DS4412 View Datasheet(PDF) - Maxim Integrated

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DS4412

Dual-Channel, I2C Adjustable Sink/Source Current DAC

Maxim Integrated 

Dual-Channel, I2C Adjustable

Sink/Source Current DAC

Detailed Description

The DS4412 contains two I2C adjustable-current

sources that are each capable of sinking and sourcing

current. Each output, OUT0 and OUT1, has 15 sink and

15 source settings that are programmed through the

I2C interface. The full-scale ranges and corresponding

step sizes of the outputs are determined by external

resistors, connected to pins FS0 and FS1, which can

adjust the output currents over a 4:1 range. The formula

to determine the positive and negative full-scale current

ranges for each of the four outputs is given by:

RFS = (VRFS / IFS) x (15 / 1.974)

where VRFS is the RFS voltage (see DC Electrical

Characteristics), and RFS is the external resistor value.

On power-up, the DS4412 outputs zero current. This is

done to prevent it from sinking or sourcing an incorrect

current before the system host controller has had a

chance to modify the device’s setting.

As a source for biasing instrumentation or other cir-

cuits, the DS4412 provides a simple and inexpensive

current source with an I2C interface for control. The

adjustable full-scale range allows the application to get

the most out of its 4-bit sink or source resolution.

When used in adjustable power-supply applications

(see Typical Operating Circuit), the DS4412 does not

affect the initial power-up supply voltage because it

defaults to providing zero output current on power-up.

As it sources or sinks current into the feedback voltage

node, it changes the amount of output voltage required

by the regulator to reach its steady state operating

point. Using the external resistor, RFS, to set the output

current range, the DS4412 provides some flexibility for

adjusting the range over which the power supply can

be controlled or margined.

Memory Organization

The DS4412’s current sources are controlled by writing

to the memory addresses in Table 1.

Table 1. Memory Addresses

MEMORY ADDRESS

(HEXADECIMAL)

0xF8

0xF9

CURRENT SOURCE

OUT0

OUT1

The format of each output control register is given by:

MSB

LSB

S

X

X

X

D3

D2

D1

D0

Where:

BIT NAME

FUNCTION

POWER-ON

DEFAULT

Determines if DAC sources

S Sign Bit or sinks current. For sink

0b

S = 0, for source S = 1.

X Reserved Reserved.

4-Bit Data Word Controlling

DAC Output. Setting 0000b

DX Data outputs zero current

regardless of the state of the

sign bit.

XXX

0000b

Example: RFS0 = 4.8kΩ and register 0xF8h is written to

a value of 0x8Ah. Calculate the output current.

IFS = (0.607V / 4.8kΩ) x (15 / 1.974) = 949.85µA

The MSB of the output register is 1, so the output is

sourcing the value corresponding to position Ah (10 dec-

imal). The magnitude of the output current is equal to:

949.85µA x (10 / 15) = 633.23µA

6 _______________________________________________________________________________________

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