AD1380

–3–

REV. B

THEORY OF OPERATION

A 16-bit A/D converter partitions the range of analog inputs into

2

quantum are represented by the same digital code, usually as-

signed to the nominal midrange value. There is an inherent

quantization uncertainty of

±1/2 LSB, associated with the reso-

lution, in addition to the actual conversion errors.

The actual conversion errors that are associated with A/D con-

verters are combinations of analog errors due to the linear cir-

cuitry, matching and tracking properties of the ladder and

scaling networks, reference error and power supply rejection.

The matching and tracking errors in the converter have been

minimized by the use of monolithic DACs that include the

scaling network. The initial gain and offset errors are specified

at

±0.1% FSR for gain and ±0.05% FSR for offset. These errors

may be trimmed to zero by the use of external trim circuits as

shown in Figures 2 and 3. Linearity error is defined for unipolar

ranges as the deviation from a true straight line transfer charac-

teristic from a zero voltage analog input, which calls for a zero

digital output, to a point which is defined as a full scale. The

linearity error is based on the DAC resistor ratios. It is unadjust-

able and is the most meaningful indication of A/D converter

accuracy. Differential nonlinearity is a measure of the deviation

in the staircase step width between codes from the ideal least

significant bit step size (Figure 1).

Monotonic behavior requires that the differential linearity error

be less than 1 LSB; however, a monotonic converter can have

missing codes. The AD1380 is specified as having no missing

codes over temperature ranges as specified on the data page.

ABSOLUTE MAXIMUM RATINGS

Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

±18 V

Logic Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . +7 V

Analog Ground to Digital Ground . . . . . . . . . . . . . . . .

±0.3 V

Analog Inputs (Pins 6, 7, 31) . . . . . . . . . . . . . . . . . . . . . .

±V

S

Output Short Circuit Duration to Ground

Sample/Hold . . . . . . . . . . . . . . . . . . . . . . . . . . . . Indefinite

Data . . . . . . . . . . . . . . . . . . . . . . 1 sec for Any One Output

Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . +175

°C

Storage Temperature . . . . . . . . . . . . . . . . . . –65

°C to +150°C

Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . +300

°C

ORDERING GUIDE

Max Linearity Temperature

Model

Error

Range

Package Option

AD1380JD

0.006% FSR

0

°C to +70°C Ceramic (DH-32E)

AD1380KD 0.003% FSR

0

°C to +70°C Ceramic (DH-32E)

There are three types of drift error over temperature: offset, gain

and linearity. Offset drift causes a shift of the transfer character-

istic left or right on the diagram over the operating temperature

range. Gain drift causes a rotation of the transfer characteristic

about the zero for unipolar ranges or minus full-scale point for

bipolar ranges. The worst case accuracy drift is the summation

of all three drift errors over temperature. Statistically, however,

the drift error behaves as the root-sum-squared (RSS) and can

be shown as:

RSS

=∈

G

O

L

2

∈

∈

∈

Figure 1. Transfer Characteristics for an Ideal Bipolar A/D

DESCRIPTION OF OPERATION

On receipt of a CONVERT START command, the AD1380

converts the voltage at its analog input into an equivalent 16-bit

binary number. This conversion is accomplished as follows: the

16-bit successive approximation register (SAR) has its 16-bit

outputs connected to both the device bit output pins and the

corresponding bit inputs of the feedback DAC. The analog

input is successively compared to the feedback DAC output,

one bit at a time (MSB first, LSB last). The decision to keep

or reject each bit is then made at the completion of each bit

comparison period, depending on the state of the comparator

at that time.

WARNING!

ESD SENSITIVE DEVICE

CAUTION

ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily

accumulate on the human body and test equipment and can discharge without detection.

Although the AD1380 features proprietary ESD protection circuitry, permanent damage may

occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD

precautions are recommended to avoid performance degradation or loss of functionality.