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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

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