®

ADS7833

10

DAC OUTPUT VOLTAGE

The value of the DAC output voltage is determined by the

Figure 2). The 8-bit DAC has 256 possible output voltages

from 0V to +2.49V. The value of 1 LSB is 0.0098V.

ANALOG-TO-DIGITAL

CONVERTERS

ARCHITECTURE

The ADCs are 12-bit, successive approximation types imple-

mented with a switched capacitor circuitry.

SPEED

The clock for the ADC conversion is supplied externally at

the CLK pin. Maximum clock frequency for specified accu-

racy is 2.1MHz. This results in a complete conversion cycle

(S/H acquisition and A/D conversion) of 6.6

µs.

INPUT/OUTPUT

The ADS7833 is designed for bipolar input voltages and

uses a binary two’s complement digital output code. A

programmable gain function is associated with each ADC.

This changes the full scale analog input range and the analog

resolution of the converter. Details are shown in Table VI.

DIFFERENTIAL AND COMMON-MODE

INPUT VOLTAGES

The ADS7833 is designed with full differential signal paths

all the way from the multiplexer inputs through to the input

of the ADCs. This was done to provide superior high

frequency noise rejection.

As is common with most differential input semiconductor

devices, there are compound restrictions on the combination

of differential and common-mode input voltages. This mat-

ter is made slightly more complicated by the fact that most

of the analog inputs are capable of being affected by the

programmable gain function. The possible differential and

single ended configurations are shown in Figures 3a and 3b.

The maximum differential and common mode restrictions

are shown in Table VII.

DESCRIPTION

GAIN SELECT CODE

01

23

GAIN

5V/V

2.5V/V

1.25V/V

1.0V/V

FULL SCALE RANGE

±0.5V

±1.0V

±2.0V

±2.5V

HEX CODE

BINARY CODE

+Full Scale (FS –1LSB)

+0.49976

+0.9995V

+1.999V

+2.499

0111 1111 1111

One Bit above Mid-Scale

+0.244mV

+0.488mV

+0.976mV

+1.22mV

001H

0000 0000 0001

Mid-Scale

0V

0V

0V

0V

0000 0000 0000

One Bit Below Mid-Scale

–0.244V

–0.488mV

–0.976mV

–1.22mV

1111 1111 1111

–Full Scale

–0.500V

–1.000V

–2.000V

–2.500V

1000 0000 0000

have a fixed

±2.5V full scale input range.

ANALOG INPUT

BINARY TWO’S COMPLIMENT FORMAT

TABLE VI. Analog Input - Digital Output Relationships.

DIGITAL OUTPUT

DIGITAL INPUT

ANALOG OUTPUT

HEX

BINARY

CODE

CODE

0000 0000

0V

0000 0001

+0.0098V

••

•

••

•

••

•

1111 1111

+2.499

TABLE V. DAC Input/Output Relationships.

GAIN SELECT CODE

0

1

2

3

Gain

5.0V/V

2.5V/V

1.25V/V

1.0V/V

Full Scale Range

±0.5V

±1.0V

±2.0V

±2.5V

Largest Positive

Common Mode

+2.7V

+2.4V

+1.9V

+1.6V

Largest Negative

Common Mode

–2.7V

–2.4V

–1.9V

–1.6V

TABLE VII. Differential and Common Mode Voltage

Restrictions.

FIGURE 3. (a) Differential Signal Source, and (b) Single

Ended Signal Source.

V

CM

+–

V

D

2

+

–

+

–

V

D

2

V

1 – 1P

V

1 – 1N

V

CM

+

–

+

–

V

1 – 1P

V

1 – 1N

V

D

V

CM

V

CM

V

D

2

V

CM

V

D

V

D

2

V

1 – 1 +

V

1 – 1 –

V

1 – 1

(A)

(B)