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参数资料
| 型号： | AD9754-EBZ |
| 厂商： | Analog Devices Inc |
| 文件页数： | 2/24页 |
| 文件大小： | 0K |
| 描述： | BOARD EVAL FOR AD9754 |
| 标准包装： | 1 |
| 系列： | TxDAC® |
| DAC 的数量： | 1 |
| 位数： | 14 |
| 采样率（每秒）： | 125M |
| 数据接口： | 并联 |
| 设置时间： | 35ns |
| DAC 型： | 电流 |
| 工作温度： | -40°C ~ 85°C |
| 已供物品： | 板 |
| 已用 IC / 零件： | AD9754 |
AD9754
–10–
REV. A
These last two equations highlight some of the advantages of
operating the AD9754 differentially. First, the differential op-
eration will help cancel common-mode error sources associated
with IOUTA and IOUTB such as noise, distortion and dc off-
sets. Second, the differential code-dependent current and
subsequent voltage, VDIFF, is twice the value of the single-
ended voltage output (i.e., VOUTA or VOUTB), thus providing
twice the signal power to the load.
Note that the gain drift temperature performance for a single-
ended (VOUTA and VOUTB) or differential output (VDIFF) of
the AD9754 can be enhanced by selecting temperature tracking
resistors for RLOAD and RSET due to their ratiometric relation-
ship as shown in Equation 8.
REFERENCE OPERATION
The AD9754 contains an internal 1.20 V bandgap reference
that can be easily disabled and overridden by an external
reference. REFIO serves as either an input or output, depending
on whether the internal or external reference is selected. If
REFLO is tied to ACOM, as shown in Figure 17, the internal
reference is activated, and REFIO provides a 1.20 V output. In
this case, the internal reference must be compensated externally
with a ceramic chip capacitor of 0.1
F or greater from REFIO
to REFLO. Also, REFIO should be buffered with an external
amplifier having an input bias current less than 100 nA if any
additional loading is required.
150pF
+1.2V REF
AVDD
REFLO
CURRENT
SOURCE
ARRAY
+5V
REFIO
FS ADJ
2k
0.1 F
AD9754
ADDITIONAL
LOAD
OPTIONAL
EXTERNAL
REF BUFFER
Figure 17. Internal Reference Configuration
The internal reference can be disabled by connecting REFLO to
AVDD. In this case, an external reference may then be applied
to REFIO as shown in Figure 18. The external reference may
provide either a fixed reference voltage to enhance accuracy and
drift performance or a varying reference voltage for gain control.
Note that the 0.1
F compensation capacitor is not required
since the internal reference is disabled, and the high input im-
pedance (i.e., 1 M
) of REFIO minimizes any loading of the
external reference.
REFERENCE CONTROL AMPLIFIER
The AD9754 also contains an internal control amplifier that is
used to regulate the DAC’s full-scale output current, IOUTFS.
The control amplifier is configured as a V-I converter, as shown
in Figure 18, such that its current output, IREF, is determined by
150pF
+1.2V REF
AVDD
REFLO
CURRENT
SOURCE
ARRAY
AVDD
REFIO
FS ADJ
RSET
AD9754
EXTERNAL
REF
IREF =
VREFIO/RSET
AVDD
REFERENCE
CONTROL
AMPLIFIER
VREFIO
Figure 18. External Reference Configuration
the ratio of the VREFIO and an external resistor, RSET, as stated
in Equation 4. IREF is copied over to the segmented current
sources with the proper scaling factor to set IOUTFS as stated in
Equation 3.
The control amplifier allows a wide (10:1) adjustment span of
IOUTFS over a 2 mA to 20 mA range by setting IREF between
62.5
A and 625 A. The wide adjustment span of I
OUTFS
provides several application benefits. The first benefit relates
directly to the power dissipation of the AD9754, which is pro-
portional to IOUTFS (refer to the Power Dissipation section). The
second benefit relates to the 20 dB adjustment, which is useful
for system gain control purposes.
The small signal bandwidth of the reference control amplifier
is approximately 0.5 MHz. The output of the control amplifier
is internally compensated via a 150 pF capacitor that limits the
control amplifier small-signal bandwidth and reduces its output
impedance. Since the –3 dB bandwidth corresponds to the
dominant pole, and hence the time constant, the settling time of
the control amplifier to a stepped reference input response can
be approximated In this case, the time constant can be approxi-
mated to be 320 ns.
There are two methods in which IREF can be varied for a fixed
RSET. The first method is suitable for a single-supply system in
which the internal reference is disabled, and the common-mode
voltage of REFIO is varied over its compliance range of 1.25 V
to 0.10 V. REFIO can be driven by a single-supply amplifier or
DAC, thus allowing IREF to be varied for a fixed RSET. Since the
1.2V
150pF
+1.2V REF
AVDD
REFLO
CURRENT
SOURCE
ARRAY
AVDD
REFIO
FS ADJ
RSET
AD9754
IREF =
VREF /RSET
AVDD
VREF
VDD
RFB
OUT1
OUT2
AGND
DB7–DB0
AD7524
AD1580
0.1V TO 1.2V
Figure 19. Single-Supply Gain Control Circuit
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| AD9755-AST | 制造商:Analog Devices 功能描述: |
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