Moteur de recherche de fiches techniques de composants électroniques
Selected language     French  ▼

Delete All


Preview PDF Download HTML

ICL7650S Datasheet(Fiches technique) 5 Page - Intersil Corporation

Numéro de pièce ICL7650S
Description  2MHz, Super Chopper-Stabilized Operational Amplifier
Télécharger  14 Pages
Scroll/Zoom Zoom In 100% Zoom Out
Fabricant  INTERSIL [Intersil Corporation]
Site Internet
Logo INTERSIL - Intersil Corporation

ICL7650S Datasheet(HTML) 5 Page - Intersil Corporation

  ICL7650S Datenblatt HTML 1Page - Intersil Corporation ICL7650S Datenblatt HTML 2Page - Intersil Corporation ICL7650S Datenblatt HTML 3Page - Intersil Corporation ICL7650S Datenblatt HTML 4Page - Intersil Corporation ICL7650S Datasheet HTML 5Page - Intersil Corporation ICL7650S Datenblatt HTML 6Page - Intersil Corporation ICL7650S Datenblatt HTML 7Page - Intersil Corporation ICL7650S Datenblatt HTML 8Page - Intersil Corporation ICL7650S Datenblatt HTML 9Page - Intersil Corporation Next Button
Zoom Inzoom in Zoom Outzoom out
 5 / 14 page
background image
desired 50% input switching duty cycle. Since the capacitors
are charged only when EXT CLOCK IN is high, a 50% - 80%
positive duty cycle is recommended, especially for higher
frequencies. The external clock can swing between V+ and V-.
The logic threshold will be at about 2.5V below V+. Note also
that a signal of about 400 Hz, with a 70% duty cycle, will be
present at the EXT CLOCK IN pin with INT/EXT high or open.
This is the internal clock signal before being fed to the divider.
In those applications where a strobe signal is available, an
alternate approach to avoid capacitor misbalancing during
overload can be used. If a strobe signal is connected to EXT
CLK IN so that it is low during the time that the overload
signal is applied to the ampli?er, neither capacitor will be
charged. Since the leakage at the capacitor pins is quite low
at room temperature, the typical ampli?er will drift less than
V/s, and relatively long measurements can be made with
little change in offset.
The two required capacitors, CEXTA and CEXTB, have
optimum values depending on the clock or chopping
frequency. For the preset internal clock, the correct value is
F, and to maintain the same relationship between the
chopping frequency and the nulling time constant this value
should be scaled approximately in proportion if an external
clock is used. A high quality ?lm type capacitor such as
mylar is preferred, although a ceramic or other lower-grade
capacitor may prove suitable in many applications. For
quickest settling on initial turn-on, low dielectric absorption
capacitors (such as polypropylene) should be used. With
ceramic capacitors, several seconds may be required to
settle to 1
All device pins are static-protected by the use of input diodes.
However, strong static fields and discharges should be avoided,
as they can cause degraded diode junction characteristics,
which may result in increased input-leakage currents.
Junction-isolated CMOS circuits inherently include a parasitic
4-layer (PNPN) structure which has characteristics similar to
an SCR. Under certain circumstances this junction may be
triggered into a low-impedance state, resulting in excessive
supply current. To avoid this condition, no voltage greater than
0.3V beyond the supply rails should be applied to any pin. In
general, the amplifier supplies must be established either at
the same time or before any input signals are applied. If this is
not possible, the drive circuits must limit input current flow to
under 1mA to avoid latchup, even under fault conditions.
The output circuit is a high-impedance type (approximately
?), and therefore with loads less than this value, the
chopper ampli?er behaves in some ways like a
transconductance ampli?er whose open-loop gain is
proportional to load resistance. For example, the open-loop
gain will be 17dB lower with a 1k
? load than with a 10k?
load. If the ampli?er is used strictly for DC, this lower gain is
of little consequence, since the DC gain is typically greater
than 120dB even with a 1k
? load. However, for wideband
applications, the best frequency response will be achieved
with a load resistor of 10k
? or higher. This will result in a
smooth 6dB/octave response from 0.1Hz to 2MHz, with
phase shifts of less than 10 degrees in the transition region
where the main ampli?er takes over from the null ampli?er.
The ultimate limitations to ultra-high precision DC amplifiers are
the thermo-electric or Peltier effects arising in thermocouple
junctions of dissimilar metals, alloys, silicon, etc. Unless all
junctions are at the same temperature, thermoelectric voltages
typically around 0.1
V/oC, but up to tens of mV/oC for some
materials, will be generated. In order to realize the extremely
low offset voltages that the chopper amplifier can provide, it is
essential to take special precautions to avoid temperature
gradients. All components should be enclosed to eliminate air
movement, especially that caused by power-dissipating
elements in the system. Low thermoelectric-efficient
connections should be used where possible and power supply
voltages and power dissipation should be kept to a minimum.
High-impedance loads are preferable, and good separation
from surrounding heat-dissipating elements is advisable.
Extra care must be taken in the assembly of printed circuit
boards to take full advantage of the low input currents of the
ICL7650S. Boards must be thoroughly cleaned with TCE or
alcohol and blown dry with compressed air. After cleaning,
the boards should be coated with epoxy or silicone rubber to
prevent contamination.
Even with properly cleaned and coated boards, leakage
currents may cause trouble, particularly since the input pins
are adjacent to pins that are at supply potentials. This
leakage can be signi?cantly reduced by using guarding to
lower the voltage difference between the inputs and adjacent
metal runs. Input guarding of the 8-pin TO-99 package is
accomplished by using a 10-lead pin circle, with the leads of
the device formed so that the holes adjacent to the inputs
are empty when it is inserted in the board. The guard, which
is a conductive ring surrounding the inputs, is connected to a
low impedance point that is at approximately the same
voltage as the inputs. Leakage currents from high-voltage
pins are then absorbed by the guard.

Html Pages

1  2  3  4  5  6  7  8  9  10  11  12  13  14 

Datasheet Download

Go To PDF Page

Lien URL

Privacy Policy
AllDATASHEET vous a-t-il été utile ?   [ DONATE ]  

propos de Alldatasheet   |   Publicit   |   Contactez-nous   |   Politique de confidentialit   |   Echange de liens   |   Manufacturer List
All Rights Reserved

Mirror Sites
English :  |   English :  |   Chinese :  |   German :  |   Japanese :
Russian :  |   Korean :  |   Spanish :  |   French :  |   Italian :
Portuguese :  |   Polish :  |   Vietnamese :