize for a 1khz pwm dimmin g signal. we recommend a value of 10 f/100v for the best compromise between pwm switchin g and led current ripple at full power.
ZXSC400EV2 ZXSC400EV2 issue 8 - november 2005 5 layout considerations pcb tracks should be kept as short as possible to m inimise ground bounce, and the ground pin of the de vice should be soldered directly to the ground plane. it is particularly important to mount the coil and th e input/output capacitors close to the device to minimise parasiti c resistance and inductance, which will degrade eff iciency. the fb pin is a high impedance input, so pcb track leng ths to this should also be kept as short as possibl e to reduce noise pickup. excess capacitance from the fb pin to ground should be avoided. below is the recommended layout of the ZXSC400EV2. l1 vin q1 u2 u1 r1 vcc pwm d1 + c1 led anode led cathode gnd ZXSC400EV2 25w led driver board zdb246r2 c3 r2 d2 + c2 lk1 d3 r3 d4 r4 c4 copyright zetex plc 2005 r5 top silk top copper bottom copper drill file
ZXSC400EV2 ZXSC400EV2 issue 8 - november 2005 6 ? zetex semiconductors plc 2005 europe the americas asia corporate headquarters zetex gmbh streitfeldstra?e 19 d-81673 mnchen germany zetex inc 700 veterans memorial hwy hauppauge, ny 11788 usa zetex (asia) ltd 3701-04 metroplaza tower 1 hing fong road, kwai fong hong kong zetex semiconductors plc zetex technology park, chadderton, ol9 9ll united kingdom telefon: (49) 89 45 49 49 0 telephone: (1) 631 360 2222 telephone: (852) 26100 611 telephone (44) 161 622 4444 fax: (49) 89 45 49 49 49 fax: (1) 631 360 8222 fax: (852) 24250 494 fax: (44) 161 622 4446 email: europe.sales@zetex.com email: usa.sales@zetex.com email: asia.sales@zetex.com email: hq@zetex.com these offices are supported by agents and distribut ors in major countries world-wide. this publication is issued to provide outline infor mation only which (unless agreed by the company in w riting) may not be used, applied or reproduced for any purpose or form part of any orde r or contract or be regarded as a representation re lating to the products or services concerned. the company reserves the right to alter w ithout notice the specification, design, price or c onditions of supply of any product or service. for the latest product information, log on to www.zetex.com
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