參數資料
| 型號： | X79002V20IT1 |
| 廠商： | Intersil |
| 文件頁數： | 8/18頁 |
| 文件大?。?/td> | 0K |
| 描述： | IC DAC NV SELECT OUT/MEM 20TSSOP |
| 標準包裝： | 2,500 |
| 設置時間： | 6µs |
| 位數： | 12 |
| 數據接口： | 串行 |
| 轉換器數目： | 1 |
| 電壓電源： | 單電源 |
| 工作溫度： | -40°C ~ 85°C |
| 安裝類型： | 表面貼裝 |
| 封裝/外殼： | 20-TSSOP（0.173"，4.40mm 寬） |
| 供應商設備封裝： | 20-TSSOP |
| 包裝： | 帶卷 (TR) |
| 輸出數目和類型： | 1 電壓，單極 |
| 采樣率（每秒）： | 417k |
16
FN8147.0
March 17, 2005
APPLICATIONS INFORMATION
Remote sensing
The output opamp included in the X79000 and X79001 is
normally configured with a gain of +1, and since the
inverting terminal is available externally, can be used for
remote load sensing (see Figure 3). This configuration is
useful for high accuracy applications which may draw
significant current from the DAC output with a finite
impedance from the DAC to the load.
The inverting
terminal must be brought as close as possible to the
load, and there must be very low differential in the
ground potentials of the two circuits.
Output Voltages Greater than 3.025V
The opamp output (Vbuf) can drive up to ±1mA and stay
within 150mV of ground and the VCC supply. Normally, if
the opamp is configured with a gain of +1, Vbuf is limited
to 3.10V max, which is the limit of the DAC Vout. If gain
is added to the opamp feedback loop, then Vbuf can
provide a higher output voltage, up to 4.85V with
VCC = 5.00V. Figure 4 shows a circuit with a gain of +2
that is configured for 4.84V max Vbuf, with VH internally
set to 2.42V (VH2, VH1, VH0 set to 1,0,0). Care must be
taken when increasing the maximum Vbuf output,
however, in this example VCC may have a range of ±5%,
or 4.75V to 5.25V. The maximum Vbuf can be expected
to reach and stay within specifications is 4.75V -
150mV = 4.600V.
If the output offset of the DAC is
included (22mV x 2, worst case), then the max output will
be 4.84V + 0.044V = 4.884V.
The designer has the
option of either realizing that the DAC may miss the
higher codes, or change the amplifier gain to a value less
than 2 (or 4.60/2.42 = 1.90, for this example) to keep all
codes and reduce the maximum Vbuf output.
Using the VH and VL pins for multiplying functions
When a time-varying waveform is applied at either
reference input pin, the output reflects a scaled version of
that waveform (see Figure 5). This waveform will follow
the DAC output voltage equation when applied to VH:
Vbuf = [(VH - VL)(n/4095)] + VL, n = 0 to 4095
(excluding DAC, Reference scaling and opamp errors)
This shows that the input range for the waveform is
limited to VL on the low side, and by the Vout range
(3.10V) on the high side. The output is scaled by the
DAC setting to allow for gain control. The maximum
output voltage can be increased as shown in Figure 4
using the opamp and Vbuf output. It is advisable that the
VH pin be driven by a low impedance source for optimal
AC performance. The minimum bandwidth of the circuit
is 50kHz over all specified voltage range, temperature
and output loading configurations.
Note that it is possible to use the VL pin in the same
fashion, with VH fixed, but the resulting waveform will
have a slightly different transfer function:
Vbuf = VH - (VH - VL)[(4095-n)/4095], n = 0 to 4095
Alternatively, the VL input could include a variable
reference, such as a temperature sensor, or a shunt
reference connected between VH and VL, which would
fix their differential (the configuration register must be
set for external VH and VL references). This provides a
DAC output which varies proportional to temperature,
yet can be set to an arbitrary voltage by the DAC for
biasing applications.
X79000, X79001, X79002
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