Datasheet

AD9760
–15–
REV. B
Note, the clock input could also be driven via a sine wave that is
centered around the digital threshold (i.e., DVDD/2), and
meets the min/max logic threshold. This will typically result in a
slight degradation in the phase noise, that becomes more notice-
able at higher sampling rates and output frequencies. Also, at
higher sampling rates, the 20% tolerance of the digital logic
threshold should be considered since it will affect the effective
clock duty cycle and subsequently cut into the required data
setup and hold times.
SLEEP MODE OPERATION
The AD9760 has a power-down function that turns off the out-
put 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 tempera-
ture range. This mode can be activated by applying a logic level
“1” to the SLEEP pin. This digital input also contains an active
pull-down circuit that ensures that the AD9760 remains enabled
if this input is left disconnected. The SLEEP input with active
pull-down requires <40 µA of drive current.
The power-up and power-down characteristics of the AD9760
are dependent upon the value of the compensation capacitor
connected to COMP1. With a nominal value of 0.1 µF, the
AD9760 takes less than 5 µs to power down and approximately
3.25 ms to power back up. Note, the SLEEP MODE should not
be used when the external control amplifier is used as shown in
Figure 45.
POWER DISSIPATION
The power dissipation, P
D
, of the AD9760 is dependent on
several factors that 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 current,
I
DVDD
. I
AVDD
is directly proportional to I
OUTFS
as shown in Fig-
ure 47 and is insensitive to f
CLOCK
.
I
OUTFS
– mA
30
0
2204 6 8 10 12141618
25
20
15
10
5
I
AVDD
– mA
Figure 47. I
AVDD
vs. I
OUTFS
Conversely, I
DVDD
is dependent on both the digital input wave-
form, f
CLOCK
, and digital supply DVDD. Figures 48 and 49
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.
RATIO (f
OUT
/f
CLK
)
18
16
0
0.01 10.1
I
DVDD
– mA
8
6
4
2
12
10
14
5MSPS
25MSPS
50MSPS
100MSPS
125MSPS
Figure 48. I
DVDD
vs. Ratio @ DVDD = 5 V
RATIO (f
OUT
/f
CLK
)
8
0
0.01 10.1
I
DVDD
– mA
6
4
2
5MSPS
25MSPS
50MSPS
100MSPS
125MSPS
Figure 49. I
DVDD
vs. Ratio @ DVDD = 3 V