DS4426T+TR MAXIM [Maxim Integrated Products], DS4426T+TR Datasheet - Page 7

• Manufacturer Part Number: DS4426T+TR
• Description: Quad-Channel, I2C-Margining IDACs with Three Channels of Power-Supply Tracking
• Manufacturer: MAXIM [Maxim Integrated Products]

Figure 1. Current DAC Detail
Figure 2. Gain Stage
Figure 3. INP and INN Differential Inputs
SINK MODE
SOURCE
OR
R
INN
INP
FS[3:0]
SHUTDOWN
MSB
-0.2
Three Channels of Power-Supply Tracking
FS[3:0]
+
-
I
I
Quad-Channel, I
2
MAX
DAC
_______________________________________________________________________________________
C CONTROL
G
CURRENT
VI
I
DAC[3:0]
G
VI
OUT[3:0]
LSB
+0.3
AT V
127 POSITIONS
EACH FOR SOURCE
AND SINK MODE
GAIN
OUT
CC
= +5.0V
V
CC
SLAVE
FEEDBACK
NODE
R
OUT[3:1] ONLY
G
TRACKING
(V
INP
- V
INN
V
)
2
C-Margining IDACs with
Using the external resistors R
current range, the DS4426 provides some flexibility for
adjusting the impedances of the feedback network or
the range over which the power supply can be con-
trolled or margined.
As a source for biasing instrumentation or other circuits,
the DS4426 provides a simple and inexpensive current
source with an I
full-scale range allows the application to get the most
out of its 7-bit sink or source resolution.
By making use of the power-supply tracking circuitry,
the DS4426 has the ability to source current on power-
up. This current is additive with the current DAC
source/sink currents and is determined by the value of
the gain resistor, R
current is controlled by the voltages presented to the
corresponding INP and INN pins, and the voltages pre-
sented to the corresponding threshold (THR) pins.
The maximum current the DS4426 can source at
power-up using the power-supply tracking circuitry
depends on the value of the supply voltage, V
the gain resistor, R
ing GAIN pin to V
can be sourced to the corresponding OUT pin can be
estimated using the following equation:
The power-supply tracking circuit can be estimated
with Figure 2.
Each pair of power-supply tracking inputs, INP and
INN, determines if and how much of the I
sourced when the power-supply tracking circuit is
enabled. When the difference between the voltage pre-
sented to INP (V
approximately +0.3V, then the maximum source cur-
rent, as determined by the value I
the OUT pin connection. When the difference between
V
current is sourced into the corresponding OUT pin. The
change in current from no current to I
mated by the power-supply tracking gain, G
Power-Supply Tracking Characteristics table).
Figure 3 shows the typical current behavior of the
power-supply tracking circuit with respect to the volt-
age difference seen at the INP and INN inputs.
INP
and V
Power-Supply Tracking Circuit
INN
Inputs for Power-Supply Tracking:
is less than approximately -0.2V, then no
2
I
C interface for control. The adjustable,
MAX
CC
INP
G
G
, and the supply voltage, V
. The maximum current (I
, connected from the correspond-
) and INN (V
≅
Maximum Source Current
(
V
CC
R
FS[3:0]
−
G
V
OUT
MAX
INN
to set the output-
)
MAX
, is sourced into
INP and INN
) is more than
MAX
can be esti-
VI
current is
MAX
CC
(see the
CC
. This
, and
) that
7