Datasheet

Detailed Description
The DS4402/DS4404 contain two/four I
2
C adjustable
current sources (Figure 1) that are each capable of
sinking and sourcing current. Each output has 31 sink
and 31 source settings that are programmed through
the I
2
C interface. The full-scale ranges (and corre-
sponding step sizes) of the outputs are determined by
external resistors that adjust the output currents over a
4:1 range. The formula to determine the external resis-
tor values (R
FS
) for each of the outputs is given by:
Equation 1:
R
FS
= (V
REF
/ I
FS
) x (31 / 4)
where I
FS
= desired full-scale current
On power-up, the DS4402/DS4404 output 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 DS4402/DS4404 provide a simple and inex-
pensive current source with an I
2
C interface for control.
The adjustable full-scale range allows the application to
get the most out of its 5-bit sink or source resolution.
When used in adjustable power-supply applications
(see the
Typical Operating Circuit ), the DS4402/DS4404
do 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.
By using the external resistor to set the output current
range, the devices provide flexibility for adjusting the
impedances of the feedback network or the range over
which the power supply can be controlled or margined.
I
2
C Slave Address
The DS4402/DS4404 respond to one of nine I
2
C slave
addresses determined by the two tri-level address
inputs. The three input states are connected to V
CC
,
connected to ground, or disconnected. To sense the
disconnected state (Figure 2), the address inputs have
weak internal resistors that pull the pins to mid-supply.
Table 1 lists the slave address determined by the
address input combinations.
DS4402/DS4404
Two/Four-Channel, I
2
C Adjustable Current DAC
_____________________________________________________________________ 5
Table 1. Slave Addresses
A1 A0
SLAVE ADDRESS
(HEXADECIMAL)
GND GND 90h
GND V
CC
92h
V
CC
GND 94h
V
CC
V
CC
96h
N.C. GND 98h
N.C. V
CC
9Ah
GND N.C. 9Ch
V
CC
N.C. 9Eh
N.C. N.C. A0h
A0
A1
I
2
C
ADDRESS
DECODE
R
IN
R
IN
V
CC
R
IN
R
IN
Figure 2. I
2
C Address Inputs