ELECTRICALLY PROGRAMMABLE ANALOG DEVICE (EPAD®) APPLICATIONS INTR

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ELECTRICALLY PROGRAMMABLE ANALOG DEVICE (EPAD®) APPLICATIONS INTR

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APPLICATION NOTE AN1108
ELECTRICALLY PROGRAMMABLE ANALOG DEVICE (EPAD®) APPLICATIONS
INTRODUCTION ALD1108E/ALD1110E first members growing family Electrically Programmable Analog Device (EPAD) integrated circuits from Advanced Linear Devices. EPAD class analog like operational amplifier converter. 1108E/ALD110E based CMOS MOSFET devices with precision electrically programmable threshold voltage, which sets their on-resistance characteristics. This programmed on-resistance turn used voltage current level with external, inexpensive fixed precision resistors. When used combination with inexpensive E100 EPAD Programmer Adapter Module, EPAD allows analog circuit trimming 20,000 discrete steps with 0.1mV increments. engineering environments, EPAD quickly easily programmed needs specific application. test environments, programmed in-system, that integral part circuit board assembly thereby providing precise control over entire system. EPAD technology designed voltage, power circuits where precision voltage current trimming function necessary. addition, provides simple, inexpensive method achieving remote trimming circuits within user-controlled environments. ALD1108E quad (4-channel) EPAD device; ALD1110E dual (2-channel) EPAD device. Both EPADs configured operate single dual channel mode, enabling unlimited variations functionality. Both EPADs supplied stand-alone, individually programmable devices encased standard packaging. They preprogrammed before being placed into circuit (applicationspecific programming), providing control standard linear functions such operational amplifiers voltage comparators. Alternatively, they integrated directly into circuit, enabling in-system programming entire assembly after been built (in-system programming). ALD1108E/ALD1110E EPADs need other active circuitry enable functionality. such, these devices extremely versatile both circuit element design component. EPAD technology presents user with wealth possible applications, limited only imagination user many ways adjustable bias voltage/current device used circuit design element. applications listed below outlines general some applications which EPAD used telecommunications, instrumentation, medical devices industrial process control systems. Note that although automation important goal, primary benefit EPAD technology that simplifies manufacturing control process, enabling electrical programming analog circuit transfer function without resorting difficult expensive trim pots even more expensive system microcontrollers, RAMs, ROMs, EPROMs, data converters entire overhead system functions. EPAD also ideal solution trimming packaged modules where trim access longer readily available. GENERAL DESCRIPTION ALD1108E/ALD1110E devices based monolithic CMOS FETs (Field Effect Transistors) with electrically programmed threshold voltages that precisely controlled stored, non-volatile charges. Control these threshold voltages enabled through DOS-based user interface, EPAD Programmer control software supplied Advanced Linear Devices. Each channel EPAD individually programmed different threshold, bias, voltage. range threshold voltage adjustment 2000mV; programming voltage resolution 0.1mV respectively. given input voltage, precisely changing threshold voltage channel (MOSFET) also changes drain on-current, resulting on-resistance characteristic that precisely controlled set.
NOTICE: Advanced Linear Devices (ALD) reserves right make changes discontinue product services identified this publication without notice. Current specifications product services should verified customer before placing orders. warrants products current specifications effect time manufacture accordance standard warranty. Unless mandated government requirements, performs certain, necessarily all, specific testing procedures deems necessary support this warranty. assumes liability circuitry described herein. Applications circuits contained herein illustrative purposes only. representation continued operation said circuits under operating conditions implied. such circuits responsibility user. circuit licenses, copyrights patents kind implied granted. does authorize warrant products designs life support applications, hereby expressly prohibit such use. rights reserved.
1998 Advanced Linear Devices, Inc. Tasman Drive, Sunnyvale, California 94089 -1706 Tel: (408) 747-1155 Fax: (408) 747-1286 http://www.aldinc.com
EPAD programming monotonic: that channel only programmed increase threshold voltage decrease drain-on current function given input bias voltage. However, each channel programmed many times before threshold limit reached. addition, baseline current level also adjusted lower, creating same effect lowering bias voltage. pair EPAD channels also connected differentially such that channel used adjust parameter direction other channel used adjust same parameter other direction, thereby providing bidirectional control capability. EPADs programmed stand-alone programming mode, application-specific programming mode, in-system programming mode, after entire assembly been built. these cases, combination E100 EPAD Programmer Adapter Module required. stand-alone programming, exact adapter module vary depending intended application. example, EA101 Adapter Module programs EPAD threshold voltages with fixed resistor. EA102 Adapter Module specially designed program EPAD with current sources Zero Temperature Coefficient (ZTC Zero tempco) current level 68µA. Both these Adapter Modules readily modified other types application-specific programming. instance, enable direct control operational amplifier, user changes resistor component values adapter module, which creates corresponding change bias drain current level. Entire lots EPADs programmed this with single adapter module. These programmed EPADs then inserted into user circuit board. With In-System Programming, ALD1108E ALD1110E device designed into application circuit where becomes integral part circuit function. device inserted into finished circuit accessed programmed through special programming cable number preassigned edge connector pins. more information please refer In-System Programming section described later. E100 EPAD Programming System contains voltage measurement voltage programming capabilities measure baseline voltage program desired value. different current levels, bias resistor values within
Adapter Module circuit board must changed. Alternatively, user switch current setting resistors which placed under software control implemented with analog relay switches.
DEFINITION TERMS
Terms that used this article defined follows: Baseline voltage level. initial threshold voltage defined drain gate diode-connected voltage drain current 1µA, when source voltage Volt. initial threshold voltage also default factory setting. However, user change this default baseline voltage drain current value threshold voltage desired value, thereby allowing device "zeroed out", "set" bias level. Bias voltage, Vbias Same threshold voltage, except drain-source bias current different from that specified threshold voltage. example, threshold voltage ALD1108E/ALD1110E specified drain source bias current 1µA. useful bias current range ALD1108E/ALD1110E from 3mA. Drain Current, Drain Current current that flows from drain source. Drain Voltage, Vds. Drain voltage voltage across drain source pins. Gate Voltage, Vgs. Gate voltage voltage across gate source pins. Threshold voltage, Threshold voltage EPAD voltage across Gate Source when forced into Drain terminal Drain Gate connected together. term threshold voltage used interchangeably with "bias voltage." Threshold voltage programming. Encompasses combinations programmed gate bias voltages, drain bias voltages drain current levels. Zero Temperature Coefficient, ZTC. Operating point EPAD where voltage current changes function temperature zero.
APPLICATION NOTE AN1108
Advanced Linear Devices
FUNCTIONAL DESCRIPTION Each EPAD's input output functional characteristics modeled MOSFET with adjustable threshold voltage. Each EPAD five terminals, namely, Gate, Drain, Source, Programming Substrate terminals. programming terminal used only during electrical programming inject charge into device. injected charge permanently stored raises threshold voltage device. given current level gate voltage, drain voltage varies according threshold voltage. After programming, programming terminal left open connected source voltage. basic connection configuration connect gate drain terminals together. selected drain current, this gate-drain connected voltage precisely using EPAD Programmer. After electrical programming, EPAD Programmer disconnected, device retains voltage indefinitely under normal operating conditions, even when power turned off. This connection configuration referred diode-connected configuration. E100 EPAD programmer injects small, measured amount charge pulsing programming terminal. EPAD programming mode when both gate terminal programming terminal pulsed together, through EPAD programmer, approximately 12V. number pulses required bring threshold voltage given voltage value determined EPAD programmer control software. that user needs input desired threshold voltage value. drain current other than desired, that current level user changing value set-current resistor EPAD Adapter Module. This drain current also bias current supplied user from application circuit, such that from external current source. Please refer individual EPAD specifications more details operating voltage current ranges. With control software supplied with EPAD Programmer Adapter Module, desired target threshold voltage value either keyboard entry, variable user-written program. gate voltage EPAD input voltage drain voltage used output voltage. When Gate Drain terminals EPAD shorted together, diode-connected configuration, Vds, equal Vgs, output voltage. many applications, desirable force EPAD dif-
ferent drain bias voltage given circuit bias current, before programming. user then determines final threshold voltage necessary adjust transfer function application circuit desired final value. final bias voltage then voltage where EPAD needs that particular circuit.
SPECIAL DESIGN FEATURES
Each channel ALD1108E/ALD1110E EPAD devices programmed separately matched pairs. certain applications, effects such temperature coefficients canceled using matched pair capability. Matched pairs also ideal applications where variables must adjusted both directions. this case, circuit parameter variable adjusted both directions allowing "trimming" "calibration" parameter variable user minimize temperature effects.
ZERO TEMPERATURE COEFFICIENT
Each channel within ALD1108E/ALD1110E positive temperature coefficient current range negative temperature coefficient current range. crossover current level zero tempco current level. ALD1108E/ALD1110E EPADs, this current level approximately 68µA. When biased this current level, drain voltage drain current have significantly reduced temperature coefficients, minimizing variation drain voltage related parameters throughout given temperature range. applications where system must have minimal variations changes temperature, matched pair circuits biased 68µA recommended. Many applications mentioned this application note biased zero tempco current. When biased zero tempco current, typical single channel voltage tempco 50ppm matched pair relative voltage tempco less than 10ppm.
COARSE FINE TRIMMING
EPADs used both coarse fine trimming applications. coarse trimming, single EPAD used conjunction with single resistor form resistor network. this configuration, depending resistor value bias current level EPAD, tempco circuit well controlled, translating relatively resolution trimming circuit stability. However, this also quick, low-cost easy voltage adjustment applica-
APPLICATION NOTE AN1108
Advanced Linear Devices
tion that readily automated. fine trimming applications, general, EPADs used matched circuit with temperature effect cancellation. EPADs within package matched design close proximity each other, their respective relative temperatures closely matched. ambient temperature changes, both EPAD channels have equal temperature effects. matched EPAD channels used circuit with temperature effect subtraction, resulting circuit that temperature-stable. general rule, temperature coefficient effects circuit with matched EPAD temperature cancellation order magnitude less than single EPAD circuits. Furthermore, zero tempco current mode, corresponding temperature coefficient effects dual EPADbased circuit reduced half orders magnitude, resulting circuit that temperature-stable suitable fine trimming applications. Note that zero tempco bias mode used both single matched pair EPAD applications, resulting either coarse fine trimming circuits that have improved temperature characteristics.
RELAXATION VOLTAGE RELAXATION TIME CONSTANT
Relaxation Voltage compensation setting which altered user. ALD1108E/ALD1110E, typical Relaxation Time Constant hours Relaxation Voltage -0.3% threshold voltage.
DESIGN PRECAUTIONS
ALD1108E/ALD1110E EPAD devices designed voltage, micropower circuits. maximum operating voltage during normal operation should remain below Volts times. Care should taken insure that application which devices used does experience positive negative transient voltages that cause terminal voltages exceed this limit. inputs unused pins except programming pins should connected that they become floating pins, since input impedance these pins very high. these pins left undefined, they cause unwanted oscillation intermittent excessive current drain. these devices built with CMOS technology, normal latchup handling precautions, operating storage temperature limits stated data sheet must observed.
After EPAD been programmed, bulk electrons stored polysilicon gate capacitor with high barrier energy remains stored indefinitely. However, small number residual electrons oxide sites near oxide-to-silicon interface gain sufficient energy become detrapped, causing small loss electrons. This loss electrons decreases exponentially with time constant. This loss electrons shown difference between initial measured threshold voltage EPAD subsequently measured threshold voltage. After short time period, threshold voltage stabilizes reaches final threshold voltage that remains fixed indefinitely thereafter. amount this residual charge loss causes small voltage drop, referred relaxation threshold voltage. Relaxation Voltage defined voltage drop after three Relaxation Time Constants. EPAD Programmer control software supplied with Adapter Module compensates Relaxation Voltage programming threshold (bias) voltage higher initial threshold voltage. control software contains default
APPLICATION NOTE AN1108
Advanced Linear Devices
APPLICATIONS application circuits described this application note have been functionally tested Advanced Linear Devices' application staff. However, these circuits illustrative purposes only, should used production specific application unless independently verified user found conformance with other user requirements. BASIC CIRCUITS basic circuit connection shown Figure this connection, gate terminal device connected drain terminal device. This connection forces gate drain voltage equal times. gate input extremely high input resistance input leakage current room temperature most nearly bias current through device flows from drain source terminal. This bias current externally combination programming, selection bias reference voltage bias resistor some applications, appropriate replace with current source that current relatively constant before after EPAD programming. simplest bias method just single resistor with value ohms. calculate value resistor first refer data sheet insure that desired current level within device specification. resistor value simply given following Ohm's equation: where nominal midpoint value desired adjustment range, power supply voltage, desired drain source current (equal current through resistor example, with ALD1108E, current level 68µA chosen minimum tempco, supply voltage 8.3V, adjustment range expected between 1.000V 2.000V, then 1.5V. With these values equation, get: 68µA Kohms
Note that above circuit current does remain constant different values, current varies with value programmed addition, magnitude current value tempco resistor also cause variation Ids. These effects reduced with circuit such shown Figure When current source connected EPAD instead biasing resistor EPAD current source variation depends primarily current source variations. different values, current from current source constant, then value also remains constant. values could change programming, constant, tempco voltage also remains constant. this case, programmed desired target value setting, capable remaining relatively temperature stable. many applications, this advantage worth extra circuitry required produce current source.
Figure Basic Circuit Connection
ALD1108E
APPLICATION NOTE AN1108
Advanced Linear Devices
Figure Basic Circuit Connection with Current Source
Figure Voltage Controlled Resistor
ALD1108E
VREF
Note: VREF connected relatively stable voltage, such reference voltage
ALD1108E
VOLTAGE CONTROLLED RESISTOR basic characteristics EPAD that MOSFET output on-resistance controlled with reference bias voltage. When EPAD biased off, when reference bias voltage (the input gate voltage) more than 0.5V below output resistance greater than Gigaohm. When bias reference voltage increased EPAD biased on-resistance Mohm. reference bias voltage above output resistance decreases. ALD1108E/ALD1110E devices, output on-resistance decreases from Mohm approximately Kohm reference voltage Volts. This represents many orders magnitude change on-resistance. given reference bias voltage, on-resistance EPAD adjustable within certain range. This useful applications where fixed reference voltage available, where many different on-resistance values desired. Figure with addition fixed resistor, circuit becomes voltage divider. output voltage varies according resistance ratios between fixed resistor EPAD on-resistance. on-resistance EPAD adjusted, output voltage changed, producing desired permanently.
MATCHED EPAD PAIRS Matched EPAD pairs used application circuits have many significant circuit advantages over single EPAD circuits. Within pair EPADs, many parameters matched parasitic temperature effects these devices manipulated cancel each other. result much more balanced temperature-stable circuit. ALD1108E, first second channels form EPAD pair third fourth channels form another. Note that matched EPAD pairs share common source connections. When connected differential configuration, EPAD channels also provide bidirectional parameter adjustment capabilities, illustrated Figure Figure output these circuits, adjusted down programming respective EPAD channel. circuit designed into application where adjustment necessary, EPAD1 EPAD2 progressively programmed, allowing multiple down adjustments noteworthy aspect this capability that overall gain circuit depends value larger values gain circuit greater, mismatched offset voltage amplified gain. best results, drain current EPADs should which effectively minimizes temperature dependence output voltage resistors also matched, situation when using resistor packs, then respective resistors also experience tempco cancellation, further enhancing overall circuit stability.
APPLICATION NOTE AN1108
Advanced Linear Devices
Figure Mached EPAD Pair With Single Supply
EPAD VOLTAGE OUTPUT WITH BUFFER simple voltage follower shown Figure voltage follower isolates output prevents from loading EPAD bias resistor causing loading effects. Again, tempco, such that current 68µA.
Figure EPAD Output With Buffer Amplifier
VS12
ALD1108E
ALD1702
tempco 68µA +5V,
ALD1108E
tempco 68µA +5V,
Figure Matched EPAD Pair With Dual Supplies
BASIC CURRENT SOURCE basic current source with output shown Figure Value resistor selected such that current through approximately 68µA temperature effects. Resistor Rset biased with same voltage registered across EPAD. This voltage bias resistor value EPAD programmed threshold voltage. tempco output current directly proportional tempco Rset. This tempco minimized selection appropriate resistor type. this circuit, output current programming EPAD threshold voltage. order output current current meter monitor through ALD1106 N-Channel MOSFET while voltage source forces voltage Vbias. Once desired current level attained, then that voltage which produces this desired current, Vbias, noted. EPAD programmed Vbias, using same supply voltage resistor This entire process fully automated with appropriate equipment, setup customized control software.
VS12
ALD1108E
tempco 68µA -5V,
APPLICATION NOTE AN1108
Advanced Linear Devices
Figure Current Source With EPAD Trimming
Vbias ALD1701 ALD1106
Figure High Output Impedance Current Mirror
CURRENT SOURCE
IREF
IOUT
VSN1
ALD1106
RSET
ALD1108E
tempco 68µA +5V,
VS12
ALD1108E
HIGH OUTPUT IMPEDANCE CURRENT MIRROR calibrated cascode current mirror shown Figure input reference current means reference bias voltage fixed resistor programming EPAD connected input reference current. output current IOUT current mirror within desired current mirror value. Although mirrored current matched input reference current, also ratioed current value, where IOUT proportional current source. output impedance this programmable current mirror approximately Mohms. current mirror Figure easily modified become electronically calibrated current source that programmed 68µA, shown Figure Note that reference voltage VREF relatively stable voltage source required. tempco RREF factor that determines tempco current source.
VS12 ALD1108E
Figure High Output Impedance Current Source
RREF
VREF
IREF
IREF
IOUT
VSN1
ALD1106
APPLICATION NOTE AN1108
Advanced Linear Devices
EPADs WITH ACTIVE CIRCUITS EPAD threshold voltage scaled, ratioed shifted with operational amplifier circuits. Many these circuits common operational amplifier circuits. these circuits illustrated below Figure Scaling Adjustable Figure Select Adjustment Range using Resistor Ratios Figure Amplify Shift EPAD Adjustment range with operational amplifier. Obviously many more types operational amplifier circuits also used with EPAD adjustment vehicle.
Figure Amplify Shift EPAD Adjustment Range with Operational Amplifier
ALD1702
+5V,
Figure Scaling Adjustable
ALD1702
(V+) ((V+)
ALD1108E
USEFUL HINTS couple useful hints designing with EPADs would appropriate here. First, general, relatively large EPAD adjustment range should used. recommended adjustment range would from range such =1.000V 2.000V range. This minimizes error budget programming voltage errors temperature effects causing shift example, assume adjustment range 1.000V 2.600V range, giving voltage programming range 1600mV. Assume further that maximum system error estimated 32mV. error voltage this case would 32mV/1600mV, percent. Matched EPAD circuit techniques zero tempco biasing further reduce error. more limited temperature ranges, such case some laboratory equipment operating environments, errors brought down about 10mV with careful design error budgeting. example, using adjustment range =1.000V 3.000V would yield error mV/2000mV, percent. lower adjusted absolute error voltage desired, voltage scaling used. Using above example, adjustment range 2000mV with error range 10mV with help some active circuitry, scaled down adjustment range 200mV with error range 1mV. Note that additional errors introduced active scaling circuit. However, keep mind that scaling-induced adjustment error fixed temperature time invariant, adjusted through EPAD programming.
ALD1108E
NOTE:
Figure Select Adjustment Range Using Resistor Ratios
ALD1702 ALD1108E
(V+) (Vt)
APPLICATION NOTE AN1108
Advanced Linear Devices
EPAD CIRCUIT WITH BI-DIRECTIONAL ADJUSTMENT applications where multiple adjustment voltage parameter necessary, EPADs employed circuit such Figure this circuit, adjusted down multiple times, programming respective EPAD. Care should used design such that amount adjustment step kept small enough that EPADs programmed upwards many times alternately. other hand, adjustment step should large enough minimize error other various error terms. resistor value should high relative value avoid excessive loading down resistor affecting bias current supplied EPAD. isolate outputs EPAD stages from output amplifier Figure same circuit buffered with unity gain buffer amplifiers, shown Figure this circuit, resistor value produce zero tempco bias current 68µA, other desired current level. differential EPAD pairs feeding same output amplifier stage output, temperature effect EPAD circuits cancels that other. resulting circuit temperature-stable. resistors also other values needed, this circuit eliminates EPAD bias current level sensitivity resistor values
Figure EPAD Circuit With Bi-directional Adjustment
VS12 1701
ALD1108E
Figure EPAD With Buffered Outputs Providing Bi-directional Adjustment
ALD4701 ALD4701 ALD4701
ALD1108E
APPLICATION NOTE AN1108
Advanced Linear Devices
NEURAL NETWORK CIRCUIT applications where neural network circuit function desired, where multiple inputs their respective weights summed output, EPAD-based neural circuit constructed shown Figure precision resolution circuit depends reference voltage, output resistor accuracy resolution available from EPAD. weights neural network, this case, corresponding resultant drain currents output result programming values. output node same time also summing node, where currents summed through output resistor, This circuit most suitably used where "learning" already accomplished, "learned" function requires hardware implementation. consideration here simplicity circuitry involved. This circuit especially appropriate cost, stand-alone hardware implementation neural networks. circuit shown Figure implements following equation: Vout
Figure Neural Network Circuit
Vin1 VREF +3.000V ALD1721E ISUM Vout
Vin2
Vin3
Vin4
ALD1108E ALD4201
I(x) where Vin(x) w(x) Isum VREF input each neural channel weight each neural channel summing resistor output node currents through EPADs reference voltage
Vout w(X) ISUM I(X)
Once weights given neural network circuit have been derived through learning process, these values programmed into each EPAD each respective neural network channel.
APPLICATION NOTE AN1108
Advanced Linear Devices
Figure Standard Stand alone EPAD Programming System
SERIES CONTROL SOFTWARE PARALLEL PRINTER CABLE E100 EPAD PROGRAMMER EPAD SERIES INTERFACE ADAPTER INTERFACE ADAPTER CABLE
Figure 15B. Series Interface Adapter Module Custom Tailored Application-Specific Conditions Environment
SERIES CONTROL SOFTWARE PARALLEL PRINTER CABLE E100 EPAD PROGRAMMER SERIES INTERFACE ADAPTER INTERFACE ADAPTER CABLE EPAD REMOTE ENVIRONMENTAL CHAMBER
Series Control Software, Interface Adapter Cable Interface Adapter customized User specific application, necessary.
Figure 15C. In-System Programming With EPAD Incorporated into User Application Circuit
REMOTE USER PROGRAM
USER CUSTOMIZED CONTROL SOFTWARE PARALLEL SOFTWARE INTERFACE CUSTOMIZED USER E100 EPAD PROGRAMMER PRINTER CABLE USER CUSTOMIZED SERIES INTERFACE ADAPTER INTERFACE ADAPTER CABLE IN-SYSTEM PROGRAMMING CABLE
EPAD
REMOTE ENVIRONMENTAL CHAMBER
USER CIRCUIT
APPLICATION
APPLICATION NOTE AN1108
Advanced Linear Devices
EPAD PROGRAMMING Figure shows standard EPAD programming system. setup programming user simple straight forward. user provides personal computer, parallel printer cable external power supply. entire system laboratory environment ready start programming matter minutes. APPLICATION-SPECIFIC PROGRAMMING applications where custom setup special conditions desired, such operating different power supply voltages, different bias current reference voltage conditions, and/or different temperature environments, supplied interface Adapter Module readily modified user reflect these conditions. addition, Adapter Module, application circuit EPAD inside environmental chamber EPAD adjustment under precise environmental conditions. diagram this setup illustrated Figure 15B. simple example Application-Specific Programming change operating voltage EPAD circuit. Adapter Module factory preset operating voltage, user application system voltage different voltage level, small supply voltage induced error introduced into system. This small error eliminated disconnecting Adapter Module from EPAD Programmer, bringing external supply into terminal instead. EPAD programmed user system supply conditions. Often this kind hardware change simple effective eliminating system errors without control software programming change. When using environmental chambers, care must taken insure that Adapter Module's voltage temperature ratings exceeded. continued high temperature applications, user advised custom adapter circuit board with connection separate high temperature socket EPAD programming.
IN-SYSTEM PROGRAMMING (ISP) some applications, user desire have EPAD soldered onto production circuit board before EPAD programming. This accomplished designing application circuit accommodate modes operation normal operating mode programming mode. Once such circuit designed, special cable enables in-system programming. Refer Figure 15C. Many preceding circuits from Figure through Figure also viewed examples EPAD programmable in-system circuits. order program EPAD in-system element, gate terminal EPAD must able pulsed EPAD Programmer. application circuit which EPAD embedded powered user-selected voltage. However, must allow gate voltages EPAD pulsed without impedance path other circuit nodes, that EPAD programmer pulsing circuit function properly. many circuits, such those Figures through bias resistor should greater than Kohms. Figure particular, resistor value should much greater than resistor value setting value greater than Kohms possible, Kohm resistor greater isolation resistor Riso used connect drain gate terminals.
Figure In-System Programming: Amplify Shift EPAD Adjustment Range with Operational Amplifier
ALD1702
RISO
+5V, (V+) (V+)
ALD1108E
APPLICATION NOTE AN1108
Advanced Linear Devices
example, circuit Figure In-System Programming, modified circuit based Figure provide conditions suitable programming mode. this case, this accomplished addition single resistor (iso). When gate terminal pulsed during programming, drain terminal effectively isolated from gate terminal. During normal operation, gate terminal voltage appreciably affected result R(iso) because gate input impedance very high. This in-system approach programming EPAD potentially most powerful adjusting system level errors involving other components, such variations unit unit sensor parameters passive component parameters. integration EPAD programming desired, while system testing and/or calibration taking place, then more circuit design software programming necessary. special In-System Programming extension cable allows temporary connection EPAD programmer insystem EPAD element directly within application circuit. cable disconnected future after programming. CONTROL SOFTWARE Control software supplied with EPAD Programmer Adapter used control programming routines send commands EPAD Programmer control, measure compute programming conditions specific adapter module. most cases, recommended custom adaptation this control software input desired voltage value that measured drain terminal EPAD. control software algorithm then takes over. When programming mode, gate programming terminals pulsed controlled, optimal sequence voltage biasing conditions. These conditions must preserved user order programming system function properly. more assistance application-specific in-system EPAD programming, please contact Advanced Linear Devices' applications engineer. have circuit question problem, e-mail (408) 747-1286 Attention: Applications E-mail: applications@aldinc.com
APPLICATION NOTE AN1108
Advanced Linear Devices

ELECTRICALLY PROGRAMMABLE ANALOG DEVICE (EPAD®) APPLICATIONS INTR

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