3-10

analog sample is taken (see the timing diagram in Figure 1).

This time delay is specified as the data latency. After the

data latency time, the digital data representing each

succeeding analog sample is output during the following

clock cycle. The digital output data is provided in offset

binary format (see Table 1, A/D Code Table).

The ISL5740 is equipped with an internal 1.25V bandgap

reference voltage generator, therefore, no external reference

when using the internal reference voltage. An external, user-

supplied, 0.1

output pin to filter any stray board noise.

The ISL5740 is designed to accept a 1.25V reference

range of

±0.5V.

The user does have the option of supplying an external 1.25V

reference voltage. As a result of the high input impedance

reference voltage being used is only required to source small

amount of reference input current.

In order to minimize overall converter noise it is

recommended that adequate high frequency decoupling be

Analog Input, Differential Connection

The analog input of the ISL5740 is a differential input that

can be configured in various ways depending on the signal

source and the required level of performance. A fully

differential connection (Figure 16 and Figure 17) will deliver

the best performance from the converter.

Since the ISL5740 is powered by a single +3V analog

supply, the analog input is limited to be between ground and

+3V. For the differential input connection this implies the

analog input common mode voltage can range from 0.25V to

2.75V. The performance of the ADC does not change

significantly with the value of the analog input common

mode voltage.

Conversely, the converter will be at negative full scale when

The analog input can be DC coupled (Figure 17) as long as

the inputs are within the analog input common mode voltage

range (0.25V

≤ VDC ≤ 2.75V).

The resistors, R, in Figure 17 are not absolutely necessary

but may be used as load setting resistors. A capacitor, C,

frequency noise on the inputs, also improving performance.

Values around 20pF are sufficient and can be used on AC

coupled inputs as well. Note, however, that the value of

capacitor C chosen must take into account the highest

frequency component of the analog input signal.

Analog Input, Single-Ended Connection

The configuration shown in Figure 18 may be used with a

single ended AC coupled input.

ISL5740

R

R

FIGURE 4. AC COUPLED DIFFERENTIAL INPUT

ISL5740

R

R

C

FIGURE 5. DC COUPLED DIFFERENTIAL INPUT

ISL5740

R

FIGURE 6. AC COUPLED SINGLE ENDED INPUT

ISL5740