REV. F

–5–

AD420

PIN DESCRIPTION

Pin #

Symbol

Function

1, 12, 13, 24

NC

No Connection. No internal connections inside device.

Auxiliary buffered +4.5 V digital logic voltage. This pin is the internal supply voltage

for the digital circuitry and can be used as a termination for pull-up resistors. An

to GND with a 0.1

µF capacitor. See Power Supplies and Decoupling section.

3

FAULT DETECT

FAULT DETECT, connected to a pull-up resistor, is asserted low when the

output current does not match the DAC’s programmed value, for example, in

case the current loop is broken.

4

RANGE SELECT 2

Selects the converter’s output operating range. One output voltage range and three

5

RANGE SELECT 1

output current ranges are available.

6

CLEAR

programmed range. After CLEAR is removed the DAC output will remain at this

value. The data in the input register is unaffected.

7

LATCH

In the three-wire interface mode a rising edge parallel loads the serial input register

data into the DAC. To use the asynchronous mode connect LATCH through a

8

CLOCK

Data Clock Input. The clock period is equal to the input data bit rate in the three-

wire interface mode and is 16 times the bit rate in asynchronous mode.

9

DATA IN

Serial Data Input.

10

DATA OUT

Serial Data Output. In the three-wire interface mode, this output can be used for

daisy-chaining multiple AD420s. In the asynchronous mode a positive pulse will

indicate a framing error after the stop-bit is received.

11

GND

Ground (Common).

14

REF OUT

+5 V Reference Output.

15

REF IN

Reference Input.

16

OFFSET TRIM

Offset Adjust.

17

Voltage Output.

18

Current Output.

19

BOOST

Connect to an external transistor to reduce the power dissipated in the AD420

output transistor, if desired.

20

CAP 1

These pins are used for internal filtering. Connect capacitors between each of these

21

CAP 2

22

NC

No Connection. Do not connect anything to this pin.

23

0.1

µF capacitor. See Power Supplies and Decoupling section.

DEFINITIONS OF SPECIFICATIONS

RESOLUTION: For 16-bit resolution, 1 LSB = 0.0015% of the

FSR. In the 4 mA–20 mA range 1 LSB = 244 nA.

INTEGRAL NONLINEARITY: Analog Devices defines inte-

gral nonlinearity as the maximum deviation of the actual, ad-

justed DAC output from the ideal analog output (a straight line

drawn from 0 to FS – 1 LSB) for any bit combination. This is

also referred to as relative accuracy.

DIFFERENTIAL NONLINEARITY: Differential nonlinearity

is the measure of the change in the analog output, normalized to

full scale, associated with an LSB change in the digital input code.

Monotonic behavior requires that the differential linearity error be

greater than –1 LSB over the temperature range of interest.

MONOTONICITY: A DAC is monotonic if the output either

increases or remains constant for increasing digital inputs with

the result that the output will always be a single-valued function

of the input.

GAIN ERROR: Gain error is a measure of the output error

between an ideal DAC and the actual device output with all 1s

loaded after offset error has been adjusted out.

OFFSET ERROR: Offset error is the deviation of the output

current from its ideal value expressed as a percentage of the full-

scale output with all 0s loaded in the DAC.

DRIFT: Drift is the change in a parameter (such as gain and

offset) over a specified temperature range. The drift temperature

coefficient, specified in ppm/

°C, is calculated by measuring the

°C, and T

the parameter by the corresponding temperature change.

CURRENT LOOP VOLTAGE COMPLIANCE: The voltage

the output current will be equal to the programmed value.