lin d oc #: 2172 description key features n 1.25a, 65v internal power switch n 3v - 25v input voltage range n current-mode operation n improved internal cycle-by-cycle current limiting n thermal shutdown n less than 10a quiescent current in microprocessor shutdown mode n external frequency synchronization possible n 100khz operating frequency the lx2172/73 are fixed-frequency, cur- rent-mode switching regulator integrated circuits. these ics contain all necessary control circuitry plus a 1.25a on-board transistor to design a complete dc:dc switching regulator with minimum exter- nal components. all functions are integrated into a single ic, available in 8-pin dip and soic or a 5-pin to-220 power package, making them extremely easy to design with and use. the lx2172/73 are optimized for boost and flyback applications, but can also be used in forward and inverting converter configuations. the lx2172 can be connected to an external clock for synchronization, and can enter micropower operation when the v c pin is pulled low. the lx2173 has an enable function, which permits extremely low micropower operation, consuming under 10a current when the enable pin is brought low. product highlight applications n boost converter n laptop / notebook computers n portable equipment n small motor applications n flyback converters 1.25a h igh -e fficiency 100 k h z s witching r egulator p reliminary d ata s heet t he i nfinite p ower of i nnova tion lx2172/73 note: all surface-mount packages are available in tape & reel. append the letter "t" to part number. (i.e. lx217xcdmt) package order information t a (c) plastic dip 8-pin 0 to 70 lx217xcm lx217xcdm lx217xcp m plastic soic 8-pin dm plastic to-220 5-pin p lx2172 sync input lx2173 low power mode (hi enable) part # pin 4 connections a vailable o ptions per p art # sepic c onverter u sing t he lx2172 input 6-24v, output 7v, 300ma = samples not yet available. l1 lx2172 d1 e 2 v c fb sync gnd v sw e 1 v in 1mh 1 2 3 4 8 7 6 5 u1 r 3 100 r 2 3.0k c 4 0.47f (see note 1) r 1 13.7k c 1 22f v in 6-24v dc c decouple 0.47f 1n5817 l2 1mh c out 220f 7v output 7v 300ma c 3 0.1f c 2 330f note 1: sync pin requirements: a) f max = 200khz b) ttl compatible level c) pulse width t p range - 0.1s < t p < 2.0s copyright ? 1998 rev. 0.4 12/98 1 11861 w estern a venue , g arden g rove , ca. 92841, 714-898-8121, f ax : 714-893-2570 l in f inity m icroelectronics i nc . note: for current data & package dimensions, visit our web site: http://www.linfinity.com.
1.25a h igh -e fficiency 100 k h z s witching r egulator lx2172/73 product databook 1996/1997 copyright ? 1998 rev. 0.4 12/98 2 p reliminary d ata s heet absolute maximum ratings (note 1) supply voltage (v in ) .................................................................................................... 25v collector supply voltage (v c ) ..................................................................................... 65v digital inputs (sync) ......................................................................................... -0.3 to 7v operating junction temperature ................................................................. 0c to 125c storage temperature range .................................................................... -65c to +150c solder temperature (soldering, 10 seconds) .......................................................... 300c package pin outs e 2 v sw e 1 v in gnd v c fb * sync / enable 1 8 27 36 45 m package (top view) dm package (top view) e 2 v sw e 1 v in gnd v c fb * sync / enable 1 8 27 36 45 note 1. exceeding these ratings could cause damage to the device. all voltages are with respect to ground. currents are positive into, negative out of the specified terminal. thermal data m package: thermal resistance-junction to ambient, q q q q q ja 95c/w dm package: thermal resistance-junction to ambient, q q q q q ja 165c/w p package: thermal resistance-junction to tab, q q q q q jt 4.5c/w thermal resistance-junction to ambient, q q q q q ja 60c/w junction temperature calculation: t j = t a + (p d x q ja ). the q ja numbers are guidelines for the thermal performance of the device/pc-board system. all of the above assume no ambient airflow. v in v sw gnd fb v c p package (top view) 1 5 tab is gnd * pin 4 = sync for lx2172, enable for lx2173/2174 5 1 3 2 7 6 8 v in gnd enable f b v c sync e1 e2 s w 100 kh z osc in 250m v 1.4v c.s. am p 0.16w 0.16w q1 q2 r s q q pw m com p pw m la tc h 0.15v s.d. com p e.a. 1.27v g m 1.4v enable com p en 2.3v v reg v reg uvlo com p en v in v in v o (n o t e 1 ) (n o t e 1 ) v ofs (0 .9 v ) v o 2.3v v reg slo pe co m p 100kh z note 1: lx2172 only: sync brought out to pin 4. enable is tied to v in . lx2173 only: enable brought out to pin 4. sync is open. block diagram
1.25a h igh -e fficiency 100 k h z s witching r egulator lx2172/73 product databook 1996/1997 3 copyright ? 1998 rev. 0.4 12/98 p reliminary d ata s heet electrical characteristics reference section parameter symbol test conditions initial accuracy v ref t j = 25oc, measured at fb pin over temperature, measured at fb pin line regulation 3v < v cc < 25v units lx2172 / 2173 min. typ. max. 1.224 1.244 1.264 v 1.214 1.244 1.274 v 0.03 % / v error amplifier section input bias current i b t j = 25oc; v fb = v ref over temperature open loop gain a vol transconductance g m t j = 25oc; v fb = v ref ; d i = 25a over temperature output sink current i ea (sink) output source current i ea (source) output hi voltage v comp-hi v fb = 1v output lo voltage v comp-lo v fb = 1.5v slew rate s 350 750 na 1100 na 500 1000 v / v 3000 4400 6000 mho 2400 7000 mho 120 200 a 120 a 1.8 2.1 2.3 v 0.2 0.3 0.52 v 2 v/sec (unless otherwise specified, these specifications apply over the ranges t a = 0 to 70oc for the lx217xc. v in = v c = 5v. all devices must be functional over junction temperature of -65c to 150c. typ. number represents t a = 25oc value.) input supply section start-up threshold normal mode quiescent current i q enable = hi, v c = 0.6v, i o = 0a v c shutdown threshold 3v < v in < v max , t j = 25c 3v < v in < v max , over temperature sleep mode current enable = hi, v c = 50mv enable = lo (lx2173 only) 2.2 2.7 2.9 v 58ma 100 150 260 mv 50 300 mv 100 a 5a oscillator section switching frequency f t a = 25oc over temperature line voltage stability v in = 3v to 25v 90 100 110 khz 85 100 115 khz 5 % output switch breakdown voltage i sw = 1.5ma output switch on resistance r on i o = 2a switch current limit i lim d.c = 50% 50% < d.c < 80% total switching loss (on time + off time) v in = 25v, d.c = 50%, i o = 1a, v sw = 60v 0.6 1.2 1.25 v 36 40 % 80 90 98 % e.a. output to pwm drive offset (vpwm) v ofs duty cycle = 0 minimum duty cycle maximum duty cycle 65 v 0.4 0.6 w 1.25 1.7 2.8 a 1.0 1.5 2.0 a 100 mw pwm section output drive section 100 ns 2a / v c.s. delay to driver output 10% over drive gbnt v c to output transconductance c.s. comparator section
1.25a h igh -e fficiency 100 k h z s witching r egulator lx2172/73 product databook 1996/1997 copyright ? 1998 rev. 0.4 12/98 4 p reliminary d ata s heet gnd 1 3 v c 21 fb 3 2 sync 4 enable 4 v in 55 e 1 6 v sw 74 e 2 8 signal ground. keep separate from power grounds (e 1 and e 2 ). output of transconductance error amplifier. an r-c compensation network is connected from this pin to the ground to stabilize the feedback loop. if this pin is pulled lower than 0.15v, the ic goes into micropower mode. error amplifier inverting input. a resistor divider from the output of the converter to this pin sets its nominal voltage. lx2172 only. this pin is used to synchronize the device directly with a logic level input pulse. external synchronization frequency must always be at a higher frequency than the minimum internal clock. when not used, should be left open. lx2173 only. this pin is the input to the enable comparator. a voltage under 1.4v will put the device in micropower mode. pin must be connected to v in when not in use. input supply voltage (3.0v to 25v). power return of first transistor (q 1 ). this pin must be connected to ground. collector of output transistors. connect to external inductor or input voltage, depending on circuit topology. grounding this pin sets the current limit point to the maximum value. if pin is left open, the current limit is set to half its maximum value. pin pin # pin # name (8-pin pkgs.) (5-pin to-220) description functional pin description functional pin description functional pin description functional pin description functional pin description electrical characteristics parameter symbol test conditions units lx2172 / 2173 min. typ. max. 0.2 2 sec 26v 0.7 v 100 400 a 15a sync pulse width sync input hi sync input lo sync input current hi input = 2v sync input current lo input = 0.4v sync input section (lx2172 only) 0.4 1.2 2.4 v 200 a 100 a enable input threshold hi input current input = 2.4v lo input current input = 0.4v enable section (lx2173 only)
1.25a h igh -e fficiency 100 k h z s witching r egulator lx2172/73 product databook 1996/1997 5 copyright ? 1998 rev. 0.4 12/98 p reliminary d ata s heet theory of operation ic operation referring to the block diagram, when v in is above the uvlo start threshold the 2.3v uvlo comparator output switches to low state, allowing q1 to turn on upon receiving a clock pulse from the internal 100khz oscillator. once q1 is on, current in the inductor ramps up. inductor current is then sensed, and amplified by a current sense amplifier and compared to a thresh- old set by the output of the error amplifier minus the offset voltage (v ofs typically 0.9v). this allows the pwm comparator to reset the flip flop, causing q1 to turn off. the oscillator then sets the flip flop, and the operation repeats itself. current limit current limiting is performed by sensing the peak switch cur- rent and turning q1 off until the next clock cycle. when the converter goes into current limit the error amplifier output goes to the rail and sets a maximum limit on the current. error amplifier the function of the error amplifier is to set a threshold voltage for inductor peak current and control the switch duty cycle so that the power supply output voltage is closely regulated. regu- lation is accomplished by sensing the output voltage and com- paring it to the internal 1.27v bandgap reference. a compensa- tion network is placed from the output of the amplifier to ground for closed loop stability purposes, as well as a high d.c. gain for tight regulation. the function of v ofs is to keep q1 off without requiring an error amplifier output to swing to ground level. it is required the v ol of the error amplifier is always less than the offset at all times. the transfer function between the error amplifier output (v c ) and peak inductor current is therefore given by: v c - v ofs = i p * g * r s where: i p = inductor peak current g = current sense gain (typically 6) r s = internal sense resistor oscillator the oscillator is designed to operate at 100khz frequency. its function is to turn the switch q1 on at a fixed 10s interval and to provide a slope compensation for the feedback loop. slope compensation is required for fixed frequency continuous cur- rent mode regulators operating above 50% duty cycle in order to prevent loop instability. the sync input is a logic input that allows easy synchronization to an external clock. synchroniza- tion is done such that the external clock terminates the cycle before the internal oscillator sets the pwm latch again. under-voltage lockout the 2.3v internal regulator is monitored as the input supply ramps up, ensuring glitch-free operation. extra pins on 8-pin device the 8-pin versions of the lx217x have the emitters of the power transistors brought out separately. connecting these pins to ground reduces errors due to ground pin voltage drops. the e 2 pin also allows the user to half the switch current limit if the pin is left open. note that the switch resistance will increase when e 2 is open, so efficiency will decrease and heat dissipation will increase, especially for currents over 300ma. micropower shutdown the lx2172/73 enter micropower shutdown mode when the v c pin is pulled below 0.15v. supply current required for biassing shutdown circuitry is less than 250a. the lx2173 has an en- able pin which allows ultra-low micropower shutdown opera- tion, consuming less than 10a.
1.25a h igh -e fficiency 100 k h z s witching r egulator lx2172/73 product databook 1996/1997 copyright ? 1998 rev. 0.4 12/98 6 p reliminary d ata s heet theory of operation preliminary data - information contained in this document is pre-production data, and is proprietary to linfinity. it may not modified in any way without the express written consent of linfinity. product referred to herein is offered in sample form only, and linfinity reserves the right to change or discontinue this proposed product at any time. figure 1 boost coverter circuit using the lx2172 / 2173 lx2172 8 7 6 5 4 3 2 1 gnd v c fb sync e 2 v sw e 1 v in v in +3v to +12 v v out +16v 100 w 22f 180h v in 1n5817 v in 1.27 w 14.7k w v out 0.03f
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