DAC250Y BURR-BROWN [Burr-Brown Corporation], DAC250Y Datasheet - Page 14

• Manufacturer Part Number: DAC250Y
• Description: Dual, 12-Bit, 125MSPS DIGITAL-TO-ANALOG CONVERTER
• Manufacturer: BURR-BROWN [Burr-Brown Corporation]

FIGURE 10. Internal Reference Configuration.
Using the internal reference, a 2k
a full-scale output of approximately 20mA. Resistors with a
tolerance of 1% or better should be considered. Selecting
higher values, the output current can be adjusted from 20mA
down to 2mA. Operating the DAC2902 at lower than 20mA
output currents may be desirable for reasons of reducing the
total power consumption, optimizing the distortion perfor-
mance, or observing the output compliance voltage limita-
tions for a given load condition.
It is recommended to bypass the REF
chip capacitor of 0.1µF or more. The control amplifier is
internally compensated, and its small signal bandwidth is
approximately 0.3MHz.
GAIN SETTING OPTIONS
The full-scale output current on the DAC2902 can be set two
ways: either for each of the two DAC channels independently
or for both channels simultaneously. For the independent gain
set mode, the GSET pin (pin 42) must be LOW (i.e. connected
to AGND). In this mode, two external resistors are required—
FIGURE 11. External Reference Configuration.
14
R
2k
I
REF
SET
=
V
R
REF
SET
0.1 F
FSA
REF
DAC2902
IN
+1.25V Ref.
Reference
External
Control
Amp
Ref
resistor value results in
IN
pin with a ceramic
R
SET
I
REF
Sources
Current
+5V
=
+V
V
R
REF
SET
A
FSA
REF
DAC2902
IN
+1.25V Ref.
one R
the FSA2 pin (pin 41). In this configuration, the user has the
flexibility to set and adjust the full-scale output current for each
DAC independently, allowing for the compensation of possible
gain mismatches elsewhere within the transmit signal path.
Alternatively, bringing the GSET pin HIGH (i.e. connected to
+V
mode. Now the full-scale output current of both DAC chan-
nels is determined by only one external R
nected to the FSA1 pin. The resistor at the FSA2 pin may be
removed, however this is not required since this pin is not
functional in this mode and the resistor has no effect to the
gain equation. The formula for deriving the correct R
remains unchanged, e.g. R
output for both DACs.
EXTERNAL REFERENCE OPERATION
The internal reference can be disabled by simply applying an
external reference voltage into the REF
case functions as an input, as shown in Figure 11. The use
of an external reference may be considered for applications
that require higher accuracy and drift performance, or to add
the ability of dynamic gain control.
While a 0.1µF capacitor is recommended to be used with the
internal reference, it is optional for the external reference
operation. The reference input, REF
impedance (1M ) and can easily be driven by various
sources. Note that the voltage range of the external reference
should stay within the compliance range of the reference
input (0.5V to 1.25V).
POWER-DOWN MODE
The DAC2902 features a power-down function that can be
used to reduce the total supply current to less than 6mA.
Applying a logic HIGH to the PD pin will initiate the power-
down mode, while a logic LOW enables normal operation.
When left unconnected, an internal active pull-down circuit
will enable the normal operation of the converter.
A
), the DAC2902 will switch into the simultaneous gain set
SET
Control
Amp
Ref
connected to the FSA1 pin (pin 44) and the other to
Sources
Current
+5V
SET
+V
= 2ký will result in a 20mA
A
IN
IN
, has a high input
pin, which in this
SET
DAC2902
resistor con-
SBAS167A
SET