8

LTC1405

over a 0V to 5V range (Figures 3a and 3b). The input

useful in applications where the peak input signal ampli-

tude may vary. The input span of the ADC can then be

adjusted to match the peak input signal, maximizing the

signal-to-noise ratio.

capacitors to ground. For best performance, 1

µF or larger

ceramic capacitors are recommended. For the case of

this case, a 0.05

µF or larger ceramic capacitor is accept-

able.

can be used by external circuitry. For single 5V supply

Driving the Analog Inputs

The differential inputs of the LTC1405 are easy to drive.

The inputs may be driven differentially or single-ended

mode signal is reduced by the high common mode rejec-

tion of the sample-and-hold circuit. Any common mode

input value is acceptable as long as the input pins stay

inputs are high impedance. At the end of conversion the

inputs draw a small current spike while charging the

sample-and-hold.

For superior dynamic performance in dual supply mode,

the LTC1405 should be operated with the analog inputs

centered at ground, and in single supply mode the inputs

should be centered at 2.5V. If required, the analog inputs

can be driven differentially via a transformer. Refer to

Table 2 for a summary of the analog input and reference

configurations and their relative advantages.

SENSE

1405 F02

–

+

R1

10k

LOGIC

2.5V

REFERENCE

2.048V

1

µF

1

µF

2k

TO

ADC

R2

10k

APPLICATIO S I FOR ATIO

LT1019A-2.5

5V

1405 F03a

1

µF

1

µF

SENSE

5V

LTC1405

1405 F03b

1

µF

1

µF

LTC1405

SENSE

2.048V

–

+

5k

5k

LTC1450

Figure 2. Reference Circuit

Figure 3a. Using the LT1019-2.5 As an

External Reference; Input Range =

±1.25V