Datasheet
IOUT1
IOUT2
50 Ω
25 Ω
R
LOAD
50 Ω
AGND
I
OUTFS
+ 32 I
REF
+ 32
V
REF
R
SET
DAC5672
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SLAS440C –NOVEMBER 2004–REVISED DECEMBER 2010
Single-Ended Configuration
Figure 24 shows the single-ended output configuration, where the output current I
OUT1
flows into an equivalent
load resistance of 25 Ω. Node IOUT2 must be connected to AGND or terminated with a resistor of 25 Ω to
AGND. The nominal resistor load of 25 Ω gives a differential output swing of 1 V
PP
when applying a 20-mA
full-scale output current.
Figure 24. Driving a Doubly-Terminated 50-Ω Cable Using a Single-Ended Output
Reference Operation
Internal Reference
The DAC5672 has an on-chip reference circuit which comprises a 1.2-V bandgap reference and two control
amplifiers, one for each DAC. The full-scale output current, I
OUTFS
, of the DAC5672 is determined by the
reference voltage, V
REF
, and the value of resistor R
SET
. I
OUTFS
can be calculated by:
(9)
The reference control amplifier operates as a V-to-I converter producing a reference current, I
REF
, which is
determined by the ratio of V
REF
and R
SET
(see Equation 9). The full-scale output current, I
OUTFS
, results from
multiplying I
REF
by a fixed factor of 32.
Using the internal reference, a 2-kΩ resistor value results in a full-scale output of approximately 20 mA. Resistors
with a tolerance of 1% or better should be considered. Selecting higher values, the output current can be
adjusted from 20 mA down to 2 mA. Operating the DAC5672 at lower than 20-mA output currents may be
desirable for reasons of reducing the total power consumption, improving the distortion performance, or
observing the output compliance voltage limitations for a given load condition.
It is recommended to bypass the EXTIO pin with a ceramic chip capacitor of 0.1 µF or more. The control
amplifier is internally compensated and its small signal bandwidth is approximately 300 kHz.
External Reference
The internal reference can be disabled by simply applying an external reference voltage into the EXTIO pin,
which in this case functions as an input. 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 0.1-µF capacitor is recommended to be used with the internal reference, it is optional for the external
reference operation. The reference input, EXTIO, has a high input impedance (1 MΩ) and can easily be driven
by various sources. Note that the voltage range of the external reference must stay within the compliance range
of the reference input.
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