Preliminary Technical Data

AD5420

Rev. PrD | Page 21 of 29

DEFAULT CONFIGURATION

On initial power-up of the AD5420, the power-on-reset circuit

ensures that all registers are loaded with zero-code, as such the

default output range is 4mA to 20mA. The current output until

a value is programmed is 0mA. An alternative current range

may be selected via the CONTROL register.

TRANSFER FUNCTION

For the 0 to 20mA, 0 to 24mA and 4 to 20mA current output

ranges the output current expressions are respectively given by;

D

mA

I

N

OUT

×

⎥⎦

⎤

⎢⎣

⎡

=

2

20

D

mA

I

N

OUT

×

⎥⎦

⎤

⎢⎣

⎡

=

2

24

mA

D

mA

I

N

OUT

4

2

16

+

×

⎥⎦

⎤

⎢⎣

⎡

=

where:

D

is the decimal equivalent of the code loaded to the DAC.

N

is the bit resolution of the DAC.

DATA REGISTER

The DATA register is addressed by setting the control word of the input shift register to 0x01. The data to be written to the DATA register

is entered in positions D15 to D0 as shown in Table 11,

Table 11. Programming the Data Register

MSB

LSB

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

DATA WORD

CONTROL REGISTER

The CONTROL register is addressed by setting the control word of the input shift register to 0x55. The data to be written to the

CONTROL register is entered in positions D15 to D0 as shown in Table 12. The CONTROL register functions are shown in Table 13.

Table 12. Programming the CONTROL Register

MSB

LSB

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

0

0

REXT

OUTEN

SR CLOCK

SR STEP

SREN

DCEN

R2

R1

R0

Table 13. Control Register Functions

Option

Description

REXT

Setting this bit selects the external current

setting resistor, Further details in Features

section

OUTEN

Output enable. This bit must be set to enable

the output.

SR CLOCK

See Features Section. Digital Slew Rate Control

SR STEP

See Features Section. Digital Slew Rate Control

SREN

Digital Slew Rate Control enable

DCEN

Daisychain enable

R2,R1,R0

Output range select. See Table 14

Table 14. Output Range Options

R2

R1

R0

Output Range Selected

1

0

1

4 to 20 mA Current Range

1

1

0

0 to 20 mA Current Range

1

1

1

0 to 24 mA Current Range