RT9378 1 ds9378-03 april 2011 www.richtek.com ordering information note : richtek products are : ` rohs compliant and compatible with the current require- ments of ipc/jedec j-std-020. ` suitable for use in snpb or pb-free soldering processes. marking information for marking information, contact our sales representative directly or through a richtek distributor located in your area. 4 chs 100ma x1/x1.5/x2 charge pump white led driver general description the RT9378 is a 4 ch wled driver with auto mode selection of x1, x1.5 and x2 mode with low dropout voltage in current sources. the RT9378 can power up to 4 white leds with regulated constant current for uniform intensity. each channel (led1 to led4) can support up to 25ma. the part maintains highest efficiency by utilizing x1/x1.5/ x2 fractional charge pump and low dropout current regulators. for the brightness control, user can easily use a pwm signal generated from gpio to control the brightness of wleds. the RT9378 is available in a wqfn-12l 2x2 package. small 0.22 f capacitors can be used for fly capacitors. it provides the best backlighting solution with high efficiency and smallest board space for portable app lication. features z z z z z efficiency up to 93% over li-ion battery discharge z z z z z typical 85% average efficiency over li-ion battery discharge z z z z z support up to 4 white leds z z z z z support up to 25ma/per channel z z z z z support up to 100ma output current z z z z z pwm brightness control z z z z z 60mv typical current source dropout z z z z z 1% typical led current accuracy z z z z z 0.7% typical led current matching z z z z z automatic x1/x1.5/x2 charge pump mode transition z z z z z low input noise and emi charge pump z z z z z 5v over voltage protection z z z z z power on/mode transition in-rush protection z z z z z 1mhz switching frequency z z z z z 0.4 a low shutdown current z z z z z rohs compliant and halogen free applications z camera phone, smart phone z white led backlighting pin configurations (top view) wqfn-12l 2x2 c1n led3 9 8 7 10 11 12 1 2 3 6 5 4 c1p gnd led1 led2 c2p vin en c2n vout led4 13 gnd typical application circuit package type qw : wqfn-12l 2x2 RT9378 lead plating system g : green (halogen free and pb free) c2n led4 vin c1p c1n c2p RT9378 en led3 led2 led1 6 5 7 8 9 1 0 vout 1f c out gnd 1 1 2 , e x p o s e d p a d ( 1 3 ) v in 2.8v to 4.5v pwm dimming c in 1f c fly2 0.22f c fly1 0.22f 3 1 1 2 4
RT9378 2 ds9378-03 april 2011 www.richtek.com function block diagram functional pin description pin no. pin name pin function 1 c1n fly capacitor 1 negative connection. 2 13 (exposed pad) gnd ground pin. the exposed pad must be soldered to a large pcb and connected to gnd for maximum power dissipation. 3 c1p fly capacitor 1 positive connection. 4 c2p fly capacitor 2 positive connection. 5 vin power input. 6 en chip enable (active high). 7 led1 current sink for led1. (if not in use, connect this pin to vin) 8 led2 current sink for led2. (if not in use, connect this pin to vin) 9 led3 current sink for led3. (if not in use, connect this pin to vin) 10 led4 current sink for led4. (if not in use, connect this pin to vin) 11 vout charge pump output. 12 c2n fly capacitor 2 negative connection. en led1 led4 led2 led3 1mhz osc pwm dimming controller soft start circuit current source shutdown delay vin vout gate driver uvlo ovp min vds + - c1p c2p c2n c1n mode decision current bias vr1 gnd 2a
RT9378 3 ds9378-03 april 2011 www.richtek.com absolute maximum ratings (note 1) z supply input voltage, v in ------------------------------------------------------------------------------------------------ ? 0.3v to 5v z output voltage, v out ----------------------------------------------------------------------------------------------------- ? 5v to 0.3v z power dissipation, p d @ t a = 25 c wqf n-12l 2x2 ------------------------------------------------------------------------------------------------------------ 0.606w z package thermal resistance (note 2) wqfn-12l 2x2, ja ------------------------------------------------------------------------------------------------------- 165 c/w z junction temperature ----------------------------------------------------------------------------------------------------- 150 c z lead temperature (soldering, 10 sec.) ------------------------------------------------------------------------------- 260 c z storage temperature range -------------------------------------------------------------------------------------------- ? 65 c to 150 c z esd susceptibility (note 3) hbm (human body mode) ---------------------------------------------------------------------------------------------- 2kv mm (ma chine mode) ------------------------------------------------------------------------------------------------------ 200v electrical characteristics (v in = 3.6v, v f = 3.5v, c in = c out = 1 f, c fly1 = c fly2 = 0.22 f, i led1 to led4 = 15ma, t a = 25 c, unless otherwise specified) parameter symbol test conditions min typ max unit input power supply input supply voltage v in 2.8 -- 4.5 v under-voltage lockout threshold v uvlo v in rising 1.8 2 2.5 v under-voltage lockout hysteresis v uvlo -- 100 -- mv quiescent current i q x1 mode -- 1 2 ma shutdown current i shdn v in = 4.5v -- 0.4 2 a led current i ledx accuracy i ledx = 25ma ? 5 0 5 % current matching i ledx = 25ma ? 2 0 2 % charge pump oscillator frequency f osc -- 1 -- mhz pwm dimming frequency minimum turn on > 20 s 1 -- 4 khz mode decision x1 mode to x2 mode transition voltage (v in falling) i out = 1 00ma, i ledx = 25ma -- 3.6 3.8 v mode transition hystersis i out = 1 00ma, i ledx = 25ma -- 200 -- mv protection function ovp v in ? v out -- 5 -- v recommended operating conditions (note 4) z junction temperature range -------------------------------------------------------------------------------------------- ? 40 c to 125 c z ambient temperature range -------------------------------------------------------------------------------------------- ? 40 c to 85 c to be continued
RT9378 4 ds9378-03 april 2011 www.richtek.com note 1. stresses listed as the above "absolute maximum ratings" may cause permanent damage to the device. these are for stress ratings. functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may remain possibility to affect device reliability. note 2. ja is measured in the natural convection at t a = 25 c on a low effective single layer thermal conductivity test board of jedec 51-3 thermal measurement standard. the case point of jc is on the exposed pad for the wqfn package. note 3. devices are esd sensitive. handling precaution is recommended. note 4. the device is not guaranteed to function outside its operating conditions. parameter symbol test conditions min typ max unit enable en low time for shutdown 3 -- -- ms logic-low v il -- -- 0.2 v en threshold voltage logic-high v ih 1 -- -- v en pull low current -- 2 -- a
RT9378 5 ds9378-03 april 2011 www.richtek.com shutdown current vs. input voltage 0 0.2 0.4 0.6 0.8 1 1.2 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 input voltage (v) shutdown current ( a) 1 efficiency vs. input voltage 0 10 20 30 40 50 60 70 80 90 100 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 input voltage (v) efficiency (%) led current vs. input voltage 15 16.5 18 19.5 21 22.5 24 25.5 27 28.5 30 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 input voltage (v) led current (ma) typical operating characteristics v in = 3.7v time (100 s/div) c2p (2v/div) v out (2v/div) en (5v/div) i in (200ma/div) x1 mode inrush current response led1 led2 led3 led4 led v f = 3.42v led v f = 3.42v x1 mode quiescent current vs. input voltage 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 input voltage (v) quiescent current (ma ) x2 mode quiescent curr ent vs. input voltage 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25 3.5 3.75 4 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 input voltage (v) quiescent current (ma )
RT9378 6 ds9378-03 april 2011 www.richtek.com v in = 2.8v x2 mode inrush current response time (100 s/div) c2p (2v/div) v out (2v/div) en (5v/div) i in (200ma/div) v in = 3.1v x1.5 mode inrush current response time (100 s/div) c2p (2v/div) v out (2v/div) en (5v/div) i in (200ma/div) v in = 3.7v x1 mode dimming operation time (1ms/div) en (2v/div) i led (10ma/div) ripple & spike c2p (5v/div) v out (20mv/div) v in (50mv/div) i in (100ma/div) time (1 s/div) v in = 3.2v
RT9378 7 ds9378-03 april 2011 www.richtek.com applications information the RT9378 uses a fractional switched capacitor charge pump to power up to four white leds with a programmable current for uniform intensity. the part integrates current sources and automatic mode selection charge pump. it maintains the high efficiency by utilizing an x1/x1.5/x2 fractional charge pump and current sources. the small equivalent x1 mode open loop resistance and ultra-low dropout voltage of current source extend the operating time of x1 mode and optimize the efficiency in white led applications. input uvlo the input operating voltage range of the led driver is from 2.8v to 4.5v. an input capacitor at the vin pin could reduce ripple voltage. it is recommended to use a ceramic 1 f or larger capacitance as the input capacitor. this RT9378 provides an under voltage lockout (uvlo) function to prevent it from unstable issue when startup. the uvlo threshold of input rising voltage is set at 2v typically with a hysteresis of 100mv. soft start the charge pump employs a soft-start feature to limit the inrush current. the soft-start circuit prevents the excessive inrush current and input voltage droop. the soft-start clamps the input current over a typical period of 50 s. mode decision the RT9378 uses a smart mode selection method to decide the working mode for optimizing the efficiency. mode decision circuit senses the output and led voltage for up/down selection. the RT9378 automatically switches to x1.5 or x2 mode whenever the dropout condition is detected from the current source and returns to x1 mode whenever the dropout condition releases. led connection the RT9378 supports up to 4 white leds. the 4 leds are connected from vin to pin7, 8, 9, and 10 respectively. if the led is not used, the led pin should be connected to vin directly. capacitor selection to get the better performance of the RT9378, the selection of peripherally appropriate capacitor and value is very important. these capacitors determine some parameters such as input/output ripple voltage, power efficiency and maximum supply current by charge pump. to reduce the input and output ripple effectively, the low esr ceramic capacitors are recommended. for led driver applications, the input voltage ripple is more important than output ripple. input ripple is controlled by input capacitor cin, increasing the value of input capacitance can further reduce the ripple. practically, the input voltage ripple depends on the power supply impedance. the flying capacitor cfly1 and cfly2 determine the supply current capability of the charge pump to influence the overall efficiency of the system. the lower value will improve efficiency. howere, it will limit the led ? s current at low input voltage. for 4 x25ma load over the entire input ra nge of 2.8v to 4.5v, it is recommended to use a 0.22 f ceramic capacitor on the flying capacitor cfly1 and cfly2. brightness control the RT9378 implements a pwm dimming method to control the brightness of white leds. when an external pwm signal is connected to the en pin, brightness of white led is adjusted by the duty cycle. the suggest pwm dimming frequency is 1khz to 4khz and the pwm minimum turn on time must be >20 s. figure 1. application circuit for one channel disabled c2n led4 vin c1p c1n c2p RT9378 en led3 led2 led1 c fly2 0.22f c fly1 0.22f 6 3 5 1 1 2 4 7 8 9 1 0 c in 1f vout 1f c out gnd 1 1 2 , e x p o s e d p a d ( 1 3 ) v bat 2.8v to 4.5v pwm dimming
RT9378 8 ds9378-03 april 2011 www.richtek.com layout considerations the RT9378 is a high-frequency switched-capacitor converter. careful pcb layout is necessary. for best performance, place all peripheral components as close to the ic as possible. place cin, cout, cfly1, and cfly2 near to vin, vout, cp1, cn1, cp2, cn2, and gnd pin respectively. a short connection is highly recommended. the following guidelines should be strictly followed when designing a pcb layout for the RT9378. ` the exposed gnd pad must be soldered to a large ground plane for heat sinking and noise prevention. the throughhole vias located at the exposed pad is connected to ground plane of internal layer. ` vin traces should be wide enough to minimize inductance and handle the high currents. the trace running from battery to chip should be placed carefully and shielded strictly. ` input and output capacitors must be placed close to the part. the connection between pins and capacitor pads should be copper traces without any through-hole via connection. ` the flying capacitors must be placed close to the part. the traces running from the pins to the capacitor pads should be as wide as possible. long traces will also produce large noise radiation caused by the large dv/dt on these pins. short trace is recommended. ` all the traces of led and vin running from pins to lcm module should be shielded and isolated by ground plane. the shielding prevents the interference of high frequency noise coupled from the charge pump. ` output capacitor must be placed between gnd and vout to reduce noise coupling from charge pump to leds. 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0 102030405060708090100110120 ambient temperature (c) maximum power dissipation (w) 1 figure 2. derating curves for RT9378 packages single layer pcb thermal considerations for continuous operation, do not exceed absolute maximum operation junction temperature. the maximum power dissipation depends on the thermal resistance of ic package, pcb layout, the rate of surroundings airflow and temperature difference between junction to ambient. the maximum power dissipation can be calculated by following formula : p d(max) = ( t j(max) ? t a ) / ja where t j(max) is the maximum operation junction temperature, t a is the ambient temperature and the ja is the junction to ambient thermal resistance. for recommended operating conditions specification of RT9378, the maximum junction temperature is 125 c. the junction to ambient thermal resistance ja is layout dependent. for wqfn-12l 2x2 packages, the thermal resistance ja is 165 c/w on the standard jedec 51-3 single layer thermal test board. the maximum power dissipation at t a = 25 c can be calculated by following formula : p d(max) = (125 c ? 25 c) / (165 c/w) = 0.606w for wqfn-12l 2x2 packages the maximum power dissipation depends on operating ambient temperature for fixed t j(max) and thermal resistance ja . for RT9378 packages, the figure 2 of derating curves allows the designer to see the effect of rising ambient temperature on the maximum power allowed.
RT9378 9 ds9378-03 april 2011 www.richtek.com c1n led3 9 8 7 10 11 12 1 2 3 6 5 4 c1p gnd led1 led2 c2p vin en c2n vout led4 13 gnd gnd battery c in c out output capacitor (c out ) should be placed close to v out and connected to grou nd plane to reduce noise coupling from charge pump to leds. input capacitor (c in ) should be placed close to v in and connected to ground pl ane. the trace of vin in the pcb should be placed far away the sensitive devices or shielded by the ground. the traces running from pins to flying capacitor should be short and wide to reduce parasitic resistance and prevent noise radiation. all the traces of led pins running from chip to leds should be wide and short to reduce the parasitic connection resistance. figure 2. pcb layout for RT9378
RT9378 10 ds9378-03 april 2011 www.richtek.com richtek technology corporation headquarter 5f, no. 20, taiyuen street, chupei city hsinchu, taiwan, r.o.c. tel: (8863)5526789 fax: (8863)5526611 information that is provided by richtek technology corporation is believed to be accurate and reliable. richtek reserves the ri ght to make any change in circuit design, specification or other related things if necessary without notice at any time. no third party intellectual property inf ringement of the applications should be guaranteed by users when integrating richtek products into any application. no legal responsibility for any said applications i s assumed by richtek. richtek technology corporation taipei office (marketing) 5f, no. 95, minchiuan road, hsintien city taipei county, taiwan, r.o.c. tel: (8862)86672399 fax: (8862)86672377 email: marketing@richtek.com outline dimension symbol dimensions in millimeters dimensions in inches min max min max a 0.700 0.800 0.028 0.031 a1 0.000 0.050 0.000 0.002 a3 0.175 0.250 0.007 0.010 b 0.150 0.250 0.006 0.010 d 1.900 2.100 0.075 0.083 e 1.900 2.100 0.075 0.083 e 0.400 0.016 d2 0.850 0.950 0.033 0.037 e2 0.850 0.950 0.033 0.037 l 0.250 0.350 0.010 0.014 w-type 12l qfn 2x2 package a a1 a3 d e 1 d2 e2 l b e see detail a 1 1 2 2 note : the configuration of the pin #1 identifier is optional, but must be located within the zone indicated. det ail a pin #1 id and tie bar mark options
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