AD9717BCPZ Analog Devices Inc, AD9717BCPZ Datasheet - Page 43

• Manufacturer Part Number: AD9717BCPZ
• Description: IC DAC DUAL 14BIT LO PWR 40LFCSP
• Manufacturer: Analog Devices Inc
• Series: TxDAC®r

Specifications of AD9717BCPZ

• Data Interface: Serial
• Number Of Bits: 14
• Number Of Converters: 2
• Voltage Supply Source: Analog and Digital
• Power Dissipation (max): 86mW
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 40-LFCSP
• Resolution (bits): 14bit
• Sampling Rate: 125MSPS
• Input Channel Type: Parallel, Serial
• Supply Current: 11mA
• Digital Ic Case Style: CSP
• No. Of Pins: 40
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Settling Time: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

REFERENCE OPERATION
The AD9714/AD9715/AD9716/AD9717 contain an internal
1.0 V band gap reference. The internal reference can be disabled
by setting Bit 0 (EXTREF) of the power-down register (Address
0x01) through the SPI interface. To use the internal reference,
decouple the REFIO pin to AVSS with a 0.1 μF capacitor, enable
the internal reference, and clear Bit 0 of the power-down register
(Address 0x01) through the SPI interface. Note that this is the
default configuration. The internal reference voltage is present
at REFIO. If the voltage at REFIO is to be used anywhere else in
the circuit, an external buffer amplifier with an input bias current
of less than 100 nA must be used to avoid loading the reference.
An example of the use of the internal reference is shown in
Figure 96.
REFIO serves as either an input or an output, depending on
whether the internal or an external reference is used. Table 17
summarizes the reference operation.
Table 17. Reference Operation
Reference Mode
Internal
External
An external reference can be used in applications requiring
tighter gain tolerances or lower temperature drift. Also, a
variable external voltage reference can be used to implement a
method for gain control of the DAC output.
Recommendations When Using an External Reference
Apply the external reference to the REFIO pin. The internal
reference can be directly overdriven by the external reference,
or the internal reference can be powered down to save power
consumption
The external 0.1 μF compensation capacitor on REFIO is not
required unless specified by the external voltage reference
manufacturer. The input impedance of REFIO is 10 kΩ when
the internal reference is powered up and 1 MΩ when it is
powered down.
0.1µF
AVSS
xR
FSADJx
SET
REFIO
Figure 96. Internal Reference Configuration
I
xREF
1.0V
V
BG
REFIO Pin
Connect 0.1 μF
capacitor
Apply external
capacitor
–
+
AD9714/AD9715/
AD9716/AD9717
CURRENT
SCALING
×32
Register Setting
Register 0x01, Bit 0 = 0
(default)
Register 0x01, Bit 0 = 1
(for power saving)
I
xOUTFS
Q DAC
I DAC
OR
Rev. A | Page 43 of 80
REFERENCE CONTROL AMPLIFIER
The AD9714/AD9715/AD9716/AD9717 contain a control
amplifier that regulates the full-scale output current, I
The control amplifier is configured as a V-I converter, as shown
in Figure 96. The output current, I
ratio of the V
Equation 4 (see the DAC Transfer Function section). I
mirrored to the segmented current sources with the proper scale
factor to set I
The control amplifier allows a 2.5:1 adjustment span of I
from 1 mA to 4 mA by setting I
(set xR
of I
the power dissipation of the AD9714/AD9715/AD9716/AD9717,
which is proportional to I
section). The second benefit relates to the ability to adjust the
output over a 8 dB range with 0.25 dB steps, which is useful for
controlling the transmitted power. The small signal bandwidth
of the reference control amplifier is approximately 500 kHz.
This allows the device to be used for low frequency, small signal
multiplying applications.
When an external resistor greater than 16 kΩ is used on the
FSADJx pins, care must be taken to maintain the high frequency
equivalent circuit to an impedance lower than 16 kΩ by
splitting the resistor into two resistors in series with a 10 nF
capacitor in parallel with the resistor to AVSS (see Figure 97).
xOUTFS
SET
provides several benefits. The first relates directly to
0.1µF
between 8 kΩ and 32 kΩ). The wide adjustment span
AD9714/AD9715/AD9716/AD9717
Figure 97. xR
xOUTFS
AVSS
REFIO
, as stated in Equation 3.
and an external resistor, xR
R < 16kΩ
10nF
SET
Configuration for Values > 16 kΩ
xOUTFS
FSADJx
xR
REFIO
xREF
SET
(see the DAC Transfer Function
between 125 μA and 31.25 μA
xREF
AD9714/AD9715/
AD9716/AD9717
, is determined by the
SET
, as stated in
xOUTFS
xREF
xOUTFS
, is
.