ZXLD1350EV3 ZXLD1350EV3 user guide iss 1 10-04-07 ZXLD1350EV3 evaluation board user guide description the ZXLD1350EV3, figure 1, is an evaluation board for ev aluating the zxld1350 350ma led driver with internal switch. the evaluation board can be used to drive 1, 2 or 3 one-watt leds, or an external choice of leds. the number of external connected leds depends on the forward voltage of the leds connected. the leds fitted on this evaluation board are from the cree ? range. the operating voltage is nominally 24v. for three 1w seri es-connected leds, the voltage can be from 12v minimum to 30v maximum. the 100uh inductor used in the circuit is based on a nominal 24v supply, which should be connected across +vin and gnd pins. note: the evaluati on board does not have reverse battery protection. the nominal current for the evaluation board is set at 300ma with a 0.33 sense resistor, rs. jumpers j1, j2 and j3 allow the selection of the number of leds to be connected in series. jumper on at j1 bypasses led d1. jumper on at j3 bypasses led d3. removi ng jumper j2 disconnects all the on-board leds from the current flow path. jumper 2 also doubles as a c onnection point for an ammeter to measure the led current. before connecting external leds across test pins led+ and led-, or across j1, remove jumper j2. jumpers j1 and j2 can be on or off. test point adj provides a connection point for dc or pwm dimming and shutdown. warning: at 24v nominal operation with 300ma output, t he leds and the pcb may be hot and the leds will be very bright. figure 1: ZXLD1350EV3 evaluation board
ZXLD1350EV3 ZXLD1350EV3 user guide iss 1 10-04-07 zxld1350 device description the zxld1350 is a continuous mode inductive driver in a tsot23-5 package, for driving one or more series connected leds efficiently from a voltage source higher than the led voltage. t he device includes the output switch and a current sense circuit, which requires an exte rnal sense resistor to set the nominal current up to 350ma. zxld1350 device features ? drives one or more series-connected 1w white leds up to 350ma. ? internal 30v switch. ? wide input voltage: 7v to 30v. ? inherent open circuit led protection. ? brightness control using dc or pwm. ? internal pwm filter. device applications ? led flashlights. ? high power led driving. ? low-voltage halogen replacement leds. ? automotive lighting. ? illuminated signs. zxld1350 device packages, pin and definitions tsot23-5 pack zxld1350 device pin definition name pin no description lx 1 drain of ndmos switch. gnd 2 ground (0v). adj 3 internal voltage ref. pin (1.25v) : ? leave floating for normal operation. ? connect to gnd to tu rn off output current. ? drive with dc voltage (0.3v to 1.25v) or with pwm signal to adjust output current or.... ? connect a capacitor from this pi n to ground to set soft-start time. isense 4 connect a sense resistor, rs, from the adj pin to vin to sense the nominal output current. nominal i out = 0.1/ rs vin 5 input voltage: 7v to 30v. decouple to ground with a 1uf or higher ceramic capacitor. ordering information evalboard order number ZXLD1350EV3 please note: evaluation boards are subject to availability and qualified leads. device order number zxld1350e5ta
ZXLD1350EV3 ZXLD1350EV3 user guide iss 1 10-04-07 ZXLD1350EV3 evaluation board reference design the ZXLD1350EV3 is configured to the reference design in figure 2. the target applicat ion is a driver for one or more series-connected 1w white leds for torches and other high powered led driving applications. the operating voltage is a nominal 24v. for three 1w series-connected leds, the voltage can be from 12v minimum to 30v maximum. the nominal current is set at 300ma with a 0.33 sense resistor, rs. for three series - connected 1?watt leds, with a nominal supply of 24v, the zxld1350 runs in continuous mode at 545khz, with a 100uh inductor. jumpers j1, j2 and j3 allow selection of the number of le ds to be connected in series. jumper on at j1 bypasses led d1. jumper on at j3 bypasses led d3. removing jumper j2 disconnects all the 1-watt leds from the current flow path. jumper 2 also doubles as a connection point for an ammeter to measure the led current. both dc and pwm dimming can be achieved by driving the adj pin. for dc dimming, the adj pin may be driven between 0.3v and 1.25v. driving the adj pin below 0.2v will shutdown the output current. for pwm dimming, an external open-collector npn transistor or open-drain n-ch annel mosfet can be used to drive the adj pin. the pwm frequency can be low, around 100hz to 1khz, or high between 10khz to 50khz. c3 should not be fitted on the evaluation board when using the pwm dimm ing feature. shorting r1 will connect the test pin adj to device pin adj. the capacitor c3 should be around 10nf to decoupl e high frequency noise at the adj pin for dc dimming. the soft-start time will be nominally 0.5ms without capa citor c3. adding c3 will incr ease the soft start time by approximately 0.5ms/nf for other reference designs or further applications information, please refer to the zxld1350 datasheet. schematic diagram figure 2 shows the schematic for t he ZXLD1350EV3 evaluation board. figure 2: schematic for the evaluation board ZXLD1350EV3 zxld1350 operation in normal operation, when voltage is applied at +vin, the zxld13350 internal ndmos switch is turned on. current starts to flow through sense resistor rs, inductor l1, and the leds. the current ramps up linearly, and the ramp rate is determined by the input voltage +vin and the inductor l1 . this rising current produces a voltage ramp across rs. the internal circuit of the zxld1350 se nses the voltage across rs and applies a proportional voltage to the input of the internal comparator. when this volt age reaches an internally se t upper threshold, the ndmos switch is turned off. the inductor current continues to flow through rs, l1, t he leds, the schottky diode sd1, and back to the supply rail, but it decays, with the rate of decay determined by the forward voltage drop of the leds and the schottky diode. this decaying current produces a falling voltage at rs, which is sensed by the zxld1350. a voltage proportional to the sense voltage across rs is applied at the input of the inter nal comparator. when this voltage falls to the internally set lower threshold, the ndmos switch is turned on again. this switch-on-and-off cycle continues to provide the average led current set by the sense resistor rs. please refer to the datasheets for the threshol d limits, zxld1350 internal circuits, electrical characteristics and parameters. warning: at a nominal 24v operation with 300ma output, the board temperature rises by around 30c from ambient after 30 minutes of operation.
ZXLD1350EV3 ZXLD1350EV3 user guide iss 1 10-04-07 materials list for the ZXLD1350EV3 evaluation board. ref value package part number manufacturer notes r s 0.33r 1%,250ppm 0805 ncst10fr330ftrf lr1206-r033fi nic components welwyn r1,r2 not fitted 0805 not fitted c1,c2 1uf, 50v 1206 c1206c105k5rac7800 nmc1206x7r105k50f kemet nic components 50v, 1206 x7r c3 not fitted 0805 not fitted l1 100uh mss6132-104 npis53d101mtrf coilcraft nic components 100uh/0.5a rms inductor sd1 40v, 1.16a sot23 zlls1000 zetex schottky diode u1 zxld1350 tsot23-5 zxld1350e5ta zetex dc-dc converter d1, d2, d3 led xr-e 7090 cree power led jp1, jp2, jp3 jumper various 2.54mm pitch jumper pin strips +vin, gnd, adj, led a, led k test loop 100-108 hughes ZXLD1350EV3 layout the top and bottom view of the evaluation board is show n here. the slugs of the 1-watt leds are connected to isolated copper 'floods' both on the top and bottom layers, with thermal inter-connection between the layers. the slugs are electrically isolated from other circuits and pads on the evaluation board. u1 +vin gnd adj ZXLD1350EV3 evaluation board bare board: z db345r1 l1 sd1 jp2 c3 copyright z et ex plc 2006 a k a k a k r1 jp3 jp1 led a led k rs c1 c2 r2 d1 d2 d3 in partnership with: figure 3: top view figure 4: bottom view
ZXLD1350EV3 ZXLD1350EV3 user guide iss 1 10-04-07 ZXLD1350EV3 connection point definition name description +vin positive supply voltage. connect a +24v positive supply to this pin. gnd supply ground (0v). connect supply ground to this pin. adj internal voltage ref. pin (1.25). this pin can be used to achieve dimming and soft-start, and for switching the output current off. ? leave floating for normal operation. ? see 'other features' section to achiev e dimming, and soft-start and for switching the output current off. led a led a connects to the anode of led d3, and is the external led anode connection point. disconnect the jumper jp2 when driving an external load. led k led k connects to the cathode of led d1, and is the external led cathode connection point. disconnect the jumper jp2 when driving external leds. zxdl1350ev2 operation ZXLD1350EV3 power up 1. connect vin to +24v of the power supply unit (psu). connect gnd to the power supply ground (0v). warning: the board does not feature reverse battery/supply protection. 2. set the psu to +24v. (+24v at vin pin with ref. to the gnd pin.) 3. turn on the psu. warning: do not stare at the leds directly. 4. ensure jumper j2 is fitted. with jp1 and jp3 disconnec ted (jumper off), all three leds should illuminate and will be regulated nominally at 300ma. 5. to change the number of leds connected in series, use jumper jp1 and jp3 to bypass leds d1 and d3 respectively. warning: the leds may be hot. other features dimming the zxld1350 provides three dimming options: dc, high-frequency pwm, and low-frequency pwm dimming. dc voltage dimming 1. switch off the power supply. 2. insert a 0r 0805 resistor across r1 pads. 3. fit a 10nf capacitor at c3 to decouple the pin. 4. drive the adj pin on the board with a dc voltage in the range 0.3v to 1.25v. 5. do not exceed 1.25v, as this represents 100% of th e led current set by rs. the current will increase in proportion to this voltage. for exam ple, if 2.5v is applied, the current will increase to 200%. that is, the current will be twice the 1.25v rating. for such over-d rive of the adj pin, the led and zxld1350 are likely to be damaged. the nominal led current (output current), i out , is given by i out = 0.08* v adj /rs where i out = the nominal led current. v adj = the dc dimming voltage at adj pin resistor. 0.08 is the multiplier for the reference voltage on adj pin. rs = the sense resistor value in ohms. do not use a resistor value lower than 0.27 . 6. the dimming ratio is around 6:1. note: as the volt age approaches 0.2v on the adj pin, the zxld1350 will shut down. 7. follow the ?ZXLD1350EV3 power up? sequence.
ZXLD1350EV3 ZXLD1350EV3 user guide iss 1 10-04-07 high frequency pwm dimming 1. switch off the power supply. 2. insert a 0r 0805 resistor across r1 pads. 3. ensure c3 is not fitted. 4. connect a pwm signal to the adj pin via an open collector npn transistor, or an open drain n-channel mosfet. 5. alternatively, drive the adj pin directly with a pwm signal. however, make sure the pwm signal voltage levels do not violate the adj pin voltage rating. dr iving the adj pin above 1.25v will exceed the maximum set current for the value of rs and may damage the device or led. 6. set the pwm frequency to between 10khz and 50khz. the cut-off frequency of the internal filter is 4khz, and exceeding the 50khz may cause modulation with the switching regulator. 7. the dimming ratio will be about 6:1, similar to t he dc dimming. the nominal le d current (output current), i out, is given by i out = 0.1*d/rs where i out = the nominal led current. rs = the sense resistor value in ohms. do not use a resistor value lower than 0.27 . d = the duty cycle of the pwm dimming frequency. 0.1v is the nominal sense voltage with adj open circuit or set to 1.25v. note: the adj pin is internally referenced to 1.25v. this pin should be left floating for normal operation without dimming. please refer to the datasheet for pwm frequency. 8. follow the ?ZXLD1350EV3 power up? sequence. low frequency pwm dimming 1. switch off the power supply. 2. insert a 0r 0805 resistor across r1 pads. 3. make sure c3 is not fitted. 4. connect a pwm signal to the adj pin via an open co llector npn transistor or an open drain n-channel mosfet. 5. alternatively, drive the adj pin directly with a pwm signal. however, make sure the pwm signal voltage levels do not violate the adj pin voltage rating. dr iving the adj pin above 1.25v will exceed the maximum set current for the value of rs and may damage the device or led 6. the pwm frequency can be low; around 100hz or up to 1khz. 7. the zxld1350 is now effectively being turned on a nd off at the pwm frequency. the dimming ratios are in the region of 100:1, much greater than the dc dimming ratio. the average l led current (output current), i out, is given by i out = 0.1*d/rs where i out = the average led current. rs = the sense resistor value in ohms. do not use a resistor value lower than 0.27 . d = the duty cycle of the pwm dimming frequency. 0.1v is the nominal sense voltage with adj open circuit or set to 1.25v. 8. follow the ?ZXLD1350EV3 power up? sequence. soft-start 1. switch off the power supply. 2. insert a 0r 0805 resistor across r1 pads. 3. fit a capacitor at c3 to decouple the pin. the value of c3 will determine the so ft-start time se tting. please see the datasheet for calculat ion of the capacitor value. 4. follow the ?ZXLD1350EV3 power up? sequence. switching the output current off 1. switch off the power supply. 2. insert a 0r 0805 resistor across r1 pads. 3. follow the ?ZXLD1350EV3 power up? sequence. 4. connect the adj pin to gnd to turn off the output current. 5. follow the ?ZXLD1350EV3 power up? sequence. the zxld 1350 internal switch remains switched off (output current off) whilst the adj pin is pulled to gnd.
ZXLD1350EV3 ZXLD1350EV3 user guide iss 1 10-04-07 changing the led current 1. switch off the power supply. 2. remove rs. 3. calculate and fit a new sense resistor, rs, the value of which is based on the required led current without dimming. rs can be calculated using following equation : rs = 0.1v/i out where i out = the led current. rs = the sense resistor value in ohms. do not use a resistor value lower than 0.27 . 0.1v is the nominal sense voltage with adj open circuit or set to 1.25v. 4. follow the ?ZXLD1350EV3 power up? sequence. using external leds or loads 1. switch off the power supply. 2. connect external leds across test pins ?led a? an d ?led k?. ?led a? is the leds' anode connection point and ?led k? is the leds' cathode connection point. t he number of external leds that can be connected depends on their operating power and forward voltage drop. for an external load other than leds, the positive terminal of the load should be connected to test pin ?led a? and the negative terminal of the load should be connected to test pin ?led k?. 3. follow the ?ZXLD1350EV3 power up? sequence. performance the system efficiency depends on the sense resistor, supply voltage, switching inductor and the number of 1w leds connected in series. the graph below shows the efficiency with a 0.33 sense resistor r s, and a 100uh inductor, for 1 to 3 series connected 1w leds. with a 24v supply, the switching frequency is typically 545khz for three series-connected 1-watt leds and 300khz for a single 1-watt led. with a 12v supply, the switching frequency is typically 160khz for three series-connected 1-watt leds and 280khz for a single 1-watt led the detailed performance information for t he device can be found in the datasheets. figure 5: efficiency vs supply voltage efficiency vs vin rsense=0.33 ohms, l=100uh (coilcraft mss6132) 75 80 85 90 95 0 5 10 15 20 25 30 35 vin (v) eff (%) 1 led 2 led 3 led
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