参数资料
型号: LTC1049CS8#PBF
厂商: Linear Technology
文件页数: 9/12页
文件大小: 0K
描述: IC OPAMP CHOP-STBL W/CAPS 8SOIC
标准包装: 100
放大器类型: 断路器(零漂移)
电路数: 1
转换速率: 0.8 V/µs
增益带宽积: 800kHz
电流 - 输入偏压: 15pA
电压 - 输入偏移: 2µV
电流 - 电源: 200µA
电压 - 电源,单路/双路(±): 4.75 V ~ 16 V,±2.38 V ~ 8 V
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 8-SOIC(0.154",3.90mm 宽)
供应商设备封装: 8-SO
包装: 管件
产品目录页面: 1321 (CN2011-ZH PDF)
其它名称: Q2242830A
LTC1049
6
1049fb
applicaTions inFormaTion
ACHIEVING PICOAMPERE/MICROVOLT PERFORMANCE
Picoamperes
In order to realize the picoampere level of accuracy of
the LTC1049, proper care must be exercised. Leakage
currents in circuitry external to the amplifier can signifi-
cantlydegradeperformance.Highqualityinsulationshould
be used (e.g., Teflon, Kel-F); cleaning of all insulating
surfaces to remove fluxes and other residues will probably
be necessary—particularly for high temperature perfor-
mance. Surface coating may be necessary to provide a
moisture barrier in high humidity environments.
Board leakage can be minimized by encircling the input
connections with a guard ring operated at a potential close
to that of the inputs: in inverting configurations, the guard
ringshouldbetiedtoground;innoninvertingconnections,
to the inverting input. Guarding both sides of the printed
circuit board is required. Bulk leakage reduction depends
on the guard ring width.
Microvolts
ThermocoupleeffectsmustbeconsiderediftheLTC1049’s
ultralow drift is to be fully utilized. Any connection of dis-
similarmetalsformsathermoelectricjunctionproducingan
electric potential which varies with temperature (Seebeck
effect).Astemperaturesensors,thermocouplesexploitthis
phenomenon to produce useful information. In low drift
amplifier circuits the effect is a primary source of error.
Connectors, switches, relay contacts, sockets, resistors,
solder, and even copper wire are all candidates for thermal
EMF generation. Junctions of copper wire from different
manufacturerscangeneratethermalEMFsof200nV/°C—
twice the maximum drift specification of the LTC1049.
The copper/kovar junction, formed when wire or printed
circuit traces contact a package lead, has a thermal EMF
of approximately 35V/°C—300 times the maximum drift
specification of the LTC1049.
Minimizing thermal EMF-induced errors is possible if
judicious attention is given to circuit board layout and
component selection. It is good practice to minimize the
number of junctions in the amplifier’s input signal path.
Avoid connectors, sockets, switches, and relays where
possible.Ininstanceswherethisisnotpossible,attemptto
balancethenumberandtypeofjunctionssothatdifferential
cancellation occurs. Doing this may involve deliberately
introducing junctions to offset unavoidable junctions.
PACKAGE-INDUCED OFFSET VOLTAGE
Package-induced thermal EMF effects are another
important source of errors. It arises at the copper/kovar
junctionsformedwhenwireorprintedcircuittracescontact
a package lead. Like all the previously mentioned thermal
EMF effects, it is outside the LTC1049’s offset nulling loop
andcannotbecancelled.Theinputoffsetvoltagespecifica-
tion of the LTC1049 is actually set by the package-induced
warm-up drift rather than by the circuit itself. The thermal
time constant ranges from 0.5 to 3 minutes, depending
on package type.
LOW SUPPLY OPERATION
The minimum supply for proper operation of the LTC1049
is typically below 4.0V (±2.0V). In single supply applica-
tions,PSRRisguaranteeddownto4.7V(±2.35V)toensure
proper operation down to the minimum TTL specified
voltage of 4.75V.
PIN COMPATIBILITY
The LTC1049 is pin compatible with the 8-pin versions of
7650, 7652 and other chopper-stabilized amplifiers. The
7650 and 7652 require the use of two external capacitors
connected to Pins 1 and 8 which are not needed for the
LTC1049.Pins1,5,and8oftheLTC1049arenotconnected
internally; thus, the LTC1049 can be a direct plug- in for
the 7650 and 7652, even if the two capacitors are left on
the circuit board.
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