Single Supply Operation DAC0800 DAC0802 Executive Summary AD

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Single Supply Operation DAC0800 DAC0802 Executive Summary AD

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Single Supply Operation DAC0800 DAC0802
Single Supply Operation DAC0800 DAC0802
Executive Summary
ADC0800 ADC0802 versatile quadrant multiplying DACs (Digital-to-Analog Converters) with current reference complementary current outputs. data sheet indicates need bipolar (positive negative) power supply voltages, consideration relative potentials allows these DACs used with positive only supplies, include single positive supply. This application note develops positive only bias voltages needed successfully operate ADC0800 DAC0802 with single supply voltage. principles here also apply DAC0808, which quadrant multiplying with single output. DAC0800 functionally equivalent industry standard DAC-08 DAC0802 equivalent industry standard DAC-08A. DAC0808 functionally equivalent industry standard MC1408. Product Applicability: DAC0800 DAC0802 DAC0808
National Semiconductor Application Note 1525 Nick Gray September 2006
varies linearly between about 1.7V -55°C about 0.95V 125°C. assumption throughout this application note Volt logic levels. TABLE DAC0800 Voltages Currents Function Logic Control (MSB) (LSB) REF+ REFCOMP +15V thru +20V thru 2.4V (logic high) 7.4V (logic high) 0.8V (logic low) 5.0V 5.8V (logic low) Normal Range) -10V +18V -15V -10V +18V Range) (V-) +28V (V-)
Overview
DAC0800, DAC0802 DAC0808 seem suffer from apparent need bipolar supplies. But, setting negative supply ground shifting other voltages Volts, these DACs will behave normally without negative supply. requirement that voltages associated with correct relative each other, that proper current levels maintained. This application note does discuss operation specifications DACs which this document applies. product data sheet information relating operation product question. Reference DAC0800 herein also includes DAC0802, which just more accurate version DAC0800. principles here apply equally well DAC0808, except that DAC0808 normally ground rather than output.
general circuit DAC0800 shown Figure
General Biasing Requirements
long relative voltages correct, DAC0800 will behave normally. With this mind, potentials around DAC0800 modified indicated Table positive supply voltage, must least more than more positive than proper operation. There will change capacitor connection should noted that this capacitor should connected directly then this connection should connected negative supply voltage grounded. Logic Control pin, controls logic threshold digital inputs. logic threshold digital input about 1.35V above this potential room temperature
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FIGURE General Circuit DAC0800 requirements reference pins that they least Volts above negative supply that resistance series with these pins equal value that value these resistors (V14 V15) IREF, where potentials which resistors pins returned IREF
AN-1525
2006 National Semiconductor Corporation
AN202077
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AN-1525
General Biasing Requirements
(Continued) reference current required equal value maximum output currents pins total these output currents always equal IOUT IOUT IREF bits this becomes IOUT IOUT IREF IOUT increases with increase digital code and/or reference current IOUT decreases with increase digital code and/or reference current. from Figure that IREF (V14 V15) IREF (10V
must never below +5V. +28V maximum output voltage indicated Table comes from maximum voltage with respect that output transistors withstand without excessive leakage breakdown. INPUT LEVEL THRESHOLD logic inputs need level shifted This done with resistors each logic input pin, shown Figure
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Unipolar Supply Modification
Again, consider relative circuit potentials maintain proper current levels, make whatever circuit changes need. REFERENCE CONSIDERATIONS modified circuit shown Figure Here find that IREF (V14 V15) 2.49k IREF (10V 2.49k 2.008 have about same reference current general case.
FIGURE Simple digital input level shifting circuit driving with devices, Figure 2.65k 3.3k, respectively. driving with 3.3V devices, 3.48k 4.75k, respectively. These resistance values would change bias voltages other than +10V shown Figure bias voltage +12V, 5.83k 4.75k, respectively, devices 5.62k 4.75k, respectively, driving with 3.3V devices. Tolerance requirements both resistors bias voltage best reference source bias voltage. OUTPUT CONSIDERATIONS DAC0800 current output. data sheet indicates connect amplifier outputs derive voltage output. Keep mind that DAC0800 outputs must never transition potential that lower than above voltage. This means that op-amp output must have non-inverting input returned voltage that least Volts, leading minimum op-amp output +5V. some cases this acceptable, most cases much more desirable have minimum output voltage zero volts. This minimum zero volts output obtained adding Zener diode series with output subtract bias potential from output, Zener diode generally large tolerance large temperature coefficient. Using LM4040-5.0 place Zener will provide same subtraction function, with better tolerance lower temperature drift. example circuit, where DAC0800 output bias shown Figure
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FIGURE Positive only supply circuit DAC0800 OUTPUT BIASING Another requirement DAC0800 that output pins must always least more positive than potential Since grounded, these output pins
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AN-1525
Unipolar Supply Modification
(Continued)
Second, maximum current through LM4040-5.0 which limits load current that value. third thing that LM4040-5.0 should have minimum current times reliably subtract from amplifier output. When amplifier output there insufficient current through LM4040-5.0, resulting inaccurate load voltage load currents. That load voltage reduced zero load currents. minimum voltage will function load impedance individual LM4040-5.0. this reason, this circuit practical applications where load current reduced value below microamps.
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FIGURE Current-to-voltage converter with offset correction. There things note about circuit Figure supply voltage should more positive than maximum amplifier output, even rail-to-rail output amplifier used. Otherwise there could linearity problems near full scale.
COMPLETE CIRCUIT EXAMPLE Figure gives complete positive supply circuit solution provide output range Op-amp rail-torail output type minimize output error very output voltages. positive supply voltage op-amp should greater than maximum output voltage.
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FIGURE complete single supply DAC0800 design with output.
Summary
DAC0800 versatile that found many uses. perceived drawback been need negative supply. However, because important thing elec-
trical component relative potentials correct currents, possible come with method eliminate need negative supply.
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Single Supply Operation DAC0800 DAC0802
Notes
National does assume responsibility circuitry described, circuit patent licenses implied National reserves right time without notice change said circuitry specifications. most current product information visit www.national.com. LIFE SUPPORT POLICY NATIONAL'S PRODUCTS AUTHORIZED CRITICAL COMPONENTS LIFE SUPPORT DEVICES SYSTEMS WITHOUT EXPRESS WRITTEN APPROVAL PRESIDENT GENERAL COUNSEL NATIONAL SEMICONDUCTOR CORPORATION. used herein: Life support devices systems devices systems which, intended surgical implant into body, support sustain life, whose failure perform when properly used accordance with instructions provided labeling, reasonably expected result significant injury user. BANNED SUBSTANCE COMPLIANCE National Semiconductor follows provisions Product Stewardship Guide Customers (CSP-9-111C2) Banned Substances Materials Interest Specification (CSP-9-111S2) regulatory environmental compliance. Details found www.national.com/quality/green. Lead free products RoHS compliant. critical component component life support device system whose failure perform reasonably expected cause failure life support device system, affect safety effectiveness.
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Single Supply Operation DAC0800 DAC0802 Executive Summary AD

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