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pwm control 1. 2 a step - down converter EC4304B e - cmos corp. ( www.ecmos.com.tw ) page 1 of 11 20 11 /1 0 /06 features ? wide input voltage range: 7v to 3 6 v ? led output current up to 1. 2 a ? soft - start ? single pin on/off and brightness control using dc voltage or pwm ? high efficiency ( up to 97%) ? up to 1mhz switching frequency ? typical 5% output current accurac y ? sot - 23, sot - 89 lead - free package . applications ? led/display back light driver ? lightings ? portable communication devices ? handheld electronics part number examples part no. package EC4304B n b2 r sot - 23 - 5 EC4304B n b 6 r sot - 89 - 5 general description the EC4304B is a continuous 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 device operates from an input supply between 7v and 3 6 v and provides an externally adjustable output current of up to 1. 2 a. depending upon supply voltage and external components, this can provide up to 42 watts of output power. the EC4304B includes the output switch and a high - side output current sensing circuit, which uses an external resistor to set the nominal average output current. 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 provide either a continuous or a gated output current. the pwm filter components are contained within the chip. the EC4304B is available in sot - 23, sot - 89 lead - free package. pin arrangement(top view) EC4304B n b 2 r EC4304B n b 6 r sot - 23 - 5 sot - 89 - 5
pwm control 1. 2 a step - down converter EC4304B e - cmos corp. ( www.ecmos.com.tw ) page 2 of 11 20 11 /1 0 /06 pin description symbo l sot - 23 sot - 89 description lx 1 1 drain of ndmos switch gnd 2 2 ground adj 3 3 multi - function on/off and brightness control pin: ? leave floating for normal operation.(vadj = vref = 1.25v giving nominal average output current ioutnom = 0.1/rs) ? drive with dc voltage ( 0v < vadj < 2.5v) to adjust output current from 0% to 200% of ioutnom ? drive with pwm signal from open - collector or open - drain transistor, to adjust output current. adjustment range 0% to 100% of ioutnom for f > 10khz and 0% to 100% of ioutnom for f < 500hz isens e 4 4 connect resistor rs from this pin to vin to define nominal average output current ioutnom = 0.1/rs vin 5 5 input voltage ( 7v to 30v). decouple to ground with 10uf or higher x7r ceramic capacitor close to device absolute maximum ratings parameter symbol value unit voltage on intput pin relative to gnd vin - 0.3 to +36 v isense pin voltage - 5 to +0.3 v adj and en pin voltage - 0.3 to +6 v operating temperature rang t a - 40 to +125 c maximum soldering temperature ( at leads, 10 sec) t lead 300 c storage temperature rang t s - 65 to +150 c power dissipation, pd @ ta = 25c sot - 23 0.35 w sot - 89 0.5 package thermal resistance, ja sot - 23 250 c/w sot - 89 200
pwm control 1. 2 a step - down converter EC4304B e - cmos corp. ( www.ecmos.com.tw ) page 3 of 11 20 11 /1 0 /06 electrical characteristics ( ta = - 40 to 85c unless otherwise noted. typical values are at ta =25c, vdd =12v) symbol description conditions min. typ. max unit v in input voltage 7 - 30 v v iru internal regulator start - up threshold v in rising 5.65 v v ird internal regulator shutdown v in falling 5.55 v i qoff quiescent supply current with output off en pin grounded 35 ua i qon quiescent supply current with output switching adj pin floating f = 250khz 1.8 5.0 ma 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 senth sense threshold hysteresis 15 % i sense i sense pin input current v sense =v in C 0.1 10 ua v ref internal reference voltage measured on adj pin with pin floating 1.25 v ? v ref / ? t temperature coefficient of v ref 50 ppm/k v adj external control voltage range on adj pin for dc brightness control* 0 2.5 v v ihen en input voltage hight 2 v v ilen en input voltage low 0.5 v r adj resistance between adj pin and v ref 0< v adj < 2.5v 200 kohm i lxm continuous lx switch current 1. 2 a r lx lx switch on resistance @ i lx = 1. 2 a 0.3 0.45 ohm i lxi lx switch leakage current 5 ua t tp thermal shutdown protect 160 c electrical characteristics ( continuous) d pwml duty cycle range of pwm signal applied to adj pin during low frequency pwm dimming mode pwm frequency<500hz pwm amplitude = v ref measured on adj pin 0.01 1 brightness control range 100:1 d pwmh duty cycle range of pwm signal applied to adj pin during high frequency pwm dimming mode pwm frequency>10khz pwm amplitude = v ref measured on adj pin 0.16 1 brightness control range 5:1 f lx operating frequency adj pin floating, l = 33uh ( 0.093 ohm) i out =1a @v led = 3.6v driving 1 led 280 khz t onmin minimum switch on time lx switch on 240 ** ns t offmin minimum switch off time lx switch off 200 ** ns t onminr recommended minimum switch 'on' time lx switch on 800 ns f lxmax recommended maximum operating frequency 1 mhz d lx recommended duty cycle range of output switch at f lxmax 0.3 0.7 t pd internal comparator propagation delay 50 ns
pwm control 1. 2 a step - down converter EC4304B e - cmos corp. ( www.ecmos.com.tw ) page 4 of 11 20 11 /1 0 /06 notes : *100% brightness corresponds to v adj = v adj(nom) = v ref . driving the adj pin above v ref will increase the v sense . threshold and output current proportionally. **parameters are not tested at production. parameters are guaranteed by design, characterization and process control. block diagram v c c v i n r s d 1 l e d l 1 l x c 1 4 . 7 u f v r e f . m n r 1 b u f f e r r 4 a d j - + - + d r i v e r e n v o l t a g e r e g u l a t o r i n t e r n a l r 2 v d d b a n d g a p o v e r t e m p . r 3 g n d
pwm control 1. 2 a step - down converter EC4304B e - cmos corp. ( www.ecmos.com.tw ) page 5 of 11 20 11 /1 0 /06 functional description the device, in conjunction with the coil ( l1) and current sense resistor ( rs), forms a selfoscillating continuous - mode buck converter. device operation operation can be best understood by assuming that the adj pin of the device is unconnected and the voltage on this pin ( v adj ) appears directly at the ( +) input of the comparator. when input voltage v in is first applied, the initial current in l1 and rs is zero and there is no output from the current sense circuit. under this condition, the ( - ) input to the comparator is at ground and its output is high. this turns mn on and switches the lx pin low, causing current to flow from v in to ground, via rs, l1 and the led(s). the current rises at a rate determined by v in and l1 to produce a voltage ramp ( v sense ) across rs. the supply referred voltage v sense is forced across internal resistor r1 by the current sense circuit and produces a proportional current in internal resistors r2 and r3. this produces a ground referred rising voltage at the ( - ) input of the comparator. when this reaches the threshold voltage ( v adj ) , the comparator output switches low and mn turns off. the comparator output also drives another nmos switch, which bypasses internal resistor r3 to provide a controlled amount of hysteresis. the hysteresis is set by r3 to be nominally 15% of v adj . when mn is off, the current in l1 continues to flow via d1 and the led(s) back to v in . the current decays at a rate determined by the led(s) and diode forward voltages to produce a falling voltage at the input of the comparator. when this voltage returns to vadj, the comparator output switches high again. this cycle of events repeats, with the comparator input ramping between limits of v adj 15%. switching thresholds with v adj = v ref , the ratios of r1, r2 and r3 define an average v sense switching threshold of 100mv ( measured on the i sense pin with respect to v in ) . the average output current i out nom is then defined by this voltage and r s according to: i outnom = 100mv/r s nominal ripple current is 15mv/r s adjusting output current the device contains a low pass filter between the adj pin and the threshold comparator and an internal current limiting resistor ( 200kohn nom) between adj and the internal reference voltage. this allows the adj pin to be overdriven with either dc or pulse signals to change the vsense switching threshold and adjust the output current. the filter is third order, comprising three sections, each with a cut - off frequency of nominally 4khz. details of the different modes of adjusting output current are given in the applications section. output shutdown the output of the low pass filter drives the shutdown circuit. when the input voltage to this circuit falls below the threshold, the internal regulator and the output switch are turned off. the voltage reference remains powered during shutdown to provide the bias current for the shutdown circuit. quiescent supply current during shutdown is nominally 35ua and switch leakage is below 5ua.
pwm control 1. 2 a step - down converter EC4304B e - cmos corp. ( www.ecmos.com.tw ) page 6 of 11 20 11 /1 0 /06 applications information 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 0.066 ohm] 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 : rs ( ohm) 0.066 0.1 0.142 0.285 nominal average output current ( ma) 1500 1000 700 350 the above values assume that the adj pin is floating and at a nominal voltage of v ref ( =1.25v). note that rs = 0.066ohm 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. ( see next section) 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 . a d j + EC4304B d c g n d g n d the nominal average output current in this case is given by: i outdc = ( v adj /1.25) x ( 0.1v / rs), [for 0 < v adj <2.5v] note that 100% brightness setting corresponds to v adj = v ref . when driving the adj pin above 1.25v, rs must be increased in proportion to prevent i outdc exceeding 1.5a maximum. the input impedance of the adj pin is 200kohm 25%. output current adjustment by pwm control directly driving adj input a pulse width modulated ( pwm) signal with duty cycle dpwm can be applied to the adj pin, as shown below, to adjust the output current to a value above or below the nominal average value set by resistor rs: p w m v a d j 0 v a d j EC4304B g n d
pwm control 1. 2 a step - down converter EC4304B e - cmos corp. ( www.ecmos.com.tw ) page 7 of 11 20 11 /1 0 /06 driving the adj input via open collector transistor 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 below: p w m a d j EC4304B g n d this scheme uses the 200k resistor between the adj pin and the internal voltage reference as a pull - up resistor for the external transistor. driving the adj input 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: m c u a d j EC4304B g n d if the nmos transistor within the microcontroller has high drain / source capacitance, this arrangement can inject a negative spike into adj input of the EC4304B and cause erratic operation but the addition of a schottky clamp diode ( cathode to adj) to ground and inclusion of a series resistor ( 10k) will prevent this. see the section on pwm dimming for more details of the various modes of control using high frequency and low frequency pwm signals. shutdown mode taking the en pin to a voltage below 0.8v for more than approximately 100us, will turn off the output and supply current will fall to a low standby level of 35ua nominal.
pwm control 1. 2 a step - down converter EC4304B e - cmos corp. ( www.ecmos.com.tw ) page 8 of 11 20 11 /1 0 /06 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 47uf is acceptable if the input source is close to the device, but higher values will improve performance at lower input voltages, especially when the source impedance is high. in order to avoid high frequency noise influence and improve circuit stability, it is recommended to shunt a value of 0.22uf capacitor. the input capacitor should be placed as close as possible to the ic. for maximum stability over temperature and voltage, capacitors with x7r, x5r, or better dielectric are recommended. capacitors with y5v dielectric are not suitable for decoupling in this application and should not be used. inductor selection recommended inductor values for the EC4304B are in the range 33uh to 100uh. 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. the inductor should be mounted as close to the device as possible with low resistance connections to the lx and vin 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. lx switch on time : t on = l ?i / ( v in C v led - i avg ( r s +r l +r lx ) ) , note: t onmin > 240ns lx switch off time : t off = l ?i / ( v led + v d + i avg ( r s +r l ) ) , note: t offmin > 200ns where: l is the coil inductance ( h) ?i is the coil peak - peak ripple current ( a) {internally set to 0.3 x i avg } rl is the coil resistance ( ohm) r s is the current sense resistance i avg is the required led current ( a) v in is the supply voltage ( v) v led is the total led forward voltage ( v) r lx is the switch resistance ( ohm) {=0.3 ohm nominal} v d is the diode forward voltage at the required load current ( v)
pwm control 1. 2 a step - down converter EC4304B e - cmos corp. ( www.ecmos.com.tw ) page 9 of 11 20 11 /1 0 /06 typical application circuits v i n 7 v t o 3 6 v r s 0 . 1 o h m c 1 4 7 u f c 2 0 . 2 2 u f l e d * c 3 l 1 4 7 u h d 1 0 . 1 u f * c 4 1 0 0 0 p f v i n n c ad j ec4304 b g n d i s e n s e l x * note : when outputs the big current, the noise are big, this and the system environment and pcb layout have the influential, may defer to the actual need to increase the capacitor filtration noise.
pwm control 1. 2 a step - down converter EC4304B e - cmos corp. ( www.ecmos.com.tw ) page 10 of 11 20 11 /1 0 /06 package dimensions sot - 23 - 5 b b 1 b 2 a 1 a c 1 c c 2 f i d h g e symbol dimension in mm dimension in inch min. typ. max. min. typ. max. a 2.60 2.80 3.00 0.102 0.110 0.118 a1 1.40 1.575 1.60 0.055 0.062 0.063 b 2.70 2.85 3.00 0.106 0.112 0.118 b1 1.90 ( bsc) 0.075 ( bsc) b2 0.95 ( bsc) 0.037 ( bsc) c 0.95 1.20 1.45 0.037 0.047 0.057 c1 0.90 1.10 1.30 0.035 0.043 0.051 c2 0 0.075 0.150 0 0.003 0.06 d 0.40 0.015 e 0.30 0.45 0.60 0.012 0.018 0.023 f 0.08 0.15 0.22 0.003 0.006 0.009 g 0.60 ( ref) h 0~8 i 5~15 5~15
pwm control 1. 2 a step - down converter EC4304B e - cmos corp. ( www.ecmos.com.tw ) page 11 of 11 20 11 /1 0 /06 package dimensions sot - 89 d p o l i s h e d ( 2 x ) e h b 1 1 2 3 l c 10 '( 2 x ) b a e e 1 symbol dimension in mm dimension in inch min. max. min. max. a 1.40 1.60 0.055 0.063 b 0.44 0.56 0.017 0.022 b1 0.36 0.48 0.014 0.019 c 0.35 0.44 0.013 0.017 d 4.40 4.60 0.173 0.181 e 2.29 2.60 0.090 0.102 h 3.94 4.25 0.155 0.167 e 1.50 bsc 0.059 bsc e1 3.00 bsc 0.118 bsc l 0.89 1.2 0.035 0.047 *note : the thermal pad on the ics bottom has to be mounted on the copper foil. to eliminate the noise influence, the thermal pad is suggested to be connected to gnd on pcb. in addition, desired thermal conductivity will be improved, if a heat - conducting copper foil on pcb is soldered with thermal pad. the thermal pad enhances the power dissipation. as a result, a large amount of current can be sunk safely in one package.

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