参数资料
| 型号： | AD5421CREZ |
| 厂商： | Analog Devices Inc |
| 文件页数： | 15/36页 |
| 文件大小： | 0K |
| 描述： | IC DAC 16BIT SPI/SRL 28TSSOP |
| 标准包装： | 50 |
| 设置时间： | 50µs |
| 位数： | 16 |
| 数据接口： | 串行，SPI? |
| 转换器数目： | 1 |
| 电压电源： | 单电源 |
| 功率耗散（最大）： | 625mW |
| 工作温度： | -40°C ~ 105°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-SOIC（0.173"，4.40mm 宽）裸露焊盘 |
| 供应商设备封装： | 28-TSSOP 裸露焊盘 |
| 包装： | 管件 |
| 输出数目和类型： | 1 电压，单极 |
| 采样率（每秒）： | * |
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AD5421
Data Sheet
Rev. G | Page 22 of 36
Loop Voltage Fault
There are two loop voltage alert bits in the fault register:
VLOOP 12V and VLOOP 6V. If the voltage between the VLOOP and
COM pins falls below 0.6 V (corresponding to a 12 V loop
supply value), the VLOOP 12V bit is set; this bit is cleared when
the voltage returns above 0.7 V. Similarly, if the voltage between
the VLOOP and COM pins falls below 0.3 V (corresponding to a
6 V loop supply value), the VLOOP 6V bit is set; this bit is cleared
when the voltage returns above 0.4 V. If the VLOOP 6V bit is set in
the fault register, the FAULT pin is set to logic high.
Figure 42 illustrates how a resistor divider enables the monitor-
ing of the loop supply with the VLOOP input. The recommended
resistor divider consists of a 1 M and a 19 M resistor that
provide a 20:1 ratio, allowing the 2.5 V input range of the VLOOP
pin to monitor loop supplies up to 50 V. With a 20:1 divider ratio,
the preset VLOOP 6V and VLOOP 12V alert bits of the fault register
generate loop supply faults according to their stated values. If
another divider ratio is used, the fault bits generate faults at values
that are not equal to 6 V and 12 V.
19M
1M
RL
LOOP–
VLOOP
COM
REGIN
VLOOP
AD5421
09128-
048
Figure 42. Resistor Divider Connection at VLOOP Pin
EXTERNAL CURRENT SETTING RESISTOR
output voltage to a current, which is then mirrored with a gain
of 221 to the LOOP pin. The stability of the loop current over
temperature is dependent on the temperature coefficient of RSET.
Table 1 and Table 2 outline the performance specifications of
24 k RSET resistor. Using the internal RSET resistor, a total unad-
justed error of better than 0.126% FSR can be expected. Using
an external resistor gives improved performance of 0.048% FSR.
This specification assumes an ideal resistor; the actual performance
depends on the absolute value and temperature coefficient of
the resistor used. For more information, see the Determining
the Expected Total Error section.
LOOP CURRENT RANGE SELECTION
To select the loop current range, connect the RANGE0
and RANGE1 pins to the COM and DVDD pins, as shown
Table 9. Selecting the Loop Current Range
RANGE1 Pin
RANGE0 Pin
Loop Current Range
COM
4 mA to 20 mA
COM
DVDD
3.8 mA to 21 mA
DVDD
COM
3.2 mA to 24 mA
DVDD
3.8 mA to 21 mA
CONNECTION TO LOOP POWER SUPPLY
The AD5421 is powered from the 4 mA to 20 mA current loop.
Typically, the power supply is located far from the transmitter
device and has a value of 24 V. The AD5421 can be connected
directly to the loop power supply and can tolerate a voltage up
to a maximum of 52 V (see Figure 43).
RL
LOOP–
DRIVE
COM
REGIN
VLOOP
AD5421
09128-
050
Figure 43. Direct Connection of the AD5421 to Loop Power Supply
loop power supply. An alternative power connection is shown
in Figure 44, which shows a depletion mode N-channel MOSFET
connected between the AD5421 and the loop power supply. The
use of this device keeps the voltage drop across the AD5421 at
approximately 12 V, limiting the worst-case on-chip power dissi-
pation to 288 mW (12 V × 24 mA = 288 mW). If the AD5421 is
connected directly to the loop supply as shown in Figure 43, the
potential worst-case on-chip power dissipation for a 24 V loop
power supply is 576 mW (24 V × 24 mA = 576 mW). The power
dissipation changes in proportion to the loop power supply voltage.
RL
200k
LOOP–
DRIVE
COM
REGIN
VLOOP
AD5421
T1
DN2540
BSP129
09128-
051
Figure 44. MOSFET Connecting the AD5421 to Loop Power Supply
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