It is recommended to decouple the V
參數(shù)資料
型號: EVAL-AD5700-1EBZ
廠商: Analog Devices Inc
文件頁數(shù): 9/24頁
文件大?。?/td> 0K
描述: BOARD EVAL HART MODEM AD5700
標(biāo)準(zhǔn)包裝: 1
主要目的: 電信,調(diào)制解調(diào)器
嵌入式:
已用 IC / 零件: AD5700
主要屬性: HART? FSK 半雙工調(diào)制解調(diào)器
已供物品:
Data Sheet
AD5700/AD5700-1
Rev. F | Page 17 of 24
APPLICATIONS INFORMATION
SUPPLY DECOUPLING
It is recommended to decouple the VCC and IOVCC supplies with
10 μF in parallel with 0.1 μF capacitors to ground. For many
applications, 1 μF in parallel with 0.1 μF ceramic capacitors to
ground should be sufficient. The REG_CAP voltage of 1.8 V is
used to supply the AD5700/AD5700-1 internal circuitry and is
derived from the VCC supply using a high efficiency clocking
LDO. Decouple this REG_CAP supply with a 1 μF ceramic
capacitor to ground. It is also required to decouple the REF pin
with a 1 μF ceramic capacitor to ground. Place decoupling
capacitors as close to the relevant pins as possible.
For loop-powered applications, it is recommended to connect a
resistance in series with the VCC supply to minimize the effect of
any noise, which may, depending on the system configuration, be
introduced onto the loop as a result of current draw variations
from the AD5700/AD5700-1. For typical applications, 470 Ω of
resistance has proven most effective. However, depending on the
application conditions, alternative values may also be acceptable
TRANSIENT VOLTAGE PROTECTION
Many industrial control applications have requirements for
HART-enabled current input and output modules. Figure 28
shows an example of a HART-enabled current input module
that contains transient voltage protection circuitry, which is
very important in harsh industrial control environments.
The module is powered from a 24 V field supply, and the 250 Ω
load is within the low impedance module itself. This configuration
is in contrast to Figure 29, which demonstrates a secondary HART
device, in which the load is outside of the module. For transient
voltage protection, a 10 V unidirectional (for protection against
positive high voltage transients) transient voltage suppressor (TVS)
is placed at the connection point of the current input module.
The TVS component that is used in a given application circuit
must have power ratings that are appropriate to the individual
system. When choosing the TVS, low leakage current is also an
important specification for maintaining the accuracy of the analog
current input. In the event of a transient spike, the 22 Ω series
resistor acts as a current limiting resistor for the FSK output pin.
The FSK input pin is inherently protected by the 150 kΩ resistor,
which forms part of the recommended external filter circuitry
at the FSK input. The voltage divider, made up of both a 75 kΩ
resistor and a 22 kΩ resistor, is used to maintain a 0.75 V dc bias
at the field side of the FSK output switch.
Figure 28. Current Input Module, HART Circuit
Figure 29. Secondary HART Device
10
43
5-
0
31
HART_OUT
ADC_IP
AGND
TXD
RXD
RTS
CD
VCC
AD5700/
AD5700-1
ADC
REF
10nF
3.3V
75k
22k
2.2F
22
6.8nF
3.3V
1.2M
300pF
150k
150pF
10F
10V
400W
MICRO-
CONTROLLER
VLOOP
24V
FI
E
LD
INS
T
RUM
E
NT
20k
250
1F
1
0435-
03
0
HART_OUT
ADC_IP
AGND
TXD
RXD
RTS
CD
AD5700/
AD5700-1
REF
10nF
3.3V
75k
22k
2.2F
50V
4.7
0.5W
6.8nF
50V
3.3V
1.2M
300pF
150k
150pF
39V
1500W
20
10V
400W
HOST
1F
VCC
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