UC1965 UC2965 UC3965 application INFO available Precision Reference with Low Offset Error Amplifier FEATURES DESCRIPTION • Accessible 2.5V Precision Reference The UC3965 is suitable for applications needing greater precision and more functionality than the TL431 type shunt regulators. The wide range VCC input capability enables the device to be biased from the secondary side output voltage rail, resulting in closed loop soft start. • 0.4% Initial Reference Accuracy • 1% Reference Accuracy over Line, Load, and Full Temperature Range • Low 1mV Offset Error Amplifier • Supports Closed Loop Soft Start • 2X Inverting Amplifier / Buffer Output • 4.1V Undervoltage Lockout • ICC 2mA at 5V • 8-Pin SOIC or DIL Package The UC3965 includes an accessible 2.5V precision reference which offers 0.4% initial and 1% reference accuracy over line, load, and full temperature range with a low offset error amplifier, a 2X inverting amplifier/buffer, and an undervoltage lockout circuit. The IC is ideally suited for applications where high precision PWM power supply regulation is required. Typically, the error amplifier is configured to compare a fraction of the to be regulated power supply voltage to the on-chip 2.5V reference. The 2X amplifier/buffer output is then used to drive a PWM controller or regulator. The UC3965 is also capable of driving an optocoupler diode for isolated applications. BLOCK DIAGRAM OFFSET VCC 1 2 + OB – GND 4 2k 7 VFB 6 VREF 5 NI VCC 3 15k COMP VREF 2.5V UVLO 5k VOUT 8 – EA + 7.5k 5k UDG-98055 SLUS300A - APRIL 1999 UC1965 UC2965 UC3965 CONNECTION DIAGRAM ABSOLUTE MAXIMUM RATINGS VCC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3V to 20V VREF. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3V to 6V VFB, COMP, NI, VOUT. . . . . . . . . . . . . . . . . . . . . –0.3V TO 6V Storage Temperature . . . . . . . . . . . . . . . . . . . −65°C to +150°C Junction Temperature . . . . . . . . . . . . . . . . . . . –55°C to +150°C Lead Temperature (Soldering, 10 sec.) . . . . . . . . . . . . . +300°C DIL-8, SOIC-8 (Top View) J or N Package, D Package Currents are positive into, negative out of the specified terminal. All voltages are with respect to ground. Consult Packaging Section of Databook for thermal limitations and considerations of packages. OFFSET 1 8 COMP VCC 2 7 VFB VOUT 3 6 VREF GND 4 5 NI ORDERING INFORMATION TEMPERATURE RANGE –55°C to +125°C –40°C to +85°C UC1965J UC2965D UC2965N UC3965D UC3965N 0°C to +70°C PACKAGE CDIP SOIC PDIP SOIC PDIP ELECTRICAL CHARACTERISTICS Unless otherwise specified, VCC = 5V, TA = TJ. PARAMETER TEST CONDITIONS MIN TYP MAX UNITS General VCC Operating Current 4.3 VCC = 5V 20 V 4 mA 200 µA 4.3 V 300 400 mV 1.5 2 Minimum Voltage to Start 3.9 4.1 Hysteresis 200 Undervoltage Current VREF VREF Initial Accuracy +25°C 2.49 2.5 2.51 V VREF Over Temperature –55°C to +125°C 2.48 2.5 2.52 V Total Output Variation Line, Load, Temperature 2.475 2.5 2.525 V Line Regulation VCC = 4.3V to 20V 2 10 mV Load Regulation 0µA to 500µA 2 10 mV Short Circuit Current VREF = 0V 2 Input Bias VCM = 2.5V 200 Input Offset Voltage VCM = 2.5V Input Offset Current VCM = 2.5V mA Error Amplifier Gain Bandwidth Product VIN = 50mV P-P (Note 1) Open Loop Gain VOUT = 1V to 3.75V 2 400 nA 1 2 mV –100 0 100 nA 6 MHz 80 100 dB UC1965 UC2965 UC3965 ELECTRICAL CHARACTERISTICS Unless otherwise specified, VCC = 5V, TA = TJ. PARAMETER TEST CONDITIONS MIN TYP MAX UNITS Error Amplifier Section (cont.) Output Low Level Output High Level IOUT = 0µA 0.8 V IOUT = 100µA 1.2 V IOUT = 0µA 4 V IOUT = –500µA 4 V Short Circuit Circuit VCOMP = 0V 8 mA CMRR VCM = 1.25V to 3.75V 70 100 dB PSRR VCC = 4.3V to 20V 70 100 dB Rising Slew Rate 2 V/µs Falling Slew Rate 0.4 V/µs Inverting Buffer Amplifier VCM = 2.5V Output Offset Voltage VCM = 2.5V Gain Bandwidth Product VIN = 50mV P-P (Note 1) Closed Loop Gain Inverting Gain Output Low Level IOUT = 0µA 0.3 V IOUT = 100µA 0.5 V 4 V Output High Level Short Circuit Circuit –20 1 2 0 20 µA Input Bias 1.5 –2.04 IOUT = 0mA –2 mV MHz –1.96 V/V IOUT = –4mA 4 V VOUT = 0V 18 mA CMRR VCM = 1.25V to 3.75V 70 100 dB PSRR VCC = 4.3V to 20V 70 100 dB Rising Slew Rate 0.9 V/µs Falling Slew Rate 0.9 V/µs Note 1: Guaranteed by design. Not 100% tested in production. PIN DESCRIPTIONS VFB: The inverting terminal of the error amplifier used as both the voltage sense input to the error amplifier and its other compensation point. COMP: The output of the error amplifier and the input to the inverting terminal of the internal output buffer. This pin is available to compensate the high frequency gain of the error amplifier. VOUT: The emitter of the output transistor. This pin is the output of the inverting buffer. This pin has the capability to drive an optocoupler or a PWM controller directly. GND: The reference and power ground for the device. NI: The non-inverting input to the error amplifier. VREF: The output of the trimmed precision reference. This reference maintains within 1% of its initial value over its entire line, load, and temperature range. OFFSET: The non-inverting input to the internal output buffer. VCC: The power input to the device. The minimum to maximum operating voltage is 4.3V to 20V. 3 UC1965 UC2965 UC3965 APPLICATION INFORMATION For designs requiring input-output isolation, the UC3965 is used in secondary side output voltage sensing. As shown in Fig. 1, the precision reference and low offset error amplifier can be used in converters, such as the isolated flyback, where the primary side error amplifier is not used or simply not present. In this case, the UCC3809 is used as the primary side controller. that insures accurate regulation of the output. The internal error amplifier drives the inverting input of the output buffer (OB) which drives an optocoupler diode. The wide range VCC voltage enables the device to be biased from the secondary side output voltage rail, resulting in closed loop soft start. As the output voltage increases beyond its desired value, the voltage difference at the error amplifier increases. This results in less drive at the inverting input of the internal buffer, increasing its output drive to the optocoupler. If the application does not require input-output isolation, this buffer could be used to drive the PWM directly. The precision reference of the UC3965 is tied to the non-inverting input of the device’s internal error amplifier. The output voltage of the converter is resistively divided and compared to this reference at the inverting input. This error amplifier has a low 1mV input offset voltage +V OUT 1 2 3 OFFSET COMP VCC VREF 2.5V UVLO VOUT 5k + OB – 4 +V IN 15k GND 2k UCC3809 2 SS 3 RT1 REF 8 VFB VCC – EA + 7.5k 5k 1 FB 8 VREF NI 7 6 5 –V OUT VDD 7 OUT 6 4 RT2 GND 5 –V IN UDG-99080 Figure 1. Typical application diagram. ADDITIONAL INFORMATION For additional application information biasing UC3965, please refer to the following publication: the [1] Application Note U-165, Design Review: Isolated 50W Flyback with the UCC3809 Primary Side Controller and the UC3965 Precision Reference and Error Amplifier, by Lisa Dinwoodie. UNITRODE CORPORATION 7 CONTINENTAL BLVD. • MERRIMACK, NH 03054 TEL. (603) 424-2410 • FAX (603) 424-3460 4