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rt9907 preliminary 1 ds9907-07 august 2007 www.richtek.com features z z z z z 1.5v to 5.5v battery input voltage range z z z z z main step-up dc-dc converter ` ` ` ` ` 1.5v to 5.5v adjustable output voltage ` ` ` ` ` up to 90% efficiency ` ` ` ` ` 2.6a, 0.3 internal power switch z z z z z two step-down dc-dc converters ` ` ` ` ` 0.8v to 5.5v adjustable output voltage ` ` ` ` ` 94% efficiency ` ` ` ` ` 100% duty cycle z z z z z up to 1.4mhz switching frequency z z z z z 1 a supply current in shutdown mode z z z z z programmable soft start function z z z z z independent enable pin (ch1, ch2, ch3) z z z z z external compensation network (ch1, ch2, ch3) z z z z z short circuit protection (ch1, ch2, ch3) z z z z z over voltage protection (ch2) z z z z z 24-lead vqfn package z z z z z rohs compliant and 100% lead (pb)-free applications z digital still camera z pdas z portable device 3 channel dc/dc converters ic with high-efficiency step-up and step-down general description the rt9907 is a three channel power-supply solution for digital still cameras and other battery-powered devices. it integrates an asynchronous step-up and two synchronous step-down dc-dc converters. the rt9907 is targeted for applications that use two aa cells or a single lithium-ion battery. the three dc-dc converters (ch1, ch2, ch3) accept input voltage from 1.5v to 5.5v. each dc-dc converter has better transient response and excellent stability by providing current-mode control and external compensation network. with built-in internal mosfet and up to 1.4mhz operating frequency, the rt9907 allows minimum bom cost and pcb area. the step-down dc-dc converters (ch2, ch3) can regulate output voltage as low as 0.8v. three operational modes are available: pwm, psm, low-dropout modes. at pwm mode, internal synchronous rectifier with low r ds(on) dramatically reduces conduction loss and achieve 94% efficiency. it enters low-dropout mode when normal pwm cannot provide regulated output voltage by continuously turning on the upper p-mosfet. no external schottky diode is required in practical application. each dc-dc converter has independent enable input and soft-start function allowing versatile power sequence combination. complete protection functions are implemented such as short circuit, over-voltage protection. the rt9907 is available in small vqfn-24l 4x4 package. pin configurations (top view) vqfn-24l 4x4 ordering information note : richtek pb-free and green 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. ` 100% matte tin (sn) plating. rt9907 package type qv : vqfn-24l 4x4 (v-type) operating temperature range p : pb free with commercial standard g : green (halogen free with commer- cial standard) comp3 vdd3 lx3 pgnd3 ss rt en1 enm vdd2 lx2 pgnd2 lx1 vdd1 gnd vddm fb1 pgnd1 comp1 en2 comp2 fb3 gnd en3 fb2 1 2 3 4 5 6 7 21 20 19 18 17 16 15 8 9 10 12 14 13 24 22 23 11 gnd 25
rt9907 preliminary 2 ds9907-07 august 2007 www.richtek.com typical application circuit figure 1. typical application circuit for 1-cell li+ battery 1-cell li+ battery 3.4v to 4.2v vdd3 enm fb3 en1 lx3 comp1 ss en3 en2 comp2 comp3 gnd vddm lx2 vdd2 fb1 vdd1 lx1 fb2 4.7 h 20k 10k 4.7nf 1nf 1nf 4.7 h 3.3v/500ma pgnd3 2 3 24 1 22 5 64 16 15 20 19 21 17 18 14 10 9 12 13 8 rt9907 rt 11 7, 23, exposed pad (25) pgnd2 pgnd1 680k 470k 100pf 150k 10 f x 4 v bat 10 f 5v/500ma 30k 1nf 100pf 200k 220k 4.7 h 1.5v/500ma v bat v bat 10 f x 4 10 f x 4 10 f 0.1 f 10 f x 2 10 f x 2 ss0520 130k chip enable 1 f
rt9907 preliminary 3 ds9907-07 august 2007 www.richtek.com figure 2. typical application circuit for 2-aa battery supply 2-aa battery 1.8v to 3.2v vdd3 enm fb3 en1 lx3 comp1 ss en3 en2 comp2 comp3 gnd vddm lx2 vdd2 fb1 vdd1 lx1 fb2 20k 10k 4.7nf 1nf 1nf 4.7 h 2.5v/300ma pgnd3 2 3 24 1 22 5 64 16 15 20 19 21 17 18 14 10 9 12 13 8 rt9907 rt 11 pgnd2 pgnd1 470k 470k 100pf 220k 10 f x 4 i/o 3.3v/500ma 30k 1nf 100pf 200k 220k 4.7 h 1.5v/300ma v bat 3.3v 10 f x 4 10 f x 4 10 f x 2 10 f x 2 ss0520 150k chip enable 10 f x 2 v bat 4.7 h 1 f 7, 23, exposed pad (25)
rt9907 preliminary 4 ds9907-07 august 2007 www.richtek.com function block diagram enm en1 en2 en3 ch1 ch2 ch3 0 x x x off off off 1 0 0 0 off off off 1 1 0 0 on off off 1 1 1 0 on on off 1 1 1 1 on on on soft-start osc pwm osc ch1 current-mode asynchronous step-up pwm boost ch2 current-mode synchronous step-down pwm buck2 ch3 current-mode synchronous step-down pwm buck3 ss rt vddm enm gnd vdd1 en1 lx1 fb1 comp1 pgnd1 vdd2 en2 lx2 fb2 comp2 pgnd2 vdd3 en3 lx3 fb3 comp3 pgnd3 thermal shutdown en
rt9907 preliminary 5 ds9907-07 august 2007 www.richtek.com pin no. pin name pin function 1 comp3 ch3 feedback compensation pin. 2 vdd3 ch3 power input pin. 3 lx3 ch3 switch node. drains of the internal p-mosfet and n-mosfet switches. connect an inductor to lx3 pins together as close as possible. 4 pgnd3 power ground for ch3. 5 ss sets the soft start interval of the conver ter. connect a capacitor from this pin to ground. 6 rt frequency setting resistor connection pin. frequency is 500khz if rt pin not connected 7, 23 gnd analog ground. 8 vddm device input power pin. 9 fb1 ch1 feedback input pin. 10 comp1 ch1 feedback compensation pin. 11 pgnd1 power ground for ch1 12 vdd1 ch1 power input pin. connect output of boost to this pin. 13 lx1 ch1 switch vode. connect an inductor to lx1 pins together as close as possible. 14 pgnd2 power ground for ch2. 15 lx2 ch2 switch node. drains of the internal p-channel and n-mosfet switches. connect an inductor to lx2 pins together as close as possible. 16 vdd2 ch2 power input pin. 17 enm whole device control pin. tie this pin higher than 1.3v to enable the device. tie below 0.4v to turn off the device. 18 en1 ch1 enable input. tie this pin higher than 1.3v to enable ch1. tie below 0.4v to turn off the ch1. 19 comp2 ch2 feedback compensation pin. 20 fb2 ch2 feedback input. 21 en2 ch2 enable input. tie this pin higher than 1.3v to enable ch2. tie below 0.4v to turn off the ch2. 22 en3 ch3 enable input. tie this pin higher than 1.3v to enable ch3. tie below 0.4v to turn off the ch3. 24 fb3 ch3 feedback input. exposed pad (25) gnd the exposed pad must be soldered to a large pcb and connected to gnd for maximum power dissipation. functional pin description
rt9907 preliminary 6 ds9907-07 august 2007 www.richtek.com electrical characteristics (v ddm =3.3v, t a = 25 c, unless otherwise specification) to be continued parameter symbol test condition min typ max units supply voltage minimum startup voltage (boost) v st boost loading < 1ma -- 1.5 -- v vddm operating voltage v vddm vddm pin voltage 2.4 -- 5.5 v vdd1, vdd2, vdd3 operating voltage v vdd1 v vdd2 , v vdd3 vdd1, vdd2, vdd3 pin voltage 1.5 5.5 v vddm over voltage protection -- 6.5 -- v supply current shutdown supply current i off v enm pin=0v -- 0.01 1 a ch1 dc/dc converter i vddm v vddm = 3.3v, v fb1 = 0.9v v enm = 3.3v, v en1 = 3.3v, v en2 = 0v, v en3 = 0v -- 250 350 a ch2 dc/dc converter supply current i vddm v vddm = 3.3v, v fb2 = 0.9v v enm = 3.3v, v en1 = 0v, v en2 = 3.3v, v en3 = 0v -- 250 350 a ch3 dc/dc converter supply current i vddm v vddm = 3.3v, v fb3 = 0.9v v enm = 3.3v, v en1 = 0v, v en2 = 0v, v en3 = 3.3v -- 250 350 a absolute maximum ratings (note 1) z supply input voltage, v ddm , v dd1 , v dd2 ,v dd3 ------------------------------------------------------------------------------------------ ? 0.3 to 7v z lx1 pin switch voltage ------------------------------------------------------------------------------------------ ? 0.3v to 7v z lx2 pin switch voltage ------------------------------------------------------------------------------------------ ? 0.3v to (v dd2 + 0.3v) z lx3 pin switch voltage ------------------------------------------------------------------------------------------ ? 0.3v to (v dd3 + 0.3v) z other i/o pin voltage --------------------------------------------------------------------------------------------- ? 0.3v to (v ddm + 0.3v) z power dissipation, p d @ t a = 25 c vqfn-24l 4x4 ----------------------------------------------------------------------------------------------------- 1.85w z package thermal resistance (note 3) vqfn-24l 4x4, ja ------------------------------------------------------------------------------------------------ 54 c/w z junction temperature range ------------------------------------------------------------------------------------ 0 c to 125 c z lead temperature (soldering, 10 sec.) ------------------ ----------------------------------------------------- 260 c z operation temperature range ---------------------------------------------------------------------------------- ? 40 c to 85 c z storage temperature range ------------------------------------------------------------------------------------ ? 65 c to 150 c z esd susceptibility (note 2) hbm (human body mode) -------------------------------------------------------------------------------------- 2kv mm (ma chine mode) ---------------------------------------------------------------------------------------------- 200v
rt9907 preliminary 7 ds9907-07 august 2007 www.richtek.com parameter symbol test condition min typ max units oscillator operation frequency range f osc rt open 475 550 625 khz ch1 maximum duty cycle d max1 -- 85 90 % ch2 maximum duty cycle d max2 -- -- 100 % ch3 maximum duty cycle d max3 -- -- 100 % feedback voltage (ch1, ch2, ch3) feedback voltage v fb ch1, ch2, ch3 0.788 0.8 0.812 v feedback voltage v fb ch1, ch2, ch3 3.0v < v ddm < 5.5v -- -- 12 mv error amplifier gm -- 0.2 -- ms compensation source current -- 22 -- a compensation sink current -- 22 -- a power switch ch1 on resistance of mosfet r ds(on) n-mosfet -- 300 400 m ch1 current limitation v vdd1 = 3.3v 2 2.6 3 a n-mosfet, v vdd2 = 3.3v -- 350 450 m ch2 on resistance of mosfet r ds(on) p-mosfet, v vdd2 = 3.3v -- 350 450 m ch2 current limitation v vdd2 = 3.3v 1.3 1.5 1.9 a n-mosfet, v vdd3 = 3.3v -- 350 450 m ch3 on resistance of mosfet r ds(on) p-mosfet, v vdd3 = 3.3v -- 350 450 m ch3 current limitation v vdd3 = 3.3v 1.3 1.5 1.9 a uvp (ch2, ch3) & over voltage protection (ch2) uvp threshold voltage @fb2, fb3 0.3 0.4 0.5 v over voltage protection @fb2 0.95 1 -- v control enm, en1, en2, en3 input high level threshold v vddm = 3.3v -- 0.8 1.3 v enm, en1, en2, en3 input low level threshold v vddm = 3.3v 0.4 0.8 -- v thermal protection thermal shutdown t sd 140 180 -- c thermal shutdown hysteresis t sd -- 10 -- c 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. devices are esd sensitive. handling precaution recommended. note 3. ja is measured in the natural convection at t a = 25 c on a low effective thermal conductivity test board of jedec 51-3 thermal measurement standard.
rt9907 preliminary 8 ds9907-07 august 2007 www.richtek.com typical operating characteristics oscillator ferquency vs. r rt 0 200 400 600 800 1000 1200 1400 1600 1800 0 100 200 300 400 500 600 r rt (k ? ) oscillator frequecny (khz) boost efficiency vs. output current 50 60 70 80 90 100 1 10 100 1000 output current (ma) efficiency (%) v out = 3.3v v in 3v 2.5v 2v 1.8v boost time (1ms/div) boost load transient response v in = 1.8v, v out = 3.3v, @i out = 100ma to 400ma output voltage deviation (100mv/div) load current (200ma/div) ( c) reference voltage vs. temperature 0.792 0.794 0.796 0.798 0.8 0.802 0.804 0.806 0.808 -50-30-101030507090 temperature reference voltage (v) boost output voltage vs. v ddm voltage 3.316 3.318 3.32 3.322 3.324 3.326 3.328 3.33 3.332 2.42.83.23.6 4 4.44.85.25.6 v ddm voltage (v) output voltage (v) v bat = 2.5v, v dd1 = 3.3v, i out = 250ma boost output voltage vs. v dd1 voltage 3.305 3.31 3.315 3.32 3.325 3.33 3.335 3.34 3.345 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v dd1 voltage (v) output voltage (v) v bat = 2.5v, v ddm = 3.3v, i out = 250ma
rt9907 preliminary 9 ds9907-07 august 2007 www.richtek.com time (1ms/div) boost load transient response v in = 2.5v, v out = 3.3v, @i out = 100ma to 400ma output voltage deviation (100mv/div) load current (200ma/div) time (1ms/div) boost load transient response v in = 2v, v out = 3.3v, @i out = 100ma to 400ma output voltage deviation (100mv/div) load current (200ma/div) boost lx & output ripple time (1us/div) v in = 1.8v, v out = 3.3v, @i out = 100ma lx 1 (2v/div) output ripple (10mv/div) boost lx & output ripple time (1us/div) v in = 2.5v, v out = 3.3v, @i out = 100ma lx 1 (2v/div) output ripple (10mv/div) boost lx & output ripple time (1us/div) v in = 1.8v, v out = 3.3v, @i out = 300ma lx 1 (2v/div) output ripple (10mv/div) time (1ms/div) boost load transient response v in = 3v, v out = 3.3v, @i out = 100ma to 400ma output voltage deviation (100mv/div) load current (200ma/div)
rt9907 preliminary 10 ds9907-07 august 2007 www.richtek.com buck2 efficiency vs. output current 30 40 50 60 70 80 90 100 1 10 100 1000 output current (ma) efficiency (%) v out = 2.5v v in = 4.5 v in = 3.8v v in = 3v buck2 efficiency vs. output current 50 60 70 80 90 100 1 10 100 1000 output current (ma) efficiency (%) v in = 4.5v v in = 3.8v v in = 3v v in = 2.5v v in = 2.2v v out = 1.5v buck2 efficiency vs. output current 50 60 70 80 90 100 1 10 100 1000 output current (ma) efficiency (%) v out = 1.8v v in = 4.5 v in = 3.8v v in = 3v v in = 2.5v boost lx & output ripple time (1us/div) v in = 2.5v, v out = 3.3v, @i out = 400ma lx 1 (2v/div) output ripple (10mv/div) boost lx & output ripple time (1us/div) v in = 3v, v out = 3.3v, @i out = 100ma lx 1 (2v/div) output ripple (10mv/div) boost lx & output ripple time (1us/div) v in = 3v, v out = 3.3v, @i out = 400ma lx 1 (2v/div) output ripple (10mv/div)
rt9907 preliminary 11 ds9907-07 august 2007 www.richtek.com time (1ms/div) buck2 load transient response v dd2 = 4.5v, v ddm = 3.3v, v out = 1.8v output voltage deviation (100mv/div) load current (200ma/div) @i out = 100ma to 400ma time (1ms/div) buck2 load transient response v dd2 = 3v, v ddm = 3.3v, v out = 1.8v output voltage deviation (100mv/div) load current (200ma/div) @i out = 100ma to 400ma time (1ms/div) buck2 load transient response v dd2 = 2.5v, v ddm = 3.3v, v out = 1.8v output voltage deviation (100mv/div) load current (200ma/div) @i out = 100ma to 400ma time (1ms/div) buck2 load transient response v dd2 = 3.8v, v ddm = 3.3v, v out = 1.8v output voltage deviation (100mv/div) load current (200ma/div) @i out = 100ma to 400ma buck2 output voltage vs. v dd2 voltage 1.804 1.806 1.808 1.81 1.812 1.814 1.816 1.818 1.82 2 2.5 3 3.5 4 4.5 v dd2 voltage (v) output voltage (v) v bat = v ddm = 3.3v, i out = 250ma buck2 output voltage vs. v ddm voltage 1.804 1.806 1.808 1.81 1.812 1.814 1.816 1.818 1.82 2 2.5 3 3.5 4 4.5 5 5.5 6 v ddm voltage (v) output voltage (v) v dd2 = 3.3v, i out = 250ma
rt9907 preliminary 12 ds9907-07 august 2007 www.richtek.com buck2 lx & output ripple time (500ns/div) v dd2 = 2.5v, v ddm = 3.3v, v out = 1.8v lx 2 (2v/div) output ripple (10mv/div) @i out = 250ma buck2 lx & output ripple time (500ns/div) v dd2 = 2.5v, v ddm = 3.3v, v out = 1.8v lx 2 (2v/div) output ripple (10mv/div) @i out = 500ma buck2 lx & output ripple time (500ns/div) v dd2 = 3v, v ddm = 3.3v, v out = 1.8v lx 2 (2v/div) output ripple (10mv/div) @i out = 250ma buck2 lx & output ripple time (500ns/div) v dd2 = 3v, v ddm = 3.3v, v out = 1.8v lx 2 (2v/div) output ripple (10mv/div) @i out = 500ma buck2 lx & output ripple time (500ns/div) v dd2 = 3.8v, v ddm = 3.3v, v out = 1.8v lx 2 (2v/div) output ripple (10mv/div) @i out = 250ma buck2 lx & output ripple time (500ns/div) v dd2 = 3.8v, v ddm = 3.3v, v out = 1.8v lx 2 (2v/div) output ripple (10mv/div) @i out = 500ma
rt9907 preliminary 13 ds9907-07 august 2007 www.richtek.com buck3 efficiency vs. output current 50 60 70 80 90 100 1 10 100 1000 output current (ma) efficiency (%) v out = 1.8v v in = 4.5v v in = 3.8v v in = 3v v in = 2.5v buck3 efficiency vs. output current 30 40 50 60 70 80 90 100 1 10 100 1000 output current (ma) efficiency (%) v out = 2.5v v in = 4.5v v in = 3.8v v in = 3v buck3 efficiency vs. output current 50 60 70 80 90 100 1 10 100 1000 output current (ma) efficiency (%) v out = 1.5v v in = 4.5v v in = 3.8v v in = 3v v in = 2.5v v in = 2.2v buck2 lx & output ripple time (500ns/div) v dd2 = 4.5v, v ddm = 3.3v, v out = 1.8v lx 2 (2v/div) output ripple (10mv/div) @i out = 500ma buck2 lx & output ripple time (500ns/div) v dd2 = 4.5v, v ddm = 3.3v, v out = 1.8v lx 2 (2v/div) output ripple (10mv/div) @i out = 250ma buck3 output voltage vs. v dd3 voltage 1.79 1.792 1.794 1.796 1.798 1.8 1.802 1.804 1.806 2 2.5 3 3.5 4 4.5 v dd3 voltage (v) output voltage (v) v bat = v ddm = 3.3v, i out = 250ma
rt9907 preliminary 14 ds9907-07 august 2007 www.richtek.com buck3 output voltage vs. v ddm voltage 1.79 1.792 1.794 1.796 1.798 1.8 1.802 1.804 1.806 2 2.5 3 3.5 4 4.5 5 5.5 6 v ddm voltage (v) output voltage (v) v dd3 = 3.3v, i out = 250ma time (1ms/div) buck3 load transient response v dd3 = 3v, v ddm = 3.3v, v out = 1.8v output voltage deviation (100mv/div) load current (200ma/div) @i out = 100ma to 400ma time (1ms/div) buck3 load transient response v dd3 = 4.5v, v ddm = 3.3v, v out = 1.8v output voltage deviation (100mv/div) load current (200ma/div) @i out = 100ma to 400ma buck3 lx & output ripple time (500ns/div) v dd3 = 2.5v, v ddm = 3.3v, v out = 1.8v @i out = 250ma lx 3 (2v/div) output ripple (10mv/div) time (1ms/div) buck3 load transient response v dd3 = 3.8v, v ddm = 3.3v, v out = 1.8v output voltage deviation (100mv/div) load current (200ma/div) @i out = 100ma to 400ma time (1ms/div) buck3 load transient response v dd3 = 2.5v, v ddm = 3.3v, v out = 1.8v output voltage deviation (100mv/div) load current (200ma/div) @i out = 100ma to 400ma
rt9907 preliminary 15 ds9907-07 august 2007 www.richtek.com buck3 lx & output ripple time (500ns/div) v dd3 = 2.5v, v ddm = 3.3v, v out = 1.8v lx 3 (2v/div) output ripple (10mv/div) @i out = 500ma buck3 lx & output ripple time (500ns/div) v dd3 = 3v, v ddm = 3.3v, v out = 1.8v lx 3 (2v/div) output ripple (10mv/div) @i out = 500ma buck3 lx & output ripple time (500ns/div) v dd3 = 3.8v, v ddm = 3.3v, v out = 1.8v lx 3 (2v/div) output ripple (10mv/div) @i out = 500ma buck3 lx & output ripple time (500ns/div) v dd2 = 4.5v, v ddm = 3.3v, v out = 1.8v lx 3 (2v/div) output ripple (10mv/div) @i out = 250ma buck3 lx & output ripple time (500ns/div) v dd3 = 3.8v, v ddm = 3.3v, v out = 1.8v lx 3 (2v/div) output ripple (10mv/div) @i out = 250ma buck3 lx & output ripple time (500ns/div) v dd3 = 3v, v ddm = 3.3v, v out = 1.8v lx 3 (2v/div) output ripple (10mv/div) @i out = 250ma
rt9907 preliminary 16 ds9907-07 august 2007 www.richtek.com buck3 lx & output ripple time (500ns/div) v dd2 = 4.5v, v ddm = 3.3v, v out = 1.8v lx 3 (2v/div) output ripple (10mv/div) @i out = 500ma
rt9907 preliminary 17 ds9907-07 august 2007 www.richtek.com application information the rt990 7 is a three-channel dc/dc converter with one voltage detector for digital still cameras and other hand- held device. the three chan nels dc/dc converters are as follows: ch1: step-up, asynchronous current mode dc/dc converter with an internal power mosfet, current limit protection and high efficiency control for wide loading range ch2: step-down, synchronous current mode dc/dc converter with internal power mosfets, current limit, short-circuit , over voltage protection and high efficiency control for wide loading range. ch3: step-down, synchronous current mode dc/dc converter with internal power mosfets, current limit, short-circuit protection and high efficiency control for wide loading range. soft-start ch1, ch2 and ch3 can be soft-started individually every time when the channel is enabled. soft-start is achieved by ramping up the voltage reference of each channel's input of error amplifier. adding a capacitor on ss pin to ground sets the ramping up speed of each voltage reference. triangle wave will be appeared on ss pin, which provides a clock base for soft-start. the soft-start timing would be setted by following formular. oscillator the internal oscillator synchronizes ch1, ch2 and ch3 pwm operation frequency. the operation frequency is set by a resistor between rt pin to ground, ranging from 550khz to 1.4mhz. step-up (boost) dc/dc converter (ch1) the step-up channel (ch1) is designed as current-mode dc/dc pwm converters with built-in internal power mos and external schottky diode. output voltage is regulated and adjustable up to 5.5v. this channel typically supplies 3.3v for main system power. at light load, efficiency is enhanced by pulse-skipping mode. in this mode, the nmos turns on by a constant pulse width. as loading increased, the converter operates at constant frequency pwm mode. the max. duty of the constant frequency is 80% for the boost to prevent high input current drawn from input. protection current limit the current of nmos is sensed cycle by cycle to prevent over current. if the current is higher than 2.6a (typical), then the nmos is off . this state is latched and then reset automatically at next clock cycle. under voltage the status of under voltage is decided by comparing fb1 voltage with 0.4v. this function is enabled after soft start finishes. if the fb1 voltage is less than 0.4v, then the nmos will be turned off immediately. and this state is latched. after a dummy count period, the controller begins a re-soft-start procedure. if the status of under voltage remain s after 4 successive times of soft-start, then ch1 is latched. over voltage the over voltage protection is used when the output of ch1 supplies the power of the main chip. if the output voltage of ch1 is over 6.5v, the main chip is shutdown and the nmos is kept off. step-down (buck) dc/dc converter (ch2, ch3) the step-down channels (ch2, ch3) are designed as synchronous current-mode dc/dc pwm converters. output voltage is regulated and adjustable down to 0.8v. the internal synchronous power switches eliminate the typical schottky free wheeling diode and improve efficiency. at light load, efficiency is enhanced by pulse-skipping mode. in this mode, the high-side pmos turns on by a constant pulse width. as loading increased, the converter operates at constant frequency pwm mode. while the input voltage is close to output voltage, the converter enters low dropout mode. duty could be as long as 100% to extend battery life. (ms) 1nf c x 10 t ss ss =
rt9907 preliminary 18 ds9907-07 august 2007 www.richtek.com protection current limit (ch2, ch3) the current of high-side pmos is sensed cycle by cycle to prevent over current. if the current is higher than 1.5a (typical), then the high-side pmos is off and the low-side nmos is on. this state is latched and then reset automatically at next clock cycle. under voltage (ch2, ch3) the status of under voltage is decided by comparing fb2 (or fb3) voltage with 0.4v. this function is enabled after soft start finishes. if the fb2 (or fb3) voltage is less than 0.4v, then the high/low-side power mos are turned off immediately. and this state is latched. after a dummy count period, the ch2 (or ch3) begins a soft-start procedure. however, if the status of under voltage remains after 3 successive times of soft-start, then ch2 (or ch3) is latched. uv remain after 3 successive soft-start how to reset? ch2 ch2 is latched, and whole ic is shut down toggle enm ch3 ch3 is latched toggle en3 or enm over voltage protection (ch2) over voltage protection (ovp) is used to protect the external parts connected to the output of ch2. if the fb2 voltage is higher than 1v, the high-side pmos is off and low-side nmos is on. this status is latched and could be reset by toggling enm. reference the chip has an internal 0.8v reference voltage, which is the inputs of the error amplifiers of the ch1, ch2, and ch3 to compare the difference of feedback voltage. the reference voltage can be set up stably when the supplied power (vddm) is above 1.5v, and en1 (or en2, en3) goes high. thermal protection thermal protection function is integrated in the chip. when the chip temperature is higher than 178 degree c, the controllers of ch1, ch2, and ch3 are shutdown. 10 degree c is the hysteresis range of temperature to prevent unstable operation when the thermal protection happens. when the thermal protection is relieved, the chip operates well again.
rt9907 preliminary 19 ds9907-07 august 2007 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 richtek technology corporation taipei office (marketing) 8f, no. 137, lane 235, paochiao road, hsintien city taipei county, taiwan, r.o.c. tel: (8862)89191466 fax: (8862)89191465 email: marketing@richtek.com outline dimension a a1 a3 d e d2 e2 l b e 1 see detail a dimensions in millimeters dimensions in inches symbol min max min max a 0.800 1.000 0.031 0.039 a1 0.000 0.050 0.000 0.002 a3 0.175 0.250 0.007 0.010 b 0.180 0.300 0.007 0.012 d 3.950 4.050 0.156 0.159 d2 2.300 2.750 0.091 0.108 e 3.950 4.050 0.156 0.159 e2 2.300 2.750 0.091 0.108 e 0.500 0.020 l 0.350 0.450 0.014 0.018 v-type 24l qfn 4x4 package 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 1 1 2 2

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