Signetics Linear Products DESCRIPTION The UC1842 family of control ICs pro- vides in an 8-Pin mini-DIP the necessary features to implement off-line, fixed-fre- quency current-mode control schemes with a minimal external parts count. This technique results in improved line regu- lation, enhanced load response charac- teristics, and a simpler, easier to design control loop. Topological advantages in- clude inherent pulse-by-pulse current limiting. Protection circuitry includes built-in un- UC1842 UC2842 UC3842 Current-Mode PWM Controller Product Specification FEATURES Low start-up current (< 1mA) Automatic feed-forward compensation Pulse-by-pulse current limiting e@ Enhanced load response characteristics Undervoltage lock-out with hysteresis Double pulse suppression e High current totem-pole output @ Internally-trimmed bandgap reference PIN CONFIGURATIONS N Package comp [7] Vee [2] isense [3] aye, [4] 18] Vacr [7] Vee [6] ouTPuT [5] GROUND TOP VIEW EDS. D Package dervoltage lock-out and current limiting. VReF Other features include fully-latched op- 400kHz operation, guaranteed Ne eration, a 1% trimmed bandgap refer- min y ence, and start-up current less than ce 1imA. APPLICATIONS Ve These devices feature a totem-pole aut. awe et mode power ourpur put designed to source and sink high PP GNO peak current from a capacitive load, DC-to-DC converters ra) Baer such as the gate of a power MOSFET. Cansistent with N-channel power de- TOP VIEW oe vices, the output is low in the OFF-state. aus BLOCK DIAGRAM Tran (12)7 Vee K ww uvLo k (995 sf (3 nS Se GND Tt if ev REF Soma 16V . 25 4] INTERNAL NJ BIAS. (7)4 [1 ow R/C, O& osc wT Ley 6(10) O OUTPUT ERROR AMP (3)2 Yep ee (ay CURRENT COMP SENSE CURRENT 68 COMPARATOR SENSE NOTE: Pin numbers in parentheses refer to the OD package. July 21, 1988 8-241 | 58) B0G365 853-0614 93932Signetics Linear Products Product Specification Current-Mode PWM Controller UC1842, UC2842, UC3842 ORDERING INFORMATION DESCRIPTION TEMPERATURE RANGE ORDER CODE 8-Pin Plastic DIP Q to +70C UC3842N 14-Pin Plastic SO 0 to +70C UC3842D 8-Pin Plastic DIP ~40 to +85C UC2842N | 14-Pin Plastic SO ~40 to +85C UC2842D 8-Pin Plastic DIP -55 to +125C UC1842N ABSOLUTE MAXIMUM RATINGS SYMBOL PARAMETER | RATING UNIT Voc Supply voitage (loc < 30mA) | Selt-Limiting Voc Supply voltage 30 v (low impedance source} lout Output current? 9 +4 A Output energy (capacitive load) 5 pd Analog inputs (Pin 2, Pin 3) -0.3 to 6.3 v Error amp output sink current 10 mA Pp Power dissipation at Ta < 70C 1 Ww (derate 12.5mW/C for Ta > 70C)* Tsta Storage temperature range -65C to +150 C TsoLp Lead temperature 300 C (soldering, 10sec max) NOTES: 1. All voltages are with respect to Pin 5. all currents are positive into tne specified terminal. 2. See section in application note an Power Dissipation Catculation. 3. This parameter is guaranteed, but not 100% tested in production. July 21, 1988 8-242Signetics Linear Products Product Specification Current-Mode PWM Controller UC1842, UC2842, UC3842 DC AND AC ELECTRICAL CHARACTERISTICS (Unless otherwise stated, these specifications apply for ~-55 s| GND | L Lo TC 16405 NOTE: Peak current (Is} is determined by the formula: 1.0V Is MAX = . s Ri S A smati AC filter may be reqiured to suppress switch transients. TYPICAL PERFORMANCE CHARACTERISTICS Error Amplifier Open-Loop Output Saturation Characteristics Frequency Response 4 T T T 100 45 Voc = 18 Ta = 28C | fs j g % zap+tt 1 ly z Ww s = g | | SINK SAT (Voy) = 8 1 ; = g SOURCE SAT (Vee - You) 4 /) Ww ao 90 i I < 9 2 Ss e x 2 = r 8 [| 8 20 -135 PEs 5 | | 0 -180 gt 7 TT wa I -20 -225 | | | 10 100 1K 10K 100K 1M 10M o FREQUENCY (Hz) aot 0.03005 04 03 05 10 OUTPUT CURRENT, SOURCE OR SINK (A) 0F077908 operao0s July 21, 1988 8-246Signetics Linear Products Product Specification Current-Mode PWM Controller UC1842, UC2842, UC3842 OPEN-LOOP LABORATORY TEST FIXTURE ner Pr Yoo nan} -_-- 47k rc Uc 1842 100k if a ~ COMP Vaer | | = tur ' ERAOR AMP 2y v J tk a ADJUST Vea Vee sour Siw = 5k > < 3 OUTPUT 47k 'sense sense l jourpur ADJUST 4 + Sf Rey a L__J = GND cy = 72116698, NOTE: High peak currents associated with capacitive loads necessitate careful grounding techniques. Timing and bypass capacitors should be connected close to Pin in a single pont ground The transistor and 5k potentiometer are used to sample the oscillator waveform and apply an adjustable ramp to Pin 3. SHUTDOWN TECHNIQUES 4.7K | SHUTDOWN > I | | I SHUTDOWN > | = TC116a68 TO CURRENT SENSE RESISTOR TC 118708 NOTE: Shutdown of the UC1842 can be accompished by two methoas: aitner 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 unti! the next clock cycle after the shutdown condition at Pins 1 and/or 3 is removed. In the examples shown, an externally-latched shutdown may be accomplished by adding an SCA which will be reset by cychng Voc below the lower UVLO threshold (10V). At this pont all internal bias is removed, allowing tne SCR to reset. July 21, 1988 8-247Signetics Linear Products Product Specification Current-Mode PWM Controller UC1842, UC2842, UC3842 OFF-LINE FLYBACK REGULATOR 3 parallel AWG 28 SPECIFICATIONS Input line voltage: Input frequency: Switching frequency: Output power: Output voitage: Output current: Line regulation: Load regulation: July 21, 1988 9OVac to 190Vac 50 or 60Hz 40kHz+ 10% 25W maximum 5Vt 5% 2 to 5A 0.01 %/V B%/A TI usp73s . p-_--O + 47k { 0 O1uF Bs0v Ty 4700uF oc FL T OUT < 56x wv Siw & in3e13 e O - 1N3613 ef. O.01uF Ll Lok 10uF 1 820k uc1a42 Veco | 7 7 T 20v pene. 20 > 3 ' | = & 2.5k t - z 2 = e 150k Vepy i ab | Jcome { | 5 36k 2 tA I | 100pF ! L al = 4 - q Veer | | > 10K 1 at Ay Cry \ OOF FR aR O00RTHE ' { GNO|5 ISOLATION i = BOUNDARY NOTES: T1 Collcraft E-4140-B Pnmary -97 turns single AWG 24 Secondary -4 turns 4 parallel AWG 22 Control -9 turns Efficiency @ 25 W, Vin = 90Vac: Vin = 130Vac: Output short-circuit current: 70 65% 2.5A average NOTE: This circuit uses a low-cost feedback scheme in which the DC voltage developed fram the prmary- side control winding is sensed by the UC 1842 error amplfer. Load regulation is therefore dependent on the coupling between secondary and contro! wind- ings, and on transformer leakage inductance. For applications requiring better load regulation, a UC1901 Isolated Feedback Generator can be used to directly sense the output voltage. 8-248 sv 2-5ASignetics Linear Products Product Specification Current-Mode PWM Controller UC1842, UC2842, UC3842 SYNCHRONIZATION AND MAXIMUM DUTY CYCLE CLAMP sv. Vee! 3 4 8 As RESET Vee ? at ? cr 71 DIScH 1 1 I i) Aye 3 Rod OUT i > NESSS ay (UCT? i ! t +4] tric i i Sl THRESH t- a GNo GND = om ' | TO OTHER a 1 * uctedzs 7O11700S NOTES: 1.44 { = ____ (Ra + 2Ra)C Ra OMax Fe aa July 21, 1988 8-249