uc1861-1868 UC2861-2868 uc3861-3868 10/98 features controls zero current switched (zcs) or zero voltage switched (zvs) quasi-resonant converters zero-crossing terminated one-shot timer precision 1%, soft-started 5v reference programmable restart delay following fault voltage-controlled oscillator (vco) with programmable minimum and maximum frequencies from 10khz to 1mhz low start-up current (150 m a typical) dual 1 amp peak fet drivers uvlo option for off-line or dc/dc applications description the uc1861-1868 family of ics is optimized for the control of zero cur- rent switched and zero voltage switched quasi-resonant converters. dif- ferences between members of this device family result from the various combinations of uvlo thresholds and output options. additionally, the one-shot pulse steering logic is configured to program either on-time for zcs systems (uc1865-1868), or off-time for zvs applications (uc1861- 1864). the primary control blocks implemented include an error amplifier to com- pensate the overall system loop and to drive a voltage controlled oscillator (vco), featuring programmable minimum and maximum frequencies. trig- gered by the vco, the one-shot generates pulses of a programmed maxi- mum width, which can be modulated by the zero detection comparator. this circuit facilitates true zero current or voltage switching over various line, load, and temperature changes, and is also able to accommodate the resonant components' initial tolerances. under-voltage lockout is incorporated to facilitate safe starts upon power-up. the supply current during the under-voltage lockout period is typically less than 150 m a, and the outputs are actively forced to the low state. (continued) block diagram resonant-mode power supply controllers udg-92018 pin numbers refer to the j and n packages. device 1861 1862 1863 1864 1865 1866 1867 1868 uvlo 16.5/10.5 16.5/10.5 36014 36014 16.5/10.5 16.5/10.5 36014 36014 outputs alternating parallel alternating parallel alternating parallel alternating parallel fixed off time off time off time off time on time on time on time on time
2 uc1861-1868 UC2861-2868 uc3861-3868 absolute maximum ratings v cc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22v output current source or sink (pins 11 & 14) . . . . . . . . . . . . . . . . . . . . . 0.5a dc pulse (0.5 m s) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5a power ground voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.2v inputs (pins 2, 3, 10, & 15) . . . . . . . . . . . . . . . . . . . . C0.4 to 7v error amp output current . . . . . . . . . . . . . . . . . . . . . . . . 2ma power dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1w junction temperature (operating). . . . . . . . . . . . . . . . . . 150 c lead temperature (soldering, 10 seconds) . . . . . . . . . . 300 c all voltages are with respect to signal ground and all currents are positive into the specified terminal. pin numbers refer to the j and n packages. consult unitrode integrated circuits da- tabook for information regarding thermal specifications and limitations of packages. dil-16, soic-16 (top view) j or n, dw packages connnection diagrams plcc-20 & lcc-20 (top view) q & l package description (cont.) uvlo thresholds for the uc1861/62/65/66 are 16.5v (on) and 10.5v (off), whereas the uc1863/64/67/68 thresholds are 8v (on) and 7v (off). after v cc ex- ceeds the uvlo threshold, a 5v generator is enabled which provides bias for the internal circuits and up to 10ma for external usage. a fault comparator serves to detect fault conditions and set a latch while forcing the output drivers low. the soft- ref pin serves three functions: providing soft start, re- start delay, and the internal system reference. each device features dual 1 amp peak totem pole output drivers for direct interface to power mosfets. the out- puts are programmed to alternate in the uc1861/63/65/67 devices. the uc1862/64/66/68 out- puts operate in unison alllowing a 2 amp peak current. package pin function function pin soft ref 1 5v 2 ni 3 inv 4 e/a out 5 sig gnd 6 range 7 r min 8 c vco 9 rc 10 zero 11 nc 12 nc 13 a out 14 pwr gnd 15 pwr gnd 16 v cc 17 b out 18
3 uc1861-1868 UC2861-2868 uc3861-3868 electrical characteristics unless otherwise stated, all specifications apply for C55 c t a 125 c for the uc186x, C25 c t a 85 c for the uc286x, and 0 c t a 70 c for the uc386x, v cc =12v, c vco =1nf, range=7.15k, r min =86.6k, c=200pf, r=4.02k, and csr=0.1 m f. t a =t j . parameter test conditions min typ max units 5v generator output voltage 12v vcc 20v, C10ma i o 0ma 4.8 5.0 5.2 v short circuit current v o = 0v C150 C15 ma soft-reference restart delay current v = 2v 10 20 35 m a soft start current v = 2v C650 C500 C350 m a reference voltage t j = 25 c, i o = 0a 4.95 5.00 5.05 v 12v v cc 20v, C200 m a i o 200 m a 4.85 5.15 v line regulation 12v v cc 20v 2 20 mv load regulation C200 m a i o 200 m a1030mv error amplifier (note 3) input offset voltage v cm = 5v, vo = 2v, i o = 0a C10 10 mv input bias current v cm = 0v C2.0 C0.3 m a voltage gain vcm = 5v, 0.5v v o 3.7v, i o = 0a 70 100 db power supply rejection ratio vcm = 5v, v o = 2v, 12v v cc 20v 70 100 db error amplifier (note 3) (cont.) common mode rejection ratio 0v vcm 6v, v o = 2v 65 100 db v out low v id = C100mv, i o = 200 m a 0.17 0.25 v v out high v id = 100mv, i o = C200 m a 3.9 4.2 v unity gain bandwidth (note 4) 0.5 0.8 mhz voltage controlled oscillator maximum frequency v id (error amp) = 100mv, t j = 25 c 450 500 550 khz v id (error amp) = 100mv 425 575 khz minimum frequency v id (error amp) = C100mv, t j = 25 c 45 50 55 khz v id (error amp) = C100mv 42 58 khz one shot zero comparator vth 0.45 0.50 0.55 v propagation delay (note 4) 120 200 ns maximum pulse width v zero = 1v 850 1000 1150 ns maximum to minimum pulse v zero = 0v ucx861 C ucx864 2.5 4 5.5 width ratio v zero = 0v ucx865 C ucx868. C55c to +85c 4 5.5 7 v zero = 0v ucx865 C ucx868, +125c 3.8 5.5 7 output stage rise and fall time c load = 1nf (note 4) 25 45 ns output low saturation i o = 20ma 0.2 0.5 v i o = 200ma 0.5 2.2 v output high saturation i o = C200ma, down from vcc 1.7 2.5 v uvlo low saturation i o = 20ma 0.8 1.5 v fault comparator fault comparator vth 2.85 3.00 3.15 v delay to output (note 4) (note 5) 100 200 ns
4 uc1861-1868 UC2861-2868 uc3861-3868 electrical characteristics unless otherwise stated, all specifications apply for C55 c t a 125 c for the uc186x, C25 c t a 85 c for the uc286x, and 0 c t a 70 c for the uc386x, v cc =12v, c vco =1nf, range=7.15k, r min =86.6k, c=200pf, r=4.02k, and csr=0.1 m f. t a =t j . parameter test conditions min typ max units uvlo vcc turn-on threshold ucx861, ucx862, ucx865, ucx866 15 16.5 18 v ucx863, ucx864, ucx867, ucx868 7 8.0 9 v vcc turn-off threshold ucx861, ucx862, ucx865, ucx866 9.5 10.5 11.5 v ucx863, ucx864, ucx867, ucx868 6 7.0 8 v icc start v cc = v cc (on) C 0.3v 150 300 m a icc run v id = 100mv 25 32 ma note 1: currents are defined as positive into the pin. note 2: pulse measurement techniques are used to insure that t j = t a . note 3: vid = v(ni) C v(inv). note 4: this parameter is not 100% tested in production but guaranteed by design. note 5: vi = 0 to 4v tr(vi) 10ns tpd = t(vo = 6v) C t(vi = 3v) uvlo & 5v generator (see figure 1): when power is applied to the chip and vcc is less than the upper uvlo threshold, icc will be less than 300 m a, the 5v gen- erator will be off, and the outputs will be actively held low. when vcc exceeds the upper uvlo threshold, the 5v generator turns on. until the 5v pin exceeds 4.9v, the outputs will still remain low. the 5v pin should be bypassed to signal ground with a 0.1 m f capacitor. the capacitor should have low equiva- lent series resistance and inductance. fault and soft-reference (see figure 1): the soft-ref pin serves three functions: system reference, re- start delay, and soft-start. designed to source or sink 200 m a, this pin should be used as the input reference for the error amplifier circuit. this pin requires a bypass ca- pacitor of at least 0.1 m f. this yields a minimum soft-start time of 1ms. under-voltage lockout sets both the fault and restart de- lay latches. this holds the outputs low and discharges the soft-ref pin. after uvlo, the fault latch is reset by the low voltage on the soft-ref pin. the reset fault latch resets the delay latch and soft-ref charges via the 0.5ma current source. the fault pin is input to a high speed comparator with a threshold of 3v. in the event of a detected fault, the fault latch is set and the outputs are driven low. if soft-ref is above 4v, the delay latch is set. restart delay is timed as soft-ref is discharged by 20 m a. when soft-ref is fully discharged, the fault latch is reset if the fault input signal is low. the fault pin can be used as a system shutdown pin. if a fault is detected during soft-start, the fault latch is set and the outputs are driven low. the delay latch will re- main reset until soft-ref charges to 4v. this sets the de- lay latch, and restart delay is timed. note that restart delay for a single fault event is longer than for recurring faults since soft-ref must be discharged from 5v instead of 4v. the restart delay to soft-start time ratio is 24:1 for a fault occurring during normal operation and 19:1 for faults oc- curring during soft-start. shorter ratios can be pro- grammed down to a limit of approximately 3:1 by the addition of a 20k w or larger resistor from soft-ref to ground. a 100k w resistor from soft-ref to 5v will have the effect of permanent shut down after a fault since the internal 20 m a current source can't pull soft-ref low. this feature can be used to require recycling vcc after a fault. care must be taken to insure soft-ref is indeed low at start up, or the fault latch will never be reset. application information
5 uc1861-1868 UC2861-2868 uc3861-3868 application information figure 1. uvlo, 5v, fault and soft-ref. udg-92020 udg-92021-1
6 figure 2. error amp, voltage controlled oscillator, and one shot udg-92022-1 udg-92023-1
7 uc1861-1868 UC2861-2868 uc3861-3868 minimum oscillator frequency is set by rmin and cvco. the minimum frequency is approximately given by the equation: f rc min min vco @ 43 . maximum oscillator frequency is set by rmin, range & cvco. the maximum frequency is approximately given by the equation: f r range c max min vco @ 33 . (// ) the error amplifier directly controls the oscillator fre- quency. e/a output low corresponds to minimum fre- quency and output high corresponds to maximum frequency. at the end of each oscillator cycle, the rc pin is discharged to one diode drop above ground. at the be- ginning of the oscillator cycle, v(rc) is less than vth1 and so the output of the zero detect comparator is ig- nored. after v(rc) exceeds vth1, the one shot pulse will be terminated as soon as the zero pin falls below 0.5v or v(rc) exceeds vth2. the minimum one shot pulse width is approximately given by the equation: tpw(min) 0.3 r c. the maximum pulse width is approximately given by: tpw(max) 1.2 rc. application information the steering logic is configured on the uc1861,63 to result in dual non-overlapping square waves at outputs a & b. this is suited to drive dual switch zvs systems. steering logic udg-92013 the steering logic is configured on the uc1862,64 to result in inverted pulse trains occurring identically at both output pins. this is suited to drive single switch zvs systems. both outputs are available to drive the same mosfet gate. it is advisable to join the pins with 0.5 ohm resistors. udg-92014 the steering logic is configured on the uc1865,67 to result in alternating pulse trains at outputs a & b. this is suited to drive dual switch zcs systems. udg-92015 the steering logic is configured on the uc1866,68 to result in non-inverted pulse trains occurring identically at both output pins. this is suited to drive single switch zcs systems. both outputs are available to drive the same mosfet gate. it is ad- visable to join the pins with 0.5 ohm resistors. udg-92016
8 uc1861-1868 UC2861-2868 uc3861-3868 application information (cont.) figure 3. current waveforms. unitrode corporation 7 continental blvd. ? merrimack, nh 03054 tel. (603) 424-2410 ? fax (603) 424-3460 udg-92017
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