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ht7939 high current and performance white led driver selection table part no. package marking ht7939 sot23-6 7939 rev 1.60 1 june 25, 2016 features input range from 2.6v~5.5v built-in power mosfet can drive up to 39 white leds with a 5v input low standby current: 0.1 a (typ.) with v en low integrated over-voltage, over-temperature and over-current protection circuits under voltage lock-out protection 1.2mhz fixed switching frequency high efficiency - up to 90% 6-pin sot23-6 package applications display backlighting automatic dvd player digital photo frame handheld computer led lighting general description the ht7939 is a high efficiency boost converter for driv - ing white leds using current mode operation. the de - vice is designed to drive up to 39 white leds from a 5v power supply. the white led current is setup using an external current setting resistor, which has a low feed- back voltage of 0.2v to minimise power losses in the re- sistor which improves efficiency. the over-voltage function prevents damage to the ic by turning off the converter when the led load is open circuit. the device includes over current protection, over tem - perature protection and under voltage protection pre - venting damage to the device when the output is overloaded.
block diagram pin assignment pin description pin no. pin name description 1 sw switching pin. internal power mosfet drain. connected to inductor and diode. 2 gnd signal ground. 3fb feedback pin. reference voltage. the ht7939 feedback voltage is 200mv. connect the sense resistor from fb to gnd to set the led current. calculate resistor value according to r mv i fb led = 200 . 4en shutdown & dimming control input. don t allow this pin to float. 5 ovp over voltage protection pin which is connected to the output. 6 vin input supply pin. the input supply pin for the ic. connect vin to a supply voltage between 2.6v~5.5v. ht7939 rev 1.60 2 june 25, 2016

absolute maximum ratings input voltage...........................................................6.0v sw voltage..............................................................38v fb voltage ..............................................................6.0v en ..........................................................................6.0v ovp voltage ............................................................38v operating temperature range ............. 40 cto+85 c storage temperature range .............. 55 c to +150c maximum junction temperature........................+150 c note: these are stress ratings only. stresses exceeding the range specified under absolute maximum ratings may cause substantial damage to the device. functional operation of this device at other conditions beyond those listed in the specification is not implied and prolonged exposure to extreme conditions may affect device reliability. electrical characteristics v in =5v, l=10 h, c1=c2=2.2 f, ta=25 c (unless otherwise specified) symbol parameter test conditions min. typ. max. unit v in input voltage 2.6 5.5 v uvlo under voltage lockout 1.8 2.1 2.4 v i in supply current switching 1.0 2.5 ma v en =0v 0.1 1.0 a error amplifier v fb feedback voltage 190 200 210 mv power switch f osc switching frequency measurement at sw pin 0.8 1.2 1.6 mhz dc maximum duty cycle 85 90 % r ds(on) sw on resistance 0.5 i sw(off) switch leakage current 0.1 1.0 a en pin v ih en voltage high v in =2.6v~5.5v 2.0 v v il en voltage low v in =2.6v~5.5v 0.8 v ovp and ocp v ovp ovp threshold no load 29 32 35 v i ocp n-channel mosfet current limit 1000 1200 ma thermal shutdown t shut thermal shutdown threshold 150 c thermal shutdown hysteresis 25 c ht7939 rev 1.60 3 june 25, 2016
ht7939 rev 1.60 4 june 25, 2016 function description vin under-voltage lockout uvlo the device contains an input under voltage lockout (uvlo) circuit. the purpose of the uvlo circuit is to en - sure that the input voltage is high enough for reliable op - eration. when the input voltage falls below the under voltage threshold, the internal fet switch is turned off. if the input voltage rises by the under voltage lockout hys - teresis, the device will restart. the uvlo threshold is set below the minimum input voltage of 2.6v to avoid any transient vin drops under the uvlo threshold and causing the converter to turn off. current limit protection the device has a cycle-by-cycle current limit to protect the internal power mosfet. if the inductor current reaches the current limit threshold, the mosfet will be turned off. it is import to note that this current limit will not protect the output from excessive current during an out - put short circuit. if an output short circuit has occurred, excessive current can damage both the inductor and di - ode. over-voltage protection ovp the device provides an over-voltage protection func - tion. if the fb pin is shorted to ground or an led is dis- connected from the circuit, the fb pin voltage will fall to zero and the internal power mosfet will switch with its full duty cycle. this may cause the output voltage to ex- ceed its maximum voltage rating, possibly damaging the ic and external components. internal over-voltage pro- tection circuitry turns off the power mosfet and shuts down the ic as soon as the output voltage exceeds the v ovp threshold. as a result, the output voltage falls to the level of the input supply voltage. the device remains in shutdown mode until the power is recycled. over-temperature protection otp a thermal shutdown is implemented to prevent dam - ages due to excessive heat and power dissipation. typically the thermal shutdown threshold is 150 c. when the thermal shutdown is triggered the device stops switching until the temperature falls below typi - cally 125 c. then the device starts switching again. application information inductor selection the selection of the inductor affects steady state op - eration as well as transient behavior and loop stability. there are three important electrical parameters which need to be considered when choosing an inductor: the value of inductor, dcr (copper wire resistance) and the saturation current. choose an inductor that can handle the necessary peak current without saturating, and ensure that the in - ductor has a low dcr to minimise power losses. a 10 h/22 h inductor should be a good choice for most ht7939 applications. however, a more exact induc - tance value can be calculated. a good rule for choosing an inductor value is to allow the peak-to-peak ripple current to be approximately 30~50% of the maximum input current. calculate the required inductance value using the following equation: in the equation above, i out(max) is the maximum load current,
i l is the peak-to-peak inductor ripple current, is the converter efficiency, f sw is the switching fre - quency and i l(peak) is the peak inductor current. output capacitor selection the output capacitor determines the steady state out- put voltage ripple. the voltage ripple is related to the capacitor s capacitance and its esr (equivalent se- ries resistance). a ceramic capacitor with a low esr value will provide the lowest voltage ripple and are therefore recommended. due to its low esr, the ca- pacitance value can be calculated by the equation: in the equation above, v ripple =peak to peak output rip - ple, f sw is the switching frequency. a1 f~10 f ceramic capacitor is suitable for most ap - plication. input capacitor selection an input capacitor is required to supply the ripple cur - rent to the inductor, while limiting noise at the input source. a low esr ceramic capacitors is required to keep the noise at the ic to a minimum. a 4.7 f~10 f ceramic capacitor is suitable for most application. this capacitor must be connected very close to the vin pin and inductor, with short traces for good noise performance. ! " #$" #! ! % & ' ( ! % & ' ! & ) ! % & ' ! % & ' * + , - . !
ht7939 rev 1.60 5 june 25, 2016 schottky diode selection the output rectifier diode conducts during the internal mosfet is turn off. the average and peak current rating must be greater than the maximum output cur - rent and peak inductor current. the reverse break - down voltage must be greater than the maximum output voltage. it is recommended to use a schottky diode with low forward voltage to minimize the power dissipation and therefore to maximize the efficiency of the converter. a 1n5819 type diode is recommended for ht7939 applications. led current selection the led current is controlled by the current sense feedback resistor r fb , the current sense feedback ref - erence voltage is 200mv. in order to have accurate led currents, precision resistors are the preferred type with a 1% tolerance. the led current can be cal - culated from the following formula. where i led is the total output led current, v fb =feed - back voltage, r fb =current sense resistor. digital and analog dimming control the led illumination level can be controlled using both digital and analog methods. the digital method uses a pwm signal applied to the en pin. this is shown in figure 13. the average led current increases proportionally with the pwm signal duty cycle. a 0% duty cycle corresponds to zero led current. a 100% duty cycle corresponds to full led current. the pwm signal frequency should be set be- low 1khz due to the delay time of device startup. there are two methods of analog led brightness con - trol. the first method uses a dc voltage to control the feedback voltage. if the dc voltage range is from 0v to 3.3v, the selection of resistors control the led cur - rent from 20ma to 0ma as shown in figure14. the other way is to use a filtered pwm signal, as shown in figure15. the filtered pwm signal application acts in the same way as the dc voltage dimming control. layout considerations circuit board layout is a very important consideration for switching regulators if they are to function properly. poor circuit layout may result in related noise problems. in order to minimize emi and switching noise, please fol - low the guidelines below: all tracks should be as wide as possible. the input and output capacitors, c1 and c2, should be placed close to the vin, vo and gnd pins. the schottky diode, d1, and inductor, l, must be placed close to the sw pin. feedback resistor, rfb, must be placed close to the fb and gnd pins. a full ground plane is always helpful for better emi performance. a recommended pcb layout with component locations is shown below. f b r f b r f b v l e d i 2 0 0 m v == top layer bottom layer
typical performance characteristics ht7939 rev 1.60 6 june 25, 2016 fig.1 efficiency vs input voltage fig.2 switching frequency vs input voltage fig.3 supply current vs input voltage fig.6 feedback voltage vs input voltage fig.5 feedback voltage vs input voltage fig.4 supply current vs input voltage fig.7 enable voltage vs input voltage fig.8 r ds(on) vs temperature
ht7939 rev 1.60 7 june 25, 2016 fig.10 open led protection fig.11 200hz pwm dimming waveform fig. 12 1khz pwm dimming waveform fig.9 switching waveform
application circuits ht7939 rev 1.60 8 june 25, 2016 1 # 3 3 $ 3 4 # 5 # 5 . 2 2 6 7 # $ 3 # 8 9 8 . 3 . 3 fig.14 application circuit for dimming control using a dc voltage # 8 9 8 . 3 1 # 3 . 3 3 $ 3 4 : ; # # ) ! & . : 1 % 1 ) & ! % 1 & & . : 1 % 1 ) & ! % 1 & & fig.12 application circuits for driving 39 wleds # 8 9 8 . 3 1 # 3 . 3 3 $ 3 4 % 7 6 < - fig.13 application circuit for dimming control using a pwm logic signal
ht7939 rev 1.60 9 june 25, 2016 1 # 3 3 # 4 # 2 & # 8 9 8 . 3 . 3 fig.16 application circuit for drive 3 high brightness leds 1 # 3 3 $ 3 4 # 5 %
7 6 < - # 5 # 3 # 5 3 # # 8 9 8 . 3 . 3 fig.15 application circuit for dimming control using a filtered pwm signal
package information ht7939 rev 1.60 10 june 25, 2016 note that the package information provided here is for consultation purposes only. as this information may be updated at regular intervals users are reminded to consult the holtek website for the latest version of the package/carton information . additional supplementary information with regard to packaging is listed below. click on the relevant section to be transferred to the relevant website page. ? further package information (include outline dimensions, product tape and reel specifications) ? packing meterials information ? carton information
6-pin sot23-6 outline dimensions symbol dimensions in inch min. nom. max. a 0.057 a1 0.006 a2 0.035 0.045 0.051 b 0.012 0.020 c 0.003 0.009 d 0.114 bsc e 0.063 bsc e 0.037 bsc e1 0.075 bsc h 0.110 bsc l1 0.024 bsc 08 symbol dimensions in mm min. nom. max. a 1.45 a1 0.15 a2 0.90 1.15 1.30 b 0.30 0.50 c 0.08 0.22 d 2.90 bsc e 1.60 bsc e 0.95 bsc e1 1.90 bsc h 2.80 bsc l1 0.60 bsc 08 ht7939 rev 1.60 11 june 25, 2016
ht7939 rev 1.60 12 june 25, 2016 copyright 2016 by holtek semiconductor inc. the information appearing in this data sheet is believed to be accurate at the time of publication. however, holtek assumes no responsibility arising from the use of the specifications described. the applications mentioned herein are used solely for the purpose of illustration and holtek makes no warranty or representation that such applications will be suitable without further modi - fication, nor recommends the use of its products for application that may present a risk to human life due to malfunction or otherwise. holtek s products are not authorized for use as critical com - ponents in life support devices or systems. holtek reserves the right to alter its products without prior notification. for the most up-to-date information, please visit our web site at http://www.holtek.com.tw.

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