p roduction d ata s heet t he i nfinite p ower of i nnovation l in f inity m icroelectronics i nc . 11861 w estern a venue , g arden g rove , ca. 92841, 714-898-8121, f ax : 714-893-2570 1 copyright ? 1995 rev. 1.2a,2005-03-09 uc184xa / 284xa / 384xa c urrent m ode pwm c ontroller description the uc184xa family of control ics provides all the necessary features to implement off-line fixed-frequency, current-mode switching power supplies with a minimum of external components. the curren t mode architecture demonstrates improved lo ad regulation, pulse- by-pulse current limiting and inherent protection of the power supply output switch. the ic includes: a bandgap reference trimmed to 1% accuracy, an error amplifier, a current sense comparator with internal clamp to 1v, a high current totem pole output stage for fast switching of power mosfet's, and an externally programmable oscillator to set frequency and maximum duty cycle. the undervoltage lock-out is designed to operate with 250a typ. start-up current, allowing an efficient bootstrap supply voltage design. available options for this family of products, such as start- up voltage hysteresis and duty cycle, are summarized below in the available options section. the uc184xa family of control ics is also available in 14-pin soic package which makes the power output stage collector and ground pins available. important: for the most current data, consult microsemi ?s website: http://www.microsemi.com product highlight c omparison of uc384 x a vs . sg384 x d ischarge c urrent uc384xa 7.5 8.3 9.3 mean sg384x min. limit 7.8 -3 s 8.8 +3s sg384x max. limit discharge cu rrent dist ribution - ma t a =25 c key features ? low start-up current. (0.5ma max.) ? trimmed oscillator discharge current. (see product highlight) ? optimized for off-line and dc-to-dc converters. ? automatic feed forward compensation. ? pulse-by-pulse current limiting. ? enhanced load response characteristics. ? under-voltage lockout with hysteresis. ? double pulse suppression. ? high-current totem pole output. ? internally trimmed bandgap reference. ? 500khz operation. ? low ro error amplifier. key features ? economical off-line flyback or forward converters. ? dc-dc buck or boost converters. ? low cost dc motor control. available options part# start-up voltage hysteresis max. duty cycle UCX842A 16v 6v <100% ucx843a 8.4v 0.8v <100% ucx844a 16v 6v <50% ucx845a 8.4a 0.8v <50% package order info m plastic dip 8-pin dm plastic soic 8-pin d plastic soic 14-pin y ceramic dip 8-pin t a ( c) rohs compliant / pb-free transition dc: 0503 rohs compliant / pb-free transition dc: 0440 0 to 70 uc384xam uc384xadm uc384xad - -40 to +85 uc284xam uc284xadm uc284xad uc284xay -55 to 125 - - - uc184xay note: available in tape & reel. append the lett ers ?tr? to the part number. (i.e. uc3842adm-tr)
c urrent m ode pwm c ontroller uc184xa/284xa/384xa product databook 1996/1997 copyright ? 1995 rev. 1.2a 10/25 2 p roduction d ata s heet absolute maximum ratings (note 1) supply voltage (low impedance source) (v cc ) ......................................................... 30v supply voltage (i cc < 30ma) .......................................................................... self limiting output current ............................................................................................................. 1a output energy (capacitive load) ................................................................................. 5j analog inputs (v fb & i sense ) ........................................................................ -0.3v to +6.3v error amp output sink current ............................................................................... 10ma power dissipation at t a = 25c (m package) .............................................................. 1w storage temperature range .................................................................... -65c to +150c lead temperature (soldering, 10 seconds) ............................................................. 300c package pin outs 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. pin numbers refer to dil packages only. 1 8 27 36 45 m & y package (top view) 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 d package: thermal resistance-junction to ambient, q q q q q ja 120c/w y package: thermal resistance-junction to ambient, q q q q q ja 130c/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 thermal data dm package (top view) v ref v cc output gnd comp v fb i sense r t /c t 1 8 27 36 45 v ref n.c. v cc v c output gnd pwr gnd comp n.c. v fb n.c. i sense n.c. r t /c t 1 14 213 312 411 510 69 78 d package (top view) comp v fb i sense r t /c t v ref v cc output gnd peak package solder reflow temp. (40 second max. exposure)..........................................260c (+0, -5) rohs / pb-free 100% matte tin lead finish
c urrent m ode pwm c ontroller uc184xa/284xa/384xa product databook 1996/1997 3 copyright ? 1995 rev. 1.2a 10/25 p roduction d ata s heet electrical characteristics (unless otherwise specified, these specifications apply over the operating ambient temperatures for uc384xa with 0c t a 70c, uc284xa with -40c t a 85c, uc184xa with -55c t a 125c; v cc =15v; r t =10k; c t =3.3nf. low duty cycle pulse testing techniques are used which maintains junction and case temperatures equal to the ambient temperature.) reference section parameter symbol test conditions output voltage v ref t j = 25c, i l = 1ma line regulation 12 v in 25v load regulation 1 i o 20ma temperature stability (note 2 & 7) total output variation over line, load, and temperature output noise voltage (note 2) v n 10hz f 10khz, t j = 25c long term stability (note 2) t a = 125c, t = 1000hrs output short circuit current i sc uc384xa units min. typ. max. min. typ. max. uc184xa/284xa 4.95 5.00 5.05 4.90 5.00 5.10 v 620 620 mv 625 625 mv 0.2 0.4 0.2 0.4 mv/c 4.9 5.1 4.82 5.18 v 50 50 v 525 525 mv -30 -100 -180 -30 -100 -180 ma oscillator section initial accuracy (note 6) t j = 25c voltage stability 12 v cc 25v temperature stability (note 2) t min t a t max amplitude (note 2) discharge current t j = 25c, v pin 4 = 2v v pin 4 = 2v, t min t a t max 47 52 57 47 52 57 khz 0.2 1 0.2 1 % 55% 1.7 1.7 v 7.8 8.3 8.8 7.8 8.3 8.8 ma 7.5 8.8 7.6 8.8 ma output low level v ol i sink = 20ma i sink = 200ma output high level v oh i source = 20ma i source = 200ma rise time (note 2) t r t j = 25c, c l = 1nf fall time (note 2) t f t j = 25c, c l = 1nf uvlo saturation v sat v cc = 5v, i sink = 10ma current sense section gain (note 3 & 4) a vol maximum input signal (note 3) v pin 1 = 5v power supply rejection ratio (note 3) psrr 12 v cc 25v input bias current i b delay to output (note 2) t pd v pin 3 = 0 to 2v output section 2.85 3 3.15 2.85 3 3.15 v/v 0.9 1 1.1 0.9 1 1.1 v 70 70 db -2 -10 -2 -10 a 150 300 150 300 ns 0.1 0.4 0.1 0.4 v 1.5 2.2 1.5 2.2 v 13 13.5 13 13.5 v 12 13.5 12 13.5 v 50 150 50 150 ns 50 150 50 150 ns 0.7 1.2 0.7 1.2 v (electrical characteristics continue next page.) error amp section input voltage v pin 1 = 2.5v input bias current i b open loop gain a vol 2 v o 4v unity gain bandwidth (note 2) ugbw t j = 25c power supply rejection ratio (note 3) psrr 12 v cc 25v output sink current i ol v pin 2 = 2.7v, v pin 1 = 1.1v output source current i oh v pin 2 = 2.3v, v pin 1 = 5v output voltage high level v oh v pin 2 = 2.3v, r l = 15k to ground output voltage low level v ol v pin 2 = 2.7v, r l = 15k to v ref 2.45 2.50 2.55 2.42 2.50 2.58 v -0.3 -1 -0.3 -2 a 65 90 65 90 db 0.7 1 0.7 1 mhz 60 70 60 70 db 26 26 ma -0.5 -0.8 -0.5 -0.8 ma 56 56 v 0.7 1.1 0.7 1.1 v
c urrent m ode pwm c ontroller uc184xa/284xa/384xa product databook 1996/1997 copyright ? 1995 rev. 1.2a 10/25 4 p roduction d ata s heet electrical characteristics (con't.) under-voltage lockout section parameter symbol test conditions start threshold x842a/4a x843a/5a min. operation voltage after turn-on x842a/4a x843a/5a uc384xa units min. typ. max. min. typ. max. uc184xa/284xa 15 16 17 14.5 16 17.5 v 7.8 8.4 9.0 7.8 8.4 9.0 v 9 10 11 8.5 10 11.5 v 7.0 7.6 8.2 7.0 7.6 8.2 v pwm section maximum duty cycle x842a/3a x844a/5a minimum duty cycle 94 96 100 94 96 100 % 47 48 50 47 48 50 % 00% total standby section start-up current operating supply current i cc zener voltage v z i cc = 25ma 0.3 0.5 0.3 0.5 ma 11 17 11 17 ma 30 35 30 35 v block diagram * - v cc and v c are internally connected for 8 pin packages. ** - power ground and ground are internally connected for 8 pin packages. *** - toggle flip flop used only in x844a and x845a series. notes: 2. these parameters, although guaranteed, are not 100% tested in production. 3. parameter measured at trip point of latch with v vfb = 0. 4. gain defined as: a vol = ; 0 v isense 0.8v. 5. adjust v cc above the start threshold before setting at 15v. 6. output frequency equals oscillator frequency for the uc1842a and uc1843a. output frequency is one half oscillator frequency for the uc1844a and uc1845a. 7. "temperature stability, sometimes referred to as average temperature coefficient, is described by the equation: temp stability = v ref (max.) & v ref (min.) are the maximum & minimum reference voltage measured over the appropriate temperature range. note that the extremes in voltage do not necessarily occur at the extremes in temperature." v ref (max.) - v ref (min.) t j (max.) - t j (min.) d v comp d v isense uvlo s / r 5v ref internal bias 34v error amp 1v current sense comparator pwm latch s r r oscillator 2r ** t *** v ref good logic 2.5v uvlo 16v (1842a/4a) 8.4v (1843a/5a) hysteresis 6v (1842a/4a) 0.8v (1843a/5a) comp current sense v fb r t /c t ground * v cc v ref 5.0v 50ma v c * output power ground **
c urrent m ode pwm c ontroller uc184xa/284xa/384xa product databook 1996/1997 5 copyright ? 1995 rev. 1.2a 10/25 p roduction d ata s heet characteristic curves figure 1. oscillator frequency vs. timing resistor 300 3.0k 100 k 0 100k r t - (ohms) oscillator frequency - (hz) 10k 1m 1.0k 10.0k 30.0k c t = 1nf c t = 2.2nf c t = 4.7nf figure 2. maximum duty cycle vs. timing resistor 300 3.0k 100 k 0 40.0 r t - (ohms) maximum duty cycle - (%) 20.0 60.0 1.0k 10.0k 30.0k 80.0 100.0 note: output drive frequency is half the oscillator frequency for the ucx844a/5a devices. 8 4 5 v ref r t /c t ground r t c t for r t > 5k, f ? 1.72 r t c t
c urrent m ode pwm c ontroller uc184xa/284xa/384xa product databook 1996/1997 copyright ? 1995 rev. 1.2a 10/25 6 p roduction d ata s heet typical application circuits figure 3. current sense spike suppression figure 4. mosfet parasitic oscillations 6 q1 v cc dc bus 5 r s r 1 ucx84xa 7 ucx84xa 3 5 6 7 r s c q1 v cc dc bus i pk i pk(max) = 1.0v r s change figure 5. external duty cycle clamp and multi-unit synchronization a resistor (r 1 ) in series with the mosfet gate will reduce overshoot & ringing caused by the mosfet input capacitance and any inductance in series with the gate drive. (note: it is very important to have a low inductance ground path to insure correct operation of the i.c. this can be done by making the ground paths as short and as wide as possible.) the rc low pass filter will eliminate the leading edge current spike caused by parasitics of power mosfet. f = (r a + 2r b )c 1.44 f = r a + 2r b r b precision duty cycle limiting as well as synchronizing several parts is possible with the above circuitry. 2 6 7 r b r a 5 1 84 3 555 timer 4 5 8 to other ucx84xa devices 0.01 ucx84xa
c urrent m ode pwm c ontroller uc184xa/284xa/384xa product databook 1996/1997 7 copyright ? 1995 rev. 1.2a 10/25 p roduction d ata s heet typical application circuits (continued) figure 6. slope compensation figure 7. open loop laboratory fixture 2 3 4 8 7 6 5 comp v fb i sense r t c t v ref v cc output ground 0.1f 0.1f a ucx84xa r t 2n2222 100k 4.7k 1k 4.7k 5k i sense adjust error amp a djust c t 1k ground output v cc v ref 1 oscillator v ref good logic s r 5v ref internal bias 8(14) 4(7) 2(3) 1(1) r f c f r d r i from v o r slope 2n222a r t 5v uvlo 2.5v error amp c t 1v 2r r c.s. comp pwm latch 5(9) 3(5) 5(8) cr s r 6(10) 7(11) 7(12) v cc dc bus v o q1 ucx84xa due to inherent instability of current mode converters running above 50% duty cycle, slope compensation should be added to eith er the current sense pin or the error amplifier. figure 6 shows a typical slope compensation technique. high peak currents associated with capacitive loads necessitate careful grounding techniques. timing and bypass capacitors sho uld be connected to pin 5 in a single point ground. the transistor and 5k potentiometer are used to sample the oscillator waveform an d apply an adjustable ramp to pin 3.
c urrent m ode pwm c ontroller uc184xa/284xa/384xa product databook 1996/1997 copyright ? 1995 rev. 1.2a 10/25 8 p roduction d ata s heet typical application circuits (continued) figure 8. off-line flyback regulator specifications input line voltage: 90vac to 130vac input frequency: 50 or 60hz switching frequency: 40khz 10% output power: 25w maximum output voltage: 5v +5% output current: 2 to 5a line regulation: 0.01%/v load regulation: 8%/a* efficiency @ 25 watts, v in = 90vac: 70% v in = 130vac: 65% output short-circuit current: 2.5amp average * this circuit uses a low-cost feedback scheme in which the dc voltage developed from the primary-side control winding is sensed by the uc3844a error amplifier. load regulation is therefore dependent on the coupling between secondary and control windings, and on transformer leakage inductance. 7 150k w 100pf v fb comp v ref r t /c t 4700f 10v 5v 2-5a isolation boundary 3600pf 400v 1n4935 820pf 2.5k w 1n4935 irf830 27k w 0.01f 10f 20v 1n4935 1k w 470pf 0.85k w mbr735 ti 4.7k w 2w 140k w 1/2w 220f 250v 4.7k w 1w 1n4004 1n4004 1n4004 1n4004 ac input v cc out cur sen gnd uc3844a 20k w 3.6k w 10k w .0022f 0.01f 16v 3 6 2 1 8 4 5
|
