Datasheet

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UCC1581

UCC2581

UCC3581

MARCH 1999 - REVISED MARCH 2003 - SLUS295B

FEATURES

•

Low 85µA Startup Current

•

Low 300µA Operating Current

•

Automatically Disabled

Startup Preregulator

•

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

Micropower Voltage Mode PWM

BLOCK DIAGRAM

DESCRIPTION

The UCC3581 voltage mode pulse width modulator is de

signed to control low power isolated DC - DC converters

in applications such as Subscriber Line Power (ISDN

I.430). Primarily used for single switch forward and

flyback converters, the UCC3581 features BiCMOS cir

cuitry for low startup and operating current, while main

taining the ability to drive power MOSFETs at

frequencies up to 100kHz. The UCC3581 oscillator al

lows the flexibility to program both the frequency and the

maximum duty cycle with two resistors and a capacitor. A

TTL level input is also provided to allow synchronization

to an external frequency source.

The UCC3581 includes programmable soft start circuitry,

overcurrent detection, a 7.5V linear preregulator to con

trol chip V

DD during startup, and an on-board 4.0V logic

supply.

The UCC3581 provides functions to maximize light load

efficiency that are not normally found in PWM controllers.

A linear preregulator driver in conjunction with an exter

nal depletion mode N-MOSFET provides initial controller

power. Once the bootstrap supply is functional, the

preregulator is shut down to conserve power. During light

load, power is saved by providing a programmable mini

mum duty cycle clamp. When a duty cycle below the

minimum is called for, the modulator skips cycles to pro

vide the correct average duty cycle required for output

regulation. This effectively reduces the switching fre

quency, saving significant gate drive and power stage

losses.

The UCC3581 is available in 14-pin plastic and ceramic

dual-in-line packages and in a 14-pin narrow body small

outline IC package (SOIC). The UCC1581 is specified for

operation from −55°C to +125°C, the UCC2581 is speci

fied for operation from −40°C to +85°C, and the

UCC3581 is specified for operation from 0°C to +70°C.

Note: Pin Connection shown for 14-pin Package

UDG-95011-1

application

INFO

available

Summary of content (16 pages)

PAGE 1
application INFO available UCC1581 UCC2581 UCC3581 Micropower Voltage Mode PWM FEATURES BLOCK DIAGRAM • Low 85µA Startup Current • Low 300µA Operating Current • Automatically Disabled Startup Preregulator • 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 DE
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UCC1581 UCC2581 UCC3581 CONNECTION DIAGRAMS ABSOLUTE MAXIMUM RATINGS Supply Voltage (IDD ≤ 10mA). . . . . . . . . . . . . . . . . . . . . . . . 15V Supply Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30mA VREF Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –10mA OUT Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ± 1A Analog Inputs EN . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3V to (VDD + 0.
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UCC1581 UCC2581 UCC3581 ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these specifications apply for VDD = 10V, 0.1µF capacitor from VDD to GND, 1.0µF capacitor from REF to GND, RT1 = 680kΩ, RT2 = 12kΩ, CT = 750pF and TA = TJ. PARAMETER TEST CONDITIONS MIN TYP MAX UNITS –150 20 150 nA 0.4 0.5 0.6 V Current Sense Section Input Bias Current Overcurrent Threshold Output Section OUT Low Level I = 100mA 0.6 1.2 V OUT High Level I = –100mA, VDD – OUT 0.6 1.
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UCC1581 UCC2581 UCC3581 APPLICATION INFORMATION The UCC3581’s oscillator allows the user the flexibility to program the frequency and the duty cycle by adjusting two resistors and a capacitor. Application Diagram Fig. 1 shows these components as RT1, RT2, and CT. RT1 programs the timing capacitor charging current which results in a linear ramp charging CT. Discharge of CT is accomplished though RT2 which results in a standard RC discharge waveform.
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UCC1581 UCC2581 UCC3581 APPLICATION INFORMATION (cont.) The externally bypassed 4.0V reference is controlled by undervoltage lockout and chip enable circuitry. The enable input is internally tied to a 10µA current source which allows the pin to be driven by an open collector driver. The part is also enabled if EN floats. The UCC3581 has a soft start function which requires a user supplied external timing capacitor.
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UCC1581 UCC2581 UCC3581 TYPICAL APPLICATION UDG-96104 Figure 3. Micropower power supply with 50% efficiency at 12.5mW load. 90 80 25V Line Efficiency [%] 70 100V Line 60 50 40 30 20 10 0 10 100 Output Load [mW] Figure 4. UCC3581 efficiency vs. line and load.
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UCC1581 UCC2581 UCC3581 APPLICATION INFORMATION (cont.) A rather large soft start capacitor was chosen to give a startup time of several hundred milliseconds, reducing the input surge current while the output is coming up. If the sync input is used, it should not be left in a high impedance state where noise could cause false triggering. If unused, it should be grounded. Note that for stability, the UCC3581 VREF bypass capacitor needs to be at least 1µF.
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UCC1581 UCC2581 UCC3581 TYPICAL CHARACTERISTIC CURVES (cont.) 40 ISOFT START [uA] 35 30 25 20 15 10 5 0 200 400 600 800 1000 1200 RT1 [kW] Figure 9. Soft start current vs. RT1. UNITRODE CORPORATION 7 CONTINENTAL BLVD. • MERRIMACK, NH 03054 TEL.
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PACKAGE OPTION ADDENDUM www.ti.
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PACKAGE OPTION ADDENDUM www.ti.com 10-Jun-2014 (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.
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PACKAGE MATERIALS INFORMATION www.ti.com 24-Jul-2013 TAPE AND REEL INFORMATION *All dimensions are nominal Device Package Package Pins Type Drawing SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant 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.
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PACKAGE MATERIALS INFORMATION www.ti.com 24-Jul-2013 *All dimensions are nominal Device Package Type Package Drawing 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.
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