The MAX3480ACPI+ requires careful layout and routing to ensure proper operation. Maxim recommends following a star topology for the RS-485 bus, keeping the transmitter and receiver lines as short as possible, and using a ground plane to reduce noise. Additionally, the device's VCC and GND pins should be decoupled with 0.1uF capacitors.
To ensure reliable operation in noisy environments, Maxim recommends using a common-mode choke or ferrite bead on the RS-485 bus, and adding a 100nF capacitor between the transmitter output and the receiver input to filter out high-frequency noise. Additionally, the device's receiver threshold can be adjusted using the RXPTH pin to optimize performance in noisy environments.
The maximum cable length supported by the MAX3480ACPI+ depends on the data rate and the type of cable used. As a general rule, Maxim recommends limiting the cable length to 4000ft (1219m) at 250kbps, 1000ft (305m) at 1Mbps, and 500ft (152m) at 10Mbps. However, the actual cable length may be shorter depending on the specific application and environment.
To implement a fail-safe biasing scheme for the RS-485 bus, Maxim recommends using a 1kΩ resistor to VCC and a 1kΩ resistor to GND on the transmitter output, and a 1kΩ resistor to VCC and a 1kΩ resistor to GND on the receiver input. This ensures that the bus is biased to a valid logic level even when the transmitter is not driving the bus.
The power-up sequence for the MAX3480ACPI+ is critical to ensure proper operation. Maxim recommends powering up the device's VCC pin first, followed by the EN pin, and then the SLEEP pin. The device should be powered up in this sequence to prevent latch-up and ensure reliable operation.
MAX3480ACPI+ datasheet
by Maxim Integrated Products
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