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?2002 fairchild semiconductor corporation www.fairchildsemi.com rev. 1.0.2 features ? low start up current ? maximum duty clamp ? uvlo with hysteresis ? operating frequency up to 500khz description the ka3842b/ka3843b/ka3844b/ka3845b are fixed frequency current-mode pwm controller. they are specially designed for off - line and dc-to-dc converter applications with minimum external components. these integrated circuits feature a trimmed oscillator for precise duty cycle control, a temperature compensated reference, high gain error amplifier, current sensing comparator and a high current totempole output for driving a power mosfet. the ka3842b and ka3844b have uvlo thresholds of 16v (on) and 10v (off). the ka3843b and ka3845b are 8.5v (on) and 7.9v (off). the ka3842b and ka3843b can operate within 100% duty cycle. the ka3844b and ka3845b can operate with 50% duty cycle. 8-dip 14-sop 1 1 internal block diagram ka3842b/ka3843b/ka3844b/ ka3845b smps controller
ka3842b/ka3843b/ka3844b/ka3845b 2 absolute maximum ratings note: 1. board thickness 1.6mm, board dimension 76.2mm 114.3mm, (reference eia / jsed51-3, 51-7) 2. do not exceeed p d and soa (safe operation area) power dissipation curve thermal data pin array parameter symbol value unit supply voltage v cc 30 v output current i o 1a analog inputs (pin 2.3) v (ana) -0.3 to 6.3 v error amp output sink current i sink (e.a) 10 ma power dissipation at t a 25 c (8dip) p d (note1,2) 1200 mw power dissipation at t a 25 c (14sop) p d (note1,2) 680 mw storage temperature range t stg -65 ~ +150 c lead temperature (soldering, 10sec) t lead +300 c characteristic symbol 8-dip 14-sop unit thermal resistance junction-ambient r thj-amb(max) 100 180 c/w 800 700 600 500 400 300 900 1000 1100 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 ambient temperature ( ) power dissipation (mw) 1200 8dip 14sop 800 700 600 500 400 300 900 1000 1100 0 1020304050 30 40 50 60 70 80 60 70 80 90 100 110 90 100 110 120 130 140 120 130 140 150 ambient temperature ( ) power dissipation (mw) 1200 8dip 14sop v cc gnd pwr gnd comp 1 n/c 2 v fb n/c 3 4 v ref n/c pwr v c 14 13 12 11 current sense 5 n/c r t/ c t 6 7 output 10 9 8 comp 1 v fb 2 current sense r t/ c t 3 4 v ref v cc output gnd 8 7 6 5 8dip,8sop 14sop v cc gnd pwr gnd comp 1 n/c 2 v fb n/c 3 4 v ref n/c pwr v c 14 13 12 11 current sense 5 n/c r t/ c t 6 7 output 10 9 8 v cc gnd pwr gnd comp 1 n/c 2 v fb n/c 3 4 v ref n/c pwr v c 14 13 12 11 current sense 5 n/c r t/ c t 6 7 output 10 9 8 comp 1 v fb 2 current sense r t/ c t 3 4 v ref v cc output gnd 8 7 6 5 comp 1 v fb 2 current sense r t/ c t 3 4 v ref v cc output gnd 8 7 6 5 8dip,8sop 14sop 8-dip
ka3842b/ka3843b/ka3844b/ka3845b 3 electrical characteristics (v cc =15v, r t =10k ? , c t =3.3nf, t a = 0 c to +70 c, unless otherwise specified) parameter symbol conditions min. typ. max. unit reference section reference output voltage v ref t j = 25 c, i ref = 1ma 4.90 5.00 5.10 v line regulation ? v ref 12v v cc 25v - 6 20 mv load regulation ? v ref 1ma i ref 20ma - 6 25 mv short circuit output current i sc t a = 25 c - -100 -180 ma oscillator section oscillation frequency f t j = 25 c475257khz frequency change with voltage ? f/ ? v cc 12v v cc 25v - 0.05 1 % oscillator amplitude v osc - -1.6-v p-p error amplifier section input bias current i bias - --0.1-2 a input voltage v i(e>a) v pin1 = 2.5v 2.42 2.50 2.58 v open loop voltage gain g vo 2v v o 4v (note3) 65 90 - db power supply rejection ratio psrr 12v v cc 25v (note3) 60 70 - db output sink current i sink v pin2 = 2.7v, v pin1 = 1.1v 2 7 - ma output source current i source v pin2 = 2.3v, v pin1 = 5v -0.6 -1.0 - ma high output voltage v oh v pin2 = 2.3v, r l = 15k ? to gnd56-v low output voltage v ol v pin2 = 2.7v, r l = 15k ? to pin 8 - 0.8 1.1 v current sense section gain g v (note 1 & 2) 2.85 3 3.15 v/v maximum input signal v i(max) v pin1 = 5v(note 1) 0.9 1 1.1 v power supply rejection ratio psrr 12v v cc 25v (note1,3) - 70 - db input bias current i bias - --3-10 a output section low output voltage v ol i sink = 20ma - 0.08 0.4 v i sink = 200ma - 1.4 2.2 v high output voltage v oh i source = 20ma 13 13.5 - v i source = 200ma 12 13.0 - v rise time t r t j = 25 c, c l = 1nf (note 3) - 45 150 ns fall time t f t j = 25 c, c l = 1nf (note 3) - 35 150 ns under-voltage lockout section start threshold v th(st) ka3842b/ka3844b 14.5 16.0 17.5 v ka3843b/ka3845b 7.8 8.4 9.0 v min. operating voltage (after turn on) v opr(min) ka3842b/ka3844b 8.5 10.0 11.5 v ka3843b/ka3845b 7.0 7.6 8.2 v
ka3842b/ka3843b/ka3844b/ka3845b 4 electrical characteristics (continued) (v cc =15v, r t =10k ? , c t =3.3nf, t a = 0 c to +70 c unless otherwise specified) adjust v cc above the start threshould before setting at 15v note: 1. parameter measured at trip point of latch 2. gain defined as: 3. these parameters, although guaranteed, are not 100 tested in production. figure 1. open loop test circuit 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 5k ? potentiometer are used to sample the oscillator waveform and apply an adjustable ramp to pin 3. parameter symbol conditions min. typ. max. unit pwm section max. duty cycle d (max) ka3842b/ka3843b 95 97 100 % d (max) ka3844b/ka3845b 47 48 50 % min. duty cycle d (min) - --0% total standby current start-up current i st - -0.451ma operating supply current i cc(opr) v pin3 =v pin2 =on - 14 17 ma zener voltage v z i cc = 25ma 30 38 - v a ? v pin1 ? v pin3 ----------------- - = ,0 v pin3 0.8v
ka3842b/ka3843b/ka3844b/ka3845b 5 figure 2. under voltage lockout during under-voltage lock-out, the output driver is biased to a high impedance state. pin 6 should be shunted to ground with a bleeder resistor to prevent activating the power switch with output leakage current. figure 3. error amp configuration figure 4. current sense circuit peak current (i s ) is determined by the formula: a small rc filter may be required to suppress switch transients. i s max () 1.0v r s ------------ =
ka3842b/ka3843b/ka3844b/ka3845b 6 figure 5. oscillator waveforms and maximum duty cycle oscillator timing capacitor, c t , is charged by v ref through r t and discharged by an internal current source. during the dis- charge time, the internal clock signal blanks the output to the low state. selection of r t and c t therefore determines both oscillator frequency and maximum duty cycle. charge and discharge times are determined by the formulas: t c = 0.55 r t c t frequency, then, is: f=(t c + t d ) -1 figure 8. shutdown techniques figure 6. oscillator dead time & frequency figure 7. timing resistance vs frequency t d r t c t i n 0.0063r t 2.7 ? 0.0063r t 4 ? ---------------------------------------- ?? ?? = forrt 5k ? f 1.8 r t c t -------------- - = , > (deadtime vs c t rt > 5k ?)
ka3842b/ka3843b/ka3844b/ka3845b 7 shutdown of the ka3842b can be accomplished by two methods; either raise pin 3 above 1v or pull pin 1 below a voltage two diode drops above ground. either method causes the output of the pwm comparator to be high (refer to block diagram). the pwm latch is reset dominant so that the output will remain low until the next clock cycle after the shutdown condition at pins 1 and/or 3 is removed. in one example, an externally latched shutdown may be accomplished by adding an sor which will be reset by cycling v cc below the lower uvlo threshold. at this point the reference turns off, allowing the scr to reset. figure 9. slope compensation a fraction of the oscillator ramp can be resistively summed with the current sense signal to provide slope compensation for converters requiring duty cycles over 50%. note that capacitor, c t , forms a filter with r2 to suppress the leading edge switch spikes. temperature ( c) figure 10. temperature drift (vref) temperature ( c) figure 11. temperature drift (ist) temperature ( c) figure 12. temperature drift (icc)
ka3842b/ka3843b/ka3844b/ka3845b 8 mechanical dimensions package dimensions in millimeters 6.40 0.20 3.30 0.30 0.130 0.012 3.40 0.20 0.134 0.008 #1 #4 #5 #8 0.252 0.008 9.20 0.20 0.79 2.54 0.100 0.031 () 0.46 0.10 0.018 0.004 0.060 0.004 1.524 0.10 0.362 0.008 9.60 0.378 max 5.08 0.200 0.33 0.013 7.62 0~15 0.300 max min 0.25 +0.10 ?.05 0.010 +0.004 ?.002 8-dip
ka3842b/ka3843b/ka3844b/ka3845b 9 mechanical dimensions (continued) package dimensions in millimeters 8.56 0.20 0.337 0.008 1.27 0.050 5.72 0.225 1.55 0.10 0.061 0.004 0.05 0.002 6.00 0.30 0.236 0.012 3.95 0.20 0.156 0.008 0.60 0.20 0.024 0.008 8.70 0.343 max #1 #7 #8 0~8 #14 0.47 0.019 () 1.80 0.071 max0.10 max0.004 max min + 0.10 -0.05 0.20 + 0.004 -0.002 0.008 + 0.10 -0.05 0.406 + 0.004 -0.002 0.016 14-sop
ka3842b/ka3843b/ka3844b/ka3845b 2/18/02 0.0m 001 stock#dsxxxxxxxx ? 2002 fairchild semiconductor corporation life support policy fairchild?s products are not authorized for use as critical components in life support devices or systems without the express written approval of the president of fairchild semiconductor corporation. as used herein: 1. life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury of the user. 2. a critical component in any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. www.fairchildsemi.com disclaimer fairchild semiconductor reserves the right to make changes without further notice to any products herein to improve reliability, function or design. fairchild does not assume any liability arising out of the application or use of any product or circuit described herein; neither does it convey any license under its patent rights, nor the rights of others. ordering information product number package operating temperature ka3842b 8-dip 0 ~ + 70 c ka3843b ka3844b ka3845b ka3842bd 14-sop ka3843bd ka3844bd ka3845bd
product folder - fairchild p/n ka3842b - smps controller fairchild semiconductor space space space search | parametric | cross reference space product folders and datasheets application notes space space space find products home >> find products >> space space space space products groups space analog and mixed signal discrete interface logic microcontrollers non-volatile memory optoelectronics markets and applications new products product selection and parametric search cross-reference search technical information buy products technical support my fairchild company ka3842b smps controller related links request samples dotted line how to order products dotted line product change notices (pcns) dotted line support dotted line distributor and field sales representatives dotted line quality and reliability dotted line design tools contents general description | features | product status/pricing/packaging | application notes general description the ka3842b/ka3843b/ka3844b/ka3845b are fixed frequency current-mode pwm controller. they are specially designed for off-line and dc-to-dc converter applications with minimum external components. these integrated circuits feature a trimmed oscillator for precise duty cycle control, a temperature compensated reference, high gain error amplifier, current sensing comparator, and a high current totempole output ideally suited for driving a power mosfet. the ka3842b and ka3844b have uvlo thresholds of 16v (on) and 10v (off) the ka3843b and ka3845b are 8.5v (on) and 7.9v (off) the ka3842b and ka3843b can operate within 100% duty cycle. the ka3844b and ka3845b can operate with 50% duty cycle. back to top features l low start up current l maximum duty clamp l uvlo with hysteresis l operating frequency up to 500khz back to top space datasheet download this datasheet pdf e-mail this datasheet [e- mail] this page print version product status/pricing/packaging file:///e|/new/html/ka3842b.html (1 of 2) [7/26/02 12:07:33 pm]
product folder - fairchild p/n ka3842b - smps controller product product status package type leads packing method KA3842BDTF full production sop 14 tape reel ka3842bd full production sop 14 rail ka3842b full production dip 8 rail back to top application notes an-4105: an-4105 design considerations for switched mode power supplies using a fairchild power switch (sps) in a flyback converter (444 k) jul 19, 2002 an-9015: an-9015 a180w, 100khz forward converter using qfet (65 k) jul 19, 2002 back to top space space home | find products | technical information | buy products | support | company | contact us | site index | privacy policy ? copyright 2002 fairchild semiconductor space space file:///e|/new/html/ka3842b.html (2 of 2) [7/26/02 12:07:33 pm]

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