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參數(shù)資料
| 型號： | AD5342 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | 2.5 V to 5.5 V, 115 uA, Parallel Interface Single Voltage-Output 8-/10-/12-Bit DACs |
| 中文描述： | 2.5 V至5.5 V，115微安，并行接口單電壓輸出DAC的8-/10-/12-Bit |
| 文件頁數(shù)： | 14/20頁 |
| 文件大?。?/td> | 359K |
| 代理商： | AD5342 |
REV. 0
AD5330/AD5331/AD5340/AD5341
–14–
Resistor String
The resistor string section is shown in Figure 28. It is simply a
string of resistors, each of value R. The digital code loaded to
the DAC register determines at what node on the string the
voltage is tapped off to be fed into the output amplifier. The
voltage is tapped off by closing one of the switches connecting
the string to the amplifier. Because it is a string of resistors, it
is guaranteed monotonic.
TO OUTPUT
AMPLIFIER
R
R
R
R
R
V
REF
Figure 28. Resistor String
DAC Reference Input
There is a reference input pin for the DAC. The reference input
is buffered on the AD5330/AD5340/AD5341 but can be config-
ured as unbuffered also. The reference input of the AD5331 is
unbuffered. The buffered/unbuffered option is controlled by the
BUF pin.
In buffered mode (BUF = 1), the current drawn from an external
reference voltage is virtually zero as the impedance is at least
10 M
. The reference input range is 1 V to 5 V with a 5 V supply.
In unbuffered mode (BUF = 0), the user can have a reference
voltage as low as 0.25 V and as high as V
DD
since there is no
restriction due to headroom and footroom of the reference ampli-
fier. The impedance is still large at typically 180 k
for 0–V
REF
mode and 90 k
for 0–2 V
REF
mode. If there is an external
buffered reference (e.g., REF192) there is no need to use the
on-chip buffer.
Output Amplifier
The output buffer amplifier is capable of generating output
voltages to within 1 mV of either rail. Its actual range depends
on V
REF
, GAIN, the load on V
OUT
, and offset error.
If a gain of 1 is selected (GAIN = 0), the output range is 0.001 V
to V
REF
.
If a gain of 2 is selected (GAIN = 1), the output range is 0.001 V
to 2 V
REF
. However, because of clamping, the maximum output
is limited to V
DD
– 0.001 V.
The output amplifier is capable of driving a load of 2 k
to
GND or V
DD
, in parallel with 500 pF to GND or V
DD
. The
source and sink capabilities of the output amplifier can be seen
in Figure 15.
The slew rate is 0.7 V/
μ
s with a half-scale settling time to
±
0.5 LSB (at eight bits) of 6
μ
s with the output unloaded. See
Figure 20.
PARALLEL INTERFACE
The AD5330, AD5331, and AD5340 load their data as a single
8-, 10-, or 12-bit word, while the AD5341 loads data as a low
byte of eight bits and a high byte containing four bits.
Double-Buffered Interface
The AD5330/AD5331/AD5340/AD5341 DACs all have double-
buffered interfaces consisting of an input register and a DAC
register. DAC data, BUF, and GAIN inputs are written to the input
register under control of the Chip Select (
CS
) and Write (
WR
).
Access to the DAC register is controlled by the
LDAC
function.
When
LDAC
is high, the DAC register is latched and the input
register may change state without affecting the contents of the
DAC register. However, when
LDAC
is brought low, the DAC
register becomes transparent and the contents of the input register
are transferred to it. The gain and buffer control signals are also
double-buffered and are only updated when
LDAC
is taken low.
Double-buffering is also useful where the DAC data is loaded in
two bytes, as in the AD5341, because it allows the whole data
word to be assembled in parallel before updating the DAC register.
This prevents spurious outputs that could occur if the DAC
register were updated with only the high byte or the low byte.
These parts contain an extra feature whereby the DAC regis-
ter is not updated unless its input register has been updated
since the last time that
LDAC
was brought low. Normally,
when
LDAC
is brought low, the DAC register is filled with the
contents of the input register. In the case of the AD5330/AD5331/
AD5340/AD5341, the part will only update the DAC register if
the input register has been changed since the last time the DAC
register was updated. This removes unnecessary crosstalk.
Clear Input (
CLR
)
CLR
is an active low, asynchronous clear that resets the input and
DAC registers.
Chip Select Input (
CS
)
CS
is an active low input that selects the device.
Write Input (
WR
)
WR
is an active low input that controls writing of data to the
device. Data is latched into the input register on the rising edge
of
WR
.
Load DAC Input (
LDAC
)
LDAC
transfers data from the input register to the DAC register
(and hence updates the outputs). Use of the
LDAC
function enables
double-buffering of the DAC data, GAIN, and BUF. There
are two
LDAC
modes:
Synchronous Mode
: In this mode the DAC register is updated
after new data is read in on the rising edge of the
WR
input.
LDAC
can be tied permanently low or pulsed as in Figure 1.
Asynchronous Mode
: In this mode the outputs are not updated
at the same time that the input register is written to. When
LDAC
goes low, the DAC register is updated with the contents of the
input register.
High-Byte Enable Input (HBEN)
High-Byte Enable is a control input on the AD5341 only that
determines if data is written to the high-byte input register or
the low-byte input register.
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