**LTC1387IG#PBF: Complete Pinout, Functionality, and Application Circuit Guide**
The **LTC1387IG#PBF** from Analog Devices is a sophisticated, low-power **multiprotocol transceiver** designed for serial communication interfaces. It integrates the necessary drivers, receivers, and circuitry to support **RS232, RS485, and RS422 standards** from a single chip, making it an incredibly versatile solution for complex systems requiring multiple communication protocols. This guide provides a detailed breakdown of its pinout, core functionality, and a typical application circuit.
### **Complete Pinout Configuration**
Housed in a 28-lead SSOP package, the LTC1387's pinout is logically organized into power, data, and control sections. Key pins include:
* **VCC (Pin 28) & GND (Pin 14):** Primary +5V supply and ground connections.
* **V+ (Pin 27) & V- (Pin 13):** Generated positive and negative supply rails for the RS232 drivers. These typically require external charge-pump capacitors (C1, C2).
* **T1OUT/T2OUT (Pins 16, 15):** RS232 Driver Outputs.
* **R1IN/R2IN (Pins 17, 18):** RS232 Receiver Inputs.
* **DI (Pin 7) & RO (Pin 6):** RS485/RS422 Differential Driver Input and Receiver Output.
* **A (Pin 4) & B (Pin 5):** RS485/RS422 Differential Driver Output/Receiver Input.
* **Y (Pin 8) & Z (Pin 9):** RS422 Differential Driver Outputs (for full-duplex RS422).
* **SHDN (Pin 1):** **Shutdown Control Pin**. Pulling this pin low places the entire device in a low-power standby mode, reducing supply current to a minimal level.
* **PRO (Pin 2) & PRO2 (Pin 3):** **Protocol Select Pins**. The logic levels applied to these pins determine the active communication standard:
* **PRO=0, PRO2=0:** RS232 Mode
* **PRO=1, PRO2=0:** RS485 (Half-Duplex) Mode
* **PRO=0, PRO2=1:** RS422 (Full-Duplex) Mode
* **EN (Pin 26):** Driver Enable (active high for RS485/RS422 modes).
* **/EN (Pin 25):** Receiver Enable (active low for RS485/RS422 modes).
### **Core Functionality and Key Features**
The LTC1387's primary function is to serve as a **protocol-selectable interface** between a logic-level UART from a microcontroller or processor and a physical communication cable. Its standout features include:
* **Triple Protocol Operation:** Seamlessly switch between RS232, RS485, and RS422 without changing hardware, offering immense design flexibility.
* **Low Power Consumption:** Designed for power-sensitive applications, featuring a **shutdown mode** that reduces current to microamps.
* **Programmable Slew Rate:** The slew rate of the RS485/RS422 driver is programmable via an external resistor (RSEL, Pin 12), allowing for optimization to reduce EMI and reflections on the network.
* **Robust ESD Protection:** Offers high levels of ESD protection on all interface lines, safeguarding the IC and the system from electrostatic discharge events.
* **Complete Interface Solution:** Integrates all necessary drivers, receivers, and charge-pump circuitry, minimizing external component count.
### **Typical Application Circuit Guide**
A basic application circuit for **RS485 half-duplex mode** is a common use case. The configuration is straightforward:
1. **Power and Charge Pump:** Connect VCC to +5V. Decouple VCC and GND with a 0.1µF capacitor. Connect capacitors C1 (1µF) between Pin 27 (V+) and Pin 28 (VCC), and C2 (1µF) between Pin 13 (V-) and GND to generate the RS232 voltages.
2. **Mode Selection:** Set PRO (Pin 2) to logic high (`1`) and PRO2 (Pin 3) to logic low (`0`) to select RS485 mode.
3. **Slew Rate Control:** Connect a resistor (typically 47kΩ) from the RSEL (Pin 12) to GND to set a controlled slew rate.
4. **RS485 Network Connection:** Connect the differential lines to pins A (Pin 4) and B (Pin 5). These pins should be connected to the twisted-pair cable with a termination resistor (120Ω) at the end of the line.
5. **Driver/Receiver Control:** Connect the **EN (Pin 26)** and **/EN (Pin 25)** pins to a GPIO from a microcontroller to control the transmit and receive states. For half-duplex operation, these are toggled opposite each other: drive EN high and /EN low to transmit data from DI (Pin 7); drive EN low and /EN high to receive data on RO (Pin 6).
For RS232 operation, the PRO pins are set to `0,0`, and the T1OUT/R1IN pins are used with standard DB9 connector circuitry.
**ICGOODFIND:** The **LTC1387IG#PBF** is an **unmatched, all-in-one solution** for engineers designing systems that must communicate over multiple industrial serial standards. Its **programmable protocol selection**, integrated power supplies, and low-power shutdown mode make it a superior choice for portable instruments, multi-protocol network equipment, and complex embedded systems where flexibility, robustness, and power efficiency are paramount.
**Keywords:** **Multiprotocol Transceiver**, **RS485/RS422/RS232**, **Shutdown Mode**, **Programmable Slew Rate**, **Protocol Select**.
