概要

機能と利点

  • Fully isolated signal and power traces
  • RS-485 half duplex tranciever circuit
  • Low power with reduced board space

回路機能とその特長

This circuit provides a half-duplex, isolated RS-485 interface using the ADM2485 high speed, isolated RS-485 transceiver and the ADP3330 high accuracy linear regulator. This circuit achieves signal and power isolation and at the same time decreases board space and power consumption.



Figure 1: Half-Duplex Isolated RS-485 Interface Using ADM2485 and ADP3330 (Simplified Schematic)

回路説明

The ADM2485 is a half-duplex RS-485 transceiver that can easily achieve a fully isolated RS-485 PROFIBUS compliant node. 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.

The oscillator outputs D1 and D2 of the ADM2485 drive the center tapped transformer T1. A pair of Schottky diodes and a smoothing capacitor are 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 1.

バリエーション回路

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, thereby ensuring enough headroom for the ADP3330 LDO to output a regulated 5 V output.

If the ADM2485 is powered by 5 V on the logic side, a 1CT:1.5CT transformer T1 is required to ensure enough headroom for the ADP3330 LDO to output a regulated 5 V output.

The external transformer used with the ADM2485 must have a center-tapped winding. The turns ratio of the transformer must be set to provide the minimum required output voltage at the maximum anticipated load current with the minimum input voltage. Table 1 shows suitable transformers for the ADM2485 circuit of Figure 1.

Table 1: Transformer Suppliers


Manufacturer
Primary Voltage 3.3V
Primary Voltage 5V
Coilcraft
DA2304-AL
DA2303-AL
C&D Technologies
782482/35C
782485/55C


製品サンプル

製品

概要

サンプル提供可能な
製品型番

ADP3330 レギュレータ、低ドロップアウト、高精度、超低静止電流、200mA、SOT-23、anyCAP®

問い合わせる

ADM2485

RS-485トランシーバ、高速(16Mbps)、2.5kV信号絶縁、半二重、トランス・ドライバ内蔵

ADM2485BRWZ

PCサイトでは製品の購入が可能です。