The MAX3535E evaluation kit (EV kit) is a fully assembled
and tested PCB that contains a 2500VRMS isolated
RS-485/RS-422 transceiver with ESD protection. The EV
kit circuit features a differential driver and one receiver.
The circuit’s receiver is a 1/8 unit load for the RS-485
bus and communicates up to 1000kbps. The MAX3535E
fail-safe circuitry and driver slew-rate features are demonstrated
and easily reconfigured.
Additionally, the EV kit features an H-bridge DC-DC
converter to power the isolated section of the MAX3535E
RS-485/RS-422 circuit. Input power to the circuit is
supplied by a +3V to +5.5VDC source. This circuit uses a
full-wave rectifier on the unregulated output and provides
unregulated voltage to the MAX3535E internal, linear
low-dropout (LDO) regulator. Using an H-bridge design
minimizes input ripple current and radiated noise.
Undervoltage lockout (UVLO) and thermal shutdown
provide for a robust, isolated RS-485/RS-422 transceiver
circuit and power supply. The surface-mount transformer
provides up to 2500VRMS galvanic isolation and the output
is powered from a center-tapped, full-wave rectifier
circuit to reduce output voltage ripple.
The isolated H-bridge DC-DC converter operation at
420kHz allows the use of ceramic-only output capacitors
and a small transformer.