參數(shù)資料
型號: ADM2485BRWZ-REEL7
廠商: Analog Devices Inc
文件頁數(shù): 8/20頁
文件大小: 0K
描述: IC TXRX ISOLATED RS-485 16SOIC
產品培訓模塊: iCoupler Digital Isolater Technology
設計資源: Half-Duplex, Isolated RS-485 Interface (CN0031)
標準包裝: 1
系列: *
其它名稱: ADM2485BRWZ-REEL7DKR
ADM2485
Rev. A | Page 16 of 20
APPLICATIONS INFORMATION
PCB LAYOUT
The ADM2485 isolated RS-485 transceiver requires no external
interface circuitry for the logic interfaces. Power supply bypassing
is required at the input and output supply pins (see Figure 33).
Bypass capacitors are most conveniently connected between
Pin 3 and Pin 4 for VDD1 and between Pin 15 and Pin 16 for
VDD2. The capacitor value must be between 0.01 μF and 0.1 μF.
The total lead length between both ends of the capacitor and
the input power supply pin must not exceed 20 mm.
Bypassing between Pin 9 and Pin 16 is also recommended
unless the ground wires on the VDD2 side are connected close to
the package.
D1
D2
GND1
VDD1
RxD
RE
RTS
TxD
VDD2
GND2
B
A
GND2
DE OUT
GND2
ADM2485
0
602
1-
029
Figure 33. Recommended Printed Circuit Board Layout
In applications involving high common-mode transients, care
must be taken to ensure that board coupling across the isolation
barrier is minimized. Furthermore, the board layout must be
designed such that any coupling that does occur equally affects
all pins on a given component side.
Failure to ensure this can cause voltage differentials between
pins exceeding the device absolute maximum ratings, thereby
leading to latch-up or permanent damage.
TRANSFORMER SUPPLIERS
The transformer primarily used with the ADM2485 must be a
center-tapped transformer winding. The turns ratio of the
transformer must be set to provide the minimum required
output voltage at the maximum anticipated load with the
minimum input voltage. Table 12 shows ADM2485 transformer
suppliers.
Table 12. Transformer Suppliers
Manufacturer
Primary Voltage 3.3 V
Primary Voltage 5 V
Coilcraft
DA2304-AL
DA2303-AL
C&D Technologies
782485/35C
782485/55C
APPLICATIONS DIAGRAM
The ADM2485 integrates a transformer driver that, when used
with an external transformer and LDO, generates an isolated
5 V power supply, to be supplied between VDD2 and GND2.
D1 and D2 of the ADM2485 drive the center-tapped
Transformer T1. A pair of Schottky diodes and a smoothing
capacitor is used to create a rectified signal from the secondary
winding. The ADP3330 linear voltage regulator provides a
regulated 5 V power supply to the ADM2485 bus-side circuitry
(VDD2), as shown in Figure 34.
When the ADM2485 is powered by 3.3 V on the logic side, a
1CT:2.2CT Transformer T1 is required to step up the 3.3 V to
6 V, ensuring enough headroom for the ADP3330 LDO to
output a regulated 5 V output.
If ADM2485 is powered by 5 V on the logic side, a 1CT:1.5CT
Transformer T1 is required, ensuring enough headroom for the
ADP3330 LDO to output a regulated 5 V output.
06
02
1
-03
0
VCC
ISO 5V
ADP3330
IN
10F
100nF
OUT
5V
SD
1N5817
VDD1 D1 D2
VDD2
GND2
ADM2485
GND
ERR
NR
22F
10F
MLC
T1
ISOLATION BARRIER
100nF
GND1
Figure 34. Applications Diagram
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