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4–20mA Loop-Powered Transmitters
Low power, single-supply operation, and easy interfac-
ing with optocouplers make the MAX1400 ideal for
loop-powered 4–20mA transmitters. Loop-powered
transmitters draw their power from the 4–20mA loop,
limiting the transmitter circuitry to a current budget of
4mA. Tolerances in the loop further limit this current
budget to 3.5mA. Since the MAX1400 consumes only
250A, a total of 3.25mA remains to power the remain-
ing transmitter circuitry. Figure 18 shows a block dia-
gram for a loop-powered 4–20mA transmitter.
Power Supplies
No specific power sequence is required for the
MAX1400; either the V+ or the VDD supply can come
up first. While the latchup performance of the MAX1400
is good, it is important that power be applied to the
MAX1400 before the analog input signals (AIN_) or the
CLKIN inputs, to avoid latchup. If this is not possible,
then the current flow into any of these pins should be
limited to 50mA. If separate supplies are used for the
MAX1400 and the system digital circuitry, then the
MAX1400 should be powered up first.
MAX1400
+5V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC
32
______________________________________________________________________________________
DAC
RGAIN
ROFST
RX
VIN+
VIN-
RSENSE
4–20mA LOOP
INTERFACE
RFDBK
RY
CC
ISOLATION
BARRIER
V+
GND
V+
4
SPI
4
SPI
3
SPI
GND
SENSOR
VOLTAGE
REGULATOR
P/C
MAX1400
Figure 18. 4–20mA Transmitter
C
+5V
+2.5V
REFIN+
REFIN-
AGND
DGND
R
THERMOCOUPLE
JUNCTION
SWITCHING
NETWORK
PGA
MAX1400
BUFFER
AIN1
AIN2
Figure 17. Thermocouple Application with MAX1400
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相关代理商/技术参数
MAX1400CAI+T 功能描述:模数转换器 - ADC 18-Bit 5Ch 4.8ksps 2.5V Precision ADC RoHS:否 制造商:Texas Instruments 通道数量:2 结构:Sigma-Delta 转换速率:125 SPs to 8 KSPs 分辨率:24 bit 输入类型:Differential 信噪比:107 dB 接口类型:SPI 工作电源电压:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-32
MAX1400CAI+W 制造商:Maxim Integrated Products 功能描述:
MAX1400CAI-T 功能描述:模数转换器 - ADC RoHS:否 制造商:Texas Instruments 通道数量:2 结构:Sigma-Delta 转换速率:125 SPs to 8 KSPs 分辨率:24 bit 输入类型:Differential 信噪比:107 dB 接口类型:SPI 工作电源电压:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-32
MAX1400EAI 功能描述:模数转换器 - ADC RoHS:否 制造商:Texas Instruments 通道数量:2 结构:Sigma-Delta 转换速率:125 SPs to 8 KSPs 分辨率:24 bit 输入类型:Differential 信噪比:107 dB 接口类型:SPI 工作电源电压:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-32
MAX1400EAI+ 功能描述:模数转换器 - ADC 18-Bit 5Ch 4.8ksps 2.5V Precision ADC RoHS:否 制造商:Texas Instruments 通道数量:2 结构:Sigma-Delta 转换速率:125 SPs to 8 KSPs 分辨率:24 bit 输入类型:Differential 信噪比:107 dB 接口类型:SPI 工作电源电压:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-32
MAX1400EAI+T 功能描述:模数转换器 - ADC 18-Bit 5Ch 4.8ksps 2.5V Precision ADC RoHS:否 制造商:Texas Instruments 通道数量:2 结构:Sigma-Delta 转换速率:125 SPs to 8 KSPs 分辨率:24 bit 输入类型:Differential 信噪比:107 dB 接口类型:SPI 工作电源电压:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-32
MAX1400EAI-T 功能描述:模数转换器 - ADC RoHS:否 制造商:Texas Instruments 通道数量:2 结构:Sigma-Delta 转换速率:125 SPs to 8 KSPs 分辨率:24 bit 输入类型:Differential 信噪比:107 dB 接口类型:SPI 工作电源电压:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-32
MAX1400EVKIT 制造商:Maxim Integrated Products 功能描述:MAX1402 EVALUATION KIT/EVALUATION SYSTEM - Boxed Product (Development Kits)