DS4422/DS4424
Two-/Four-Channel, I
2
C, 7-Bit Sink/Source
Current DAC
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Detailed Description
The DS4422/DS4424 contain two or four I
2
C adjustable
current sources that are each capable of sinking and
sourcing current. Each output (OUT0, OUT1, OUT2, and
OUT3) has 127 sink and 127 source settings that can be
controlled by the I
2
C interface. The full-scale ranges
and corresponding step sizes of the outputs are deter-
mined by external resistors, connected to pins FS0, FS1,
FS2, and FS3, that can adjust the output current over a
4:1 range. Pins OUT2, OUT3, FS2, and FS3 are only
available on the DS4424.
The formula to determine R
FS
(connected to the FSx
pins) to attain the desired full-scale current range is:
Equation 1:
Where I
FS
is the desired full-scale current value, V
RFS
is
the R
FS
voltage (see the
DC Electrical Characteristics
table), and R
FS
is the external resistor value.
To calculate the output current value (I
OUT
) based on the
corresponding DAC value (see Table 1 for corresponding
memory addresses), use equation 2.
Equation 2:
On power-up the DS4422/DS4424 output zero current.
This is done to prevent them from sinking or sourcing an
incorrect amount of current before the system host con-
troller has had a chance to modify the device’s setting.
As a source for biasing instrumentation or other circuits,
the DS4422/DS4424 provide a simple and inexpensive
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 7-bit sink or source resolution.
When used in adjustable power-supply applications
(see
Typical Operating Circuit
), the DS4422/DS4424 do
not affect the initial power-up voltage of the supply
because they default to providing zero output current on
power-up. As the devices source or sink current into the
feedback-voltage node, they change the amount of out-
put voltage required by the regulator to reach its steady-
state operating point. Using the external resistor, R
FS
, to
set the output current range, the DS4422/DS4424 pro-
vide some 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 DS4422/DS4424 respond to one of four I
2
C slave
addresses determined by the two address inputs, A0
and A1. The address inputs should be connected to
either V
CC
or ground. Table 1 lists the slave addresses
determined by the address input combinations.
Memory Organization
To control the DS4422/DS4424’s current sources, write
to the memory addresses listed in Table 2.
The format of each output control register is given by:
Where:
