Datasheet

REV. 0
AD9752
–13–
SLEEP MODE OPERATION
The AD9752 has a power-down function which turns off the
output current and reduces the supply current to less than
8.5 mA over the specified supply range of 2.7 V to 5.5 V and
temperature range. This mode can be activated by applying a
logic level “1” to the SLEEP pin. This digital input also con-
tains an active pull-down circuit that ensures the AD9752 re-
mains enabled if this input is left disconnected. The AD9752
takes less than 50 ns to power down and approximately 5 µs to
power back up.
POWER DISSIPATION
The power dissipation, P
D
, of the AD9752 is dependent on
several factors which include: (1) AVDD and DVDD, the
power supply voltages; (2) I
OUTFS
, the full-scale current output;
(3) f
CLOCK
, the update rate; (4) and the reconstructed digital
input waveform. The power dissipation is directly proportional
to the analog supply current, I
AVDD
, and the digital supply cur-
rent, I
DVDD
. I
AVDD
is directly proportional to I
OUTFS
as shown in
Figure 25 and is insensitive to f
CLOCK
.
Conversely, I
DVDD
is dependent on both the digital input wave-
form, f
CLOCK
, and digital supply DVDD. Figures 26 and 27
show I
DVDD
as a function of full-scale sine wave output ratios
(f
OUT
/f
CLOCK
) for various update rates with DVDD = 5 V and
DVDD = 3 V, respectively. Note, how I
DVDD
is reduced by more
than a factor of 2 when DVDD is reduced from 5 V to 3 V.
I
OUTFS
– mA
35
5
2204 6 8 1012 141618
30
25
20
15
10
I
AVDD
– mA
Figure 25. I
AVDD
vs. I
OUTFS
RATIO (f
CLOCK
/f
OUT
)
18
16
0
0.01 10.1
I
DVDD
– mA
8
6
4
2
12
10
14
125MSPS
100MSPS
50MSPS
25MSPS
5MSPS
Figure 26. I
DVDD
vs. Ratio @ DVDD = 5 V
RATIO (f
CLOCK
/f
OUT
)
8
0
0.01 10.1
I
DVDD
– mA
6
4
2
125MSPS
100MSPS
50MSPS
25MSPS
5MSPS
Figure 27. I
DVDD
vs. Ratio @ DVDD = 3 V
APPLYING THE AD9752
OUTPUT CONFIGURATIONS
The following sections illustrate some typical output configura-
tions for the AD9752. Unless otherwise noted, it is assumed
that I
OUTFS
is set to a nominal 20 mA. For applications requir-
ing the optimum dynamic performance, a differential output
configuration is suggested. A differential output configuration
may consist of either an RF transformer or a differential op amp
configuration. The transformer configuration provides the opti-
mum high frequency performance and is recommended for any
application allowing for ac coupling. The differential op amp
configuration is suitable for applications requiring dc coupling, a
bipolar output, signal gain and/or level shifting.
A single-ended output is suitable for applications requiring a
unipolar voltage output. A positive unipolar output voltage will
result if IOUTA and/or IOUTB is connected to an appropri-
ately sized load resistor, R
LOAD
, referred to ACOM. This con-
figuration may be more suitable for a single-supply system
requiring a dc coupled, ground referred output voltage. Alterna-
tively, an amplifier could be configured as an I-V converter thus
converting IOUTA or IOUTB into a negative unipolar voltage.
This configuration provides the best dc linearity since IOUTA
or IOUTB is maintained at a virtual ground. Note, IOUTA
provides slightly better performance than IOUTB.
DIFFERENTIAL COUPLING USING A TRANSFORMER
An RF transformer can be used to perform a differential-to-
single-ended signal conversion as shown in Figure 28. A
differentially coupled transformer output provides the optimum
distortion performance for output signals whose spectral content
lies within the transformer’s passband. An RF transformer such
as the Mini-Circuits T1-1T provides excellent rejection of
common-mode distortion (i.e., even-order harmonics) and noise
over a wide frequency range. It also provides electrical isolation
and the ability to deliver twice the power to the load. Trans-
formers with different impedance ratios may also be used for
impedance matching purposes. Note that the transformer
provides ac coupling only.