 |
|
| If you can't view the Datasheet, Please click here to try to view without PDF Reader . |
|
|
|
| If you can't view the Datasheet, Please click here to try to view without PDF Reader . |
|
|
| Datasheet File OCR Text: |
| MT7200 350ma led driver with internal switch MT7200 rev. 1.1 www.maxictech.com copyright ? 2008 maxic technology corporation page 1 description the MT7200 is a cont inuous mode inductive step-down converter, designed for driving single or multiple series connected leds efficiently from a voltage source higher than the led voltage. the dev ice operates from an input supply between 7~40v and provides an externally adjustable output current of up to 350ma. depending upon supply voltage and external components, this can provide up to 8 watts of output power. the MT7200 includes the output switch and a high-side output current s ensing circuit, which uses an external resistor to set the nominal average output current. features ? pass 4kv esd test ? simple low parts count ? 350ma output current ? single pin on/off and brightness control using dc voltage or pwm ? internal pwm filter ? soft-start ? high efficiency (up to 97%) ? wide input voltage range: 7v to 40v ? output shutdown ? up to 1mhz switching frequency ? inherent open-circuit led protection ? typical 4% output current accuracy application circuit output current can be adjusted above, or below the set value, by applying an external control signal to the 'adj' pin. the adj pin will accept either a dc voltage or a pwm waveform. depending upon the control frequency, this will prov ide either a continuous or a gated output current. the pwm filter components are contained within the chip. the pwm filter provides a soft-start feature by controlling the rise of input/output current. the soft-start time can be increased using an external capacitor from the adj pin to ground. applying a voltage of 0.2v or lower to the adj pin turns the output off and switches the device into a low current standby state. the device is assembled in a sot23-5/sot89-5 pin package. application ? low voltage halogen replacement leds ? automotive lighting ? low voltage industrial lighting ? led back-up lighting ? illuminated signs pin configuration lx 1 2 3 5 4 gnd adj v in i sense sot89-5 (top view)
MT7200 350ma led driver with internal switch MT7200 rev. 1.1 www.maxictech.com copyright ? 2008 maxic technology corporation page 2 absolute maximum ratings (voltages to gnd unless otherwise stated) input voltage (v in ) -0.3v to +40v i sense voltage (v sense ) +0.3v to -5v (measured with respect to vin) lx output voltage (v lx ) -0.3v to +40v adjust pin input voltage (v adj ) -0.3v to +6v switch output current (i lx ) 500ma power dissipation (p tot ) 450mw operating temperature (t op ) -40 to 105c storage temperature (t st ) -55 to 150c junction temperature (t j max ) 150c thermal resistance junction to ambient (r ja ) 200c/w pin description name pin no. description lx 1 drain of power mos switch gnd 2 ground adj 3 multi-function on/off and brightness control pin: ? leave floating for normal operation.(v adj =v ref =1.20 giving nominal average output current i outnom =0.1/r s ) ? drive to voltage below 0.2v to turn off output current ? drive with dc voltage (0.3v MT7200 350ma led driver with internal switch MT7200 rev. 1.1 www.maxictech.com copyright ? 2008 maxic technology corporation page 3 electrical characteristics (test conditions: v in =12v, t amb =25c unless otherwise stated) symbol parameter conditions min typ max unit v in input voltage 7 v v su internal regulator start-up threshold v in rising 4.8 v i inqoff quiescent supply current with output off adj pin grounded 45 a i inqon quiescent supply current with output on adj pin floating f=250khz 250 500 a v sense mean current sense threshold voltage (defines led current setting accuracy) measured on i sense pin with respect to v in v adj =1.25v 95 100 105 mv v sensehys sense threshold hysteresis 15 % i sense i sense pin input current v sense =v in -0.1 1.25 10 a v ref internal reference voltage measured at adj pin with pin floating 1.20 v v ref / t temperature coefficient of v ref 50 ppm/c v adj external control voltage range on adj pin for dc brightness control 0.3 2.5 v v adjoff dc voltage on adj pin to switch device from on state to off state v adj falling 0.2 v v adjon dc voltage on adj pin to switch device from off state to on state v adj rising 0.25 v r adj resistance between adj pin and v ref 170 200 260 k ? i lxmean continuous lx switch current 0.37 a r lx lx switch ?on? resistance 1.5 2 ? i lx(leak) lx switch leakage current 1 a d pwm(lf) duty cycle range of pwm signal applied to adj pin during low frequency pwm dimming mode frequency < 500hz amplitude = v ref measured on adj pin 0.01 1 brightness control range 100:1 40 MT7200 350ma led driver with internal switch MT7200 rev. 1.1 www.maxictech.com copyright ? 2008 maxic technology corporation page 4 d pwm(hf) duty cycle range of pwm signal applied to adj pin during high frequency pwm dimming mode frequency > 10khz amplitude = v ref measured on adj pin 0.16 1 brightness control range 5:1 t ss soft start time time taken for output current to reach 90% of final value after voltage on adj pin has risen above 0.3v 800 s f lx operating frequency adj pin floating l=100 h i out =350ma@v led =3 .4v driving 1 led 350 khz t onmin minimum ?on? time lx switch ?on? 200 ns t offmin minimum ?off? time lx switch ?off? 200 ns f lxmax recommanded maximum operating frequency 1.1 mhz d lx recommanded duty cycle range of output switch at f lxmax 0.3 0.7 t pd internal comparator propagation delay 50 ns block diagram . MT7200 350ma led driver with internal switch MT7200 rev. 1.1 www.maxictech.com copyright ? 2008 maxic technology corporation page 5 typical operat ing conditions 60.00% 65.00% 70.00% 75.00% 80.00% 85.00% 90.00% 95.00% 100.00% 5 1015202530 efficiency vin(v) efficiency ? vs. ? vin(l=47uh) 1led 2led 3led 4led 5led 6led 7led 0 200 400 600 800 1000 1200 1400 1600 5 1015202530 frequency(khz) vin(v) frequency ? vs. ? vin(l=47uh) ?? 1led 2led 3led 4led 5led 6led 7led 60.00% 65.00% 70.00% 75.00% 80.00% 85.00% 90.00% 95.00% 100.00% 5 1015202530 efficiency vin(v) efficiency ? vs. ? vin(l=100uh) 1led 2led 3led 4led 5led 6led 7led 0.00% 10.00% 20.00% 30.00% 40.00% 50.00% 60.00% 70.00% 80.00% 90.00% 100.00% 5 1015202530 dutycycle vin(v) dutycycle ? vs. ? vin(l=47uh) ?? 1led 2led 3led 4led 5led 6led 7led \ 6.00% \ 4.00% \ 2.00% 0.00% 2.00% 4.00% 6.00% 8.00% 10.00% 5 1015202530 deviation ? from ? nominal ? set ? current vin(v) output ? current ? variation ? vs. ? vin(l=47uh) ?? 1led 2led 3led 4led 5led 6led 7led 0.00% 10.00% 20.00% 30.00% 40.00% 50.00% 60.00% 70.00% 80.00% 90.00% 100.00% 5 1015202530 dutycycle vin(v) dutycycle ? vs. ? vin(l=100uh) ?? 1led 2led 3led 4led 5led 6led 7led MT7200 350ma led driver with internal switch MT7200 rev. 1.1 www.maxictech.com copyright ? 2008 maxic technology corporation page 6 0 100 200 300 400 500 600 700 800 900 5 1015202530 frequency(khz) vin(v) frequency ? vs. ? vin(l=100uh) ?? 1led 2led 3led 4led 5led 6led 7led 60.00% 65.00% 70.00% 75.00% 80.00% 85.00% 90.00% 95.00% 100.00% 5 1015202530 efficiency vin(v) efficiency ? vs. ? vin(l=220uh) 1led 2led 3led 4led 5led 6led 7led 0 50 100 150 200 250 300 350 400 450 5 1015202530 frequency(khz) vin(v) frequency ? vs. ? vin(l=220uh) ?? 1led 2led 3led 4led 5led 6led 7led 0.00% 1.00% 2.00% 3.00% 4.00% 5.00% 6.00% 7.00% 8.00% 9.00% 10.00% 5 1015202530 deviation ? from ? nominal ? set ? current vin(v) output ? current ? variation ? vs. ? vin(l=100uh) ?? 1led 2led 3led 4led 5led 6led 7led 0.00% 10.00% 20.00% 30.00% 40.00% 50.00% 60.00% 70.00% 80.00% 90.00% 100.00% 5 1015202530 dutycycle vin(v) dutycycle ? vs. ? vin(l=220uh) ?? 1led 2led 3led 4led 5led 6led 7led \ 1.00% 0.00% 1.00% 2.00% 3.00% 4.00% 5.00% 6.00% 7.00% 8.00% 5 1015202530 deviation ? from ? nominal ? set ? current vin(v) output ? current ? variation ? vs. ? vin(l=220uh) ?? 1led 2led 3led 4led 5led 6led 7led MT7200 350ma led driver with internal switch MT7200 rev. 1.1 www.maxictech.com copyright ? 2008 maxic technology corporation page 7 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 00.511.522.5 output ? current(a) vadj(v) output ? current ?? vs. ? vadj(l=47uh) ?? rs=0.25ohm rs=0.51ohm 1.15 1.16 1.17 1.18 1.19 1.2 1.21 1.22 1.23 1.24 1.25 \ 40 10 60 110 vadj(v) temperature(deg ? c) vadj ? vs. ? temperature(l=47uh) ?? 1.15 1.16 1.17 1.18 1.19 1.2 1.21 1.22 1.23 1.24 1.25 5 1015202530 vadj(v) vin(v) vadj ? vs. ? vin(l=47uh) ?? \ 2.50% \ 1.25% 0.00% 1.25% 2.50% \ 40 0 40 80 120 output ? current ? change temperature(deg ? c) output ? current ? change ? vs. ? temperature( vin=7v, ? l=47uh) ?? \ 3.50% \ 1.75% 0.00% 1.75% 3.50% \ 40 0 40 80 120 output ? current ? change temperature(deg ? c) output ? current ? change ? vs. ? temperature(vin=18v, ? l=47uh) ?? MT7200 350ma led driver with internal switch MT7200 rev. 1.1 www.maxictech.com copyright ? 2008 maxic technology corporation page 8 application notes setting nominal average output current with external resistor r s the nominal average output current in the led(s) is determined by the value of the external current sense resistor (r s ) connected between v in and i sense and is given by: i outnom = 0.1/r s [for rs>0.27] the table below gives values of nominal average output current for several preferred values of current setting resistor (r s ) in the typical application circuit shown on page 1: rs( ? ) nominal averageoutput current (ma) 0.27 370 0.3 333 0.33 300 0.39 256 the above values assume that the adj pin is floating and at a nominal voltage of v ref . note that r s =0.27 ? is the minimum allowed value of sense resistor under these conditions to maintain switch current below the specified maximum value. it is possible to use different values of r s if the adj pin is driven from an external voltage. output current adjustment by external dc control voltage the adj pin can be driven by an external dc voltage (v adj ), as shown, to adjust the output current to a value above or below the nominal average value defined by r s . the nominal average output current in this case is given by: i outdc = v adj /1.2/r s [for 0.3 MT7200 350ma led driver with internal switch MT7200 rev. 1.1 www.maxictech.com copyright ? 2008 maxic technology corporation page 9 the recommended method of driving the adj pin and controlling the amplitude of the pwm waveform is to use a small npn switching transistor as shown. 3. driving the adj from a microcontroller another possibility is to drive the device from the open drain output of a microcontroller. the diagram below shows one method of doing this: shutdown mode taking the adj pin to a voltage below 0.2v for more than approximately 100 s, will turn off the output and supply curr ent will fall to a low standby level of 50 a nominal. note that the adj pin is not a logic input. taking the adj pin to a voltage above v ref will increase output current above the 100% nominal average value. inherent open-circuit led protection if the connection to the led(s) is open-circuited, the coil is isolated from the lx pin of the chip, so the device will not be damaged, unlike in many boost converters, where the back emf may damage the internal switch by forcing the drain above its breakdown voltage. capacitor selection a low esr capacitor should be used for input decoupling, as the esr of this capacitor appears in series with the supply source impedance and lowers overall efficiency. this capacitor has to supply the relatively high peak current to the coil and smooth the current ripple on the input supply. a minimum value of 1 f is acceptable if the in put source is close to the device, but higher values will improve performance at lower input voltages, especially when the sour ce impedance is high. the input capacitor s hould be placed as close as possible to the ic. inductor selection recommended inductor values for the MT7200 are in the range 27 h to 100 h. higher values of inductance are recommended at higher supply voltages in order to minimize errors due to switching delays, which result in increased ripple and lower efficiency. higher values of inductance also result in a smaller change in output current over the supply voltage range. (see graphs). the inducto r should be mounted as close to the device as possible with low resistance connections to the lx and v in pins. the chosen coil should have a saturation current higher than the peak output current and a continuous current rating above the required mean output current. the inductor value should be chosen to maintain operating duty cycle and switch 'on'/'off' times within the specified limits over the supply voltage and load current range. the following equations can be used as a guide: lx switch 'on' time t on li v in v led i r s r l r lx note: t onmin >200ns lx switch 'off' time v in i sense lx adj gnd 0.33 ? 1 f 47 h MT7200 0 pwm 1 mcu MT7200 350ma led driver with internal switch MT7200 rev. 1.1 www.maxictech.com copyright ? 2008 maxic technology corporation page 10 t off li v d v led i r s r l note: t offmin >200ns where: l is the coil inductance (h) r l is the coil resistance ( ? ) i avg is the required led current (a) i is the coil peak-peak ripple current (a) {internally set to 0.3 x iavg} v in is the supply voltage (v) v led is the total led forward voltage (v) r lx is the switch resistance ( ? ) v d is the diode forward voltage at the required load current (v) diode selection it is important to select parts with a peak current rating above the peak coil current and a continuous current rating higher than the maximum output load current. it is very important to consider the reverse leakage of the diode when operating above 85c. excess leakage will increase the power dissipation in the device. reducing output ripple peak to peak ripple curr ent in the led can be reduced, if required, by shunting a capacitor cled across the led(s), a value of 1 f will reduce nominal ripple current by a factor three (approx.). proportionally lower ripple can be achieved with higher capacitor values. note that the capacitor will not affect operating frequency or efficiency, but it will increase start-up delay, by reducing the rate of rise of led voltage. operation at low supply voltage the internal regulator di sables the drive to the switch until the supply has risen above the startup threshold (v su ). above this threshold, the device will start to operate. however, with the supply voltage be low the specified minimum value, the switch duty cycle will be high and the device power dissipation will be at a maximum. care should be taken to avoid operating the device under such conditions in the application, in order to minimize the risk of exceeding the maximum allowed die temperature. note that when driving loads of two or more leds, the forward drop will normally be sufficient to prevent t he device from switching below approximately 6v. this will minimize the risk of damage to the device. layout considerations lx pin the lx pin of the devic e is a fast switching node, so pcb tracks should be kept as short as possible. to minimize ground 'bounce', the ground pin of the device should be soldered directly to the ground plane. coil and decoupling capacitors and current sense resistor it is particularly important to mount the coil and the input decoupling capacitor as close to the device pins as possible to minimize parasitic resistance and inductance, which will degrade efficiency. it is also important to minimize any track resistance in series with current sense resistor r s . it?s best to connect v in directly to one end of r s and i sense directly to the opposite end of r s with no other currents flowing in these tracks. it is important that the cathode current of the schottky diode does not flow in a track between r s and v in as this may give an apparent higher measure of current than is actual because of track resistance. MT7200 350ma led driver with internal switch MT7200 rev. 1.1 www.maxictech.com copyright ? 2008 maxic technology corporation page 11 adj pin the adj pin is a high impedance input for voltages up to 1.35v so, when left floating, pcb tracks to this pin should be as short as possible to reduce noise pickup. a 100nf capacitor from the adj pin to ground will reduce frequency modulation of the output under these conditions. an additional rc low pass filter (10k ? /100 f) can also be used when driving the adj pin from an external circuit. this lpf will provide filtering for low frequency noise and provide protection against high voltage transients. high voltage tracks avoid running any high voltage tracks close to the adj pin, to reduce the risk of leakage pin currents due to board contamination. the adj is soft-clamped for vo ltages above 1.35v to desensitize it to leakage that might raise the adj pin voltage and cause excessive output current. however, a ground ring placed around the adj pin is recommended to minimize changes in output cu rrent under these conditions. evaluation board the MT7200 evaluation boards are available on request. MT7200 350ma led driver with internal switch MT7200 rev. 1.1 www.maxictech.com copyright ? 2008 maxic technology corporation page 12 demo board schematic parts list qty. reference description size 4 d4,d5,d6,d7 schottky diode dfls240 powerdi 1 ds schottky diode, bat54c sot23-3 1 cin input capacitor 100uf ac 1uf dc 1 cadj dimming capacitor 0603 1 radj dimming resistor 0603 1 l loop inductor, typically 47uh 1 rsns current sensing resisitor 0603 1 MT7200 ic, MT7200, 350ma led driver sot23-5/sot89-5 photo MT7200 350ma led driver with internal switch MT7200 rev. 1.1 www.maxictech.com copyright ? 2008 maxic technology corporation page 13 package information sot23-5 symbol dimensions in millimeters dimensions in inches min max min max a 1.050 1.250 0.041 0.049 a1 0.000 0.100 0.000 0.004 a2 1.050 1.150 0.041 0.045 b 0.300 0.500 0.012 0.020 c 0.100 0.200 0.004 0.008 d 2.820 3.020 0.111 0.119 e 1.500 1.700 0.059 0.067 e1 2.650 2.950 0.104 0.116 e 0.950(bsc) 0.037(bsc) e1 1.800 2.000 0.071 0.079 l 0.300 0.600 0.012 0.024 0 8 0 8 e e1 d b l 0.25 c MT7200 350ma led driver with internal switch MT7200 rev. 1.1 www.maxictech.com copyright ? 2008 maxic technology corporation page 14 sot89-5 symbol dimensions in millimeters dimensions in inches min max min max a 1.400 1.600 0.055 0.063 b 0.320 0.520 0.013 0.020 b1 0.360 0.560 0.014 0.022 c 0.350 0.440 0.014 0.017 d 4.400 4.600 0.173 0.181 d1 1.400 1.800 0.055 0.071 e 2.300 2.600 0.091 0.102 e1 3.940 4.250 0.155 0.167 e 1.500typ 0.060typ e1 2.900 3.100 0.114 0.122 l 0.900 1.100 0.035 0.043 MT7200 350ma led driver with internal switch MT7200 rev. 1.1 www.maxictech.com copyright ? 2008 maxic technology corporation page 15 maxic technology corporation(hong kong office) rm d1, 7th floor, jianan commercial building, no. 49-51, suhong str., sheung wan, hong kong maxic technology corporation (beijing office) room 911, building 3, zi jin digital garden , hai dian district, beijing, china, 100190 tel: 86-10-62662828 fax: 86-10-62662951 web: www.maxictech.com e-mail: sales@maxictech.com , info@maxictech.com |
Price & Availability of MT7200
 |
|
|
|
|
All Rights Reserved © IC-ON-LINE 2003 - 2022 |
| [Add Bookmark] [Contact Us] [Link exchange] [Privacy policy] |
|
Mirror Sites : [www.datasheet.hk]
[www.maxim4u.com] [www.ic-on-line.cn]
[www.ic-on-line.com] [www.ic-on-line.net]
[www.alldatasheet.com.cn]
[www.gdcy.com]
[www.gdcy.net] |