application UCC1581 INFO UCC2581 available UCC3581 Micropower Voltage Mode PWM FEATURES BLOCK DIAGRAM • Low 85µA Startup Current • Low 300µA Operating Current • Automatically Disabled StartupPreregulator • Programmable Minimum Duty Cycle with Cycle Skipping • Programmable Maximum Duty Cycle • Output Current 1A Peak Source and Sink • Programmable Soft Start • Programmable Oscillator Frequency • External Oscillator Synchronization Capability Note:Pin Connection shown for 14-pin Package UDG-95011-1 DESCRIPTION TheUCC3581voltagemodepulsewidthmodulatorisde- A linear preregulator driver in conjunction with an exter- signed to control low power isolated DC - DC converters nal depletion mode N-MOSFET provides initial controller in applications such as Subscriber Line Power (ISDN power. Once the bootstrap supply is functional, the I.430). Primarily used for single switch forward and preregulatorisshutdowntoconservepower.Duringlight flyback converters, the UCC3581 features BiCMOS cir- load, power is saved by providing a programmable mini- cuitry for low startup and operating current, while main- mum duty cycle clamp. When a duty cycle below the taining the ability to drive power MOSFETs at minimum is called for, the modulator skips cycles to pro- frequencies up to 100kHz. The UCC3581 oscillator al- vide the correct average duty cycle required for output lows the flexibility to program both the frequency and the regulation. This effectively reduces the switching fre- maximumdutycyclewithtworesistorsandacapacitor.A quency, saving significant gate drive and power stage TTL level input is also provided to allow synchronization losses. to an external frequency source. The UCC3581 is available in 14-pin plastic and ceramic The UCC3581 includes programmable soft start circuitry, dual-in-line packages and in a 14-pin narrow body small overcurrent detection, a 7.5V linear preregulator to con- outlineICpackage(SOIC).TheUCC1581isspecifiedfor trol chip VDD during startup, and an on-board 4.0V logic operation from −55°C to +125°C, the UCC2581 is speci- supply. fied for operation from −40°C to +85°C, and the The UCC3581 provides functions to maximize light load UCC3581 is specified for operation from 0°C to +70°C. efficiencythatarenotnormallyfoundinPWMcontrollers. MARCH 1999 - REVISED MARCH 2003 - SLUS295B

UCC1581 UCC2581 UCC3581 ABSOLUTE MAXIMUM RATINGS CONNECTION DIAGRAMS Supply Voltage (IDD≤10mA). . . . . . . . . . . . . . . . . . . . . . . .15V DIL-14,SOIC-14(Top View) Supply Current. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30mA N or J,D Packages V Current. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .–10mA REF OUT Current. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .±1A Analog Inputs EN. . . . . . . . . . . . . . . . . . . . . . . . . . . .–0.3V to (VDD+ 0.3V) VC,ISEN, SYNC,DCMIN. . . . . . . . . .–0.3V to (V + 0.3V) REF Power Dissipation atT = 25°C D (N, J, Q, L Package) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1W (D Package). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .0.65W Storage Temperature. . . . . . . . . . . . . . . . . . .–65°C to +150°C Junction Temperature . . . . . . . . . . . . . . . . . . .–55C to +150°C Lead Temperature (Soldering, 10 sec.). . . . . . . . . . . . .+300°C Unless otherwise specified, all voltages are with respect to Ground.Currentspositiveinto,negativeoutofthespecifiedter- minal.ConsultPackagingSectionofDatabookforthermallimi- tations and considerations of packages. ORDERING INFORMATION TEMPERATURE RANGE PACKAGE UCC1581J –55°C to +125°C CDIP UCC2581D –40°C to +85°C SOIC UCC2581N –40°C to +85°C PDIP UCC3581D 0°C to +70°C SOIC UCC3581N 0°C to +70°C PDIP ELECTRICAL CHARACTERISTICS:Unless otherwise stated, these specifications apply forVDD= 10V, 0.1µF capacitor fromVDDtoGND, 1.0µF capacitor from REF toGND, RT1 = 680kΩ, RT2 = 12kΩ, CT = 750pF and TA=TJ. PARAMETER TEST CONDITIONS MIN TYP MAX UNITS Reference Section Output Voltage I = –0.2mA 3.94 4.0 4.06 V Load Regulation –5.0mA < I < –0.2mA 20 45 mV UndervoltageLockout Section Start Threshold 6.7 7.3 7.9 V Minimum Operating Voltage After Start 6.2 6.8 7.4 V Hysteresis 0.2 0.5 0.8 V LinearPreregulatorSection RegulatedVDDVoltage 7.0 7.5 8.0 V RegulatedVDDtoUVLODelta 100 230 600 mV VDDOverride Threshold 8.2 V Oscillator Section Frequency 25°C 18 19.5 21 kHz Temperature Stability (Note 1) 3.0 % CT Peak Voltage (Note 1) 2.5 V CT Valley Voltage (Note 1) 1.0 V SYNCVIH 1.9 2.1 2.3 V SYNCVIL (Note 1) 1.8 V PWMSECTION Maximum Duty Cycle 81 84 87 % Minimum Duty Cycle (VC < 1.0V)DCMIN= 0V 0 % (VC > 1.0V at start of cycle)DCMIN= 1.18V 7 10 13 % Input Bias Current (DCMIN), (Note 1) –150 20 150 nA (VC), (Note 1) –150 20 150 nA 2

UCC1581 UCC2581 UCC3581 ELECTRICAL CHARACTERISTICS:Unless otherwise stated, these specifications apply forVDD= 10V, 0.1µF capacitor fromVDDtoGND, 1.0µF capacitor from REF toGND, RT1 = 680kΩ, RT2 = 12kΩ, CT = 750pF and TA=TJ. PARAMETER TEST CONDITIONS MIN TYP MAX UNITS Current Sense Section Input Bias Current –150 20 150 nA OvercurrentThreshold 0.4 0.5 0.6 V Output Section OUT Low Level I = 100mA 0.6 1.2 V OUT High Level I = –100mA,VDD– OUT 0.6 1.2 V Rise/Fall Time (Note 1) 20 100 ns Soft start Section Soft start Current SS = 2V –9 –11.5 –14 µA Chip Enable Section VIH 1.9 2.0 2.1 V VIL 1.7 1.8 1.9 V Hysteresis 180 230 280 mV Source Current 5 10 15 µA Overall Section Start-Up Current VDD< Start Threshold 85 130 µA Operating Supply Current VC = 0V 300 600 µA VDDZenerShunt Voltage I = 10mA 13.5 15 16.5 V DD IDDStand-by Shunt Voltage EN = 0V 100 150 µA Note 1:Guaranteed by design.Not 100% tested in production PIN DESCRIPTIONS CT: Oscillator timing capacitor pin. Minimum value is 2.0V The oscillator charging current is9.2• . 100pF. RT1 DCMIN: Input for programming minimum duty cycle See Application Diagram Fig.1. where pulse skipping begins. This pin can be grounded 2.0V   The current into this pin is . to disable minimum duty cycle feature and pulse RT1 skipping. The value of RT1should be between 220k and 1MΩ. EN: Enable input. This pin has an internal 10µA pull-up. AlogiclowinputinhibitsthePWMoutputandcausesthe RT2: Resistor pin to program oscillator discharge time. soft start capacitor to be discharged. The minimum value of RT2 is 10kΩ. See Application Diagram Fig.1. GND:Circuit ground. SS: Soft start capacitor pin. The charging current out of GT: Pin for controlling the gate of an external depletion SS is 3.75X the current in RT1. mode N-MOSFET for the startup supply. The external N-MOSFET regulates VDD to 7.5V until the bootstrap SYNC: Oscillator synchronization pin. Rising edge supply comes up, thenGTgoes low. triggered CMOS/TTL compatible input with a 2.1V threshold. SYNC should be grounded if not used. The ISEN:Input for overcurrent comparator.This function can minimum pulse width of the SYNC signal is 100ns. be used for pulse-by-pulse current limiting.The threshold is 0.5V nominal. VC: Control voltage input to PWM comparator. The nominal control range of VC is 1.0V to 2.5V. OUT:Gate drive output to externalN-MOSFET. VDD: Chip input power with an 15V internal clamp.VDD REF: 4.0V reference output. A minimum value bypass is regulated by startup FET to 7.5V until the bootstrap capacitor of 1.0µF is required for stability. voltage comes up. VDD should be bypassed at the chip RT1: Resistor pin to program oscillator charging current. with a 0.1µF minimum capacitor. 3

UCC1581 UCC2581 UCC3581 APPLICATION INFORMATION The UCC3581’s oscillator allows the user the flexibility to program the frequency and the duty cycle by adjusting RT2 two resistors and a capacitor.Application Diagram Fig.1 showsthesecomponentsasRT1,RT2,andCT.RT1pro- UCC3581 gramsthetimingcapacitorchargingcurrentwhichresults 1 CT RT2 14 V in a linear ramp charging CT. Discharge of CT is accom- CT IN plished though RT2 which results in a standard RC dis- BSS129OR SYNC 13 EQUIV. 2 GT charge waveform.The oscillator on-time (CT charging) is D2 calculated by the formula 3 VDD RT1 12 1µF t =0.082•RT1•C . RT1 ON T The off-time (CTdischarging) is calculated by the formula EN 11 t =0.95•RT1•C . Q1 SS 10 OFF T 4 OUT Resistor RT1 programs the charging current. The current CSS REF is: 5 GND DCMIN 9 2.0V . RT1 6 REF REF 1µF REF CT charging current is 9.2 times the current in RT1.RT1 can range from 220kΩ to 1MΩ. Minimum capacitor size 7 ISEN VC 8 is 100pF, and minimum RT2size is 10k. VIN U1 D1 A Block Diagram of the Oscillator is shown in Fig.2.The REF& oscillator also has an external synchronization pin. E/A U1 When a low to high level is detected, and if the oscilla- RL tor’s output is in the high state (CT charging), the oscilla- T1 tor output immediately goes low and CT starts UDG-99043 discharging. The sync input is rising edge sensitive and is ignored when the oscillator output is low. Figure 1.Application diagram. UDG-96105 Figure 2.Oscillator. 4

UCC1581 UCC2581 UCC3581 APPLICATION INFORMATION (cont.) The externally bypassed 4.0V reference is controlled by A TypicalMicropowerApplication undervoltage lockout and chip enable circuitry. The en- The circuit shown in Fig. 3 illustrates the use of the able input is internally tied to a 10µA current source UCC3581 in a micropower application. The isolated 5V which allows the pin to be driven by an open collector flyback power supply uses a minimum of parts and oper- driver. The part is also enabled if EN floats. The atesoveran8:1inputvoltagerange(15VDCto120VDC) UCC3581 has a soft start function which requires a user while delivering a regulated 5V output with a load swing supplied external timing capacitor. When in soft start from 0W to 1W.It operates in the discontinuous mode at mode, the soft start capacitor, CSS, is charged with a light load or high line, and continuous mode at heavier constant current source. The soft start current is 3.75X loads and lower line voltages. Higher input line voltages the current in RT1. are possible by simply increasing the voltage ratings of There is an on-chip control amplifier, which when driving C1, Q1, D1 and D2. the gate of an external depletion mode N-MOSFET, acts The most notable feature of the design is its efficiency. as a 7.5V linear preregulator supplying VDDdirectly from With a load of 1 watt, the typical efficiency is 82%, drop- the primary input power line. The preregulator may sub- ping to 70% around 50mW.With a load of only 12.5mW, sequentlybefullydisabledbyatertiarybootstrapwinding the efficiency remains as high as 50%.At this load, with providing a minimum of 8.2V to theVDDpin. an input of 50V, the total input current is only 500µA. Computation ofDCMIN Notethatthepowersupplycanbedisabledbypullingthe UCC3581 enable pin low, in which case the input current DCMINfor a given duty cycle is calculated as follows: drops to less than 150µA. ( ) t +t ∆V=i •DC• ON OFF The UCC3581 achieves very low losses by means of low OSC C T quiescent current and pulse skipping at light loads which where: reducesswitchinglosses.Thedegreeofpulseskippingis controlled by programming the minimum duty cycle. In • i= oscillator charge current = 9.2 . (2.0V/RT1) this example, the frequency is 35kHz at maximum load • DC = Duty Cycle, as a fraction of 1 and drops to <2kHz at 12.5mW load (minimum pulse width of around 6µsec, or 21% duty cycle at 35kHz). • t = 0.082•RT1•CT ON Another way losses are reduced is operating with a VDD • t = 0.95•RT2•CT of around 10V rather than the more common 12V to 16V. OFF At such light primary currents, the MOSFET remains in • C = Oscillator Capacitor T full saturation with a gate drive voltage well below 10V. The CT pin ramp slews from 1V to 2.5V. Therefore, add Gate drive losses are minimized by choosing a MOSFET ∆Vto 1V to getDCMINvoltage. with low total gate charge, in this case only 8nC maxi- Example: For 10% duty cycle with RT1 = 680kΩ, RT2 = mum.Bychoosingalargegatedriveresistor,EMIismin- 12kΩ, and CT = 705pF, imized by reducing peak currents.Due to pulse skipping, switching times are less critical for efficiency at light load. ( ) The shunt regulator (LM3411) and optocoupler t +t ∆V=i •DC• ON OFF (MOC8100) are also key to the efficiency at such light OSC C T loads, and were chosen for their low operating current. TheLM3411hasaquiescentcurrentofonly150µAmax- 9.2•628.00Vk•(0.1)•4.182•10−5sec+8.55•10−6sec iImnuamdd(itcioonm,pbaerceadutsoe1itmisAnfootrathtehrmeeorteercmoimnamlodnevTicLe4,3th1e). = LM3411’s quiescent current does not flow in the 750•10−12 optocoupler LED. Since this bias current is not in the ∆V=0.18V feedbackcontrol path,ahighervaluepull-upresistorcan be used on the optocoupler output transistor, further re- Therefore, ducing losses. DCMIN=1V+0.18V=1.18V 5

UCC1581 UCC2581 UCC3581 TYPICAL APPLICATION UDG-96104 Figure 3.Micropowerpower supply with 50% efficiency at 12.5mW load. 90 80 25V Line 70 ] 60 100V Line % [ y 50 c n e i 40 c i f f E 30 20 10 0 10 100 1000 Output Load [mW] Figure 4.UCC3581 efficiency vs.line and load. 6

UCC1581 UCC2581 UCC3581 APPLICATION INFORMATION (cont.) A rather large soft start capacitor was chosen to give a Ifthesyncinputisused,itshouldnotbeleftinahighim- startup time of several hundred milliseconds, reducing pedance state where noise could cause false triggering. the input surge current while the output is coming up. If unused, it should be grounded. Note that for stability, the UCC3581 VREF bypass capaci- ThetransformerwasdesignedwithastandardMagnetics tor needs to be at least 1µF.The VDD supply also needs RM8 ferrite core using P material, gapped for an AL of 2 some capacitance to hold it up between pulses at light 1600mH/1000Turn . The primary consists of 44 turns, load and high line, where the frequency may drop to less while the 5V secondary has 10 turns and the bootstrap than 1kHz due to pulse skipping. Otherwise it may drop winding 18 turns. For simplicity, all the windings can be low enough for the startup MOSFET to be biased on, #28AWG.Atwosectionbobbinwasusedtoprovidehigh lowering efficiency. primary to secondary isolation. A much smaller design, with reduced isolation, could have been done for this low power level. TYPICAL CHARACTERISTIC CURVES 4.10 140 470k/47k 4.08 120 4.06 4.04 Hz] 100 680k/12k k V] 4.02 Y[ 80 [ C EF 4.00 N VR 3.98 UE 60 Q 3.96 E R 40 1M/10k 3.94 F 3.92 20 220k/10k 3.90 0 -75 -50 -25 0 25 50 75 100 125 100 1000 10000 TEMPERATURE[°C] CT[pF] Figure 5.Reference voltage vs.temperature. Figure 6.Frequency vs.CT vs.RT1 and RT2. 1600 100 1M/10K 1nFLOAD 1400 90 %] 1200 80 [ 680K/12K E 1000 CL 70 A] Y [u 800 C 60 220K/10K DD Y I 600 NO UT 50 LOAD D 400 470K/47K 40 200 30 0 0 20 40 60 80 100 0 20 40 60 80 100 FREQUENCY[kHz] FREQUENCY[kHz] Figure 7.Duty cycle vs.frequency vs.RT1 / RT2. Figure 8.I vs.frequency RT1 = 680k,RT2 = 12k. DD 7

UCC1581 UCC2581 UCC3581 TYPICAL CHARACTERISTIC CURVES (cont.) 40 35 30 A] [u 25 T R A 20 T S FT 15 O S I 10 5 0 200 400 600 800 1000 1200 RT1[kW] Figure 9.Soft start current vs.RT1. UNITRODE CORPORATION 7 CONTINENTAL BLVD.(cid:127) MERRIMACK, NH 03054 TEL.(603) 424-2410 FAX (603) 424-3460 8

PACKAGE OPTION ADDENDUM www.ti.com 6-Feb-2020 PACKAGING INFORMATION Orderable Device Status Package Type Package Pins Package Eco Plan Lead/Ball Finish MSL Peak Temp Op Temp (°C) Device Marking Samples (1) Drawing Qty (2) (6) (3) (4/5) UCC2581D ACTIVE SOIC D 14 50 Green (RoHS NIPDAU Level-2-260C-1 YEAR -40 to 85 UCC2581D & no Sb/Br) UCC2581DTR ACTIVE SOIC D 14 2500 Green (RoHS NIPDAU Level-2-260C-1 YEAR -40 to 85 UCC2581D & no Sb/Br) UCC2581DTRG4 ACTIVE SOIC D 14 2500 Green (RoHS NIPDAU Level-2-260C-1 YEAR -40 to 85 UCC2581D & no Sb/Br) UCC3581D ACTIVE SOIC D 14 50 Green (RoHS NIPDAU Level-2-260C-1 YEAR 0 to 70 UCC3581D & no Sb/Br) UCC3581DTR ACTIVE SOIC D 14 2500 Green (RoHS NIPDAU Level-2-260C-1 YEAR 0 to 70 UCC3581D & no Sb/Br) (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may reference these types of products as "Pb-Free". RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption. Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based flame retardants must also meet the <=1000ppm threshold requirement. (3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. (4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device. (5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation of the previous line and the two combined represent the entire Device Marking for that device. (6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish value exceeds the maximum column width. Addendum-Page 1

PACKAGE OPTION ADDENDUM www.ti.com 6-Feb-2020 Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release. In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis. Addendum-Page 2

PACKAGE MATERIALS INFORMATION www.ti.com 24-Jul-2013 TAPE AND REEL INFORMATION *Alldimensionsarenominal Device Package Package Pins SPQ Reel Reel A0 B0 K0 P1 W Pin1 Type Drawing Diameter Width (mm) (mm) (mm) (mm) (mm) Quadrant (mm) W1(mm) UCC2581DTR SOIC D 14 2500 330.0 16.4 6.5 9.0 2.1 8.0 16.0 Q1 UCC3581DTR SOIC D 14 2500 330.0 16.4 6.5 9.0 2.1 8.0 16.0 Q1 PackMaterials-Page1

PACKAGE MATERIALS INFORMATION www.ti.com 24-Jul-2013 *Alldimensionsarenominal Device PackageType PackageDrawing Pins SPQ Length(mm) Width(mm) Height(mm) UCC2581DTR SOIC D 14 2500 367.0 367.0 38.0 UCC3581DTR SOIC D 14 2500 367.0 367.0 38.0 PackMaterials-Page2

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