View MAX16801A_2707976.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. general description the MAX16801A/b/max16802a/b high-brightness (hb) led driver-control ics contain all the circuitry required for the design of wide-input-voltage-range led drivers for general lighting and display applications. the max16801 is well suited for universal input (rectified 85vac to 265vac) led drivers, while the max16802 is intended for low-input-voltage (10.8vdc to 24vdc) led drivers. when the led current needs to be tightly regulated, an additional on-board error amplifier with 1% accurate ref- erence can be utilized. a wide dimming range can be implemented by using low-frequency pwm dimming. the max16801/max16802 feature an input undervoltage lockout (uvlo) for programming the input-supply start voltage, and to ensure proper operation during brownout conditions. the max16801 has an internal-bootstrap undervoltage lockout circuit with a large hysteresis that simplifies offline led driver designs. the max16802 does not have this internal bootstrap circuit and can be biased directly from a +12v rail. the 262khz fixed switching frequency is internally trimmed, allowing for optimization of the magnetic and fil- ter components, resulting in a compact, cost-effective led driver. the MAX16801A/max16802a are offered with 50% maximum duty cycle. the max16801b/max16802b are offered with 75% maximum duty cycle. these devices are available in an 8-pin max ? package and operate over the -40c to +85c temperature range. applications features ? suitable for buck, boost, flyback, sepic, and other topologies ? up to 50w or higher output power ? universal offline input voltage range: rectified 85vac to 265vac (max16801) ? in pin directly driven from 10.8vdc to 24vdc input (max16802) ? internal error amplifier with 1% accurate reference for precise led current regulation ? pwm or linear dimming ? fixed switching frequency of 262khz 12% ? thermal shutdown ? digital soft-start ? programmable input startup voltage ? internal bootstrap uvlo with large hysteresis (max16801) ? 45a (typ) startup supply current, 1.4ma (typ) operating supply current ? 50% (MAX16801A/max16802a) or 75% (max16801b/max16802b) maximum duty cycle ? available in a tiny 8-pin max package MAX16801A/b/max16802a/b offline and dc-dc pwm controllers for high-brightness led drivers ________________________________________________________________ maxim integrated products 1 ordering information 19-3880; rev 2; 1/10 part temp range pin- package max16801 aeua+ -40c to +85c 8 max max16801beua+ -40c to +85c 8 max max16802 aeua+ -40c to +85c 8 max max16802beua+ -40c to +85c 8 max + denotes lead-free package. offline and dc-dc led drivers rgb back light for lcd tvs and monitors commercial and industrial lighting decorative and architectural lighting evaluation kit available q1 max16802b 10.8vdc to 24vdc pwm gnd c1 r1 l1 d1 c2 c3 leds cs comp dim/fb uvlo/en in v cc ndrv gnd enable typical operating circuit warning: the max16801/max16802 are designed to work with high voltages. exercise caution. ?ax is a registered trademark of maxim integrated products, inc.
MAX16801A/b/max16802a/b offline and dc-dc pwm controllers for high-brightness led drivers 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v in = +12v (max16801: v in must first be brought up to +23.6v for startup), 10nf bypass capacitors at in and v cc , c ndrv = 0f, v uvlo = +1.4v, v dim/fb = +1.0v, comp = unconnected, v cs = 0v, t a = -40c to +85c, unless otherwise noted. typical values are at t a = +25c.) (note 1) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. in to gnd .......................................................................... -0.3v to +30v v cc to gnd ...................................................................... -0.3v to +13v dim/fb, comp, uvlo, cs to gnd..........................-0.3v to +6v ndrv to gnd.............................................-0.3v to (v cc + 0.3v) continuous power dissipation (t a = +70c) 8-pin max (derate 4.5mw/c above +70c) ..............362mw operating temperature range ...........................-40c to +85c storage temperature range ............................-65c to +150c junction temperature ......................................................+150c lead temperature (soldering, 10s) .................................+300c parameter symbol conditions min typ max units undervoltage lockout/startup bootstrap uvlo wake-up level v suvr v in rising (max16801 only) 19.68 21.6 23.60 v bootstrap uvlo shutdown level v suvf v in falling (max16801 only) 9.05 9.74 10.43 v uvlo/en wake-up threshold v ulr2 uvlo/en rising 1.188 1.28 1.371 v uvlo/en shutdown threshold v ulf2 uvlo/en falling 1.168 1.23 1.291 v uvlo/en input current i uvlo t j = +125c 25 na uvlo/en hysteresis 50 mv in supply current in undervoltage lockout i start v in = +19v, for max16801 only when in bootstrap uvlo 45 90 a in voltage range v in 10.8 24 v t extr uvlo/en steps up from +1.1v to +1.4v 12 uvlo/en propagation delay t extf uvlo/en steps down from +1.4v to +1.1v 1.8 s t buvr v in steps up from +9v to +24v 5 bootstrap uvlo propagation delay t buvf v in steps down from +24v to +9v 1 s internal supply v cc regulator set point v ccsp v in = +10.8v to +24v, sinking 1a to 20ma from v cc 7 10.5 v in supply current after startup i in v in = +24v 1.4 2.5 ma shutdown supply current uvlo/en = low 90 a gate driver r on ( low ) measured at ndrv sinking, 100ma 2 4 driver output impedance r on ( high ) measured at ndrv sourcing, 20ma 4 12 ? driver peak sink current 1a driver peak source current 0.65 a pwm comparator comparator offset voltage vo pwm v comp - v cs 1.15 1.38 1.70 v cs input bias current i cs v cs = 0v -2 +2 a comparator propagation delay t pwm v cs = +0.1v 60 ns minimum on-time t on ( min ) 150 ns
MAX16801A/b/max16802a/b offline and dc-dc pwm controllers for high-brightness led drivers _______________________________________________________________________________________ 3 note 1: all devices are 100% tested at t a = +85c. all limits over temperature are guaranteed by characterization. note 2: v ref is measured with dim/fb connected to the comp pin (see the functional diagram ). note 3: the max16801 is intended for use in universal input offline drivers. the internal clamp circuit is used to prevent the boot- strap capacitor (c1 in figure 5) from charging to a voltage beyond the absolute maximum rating of the device when en/uvlo is low. the maximum current to in (hence to clamp) when uvlo is low (device in shutdown), must be externally limited to 2ma (max). clamp currents higher than 2ma may result in clamp voltage higher than +30v, thus exceeding the absolute maximum rating for in. for the max16802, do not exceed the +24v maximum operating voltage of the device. electrical characteristics (continued) (v in = +12v (max16801: v in must first be brought up to +23.6v for startup), 10nf bypass capacitors at in and v cc , c ndrv = 0f, v uvlo = +1.4v, v dim/fb = +1.0v, comp = unconnected, v cs = 0v, t a = -40c to +85c, unless otherwise noted. typical values are at t a = +25c.) (note 1) parameter symbol conditions min typ max units current-sense comparator current-sense trip threshold v cs 262 291 320 mv cs input bias current i cs v cs = 0v -2 +2 a propagation delay from comparator input to ndrv t pwm 50mv overdrive 60 ns switching frequency f sw 230 262 290 khz max1680_a 50 50.5 maximum duty cycle d max max1680_b 75 76 % in clamp voltage in clamp voltage v inc 2ma sink current, max16801 only (note 3) 24.1 26.1 29.0 v error amplifier voltage gain r load = 100k ? 80 db unity-gain bandwidth r load = 100k ? , c load = 200pf 2 mhz phase margin r load = 100k ? , c load = 200pf 65 d eg r ees dim/fb input offset voltage 3mv high 2.2 3.5 comp clamp voltage low 0.4 1.1 v source current 0.5 ma sink current 0.5 ma reference voltage v ref (note 2) 1.218 1.230 1.242 v input bias current 50 na comp short-circuit current 8ma thermal shutdown thermal-shutdown temperature 130 ?c thermal hysteresis 25 ?c digital soft-start soft-start duration 15,872 clock cycles reference voltage steps during soft-start 31 steps reference voltage step 40 mv
MAX16801A/b/max16802a/b offline and dc-dc pwm controllers for high-brightness led drivers 4 _______________________________________________________________________________________ typical operating characteristics (v uvlo/en = +1.4v, v fb = +1v, comp = unconnected, v cs = 0v, t a = +25c, unless otherwise noted.) bootstrap uvlo wake-up level vs. temperature max16801 toc01 temperature ( c) v in (v) 60 40 20 0 -20 21.35 21.40 21.45 21.50 21.55 21.60 21.30 -40 80 max16801 v in rising bootstrap uvlo shutdown level vs. temperature max16801 toc02 temperature ( c) v in (v) 60 40 20 0 -20 9.8 9.9 10.0 10.1 9.7 -40 80 max16801 v in falling uvlo/en wake-up threshold vs. temperature max16801 toc03 temperature ( c) uvlo/en (v) 60 40 20 0 -20 1.255 1.260 1.265 1.270 1.275 1.280 1.250 -40 80 uvlo/en rising uvlo/en shutdown threshold vs. temperature max16801 toc04 temperature ( c) uvlo/en (v) 60 40 20 0 -20 1.15 1.20 1.25 1.30 1.10 -40 80 uvlo/en falling v in supply current in undervoltage lockout vs. temperature max16801 toc05 temperature ( c) i start ( a) 60 40 20 0 -20 43 44 45 46 47 48 49 50 51 52 42 -40 80 v in = 19v max16801 when in bootstrap uvlo max16802 when uvlo/en is low v in supply current after startup vs. temperature max16801 toc06 temperature ( c) i in (ma) 60 40 20 0 -20 1.2 1.3 1.4 1.5 1.1 -40 80 v in = 24v v cc regulator set point vs. temperature max16801 toc07 temperature ( c) v cc (v) 60 40 20 0 -20 9.3 9.5 9.4 9.7 9.6 9.8 9.2 -40 80 v in = 19v no load ndrv output is not switching, v fb = 1.5v ndrv output is switching v cc regulator set point vs. temperature max116801 toc08 temperature ( c) v cc (v) 60 40 20 0 -20 8.2 8.5 8.6 8.4 8.3 8.8 8.7 8.9 8.1 -40 80 v in = 10.8v 10ma load 20ma load current-sense threshold vs. temperature max16801 toc09 temperature ( c) current-sense threshold ( v) 60 40 20 0 -20 275 290 295 285 280 305 300 310 270 -40 80 +3 -3 mean total number of devices = 100
MAX16801A/b/max16802a/b offline and dc-dc pwm controllers for high-brightness led drivers _______________________________________________________________________________________ 5 current-sense threshold max16801 toc10 current-sense threshold (mv) percentage of units (%) 310 300 290 280 270 5 10 15 20 25 30 0 260 320 total number of devices = 200 switching frequency vs. temperature max16801 toc11 temperature ( c) switching frequency (khz) 60 40 20 0 -20 245 260 265 255 250 275 270 280 240 -40 80 +3 -3 mean total number of devices = 100 switching frequency max16801 toc12 switching frequency (khz) percentage of units (%) 280 270 260 250 240 5 10 15 20 25 30 0 230 290 total number of devices = 200 propagation delay from current-sense comparator input to ndrv vs. temperature max16801 toc13 temperature ( c) t pwm (ns) 60 40 20 0 -20 55 60 65 70 75 50 -40 80 uvlo/en propagation delay vs. temperature max16801 toc14 temperature ( c) undervoltage lockout delay ( s) 60 40 20 0 -20 4 3 2 1 7 6 5 13 12 11 10 9 8 14 0 -40 80 uvlo/en rising uvlo/en falling reference voltage vs. temperature max16801 toc15 temperature ( c) reference voltage (v) 60 40 20 0 -20 1.226 1.227 1.228 1.229 1.230 1.225 -40 80 v in = 12v input current vs. input clamp voltage max16801 toc16 input voltage (v) input current (ma) 27.5 25.0 20.0 22.5 15.0 17.5 12.5 1 2 3 4 5 6 7 8 9 10 0 10.0 30.0 input clamp voltage vs. temperature max16801 toc17 temperature ( c) input clamp voltage (v) 60 40 20 0 -20 25.2 25.4 25.6 25.8 26.0 26.2 26.4 26.6 26.8 27.0 25.0 -40 80 i in = 2ma ndrv output impedance vs. temperature max16801 toc18 temperature ( c) r on ( ? ) 60 40 20 0 -20 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 1.2 -40 80 v in = 24v sinking 100ma typical operating characteristics (continued) (v uvlo/en = +1.4v, v fb = +1v, comp = unconnected, v cs = 0v, t a = +25c, unless otherwise noted.)
MAX16801A/b/max16802a/b detailed description the max16801/max16802 family of devices is intend- ed for constant current drive of high-brightness (hb) leds used in general lighting and display applications. they are specifically designed for use in isolated and nonisolated circuit topologies such as buck, boost, fly- back, and sepic, operating in continuous or discontin- uous mode. current mode control is implemented with an internally trimmed, fixed 262khz switching frequen- cy. a bootstrap uvlo with a large hysteresis (11.9v), very low startup current, and low operating current result in an efficient universal-input led driver. in addi- tion to the internal bootstrap uvlo, these devices also offer programmable input startup voltage programmed through the uvlo/en pin. the max16801 is well suited for universal ac input (rectified 85vac to 265vac) dri- vers. the max16802 is well suited for low input voltage (10.8vdc to 24vdc) applications. the max16801/max16802 regulate the led current by monitoring current through the external mosfet cycle by cycle. offline and dc-dc pwm controllers for high-brightness led drivers 6 _______________________________________________________________________________________ pin description ndrv output impedance vs. temperature max16801 toc19 temperature ( c) r on ( ? ) 60 40 20 0 -20 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 3.0 -40 80 v in = 24v sourcing 20ma error-amplifier open-loop gain and phase vs. frequency max16801 toc20 frequency (hz) gain (db) 10m 1m 10k 1k 100k 10 100 1 -80 -60 -20 -40 0 -70 20 60 40 80 100 120 -100 phase (degrees) -150 -130 -90 -110 -50 -10 -30 10 30 50 -170 0.1 100m gain phase typical operating characteristics (continued) (v uvlo/en = +1.4v, v fb = +1v, comp = unconnected, v cs = 0v, t a = +25c, unless otherwise noted.) pin name function 1 uvlo/en externally programmable undervoltage lockout. uvlo programs the input start voltage. connect uvlo to gnd to disable the device. 2 dim/fb low-frequency pwm dimming input/error-amplifier inverting input 3 comp error-amplifier output. connect the compensation components between dim/fb and comp in high- accuracy led current regulation. 4cs current-sense connection for current regulation. connect to high side of sense resistor. an rc filter may be necessary to eliminate leading-edge spikes. 5 gnd power-supply ground 6 ndrv external n-channel mosfet gate connection 7v cc gate-drive supply. internally regulated down from in. decouple with a 10nf or larger capacitor to gnd. 8in ic supply. decouple with a 10nf or larger capacitor to gnd. for bootstrapped operation (max16801), connect a startup resistor from the input supply line to in. connect the bias winding supply to this point (see figure 5). for the max16802, connect in directly to a +10.8v to +24v supply.
when in the bootstrapped mode with a transformer (figure 5), the circuit is protected against most output short-circuit faults when the tertiary voltage drops below +10v, causing the uvlo to turn off the gate drive of the external mosfet. this re-initiates a startup sequence with soft-start. when the led current needs to be tightly regulated, an internal error amplifier with 1% accurate reference can be used (figure 9). this additional feedback minimizes the impact of passive circuit component variations and tolerances, and can be implemented with a minimum number of additional external components. a wide dimming range can be implemented using a low-frequency pwm dimming signal fed directly to the dim/fb pin. led driver circuits designed with the max16801 use a high-value startup resistor r1 that charges a reservoir capacitor c1 (figure 5 or figure 9). during this initial period, while the voltage is less than the internal boot- strap uvlo threshold, the device typically consumes only 45a of quiescent current. this low startup current and the large bootstrap uvlo hysteresis help minimize the power dissipation across r1, even at the high end of the universal ac input voltage. an internal shutdown circuit protects the device when- ever the junction temperature exceeds +130c (typ). dimming linear dimming can be implemented by creating a summing node at cs, as shown in figures 6 and 7. low-frequency pwm (chopped-current) dimming is possible by applying an inverted-logic pwm signal to the dim/fb pin of the ic (figure 8). this might be a pre- ferred way of dimming in situations where it is critical to retain the light spectrum unchanged. it is accom- plished by keeping constant the amplitude of the chopped led current. max16801/max16802 biasing implement bootstrapping from the transformer when it is present (figure 5). biasing can also be realized directly from the leds in non-isolated topologies (figure 1). bias the max16802 directly from the input voltage of 10.8vdc to 24vdc. the max16802 can also be used MAX16801A/b/max16802a/b offline and dc-dc pwm controllers for high-brightness led drivers _______________________________________________________________________________________ 7 max16801b ac in bridge rectifier c1 r1 r5 r6 r2 q1 r3 r4 c4 d3 l1 v cc ndrv comp dim/fb uvlo/en in gnd c2 c3 cs total led voltage: 11v to 23v figure 1. biasing the ic using leds in nonisolated flyback driver
in applications with higher input dc voltages by imple- menting resistor-zener bias (figure 2a) or transistor- zener-resistor bias (figure 2b). max16801/max16802 undervoltage lockout the max16801/max16802 have an input voltage uvlo/en pin. the threshold of this uvlo is +1.28v. before any operation can commence, the voltage on this pin has to exceed +1.28v. the uvlo circuit keeps the cpwm comparator, ilim comparator, oscillator, and output driver in shutdown to reduce current con- sumption (see the functional diagram ). use this uvlo function to program the input start voltage. calculate the divider resistor values, r2 and r3 (figure 5), by using the following formulas: the value of r3 is calculated to minimize the voltage- drop error across r2 as a result of the input bias cur- rent of the uvlo/en pin. v ulr2 = +1.28v, i uvlo = 50na (max), v in is the value of the input-supply voltage where the power supply must start. where i uvlo is the uvlo/en pin input current, and v ulr2 is the uvlo/en wake-up threshold. max16801 bootstrap undervoltage lockout in addition to the externally programmable uvlo func- tion offered in both the max16801/max16802, the max16801 has an additional internal bootstrap uvlo that is very useful when designing high-voltage led drivers (see the functional diagram ). this allows the device to bootstrap itself during initial power-up. the max16801 attempts to start when v in exceeds the bootstrap uvlo threshold of +23.6v. during startup, the uvlo circuit keeps the cpwm comparator, ilim comparator, oscillator, and output driver shut down to reduce current consumption. once v in reaches +23.6v, the uvlo circuit turns on both the cpwm and ilim comparators, as well as the oscillator, and allows the output driver to switch. if v in drops below +9.7v, the uvlo circuit will shut down the cpwm comparator, ilim comparator, oscillator, and output driver thereby returning the max16801 to the startup mode. max16801 startup operation in isolated led driver applications, v in can be derived from a tertiary winding of a transformer. however, at startup there is no energy delivered through the trans- former. therefore, a special bootstrap sequence is required. figure 3 shows the voltages on in and v cc during startup. initially, both v in and v cc are 0v. after the line voltage is applied, c1 charges through the startup resistor r1 to an intermediate voltage. at this point, the internal regulator begins charging c2 (see figure 5). the max16801 uses only 45a of the current supplied by r1, and the remaining input current charges c1 and c2. the charging of c2 stops when the v cc voltage reaches approximately +9.5v, while the voltage across c1 continues rising until it reaches r vv v r in ulr ulr 23 2 2 = ? r vv ivv ulr in uvlo in ulr 3 500 2 2 ? () ? MAX16801A/b/max16802a/b offline and dc-dc pwm controllers for high-brightness led drivers 8 _______________________________________________________________________________________ in vdc r d (a) max16802a in vdc q r dc (b) max16802a figure 2. (a) resistor-zener and (b) transistor-zener-resistor bias arrangements
the wake-up level of +23.6v. once v in exceeds the bootstrap uvlo threshold, ndrv begins switching the mosfet and transfers energy to the secondary and tertiary outputs. if the voltage on the tertiary output builds to a value higher than +9.7v (the bootstrap uvlo lower threshold), then startup has been accom- plished and sustained operation commences. if v in drops below +9.7v before startup is complete, the device goes back to low-current uvlo. in this case, increase c1 in order to store enough energy to allow for the voltage at the tertiary winding to build up. soft-start the max16801/max16802 soft-start feature allows the led current to ramp up in a controlled manner. soft- start begins after uvlo deasserts. the voltage applied to the noninverting node of the amplifier ramps from 0 to +1.23v over a 60ms soft-start timeout period. figure 4 shows a typical 0.5a output current during startup. note the staircase increase of the led current. this is a result of the digital soft-starting technique used. unlike other devices, the reference voltage to the internal amplifier is soft-started. this method results in superior control of the led current. n-channel mosfet switch driver the ndrv pin drives an external n-channel mosfet. the ndrv output is supplied by the internal regulator (v cc ), which is internally set to approximately +9.5v. for the universal input voltage and applications with a transformer, the mosfet used must be able to with- stand the dc level of the high-line input voltage plus the reflected voltage at the primary of the transformer. for most offline applications that use the discontinuous flyback topology, this requires a mosfet rated at 600v. ndrv can source/sink in excess of the 650ma/1000ma peak current. select a mosfet that yields acceptable conduction and switching losses. internal error amplifier the max16801/max16802 include an internal error amplifier that can be used to regulate the led current very accurately. for example, see the nonisolated power supply in figure 5. calculate the led current using the following equation: where v ref = +1.23v. the amplifiers noninverting input is internally connected to a digital soft-start circuit that gradually increases the reference voltage during startup and is applied to this pin. this forces the led current to come up in an orderly and well-defined man- ner under all conditions. i v r led ref = 7 MAX16801A/b/max16802a/b offline and dc-dc pwm controllers for high-brightness led drivers _______________________________________________________________________________________ 9 100ms/div max16801 v in pin v cc 2v/div 0 5v/div figure 3. v in and v cc during startup when using the max16801 in bootstrapped mode 10ms/div 100ma/div 0 figure 4. typical current soft-start during initial startup
MAX16801A/b/max16802a/b offline and dc-dc pwm controllers for high-brightness led drivers 10 ______________________________________________________________________________________ applications information startup time considerations for high- brightness led drivers using max16801 the in bypass capacitor c1 supplies current immedi- ately after wake-up (figure 5). the size of c1 and the connection configuration of the tertiary winding deter- mine the number of cycles available for startup. large values of c1 increase the startup time but also supply gate charge for more cycles during initial startup. if the value of c1 is too small, v in drops below +9.7v because ndrv does not have enough time to switch and build up sufficient voltage across the tertiary wind- ing that powers the device. the device goes back into uvlo and does not start. use low-leakage capacitors for c1 and c2. assuming that offline led drivers keep typical startup times to less than 500ms even in low-line conditions (85vac input for universal offline applications), size the startup resistor r1 to supply both the maximum startup bias of the device (90a, worst case) and the charging current for c1 and c2. the bypass capacitor c2 must charge to +9.5v and c1 to +24v, all within the desired time period of 500ms. because of the internal 60ms soft-start time of the max16801, c1 must store enough charge to deliver current to the device for at least this much time. to cal- culate the approximate amount of capacitance required, use the following formula: where i in is the max16801s internal supply current after startup (1.4ma), q gtot is the total gate charge for q1, f sw is the max16801s switching frequency (262khz), v hyst is the bootstrap uvlo hysteresis (11.9v) and t ss is the internal soft-start time (60ms). for example: choose the 15f standard value. assuming c1 > c2, calculate the value of r1 as follows: where v in(min) is the minimum input supply voltage for the application, v suvr is the bootstrap uvlo wake-up level (+23.6v, max), and i start is the in supply current at startup (90a, max). for example, for the minimum ac input of 85v: choose the 120k ? standard value. choose a higher value for r1 than the one calculated above if longer startup time can be tolerated in order to minimize power loss on this resistor. the above startup method is applicable to a circuit sim- ilar to the one shown in figure 5. in this circuit, the ter- tiary winding has the same phase as the output windings. thus, the voltage on the tertiary winding at any given time is proportional to the output voltage and goes through the same soft-start period as the output voltage. the minimum discharge voltage of c1 from +22v to +10v must be greater than the soft-start time of 60ms. another method of bootstrapping the circuit is to have a separate bias winding than the one used for regulating the output voltage and to connect the bias winding so that it is in phase with the mosfet on time (see figure 9). in this case, the amount of capacitance required is much smaller. however, in this mode, the input voltage range has to be less than 2:1. another consideration is whether the bias winding is in phase with the output. if so, the led driver circuit hiccups and soft-starts under output short- circuit conditions. however, this property is lost if the bias winding is in phase with the mosfet on time. i vf ms ma r v c1 24 15 500 072 1 120 = () () () = = ? . 2 24 072 90 119 v ma a k .() + () = ? i vc ms r vv ii c suvr in min suvr c start 1 1 1 500 1 = () = ? + () ig nc khz ma c ma ma ms v f ()( ) . .. . = = = + () () () = 8 262 2 1 1 14 21 60 12 17 5 iq f c iit v g gtot sw in g ss hyst = = + () () 1
MAX16801A/b/max16802a/b offline and dc-dc pwm controllers for high-brightness led drivers ______________________________________________________________________________________ 11 max16801 v supply in v out v cc r1 r6 r5 c1 c2 c3 c4 leds q1 d1 t1 r7 r4 r3 d2 r2 cs ndrv comp gnd dim/fb uvlo/en gnd figure 5. offline, nonisolated, flyback led driver with programmable input-supply start voltage application circuits figure 5 shows an offline application of an hb led dri- ver using the max16801. the use of transformer t1 allows significant design flexibility. use the internal error amplifier for a very accurate led current control. figure 6 shows a discontinuous flyback led driver with linear dimming capability. the total led voltage can be lower or higher than the input voltage. figure 7 shows a continuous-conduction-mode hb led buck driver with linear dimming and just a few external components. figure 8 shows an offline isolated flyback hb led dri- ver with low-frequency pwm using max16801. the pwm signal needs to be inverted (see the functional diagram ). transformer t1 provides full safety isolation and operation from universal ac line (85vac to 265vac).
MAX16801A/b/max16802a/b offline and dc-dc pwm controllers for high-brightness led drivers 12 ______________________________________________________________________________________ ndrv gnd gnd cs c1 c2 c3 c4 led(s) r1 r3 r2 r5 q1 l1 1 2 8 7 in v in 10.8v to 24v dimming v cc dim/fb comp uvlo/en 3 4 6 5 max16802b r4 d1 figure 6. max16802 flyback hb led driver with dimming capability, 10.8v to 24v input voltage range ndrv gnd gnd cs c1 c2 c3 c4 led(s) r1 r3 r2 r4 r5 q1 d1 l1 1 2 8 7 in v in 10.8v to 24v dimming v cc dim/fb comp uvlo/en 3 4 6 5 max16802b figure 7. max16802 buck hb led driver with dimming capability, 10.8v to 24v input voltage range
MAX16801A/b/max16802a/b offline and dc-dc pwm controllers for high-brightness led drivers ______________________________________________________________________________________ 13 max16801b in v cc r1 optional only when pwm dimming is used c1 *pwm c2 c5 q1 d1 d3 t1 r4 r3 d2 leds r2 cs ndrv gnd dim/fb uvlo/en c3 c4 c6 bridge rectifier universal ac input * warning: pwm dimming signal is shown at the primary side. use an optocoupler for safety isolation of the pwm signal. figure 8. universal ac input, offline, isolated flyback hb led driver with low-frequency pwm dimming max16801 +v in in v out v cc r1 r6 r5 r7 c1 c2 c5 r10 r9 r8 r11 c3 z1 c4 q1 d1 t1 r4 u3 tlv431 r3 d3 r2 cs ndrv comp gnd dim/fb uvlo/en u2 opto trans u2 opto led gnd figure 9. universal input, offline, high-accuracy current regulation in an isolated flyback hb led driver
MAX16801A/b/max16802a/b offline and dc-dc pwm controllers for high-brightness led drivers 14 ______________________________________________________________________________________ functional diagram in uvlo comp fb s in reg_ok v cc v cc v l q r cs digital soft-start error amp reference 1.23v in clamp 26.1v cpwm *oscillator 264khz thermal shutdown lim 1.38v v cs 0.3v 21.6v 9.74v 1.28v 1.23v bootstrap uvlo** (internal 5.25v supply) regulator driver uvlo ndrv gnd *MAX16801A/max16802a: 50% maximum duty cycle max16801b/max16802b: 75% maximum duty cycle **max16801 only max16801 max16802 v opwm part bootstrap uvlo startup voltage (v) max duty cycle (%) MAX16801A yes 22 50 max16801b yes 22 75 max16802a no 10.8* 50 max16802b no 10.8* 75 * the max16802 does not have an internal bootstrap uvlo. the max16802 starts operation as long as the v cc pin is high- er than +7v, (the guaranteed output with an in pin voltage of +10.8v), and the uvlo/en pin is high. 1 2 8 7 3 4 6 5 max16801 max16802 uvlo/en top view in v cc ndrv gnd dim/fb comp cs max pin configuration selector guide
MAX16801A/b/max16802a/b offline and dc-dc pwm controllers for high-brightness led drivers ______________________________________________________________________________________ 15 package information for the latest package outline information and land patterns, go to www.maxim-ic.com/packages . note that a +, #, or - in the package code indicates rohs status only. package drawings may show a different suffix character, but the drawing pertains to th e package regardless of rohs status. package type package code document no. 8 max 21-0036
MAX16801A/b/max16802a/b offline and dc-dc pwm controllers for high-brightness led drivers maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 16 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ? 2010 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. revision history revision number revision date description pages changed 0 10/05 initial release 1 1/06 max16802aeua+ parts are available 1 2 1/10 corrected formulas, updated subscripts, and removed package outline 1, 2, 3, 6C14

▲Up To Search▲

Price & Availability of MAX16801A

	To Download MAX16801A Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .