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UC1901 UC2901 UC3901
Isolated Feedback Generator
FEATURES
* An Amplitude-Modulation System for Transformer Coupling an Isolated Feedback Error Signal * Low-Cost Alternative to Optical Couplers * Internal 1% Reference and Error Amplifier * Internal Carrier Oscillator Usable to 5MHz * Modulator Synchronizable to an External Clock * Loop Status Monitor
DESCRIPTION
The UC1901 family is designed to solve many of the problems associated with closing a feedback control loop across a voltage isolation boundary. As a stable and reliable alternative to an optical coupler, these devices feature an amplitude modulation system which allows a loop error signal to be coupled with a small RF transformer or capacitor. The programmable, high-frequency oscillator within the UC1901 series permits the use of smaller, less expensive transformers which can readily be built to meet the isolation requirements of today's line-operated power systems. As an alternative to RF operation, the external clock input to these devices allows synchronization to a system clock or to the switching frequency of a SMPS. An additional feature is a status monitoring circuit which provides an activelow output when the sensed error voltage is within 10% of the reference. The DRIVERA output, DRIVERB output, and STATUS output are disabled until the input supply has reached a sufficient level to allow proper operation of the device. Since these devices can also be used as a DC driver for optical couplers, the benefits of 4.5 to 40V supply operation, a 1% accurate reference, and a high gain general purpose amplifier offer advantages even though an AC system may not be desired.
UC1901 SIMPLIFIED SCHEMATIC
UDG-98080
11/98
UC1901 UC2901 UC3901 ABSOLUTE MAXIMUM RATINGS (Note 1)
Input Supply Voltage, VIN . . . . . . . . . . . . . . . . . . . . . . . . . . 40V Reference Output Current . . . . . . . . . . . . . . . . . . . . . . . -10mA Driver Output Currents . . . . . . . . . . . . . . . . . . . . . . . . . . -35mA Status Indicator Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . 40V Status Indicator Current . . . . . . . . . . . . . . . . . . . . . . . . . . 20mA Ext. Clock Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40V Error Amplifier Inputs . . . . . . . . . . . . . . . . . . . . . -0.5V to +35V Power Dissipation at TA = 25C . . . . . . . . . . . . . . . . . . 1000mW Power Dissipation at TC = 25C . . . . . . . . . . . . . . . . . 2000mW Operating Junction Temperature . . . . . . . . . . -55C to +150C Storage Temperature . . . . . . . . . . . . . . . . . . . -65C to +150C Lead Temperature (Soldering, 10 seconds) . . . . . . . . . . 300C
CONNECTION DIAGRAMS
DIL-14, SOIC-14 (TOP VIEW) J or N Package, D Package
Note 1: Voltages are referenced to ground, Pin 7. Currents are positive into, negative out of the specified terminal. Note 2: Consult Packaging section of Databook for thermal limitations and considerations of package.
SOIC-16 Wide (TOP VIEW) DW Package
PLCC-20, LCC-20 (TOP VIEW) Q, L Packages
TEMPERATURE AND PACKAGE SELECTION GUIDE
TEMPERATURE RANGE -55C to +125C -40C to +85C 0C to +70C AVAILABLE PACKAGES J, L D, DW, J, N, Q D, DW, J, N, Q
UC1901 UC2901 UC3901
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UC1901 UC2901 UC3901 ELECTRICAL CHARACTERISTICS Unless otherwise stated, these specifications apply for VIN = 10V, RT = 10k, CT =
820pF, TA = TJ. PARAMETER Reference Section Output Voltage TEST CONDITIONS UC1901/UC2901 MIN TYP MAX 1.485 1.470 1.5 1.5 2 4 -35 1 -1 0.1 60 80 100 0.7 150 -3 1 0.3 12 2.8 700 -35 25 150 .15 5 0.5 1.6 135 8 150 15 .05 5 3.9 3.9 -2 165 0.45 1 8 4.5 4.5 -30 130 8 150 15 .05 5 3.9 3.9 -2 1.515 1.530 10 10 -55 4 -3 1 40 60 80 0.4 90 -2 MIN 1.47 1.455 UC3901 UNITS TYP MAX 1.5 1.5 2 4 -35 1 -1 0.1 60 80 100 0.7 150 -3 1 0.3 12 2.8 700 -35 25 150 .15 5 0.5 1.6 170 0.45 5 10 4.5 4.5 -30 1.53 1.545 15 15 -55 8 -6 2 V mV mV mV mV A A dB dB dB V A mA MHz V/S dB V A mA MHz kHz kHz %/V MHz V V mV V mA A mA V V mV
TJ = 25C TMIN TJ TMAX Line Regulation VIN = 4.5 to 35V Load Regulation IOUT = 0 to 5mA Short Circuit Current TJ = 25C Error Amplifier Section (To Compensation Terminal) Input Offset Voltage VCM = 1.5V Input Bias Current VCM = 1.5V Input Offset Current VCM = 1.5V Small Signal Open Loop Gain CMRR VCM = 0.5 to 7.5V PSRR VIN = 2 to 25V Output Swing, VO Maximum Sink Current Maximum Source Current Gain Band Width Product Slew Rate Modulators/Drivers Section (From Compensation Terminal) Voltage Gain Output Swing Driver Sink Current Driver Source Current Gain Band Width Product Oscillator Section Initial Accuracy TJ = 25C TMIN TJ TMAX Line Sensitivity VIN = 5 to 35V Maximum Frequency RT = 10k, CT = 10pF Ext. Clock Low Threshold Pin 1 (CT) = VIN Ext. Clock High Threshold Pin 1 (CT) = VIN Status Indicator Section Input Voltage Window @ E/A Inputs, VCM = 1.5V Saturation Voltage E/A Input = 0V, ISINK = 1.6mA Max. Output Current Pin 13 = 3V, E/A Input = 0.0V Leakage Current Pin 13 = 40V, E/A Input = 0.2V Supply Current VIN = 35V UVLO Section Drivers Enabled Threshold At Input Supply VIN Status Output Enabled At Input Supply VIN Threshold Change in Reference Output When VIN Reaches UVLO Threshold
40 60 80 0.4 90 -2
11 1.6 500 -15
13
10 1.6 500 -15
14
140 130
160 170 .35
130 120
170 180 .60
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UC1901 UC2901 UC3901
Note:
Transformer Data: N1 = N2 = 20TAWG 26 Core = Ferroxcube 3E2A Ferrite, 0.5" O.D. toroid Carrier Frequency = 1MHz
Figure 1. Transformer Coupled Open Loop Transfer Function
Figure 2. Oscillator Frequency
Figure 3. Typical Driver Output Swing vs Temperature
APPLICATION INFORMATION
The error amplifier compensation terminal, Pin 12, is intended as a source of feedback to the amplifier's inverting input at Pin 11. For most applications, a series DC blocking capacitor should be part of the feedback network. The amplifier is internally compensated for unity feedback. The waveform at the driver outputs is a squarewave with an amplitude that is proportional to the error amplifier input signal. There is a fixed 12dB of gain from the error amplifier compensation pin to the modulator driver outputs. The frequency of the output waveform is controlled by either the internal oscillator or an external clock signal. 4 With the internal oscillator the squarewave will have a fixed 50% duty cycle. If the internal oscillator is disabled by connecting Pin 1, CR, to VIN then the frequency and duty cycle of the output will be determined by the input clock waveform at Pin 2. If the oscillator remains disabled and there is not clock input at Pin 2, there will be a linear 12dB of signal gain to one or the other of the driver outputs depending on the DC state of Pin 2. The driver outputs are emitter followers which will source a minimum of 15mA of current. The sink current, internally limited at 700A, can be increased by adding resistors to ground at the driver outputs.
UC1901 UC2901 UC3901 APPLICATION INFORMATION (continued)
Figure 4. R.F. Transformer Coupled Feedback
Figure 5. Feedback Coupled at Switching Frequency
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UC1901 UC2901 UC3901 TYPICAL APPLICATION
UDG-98196
Figure 6. Optically Coupled DC Feedback
UNITRODE CORPORATION 7 CONTINENTAL BLVD. * MERRIMACK, NH 03054 TEL. (603) 424-2410 * FAX (603) 424-3460
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IMPORTANT NOTICE Texas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue any product or service without notice, and advise customers to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. TI warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with TI's standard warranty. Testing and other quality control techniques are utilized to the extent TI deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed, except those mandated by government requirements. CERTAIN APPLICATIONS USING SEMICONDUCTOR PRODUCTS MAY INVOLVE POTENTIAL RISKS OF DEATH, PERSONAL INJURY, OR SEVERE PROPERTY OR ENVIRONMENTAL DAMAGE ("CRITICAL APPLICATIONS"). TI SEMICONDUCTOR PRODUCTS ARE NOT DESIGNED, AUTHORIZED, OR WARRANTED TO BE SUITABLE FOR USE IN LIFE-SUPPORT DEVICES OR SYSTEMS OR OTHER CRITICAL APPLICATIONS. INCLUSION OF TI PRODUCTS IN SUCH APPLICATIONS IS UNDERSTOOD TO BE FULLY AT THE CUSTOMER'S RISK. In order to minimize risks associated with the customer's applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. TI assumes no liability for applications assistance or customer product design. TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other intellectual property right of TI covering or relating to any combination, machine, or process in which such semiconductor products or services might be or are used. TI's publication of information regarding any third party's products or services does not constitute TI's approval, warranty or endorsement thereof.
Copyright (c) 1999, Texas Instruments Incorporated

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