AD9763ASTZ Analog Devices Inc, AD9763ASTZ Datasheet - Page 20

• Manufacturer Part Number: AD9763ASTZ
• Description: IC DAC 10BIT DUAL 125MSPS 48LQFP
• Manufacturer: Analog Devices Inc
• Series: TxDAC+®r

Specifications of AD9763ASTZ

• Data Interface: Parallel
• Settling Time: 35ns
• Number Of Bits: 10
• Number Of Converters: 2
• Voltage Supply Source: Analog and Digital
• Power Dissipation (max): 450mW
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 48-LQFP
• Resolution (bits): 10bit
• Sampling Rate: 125MSPS
• Input Channel Type: Parallel
• Supply Voltage Range - Analog: 3V To 5.5V
• Supply Voltage Range - Digital: 2.7V To 5.5V
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: AD9763-EBZ - BOARD EVAL FOR AD9763
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

AD9763
Note that the units in Figure 40 are given in units of amps out/
volts in. Noise on the analog power supply has the effect of
modulating the internal current sources and, therefore, the
output current. The voltage noise on AVDD, therefore, is added
in a nonlinear manner to the desired I
dependent, thus producing mixing effects that can modulate
low frequency power supply noise to higher frequencies. Worst
case PSRR for either one of the differential DAC outputs occurs
when the full-scale current is directed towards that output. As a
result, the PSRR measurement in Figure 40 represents a worst-
case condition where the digital inputs remain static and the
full-scale output current of 20 mA is directed to the DAC
output being measured.
The following example serves to illustrate the effect of supply
noise on the analog supply. Suppose a switching regulator with
a switching frequency of 250 kHz produces 10 mV of noise
and, for simplicity’s sake (ignore harmonics), all of this noise
is concentrated at 250 kHz. To calculate how much of this
undesired noise appears as current noise superimposed on the
full-scale current of the DAC, I
PSRR in dB using Figure 40 at 250 kHz. To calculate the PSRR
for a given R
from A/V to V/V, adjust the curve in Figure 40 by the scaling
factor 20×log(R
is reduced by 34 dB (PSRR of the DAC at 250 kHz, 85 dB in
Figure 40, becomes 51 dB V
LOAD
LOAD
such that the units of PSRR are converted
). For instance, if R
OUT
/V
OUTFS
IN
).
, one must determine the
OUT
LOAD
. PSRR is very code-
is 50 Ω, the PSRR
Rev. D | Page 20 of 32
Proper grounding and decoupling is a primary objective in any
high speed, high resolution system. The AD9763 features
separate analog and digital supply and ground pins to optimize
the management of analog and digital ground currents in a system.
In general, decouple the analog supply (AVDD) to the analog
common (ACOM) as close to the chip as physically possible.
Similarly, decouple the digital supply (DVDD) to the digital
common (DCOM) as close to the chip as physically possible.
For those applications that require a single 5 V or 3.3 V supply
for both the analog and digital supplies, a clean analog supply
can be generated using the circuit shown in Figure 41. The
circuit consists of a differential LC filter with separate power
supply and return lines. Lower noise can be attained by using
low ESR type electrolytic and tantalum capacitors.
TTL/CMOS
CIRCUITS
LOGIC
POWER SUPPLY
Figure 41. Differential LC Filter for Single 5 V and 3.3 V Applications
5V
FERRITE
BEADS
ELECTROLYTIC
100µF
TANTALUM
10µF
TO
22µF
CERAMIC
0.1µF
AVDD
ACOM