AD420 查看數據表（PDF） - Analog Devices

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AD420

Serial Input 16-Bit 4 mA–20 mA, 0 mA–20 mA DAC

Analog Devices 

AD420

Data Sheet

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

NC 1

24 NC

VLL 2

FAULT DETECT 3

23 VCC

22 NC

RANGE SELECT 2 4

21 CAP 2

RANGE SELECT 1 5 AD420 20 CAP 1

CLEAR 6 TOP VIEW 19 BOOST

(Not to Scale)

LATCH 7

18 IOUT

CLOCK 8

17 VOUT

DATA IN 9

16 OFFSET TRIM

DATA OUT 10

15 REF IN

GND 11

14 REF OUT

NC 12

13 NC

NC = NO CONNECT

Figure 2. Pin Configuration

Table 4. Pin Function Descriptions

Pin No. Mnemonic

Function

1, 12,

NC

13, 24

No Connection. No internal connections inside device.

2

VLL

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 external +5 V power supply can be

connected to VLL. It will override this buffered voltage, thus reducing the internal power dissipation. The

VLL pin should be decoupled to GND with a 0.1 µF capacitor. See the 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

Valid VIH unconditionally forces the output to go to the minimum of its 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 3-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 current limiting resistor to VCC.

8

CLOCK

Data Clock Input. The clock period is equal to the input data bit rate in the 3-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 3-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

VOUT

Voltage Output.

18

IOUT

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

pins and VCC. Refer to the description of current output operation.

22

NC

No Connection. Do not connect anything to this pin.

23

VCC

Power Supply Input. The VCC pin should always be decoupled to GND with a 0.1 µF capacitor. See the

Power Supplies and Decoupling section.

Rev. I | Page 6 of 16

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