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THIS DOCUMENT IS FOR MAINTENANCE PURPOSES ONLY AND IS NOT RECOMMENDED FOR NEW DESIGNS
DS2347 - 3.0
ZN423
PRECISION VOLTAGE REFERENCE SOURCE
The ZN423 is a monolithic integrated circuit using the energy bandgap voltage of a base-emitter junction to produce a precise, stable, reference source of 1.26V. This is derived via an external dropping resistor for supply voltages of 1.5V upwards. The temperature coefficient of the ZN423, unlike conventional Zener diodes, remains constant with reference current. the noise figure associated with breakdown mechanisms is also considerably reduced.
FEATURES
s s s s s s s s Low Voltage Low Temperature Coefficient Very Good Long Term Stability Low Slope Resistance Low RMS Noise Tight Tolerance High Power Supply Rejection Ratio 2-Lead TO-18 Metal Can Package ZN423 (CM-2)
Fig.1 Pin connections (bottom view)
ABSOLUTE MAXIMUM RATINGS
Reference current, IREF Operating temperature range: Storage temperature range: 20mA -55C to +125C -65C to +165C
ORDERING INFORMATION
Device Type ZN423 Operating Temperature -55C to +125C Package CM2
Fig.2 Circuit diagram
ELECTRICAL CHARACTERISTICS
Test conditions (unless otherwise stated): Tamb = 25C, Shaping capacitor, CS = 0.1F Value Characteristic Symbol Min. Output voltage Slope resistance Reference current Temperature coefficient External resistor RMS noise voltage Power supply ratio VREF RREF IREF REXT PSRR 1.2 1.5 30 100 6 60 Typ. 1.26 0.5 Max. 1.32 1.5 12 V mA Unit Conditions
IREF = 5mA
ppm/C REXT = (VCC-VREF)/IREF V 1Hz to 10kHz dB PSRR = REXT/RREF, VREF = 1.26V, IREF = 2.5mA, VCC = 5.0V
ZN423
Reference current IREF (max.) v operating temperature.
Fig.3 Derating curve
Fig.4 Slope resistance v frequency (IREF = 5mA)
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ZN423
Fig.5 5V, 0.5A power supply
APPLICATIONS
5V, 0.5A Power Supply The circuit shown in Fig.5 is essentially a constant current source modified by the feedback components R2 and R3 to give a constant voltage output. The output of the ZN424P need only be 2V above the negative rail, by placing the load in the collector of the output transistor TR2. Current control is achieved by TR1 and R5. The simple circuit has the following performance characteristics: Output noise and ripple (full load) = 1mV rms Load regulation (0 to 0.5A) = 0.1% Temperature coefficient = 100ppm/C Current limit = 0.65A 5V, 1.0A Power Supply The circuit detailed in Fig.6 provides improved performance over that in Fig.5. This is achieved by feeding the ZN423 reference and the ZN424P error amplifier from a more stable source, derived from the emitter-follower stage (TR1). The supply rejection ratio is improved by the factor R1/R5, where R5 is the slope resistance of the ZN423. The output voltage is given by: (R3 + R4) VREF R3 and may be adjusted by replacing R3 with a 220 and a 500 preset potentiometer. The output is protected against short circuits by TR2 setting a current limit of 1.6A.
Fig.6 5V, 1.0A power supply
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ZN423
Fig.7 0V to 12V, 1A power supply
0V to 12V, 1A Power Supply The circuit of Fig.7 provides a continuously variable, highly stable voltage for load currents up to 1A. The output voltage is given by: VO = (VR5 + VR6) R4 VREF
low output resistance at frequencies above 100kHz. The power supply has the following performace characteristics: Output noise and ripple (full load) <100V rms Output resistance (0 to 1A) 1M Temperature coefficient 100ppm/C Variable 100mA to 2A Current Source In the circuit of Fig.8 the output current is set by the resistor R in the collector of TR2, which may be switched to offer a range of output currents from 100mA to 2A with fine control by means of VR3 which varies the reference voltage to the noninverting input of the ZN424P. The feedback path from the output to the inverting input of the ZN424P maintains a constant voltage across R, equal to (VCC - VIN) and hence a constant current to the load given by (VCC - VIN)/R.
and is controlled by VR5 and VR6 which should be high quality components (preferably wire wound). The emitter follower stages TR1 and TR2 buffer the bias and reference from the output stages. The negative rail allows the output to operate down to 0V. The current limit stage monitors output current through R15. As the potential across R15 increases due to load current, TR4 conducts and supplies base current for TR3, thus diverting part of the output from the ZN424P via TR3 to TR5. Shaping is achieved by the network C5, R8 together with the output decoupling capacitors which also maintain
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ZN423
Fig.8 Variable current sources
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ZN423
HEADQUARTERS OPERATIONS GEC PLESSEY SEMICONDUCTORS Cheney Manor, Swindon, Wiltshire SN2 2QW, United Kingdom. Tel: (0793) 518000 Fax: (0793) 518411 GEC PLESSEY SEMICONDUCTORS P.O. Box 660017 1500 Green Hills Road, Scotts Valley, California 95067-0017, United States of America. Tel: (408) 438 2900 Fax: (408) 438 5576
CUSTOMER SERVICE CENTRES * FRANCE & BENELUX Les Ulis Cedex Tel: (1) 64 46 23 45 Fax : (1) 64 46 06 07 * GERMANY Munich Tel: (089) 3609 06-0 Fax : (089) 3609 06-55 * ITALY Milan Tel: (02) 66040867 Fax: (02) 66040993 * JAPAN Tokyo Tel: (03) 5276-5501 Fax: (03) 5276-5510 * NORTH AMERICA Scotts Valley, USA Tel (408) 438 2900 Fax: (408) 438 7023. * SOUTH EAST ASIA Singapore Tel: (65) 3827708 Fax: (65) 3828872 * SWEDEN Stockholm, Tel: 46 8 702 97 70 Fax: 46 8 640 47 36 * UK, EIRE, DENMARK, FINLAND & NORWAY Swindon Tel: (0793) 518510 Fax : (0793) 518582 These are supported by Agents and Distributors in major countries world-wide.
(c) GEC Plessey Semiconductors 1994 Publication No. DS2347 Issue No. 3.0 May 1994
This publication is issued to provide information only which (unless agreed by the Company in writing) may not be used, applied or reproduced for any purpose nor form part of any order or contract nor to be regarded as a representation relating to the products or services concerned. No warranty or guarantee express or implied is made regarding the capability, performance or suitability of any product or service. The Company reserves the right to alter without prior knowledge the specification, design or price of any product or service. Information concerning possible methods of use is provided as a guide only and does not constitute any guarantee that such methods of use will be satisfactory in a specific piece of equipment. It is the user's responsibility to fully determine the performance and suitability of any equipment using such information and to ensure that any publication or data used is up to date and has not been superseded. These products are not suitable for use in any medical products whose failure to perform may result in significant injury or death to the user. All products and materials are sold and services provided subject to the Company's conditions of sale, which are available on request.
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