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LTC1047
1047fa
Input Considerations
Frequently circuits built with parts as precise as the
LTC1047 show errors at the output far greater than the
designer expects. Rarely is the problem the op amp; more
often the surrounding circuitry is causing errors several
orders of magnitude greater than those due to the LTC1047.
Such obscure effects as leakage between pins, due to
residual solder flux and thermocouple effects between the
tin/lead solder and the copper PC board traces, can
overwhelm the pA-level bias currents and the µV-level
offset of the LTC1047. For a more complete description of
these types of problems (and some advice on avoiding
them), see the LTC1051/LTC1053 data sheet.
Input Capacitance
The LTC1047 has approximately 12pF of capacitance at
each input pin. This will react with large series resistors to
form a pole at the input, degrading the LTC1047's phase
margin. The problem is especially common with
micropower parts like the LTC1047 because high value
resistors are often used to minimize power dissipation. As
a rule of thumb, bypass feedback resistors larger than 7k
with a 20pF capacitor to minimize this effect.
Aliasing
Like all sampled data systems, the LTC1047 will alias input
signals near its internal sampling frequency. The design
includes internal circuitry to minimize this effect; as a
result, most applications do not exhibit aliasing problems.
For a complete discussion of the correction circuitry and
aliasing behavior, refer to the LTC1051/LTC1053 data
sheet.
Single Supply Operation
The LTC1047 is compatible with all single supply
applications. It has an input common mode range which
includes V
–
, and an output which will swing within
millivolts of the negative power supply. The LTC1047 is
guaranteed functional down to 4.75V total supply,
allowing it to run from minimum TTL voltage all the way up
to 16V. See the Typical Applications section for examples
of single supply operation.
APPLICATIO S I FOR ATIO
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