 |
|
| If you can't view the Datasheet, Please click here to try to view without PDF Reader . |
|
|
|
| If you can't view the Datasheet, Please click here to try to view without PDF Reader . |
|
|
| Datasheet File OCR Text: |
| uc2842b/3b/4b/5b uc3842b/3b/4b/5b march 1999 high performance current mode pwm controller . trimmed oscillator for precise fre- quency control . oscillator frequency guaranteed at 250khz . current mode operation to 500khz . automatic feed forward compensa- tion . latching pwm for cycle-by-cycle current limiting . internally trimmed reference with undervoltage lockout . high current totem pole output . undervoltage lockout with hyster- esis . low start-up and operating current description the uc384xb family of control ics provides the nec- essary features to implement off-line or dc to dc fixed frequency current mode control schemes with a minimal external parts count. internally imple- mented circuits include a trimmed oscillator for pre- cise duty cycle control under voltage lock- out featuring start-up current less than 0.5ma, a pre- cision reference trimmed for accuracy at the error amp input, logic to insure latched operation, a pwm comparator which also provides current limit control, and a totem pole output stage designed to source or sink high peak current. the output stage, suitable for driving n-channel mosfets, is low in the off- state. differences between members of this family are the under-voltage lockout thresholds and maximum duty cycle ranges. the uc3842b and uc3844b have uvlo thresholds of 16v (on) and 10v (off), ideally suited off-line applications the corresponding thresh- olds for the uc3843b and uc3845b are 8.5 v and 7.9 v. the uc3842b and uc3843b can operate to duty cycles approaching 100%. a range of the zero to < 50 % is obtained by the uc3844b and uc3845b by the addition of an internal toggle flip flop which blanks the output off every other clock cycle. block diagram (toggle flip flop used only in uc3844b and uc3845b) uvlo s/r 5v ref 34v internal bias vref good logic 2.50v t s r osc r1v current sense comparator 2r + - pwm latch 7 5 4 2 1 3 8 6 error amp. vi ground rt/ct vfb comp current sense vref 5v 50ma output d95in331 minidip ? so8 uc3842b 1/15
* all voltages are with respect to pin 5, all currents are positive into the specified terminal. pin connection (top view) comp v fb i sense r t /c t ground output vi v ref 1 3 2 4 6 5 7 8 d95in332 minidip/so8 ordering numbers so8 minidip uc2842bd1; uc3842bd1 uc2843bd1; uc3843bd1 uc2844bd1; uc3844bd1 uc2845bd1; uc3845bd1 uc2842bn; uc3842bn uc2843bn; uc3843bn uc2844bn; uc3844bn uc2845bn; uc3845bn absolute maximum ratings symbol parameter value unit v i supply voltage (low impedance source) 30 v v i supply voltage (ii < 30ma) self limiting i o output current 1 a e o output energy (capacitive load) 5 m j analog inputs (pins 2, 3) C 0.3 to 5.5 v error amplifier output sink current 10 ma p tot power dissipation at t amb 25 c (minidip) 1.25 w p tot power dissipation at tamb 25 c (so8) 800 mw t stg storage temperature range C 65 to 150 c t j junction operating temperature C 40 to 150 c t l lead temperature (soldering 10s) 300 c pin functions no function description 1 comp this pin is the error amplifier output and is made available for loop compensation. 2v fb this is the inverting input of the error amplifier. it is normally connected to the switching power supply output through a resistor divider. 3i sense a voltage proportional to inductor current is connected to this input. the pwm uses this information to terminate the output switch conduction. 4r t /c t the oscillator frequency and maximum output duty cycle are programmed by connecting resistor r t to vref and cpacitor c t to ground. operation to 500khz is possible. 5 ground this pin is the combined control circuitry and power ground. 6 output this output directly drives the gate of a power mosfet. peak currents up to 1a are sourced and sunk by this pin. 7v cc this pin is the positive supply of the control ic. 8v ref this is the reference output. it provides charging current for capacitor c t through resistor r t . uc2842b/3b/4b/5b - uc3842b/3b/4b/5b 2/15 electrical characteristics ( [note 1] unless otherwise stated, these specifications apply for -25 < t amb < 85 c for uc284xb; 0 < t amb < 70 c for uc384xb; v i = 15v (note 5); r t = 10k; c t = 3.3nf) symbol parameter test conditions uc284xb uc384xb unit min. typ. max. min. typ. max. reference section v ref output voltage t j = 25 c i o = 1ma 4.95 5.00 5.05 4.90 5.00 5.10 v d v ref line regulation 12v v i 25v 220 220mv d v ref load regulation 1 i o 20ma 325 325mv d v ref / d t temperature stability (note 2) 0.2 0.2 mv/ c total output variation line, load, temperature 4.9 5.1 4.82 5.18 v e n output noise voltage 10hz f 10khz t j = 25 c (note 2) 50 50 m v long term stability t amb = 125 c, 1000hrs (note 2) 525 525mv i sc output short circuit -30 -100 -180 -30 -100 -180 ma oscillator section f osc frequency t j = 25 c t a = t low to t high t j = 25c (r t = 6.2k, c t = 1nf) 49 48 225 52 C 250 55 56 275 49 48 225 52 C 250 55 56 275 khz khz khz d f osc / d v frequency change with volt. v cc = 12v to 25v C 0.2 1 C 0.2 1 % d f osc / d t frequency change with temp. t a = t low to t high C1CC0.5C% v osc oscillator voltage swing (peak to peak) C 1.6 C C 1.6 C v i dischg discharge current (v osc =2v) t j = 25c t a = t low to t high 7.8 7.5 8.3 C 8.8 8.8 7.8 7.6 8.3 C 8.8 8.8 ma ma error amp section v 2 input voltage v pin1 = 2.5v 2.45 2.50 2.55 2.42 2.50 2.58 v i b input bias current v fb = 5v -0.1 -1 -0.1 -2 m a a vol 2v v o 4v 65 90 65 90 db bw unity gain bandwidth t j = 25c 0.7 1 0.7 1 mhz psrr power supply rejec. ratio 12v v i 25v 60 70 60 70 db i o output sink current v pin2 = 2.7v v pin1 = 1.1v 2 12 2 12 ma i o output source current v pin2 = 2.3v v pin1 = 5v -0.5 -1 -0.5 -1 ma v out high v pin2 = 2.3v; r l = 15k w to ground 5 6.2 5 6.2 v v out low v pin2 = 2.7v; r l = 15k w to pin 8 0.8 1.1 0.8 1.1 v current sense section g v gain (note 3 & 4) 2.85 3 3.15 2.85 3 3.15 v/v v 3 maximum input signal v pin1 = 5v (note 3) 0.9 1 1.1 0.9 1 1.1 v svr supply voltage rejection 12 v i 25v (note 3) 70 70 db i b input bias current -2 -10 -2 -10 m a delay to output 150 300 150 300 ns thermal data symbol description minidip so8 unit r th j-amb thermal resistance junction-ambient. max. 100 150 c/w uc2842b/3b/4b/5b - uc3842b/3b/4b/5b 3/15 notes : 1. max package power dissipation limits must be respected; low duty cycle pulse techniques are used during test maintain t j as close to t amb as possible. 2. these parameters, although guaranteed, are not 100% tested in production. 3. parameter measured at trip point of latch with v pin2 = 0. 4. gain defined as : d v pin1 a = ; 0 v pin3 0.8 v d v pin3 5. adjust v i above the start threshold before setting at 15 v. electrical characteristics (continued) symbol parameter test conditions uc284xb uc384xb unit min. typ. max. min. typ. max. output section v ol output low level i sink = 20ma 0.1 0.4 0.1 0.4 v i sink = 200ma 1.6 2.2 1.6 2.2 v v oh output high level i source = 20ma 13 13.5 13 13.5 v i source = 200ma 12 13.5 12 13.5 v v ols uvlo saturation vcc = 6v; i sink = 1ma 0.1 1.1 0.1 1.1 v t r rise time t j = 25 c c l = 1nf (2) 50 150 50 150 ns t f fall time t j = 25 c c l = 1nf (2) 50 150 50 150 ns under-voltage lockout section start threshold x842b/4b 15 16 17 14.5 16 17.5 v x843b/5b 7.8 8.4 9.0 7.8 8.4 9.0 v min operating voltage after turn-on x842b/4b 9 10 11 8.5 10 11.5 v x843b/5b 7.0 7.6 8.2 7.0 7.6 8.2 v pwm section maximum duty cycle x842b/3b 94 96 100 94 96 100 % x844b/5b 474850474850 % minimum duty cycle 0 0 % total standby current i st start-up current v i = 6.5v for ucx843b/45b 0.3 0.5 0.3 0.5 ma v i = 14v for ucx842b/44b 0.3 0.5 0.3 0.5 ma i i operating supply current v pin2 = v pin3 = 0v 12 17 12 17 ma v iz zener voltage i i = 25ma 30 36 30 36 v uc2842b/3b/4b/5b - uc3842b/3b/4b/5b 4/15 figure 1: open loop test circuit. r t a 2n2222 4.7k w 1k w error amp. adjust 4.7k w 5k w i sense adjust 100k w comp v fb i sense r t /c t 1 2 3 4 c t 7 6 5 8 v ref v i output ground 0.1 m f 0.1 m f v ref v i output ground 1w 1k w d95in343 high peak currents associated with capacitive loads necessitate careful grounding techniques. timing and bypass capacitors should be connected close to pin 5 in a single point ground. the transistor and 5 k w potentiometer are used to sample the oscillator waveform and apply an adjustable ramp to pin 3. 10k 20k 30k 50k 100k 200k 300k 500k f osc (khz) 1 2 5 10 20 50 d95in333 c t =10nf c t =5nf c t =2nf c t =1nf c t =500pf c t =200pf c t =100pf v i =15v t a =25?c rt (k w ) 0.8 figure 2: timing resistor vs. oscillator fre- quency 10k 20k 30k 50k 100k 200k 300k 500k fosc(khz) 1 2 3 5 10 20 30 50 % c t =10nf c t =5nf c t =2nf c t =1nf c t =500pf c t =200pf c t =100pf d95in334 v i =15v t a =25?c figure 3: output dead-time vs. oscillator fre- quency uc2842b uc2842b/3b/4b/5b - uc3842b/3b/4b/5b 5/15 -55 -25 0 25 50 75 100 t a (?c) 7.0 7.5 8.0 8.5 i dischg (ma) d95in335 v i =15v v osc =2v figure 4: oscillator discharge current vs. tem- perature. 1235 40 50 60 70 80 90 d max (%) 0.8 r t (k w ) d95in336 v i =15v c t =3.3nf t a =25?c i dischg =7.5ma i dischg =8.8ma figure 5: maximum output duty cycle vs. tim- ing resistor. 10 100 1k 10k 100k 1m f(hz) -20 0 20 40 60 80 (db) 180 150 120 90 60 30 f d95in337 v i =15v v o =2v to 4v r l =100k t a =25?c gain phase figure 6: error amp open-loop gain and phase vs. frequency. 0246v o (v) 0.0 0.2 0.4 0.6 0.8 1.0 v th (v) d95in338 v i =15v t a =-40?c t a =125?c t a =25?c figure 7: current sense input threshold vs. er- ror amp output voltage. 0 20406080100i ref (ma) d95in339 0 10 20 30 40 50 60 v i =15v t a =-40?c t a =125?c t a =25?c figure 8: reference voltage change vs. source current. -55 -25 0 25 50 75 100 t a (?c) d95in340 50 60 70 80 90 100 i sc (ma) v i =15v r l 0.1 w figure 9: reference short circuit current vs. temperature. uc2842b/3b/4b/5b - uc3842b/3b/4b/5b 6/15 0 200 400 600 i o (ma) 0 1 2 3 -2 -1 v sat (v) d95in341 v i =15v 80 m s pulsed load 120hz rate t a =-40?c t a =25?c v i t a =-40?c t a =25?c gnd sink saturation (load to v i ) source saturation (load to ground) figure 10: output saturation voltagevs. load current. 0 102030v i (v) 0 5 10 15 20 i i (ma) ucx843/45 ucx842/44 r t =10k c t =3.3nf v fb =0v i sense =0v t a =25?c d95in342 figure 11: supply current vs. supply voltage. figure 12: output waveform. figure 13: output cross conduction 5v reg oscillator pwm clock 8 4 5 6 r t c t gnd output 7 v i i d ct output large r t /small c t ct output small r t /large c t d95in344 figure 14: oscillator and output waveforms. v i =15v c l = 1.0nf t a = 25c 90% 10% 50ns/div v i =30v c l = 15pf t a = 25c v o i cc 100ns/div 100ma/div 20v/div uc2842b/3b/4b/5b - uc3842b/3b/4b/5b 7/15 figure 15 : error amp configuration. z i z f 1ma 2 1 v fb comp 2.5v d95in345 + - figure 16 : under voltage lockout. uc3842b uc3844b uc3843b uc3845b 16v 8.4v 10v 7.6v v on v off v i on/off command to rest of ic 7 <0.5ma <17ma i cc v cc v off v on d95in346 figure 17 : current sense circuit . error ampl. 2r r1v current sense comparator 1 current sense comp c r s r 3 5 gnd i s d95in347 peak current (i s ) is determined by the formula 1.0 v i s max ? r s a small rc filter may be required to suppress switch transients. during uvlo, the output is low uc2842b/3b/4b/5b - uc3842b/3b/4b/5b 8/15 figure 18 : slope compensation techniques. r s r 1 i s r slope c t r t v reg 8 r t /c t i sense 4 3 5 gnd r s r 1 i s r slope c t r t v reg 8 r t /c t i sense 4 3 5 gnd d95in348 figure 19 : isolated mosfet drive and current transformer sensing. 7 6 comp/latch isolation boundary d95in349 5.0v ref v cc + - + - q s r + - 3 r r s n s c v in q1 n p v gs waveforms + 0 + 0 - - 50% dc 25% dc i pk = v (pin 1) -1.4 3r s n s n p () uc3842b uc3842b uc2842b/3b/4b/5b - uc3842b/3b/4b/5b 9/15 figure 20 : latched shutdown. d95in350 bias + - ea r + osc 2n 3905 2n 3903 1ma r r 2r 1 2 8 4 scr must be selected for a holding current of less than 0.5ma at t a(min) . the simple two transistor circuit can be used in place of the scr as shown. all resistors are 10k. 5 d95in351 + - ea r i + 1ma r d r 2r 5 c f r f 1 2 from v o 2.5v + - ea r p + 1ma r d r 2r 5 c f r f 1 2 from v o 2.5v error amp compensation circuit for stabilizing any current-mode topology except for boost and flyback converters operating with continuous inductor current. c p r i error amp compensation circuit for stabilizing current-mode boost and flyback topologies operating with continuous inductor current. figure 21: error amplifier compensation uc2842b/3b/4b/5b - uc3842b/3b/4b/5b 10/15 d95in353 + - + r a 1 7 f = r bias osc c 6 v ref r r b + - + - ea r 2r r s q 84 5 2 3 5k 5k 5k ne555 8 4 2 1 5 to additional ucx84xas 1.44 (r a + 2r b )c d max = r b r a + 2r b figure 23: external duty cycle clamp and multi unit synchronization. d95in352 + - ea + r 2r 5 r t 1 2 external sync input the diode clamp is required if the sync amplitude is large enough to cause the bottom side of c t to go more than 300mv below ground r bias osc c t 0.01 m f 47 w 4 8 v ref r figure 22: external clock synchronization. uc2842b/3b/4b/5b - uc3842b/3b/4b/5b 11/15 d95in354 + r bias osc c r + - + - ea r 2r r s q 8 4 2 1 5 1ma 1v + - 5v ref 1m w figure 24: soft-start circuit d95in355 + r bias osc c r + - + - ea r 2r r s q 8 4 2 1 5 1ma 1v + - 5v ref r2 r1 v clamp + - comp/latch 7 r s v cc q1 v in 7 6 5 bc109 v clamp = r 1 r 1 + r 2 where 0 minidip dim. mm inch min. typ. max. min. typ. max. a 3.32 0.131 a1 0.51 0.020 b 1.15 1.65 0.045 0.065 b 0.356 0.55 0.014 0.022 b1 0.204 0.304 0.008 0.012 d 10.92 0.430 e 7.95 9.75 0.313 0.384 e 2.54 0.100 e3 7.62 0.300 e4 7.62 0.300 f 6.6 0.260 i 5.08 0.200 l 3.18 3.81 0.125 0.150 z 1.52 0.060 outline and mechanical data uc2842b/3b/4b/5b - uc3842b/3b/4b/5b 14/15 information furnished is believed to be accurate and reliable. however, stmicroelectronics assumes no responsib ility for the conse- quences of use of such information nor for any infringement of patents or other rights of third parties which may result from i ts use. no license is granted by implication or otherwise under any patent or patent rights of stmicroelectronics. specification mentioned in this publication are subject to change without notice. this publication supersedes and replaces all information previously supplied. stmi- croelectronics products are not authorized for use as critical components in life support devices or systems without express wr itten approval of stmicroelectronics. the st logo is a registered trademark of stmicroelectronics ? 1999 stmicroelectronics C printed in italy C all rights reserved stmicroelectronics group of companies australia - brazil - canada - china - france - germany - italy - japan - korea - malaysia - malta - mexico - morocco - the neth erlands - singapore - spain - sweden - switzerland - taiwan - thailand - united kingdom - u.s.a. http://www.st.com uc2842b/3b/4b/5b - uc3842b/3b/4b/5b 15/15 about st products applications support buy news & events st worldwide contact us login search the site part number search search for part #: e-uc3845bd1 example: *74*00* matching documents: 1 - 1 of 1 generic part number(s) orderable part number(s) status product page/ datasheet description uc3845b e - uc3845bd1 e - uc3845bd1013tr nrnd nrnd high performance current mode pwm controller power management | ac - dc conversion | pwm controllers search time: 0.076s all rights reserved ? 2007 stmicroelectronics :: terms of use :: privacy policy pa g e 1 of 1 stmicroelectronics | part number search 23-au g -2007 mhtml:file://c:\temp \sgst\e-uc3845bd1.mht about st products applications support buy news & events st worldwide contact us login search the site part number search search for part #: e-uc3845bd1 example: *74*00* matching documents: 1 - 1 of 1 generic part number(s) orderable part number(s) status product page/ datasheet description uc3845b e - uc3845bd1 e - uc3845bd1013tr nrnd nrnd high performance current mode pwm controller power management | ac - dc conversion | pwm controllers search time: 0.074s all rights reserved ? 2007 stmicroelectronics :: terms of use :: privacy policy pa g e 1 of 1 stmicroelectronics | part number search 23-au g -2007 mhtml:file://c:\temp\s gst\E-UC3845BD1013TR.mht about st products applications support buy news & events st worldwide contact us login search the site part number search search for part #: e-uc3845bn example: *74*00* matching documents: 1 - 1 of 1 generic part number(s) orderable part number(s) status product page/ datasheet description uc3845b e - uc3845bn nrnd high performance current mode pwm controller power management | ac - dc conversion | pwm controllers search time: 0.074s all rights reserved ? 2007 stmicroelectronics :: terms of use :: privacy policy pa g e 1 of 1 stmicroelectronics | part number search 23-au g -2007 mhtml:file://c:\temp \sgst\e-uc3845bn.mht |
Price & Availability of E-UC3845BD1013TR
 |
|
|
|
|
All Rights Reserved © IC-ON-LINE 2003 - 2022 |
| [Add Bookmark] [Contact Us] [Link exchange] [Privacy policy] |
|
Mirror Sites : [www.datasheet.hk]
[www.maxim4u.com] [www.ic-on-line.cn]
[www.ic-on-line.com] [www.ic-on-line.net]
[www.alldatasheet.com.cn]
[www.gdcy.com]
[www.gdcy.net] |