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THIS DOCUMENT IS FOR MAINTENANCE PURPOSES ONLY AND IS NOT RECOMMENDED FOR NEW DESIGNS
MAY 1994
DS3021-2.2
ZN426E8
8-BIT D-A CONVERTER
The ZN426 is a monolithic 8-bit D-A converter containing an R-2R ladder network of diffused resistors with precision bipolar switches, and a 2.5V precision voltage reference.
FEATURES s 1/2 LSB Linearity Error s Guaranteed Monolithic over the Full Operating Temperature Range s 0C to +70C s TTL and 5V CMOS Compatible s Single 5V Supply s Settling Time 1 microsecond Typical s Only Reference Capacitor and Resistor Required ABSOLUTE MAXIMUM RATINGS
Supply voltage +7.0V Max.voltage, logic and VREF inputs+5.5V Operating temperature range0C to +70C Storage temperature range-55C to +125C
BIT 3 BIT 2 (MSB) BIT 1 ANALOG OUTPUT V REF IN V REF OUT 0V
1 2 3 4 5 6 7
14 13 12 ZN426E8 11 10 9 8
V CC (+5V) BIT 4 BIT 5 BIT 6 BIT 7 BIT 8 (LSB) NC
DP14
Fig.1 Pin connections (not to scale) - top view
ORDERING INFORMATION
Ambient operating temperature 0C to +70C Package, ZN426E8DP14
Fig.2 System diagram
ZN426
ELECTRICAL CHARACTERISTICS
(at Tamb = 25C and VCC = +5V unless otherwise specified) Parameter Converter Resolution Non-linearity Differential non-linearity Settling time to 0.5LSB Settling time to 0.5LSB Offset voltage ZN426E8 and D VOS temperature coefficient Full-scale output Full-scale temp. coefficient Non-linearity temp. coefficient Analog output resistance External reference voltage Supply voltage Supply current High level input voltage Low level input voltage High level input current VCC IS VIH VIL IIH RO VOS Symbol Min. Typ. Max. Units Conditions
8 2.545 0 4.5 2.0 -
0.5 1.0 2.0 3.0 5 2.550 3 7.5 10 5 -
0.5 5.0 2.555 3.0 5.5 9 0.7 10 100 -0.18
bits LSB LSB s s mV V/C V ppm/C ppm/C k V V mA V V A A mA VCC = max. VI = 2.4V VCC = max. VI = 5.5V VCC = max. VI = 0.3V Note 2 RREF = 390 RREF = 390 RREF = 390 All bits ON Ext. VREF = 2.560V Ext. VREF = 2.560V Relative to F.S.R. Note 1 1LSB step All bits ON to OFF or OFF to ON All bits OFF
Low level input current Internal voltage reference Output voltage Slope resistance VREF temperature coefficient
IIL
-
VREF RS
2.475 -
2.55 1 40
2.626 2 -
V ppm/C
NOTE 1: Monotonic over full temperature range. NOTE 2:The internal reference requires a 1F stabilising capacitor between VREF OUT and 0V and a 390 resistor, RREF, between VCC and VREF OUT.
INTRODUCTION
The ZN426 is an 8-bit D-A converter. It contains an advanced design of R-2R ladder network and an array of precision bipolar switches plus a 2.5V precision voltage reference on a single monolithic chip. The special design of the ladder network results in full 8-bit accuracy using normal defused resistors. The use of on-chip voltage reference is pin optional to retain flexibility. An external fixed or varying reference may therefore be substituted. In this case there is no need to supply power to the internal reference so RREF and CREF can be omitted.
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ZN426
The converter is of the voltage switching type and uses an R-2R resistor ladder network as shown in Fig.3. Each 2R element is connected either to 0V or VREF by transistor switches specially designed for low offset voltage (typically 1mV). Binary weighted voltages are produced at the output of the R-2R ladder, the value depending on the digital number applied to the bit inputs.
Fig.3 The R-2R ladder network
APPLICATIONS
8-bit D-A Converter The ZN426 gives an analog voltage output directly from pin 4 therefore the usual current to voltage converting amplifier is not required. The output voltage drift, due to the temperature coefficient of the analog output resistance RO, will be less than 0.004% per C (or 1LSB/100C) if RL is chosen to be 650k. In order to remove the offset voltage and to calibrate the converter a buffer amplifier is necessary. Fig.4 shows a typical scheme using the internal reference voltage. To minimise temperature drift in this and similar applications the source resistance to the inverting input of the operational amplifier should be approximately 6k. The calibration procedure is as follows: i. ii. Set all bits to OFF (low) and adjust R2 until VOUT = 0.000V. Set all bits to ON (high) and adjust R1 until VOUT = Normal full-scale reading - 1LSB
iii. Repeat i. and ii. e.g. Set F.S.R. to + 3.840V - 1LSB =3.825V (1LSB = 3.84 =15.0mV) 256
Fig.4 8-bit D-A converter
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ZN426
Alternative Output Buffer Using the 741 The circuit of Fig.5, employing the 741 operational amplifier, may be used as the output buffer.
Fig.5 The ZLD741 as output buffer
HEADQUARTERS OPERATIONS GEC PLESSEY SEMICONDUCTORS Cheney Manor, Swindon, Wiltshire, United Kingdom. SN2 2QW Tel: (01793) 518000 Fax: (01793) 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 * TAIWAN, ROC Taipei Tel: 886 2 5461260 Fax: 886 2 7190260 * UK, EIRE, DENMARK, FINLAND & NORWAY Swindon Tel: (01793) 518510 Fax: (01793) 518582 These are supported by Agents and Distributors in major countries world-wide. (c) GEC Plessey Semiconductors 1994 Publication No. DS3021 Issue No. 2.2 May 1994 TECHNICAL DOCUMENTATION - NOT FOR RESALE. PRINTED IN UNITED KINGDOM
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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