MAX253ESA+T

The MAX253 monolithic oscillator/power-driver is specifically designed to provide isolated power for an isolated RS-485 or RS-232 data interface. The device drives a center-tapped transformer primary from a 5V or 3.3V DC power supply. The secondary can be wound to provide any isolated voltage needed at power levels up to 1W. The MAX253 consists of a CMOS oscillator driving a pair of N-channel power switches. The oscillator runs at double the output frequency, driving a toggle flipflop to ensure 50% duty cycle to each of the switches. Internal delays are arranged to ensure break-beforemake action between the two switches. The SD pin puts the entire device into a low-power shutdown state, disabling both the power switches and oscillator. The MAX253 is an isolated power-supply transformer driver specifically designed to form the heart of a fully isolated RS-485 data interface. Completely isolated communications are obtained by combining the MAX253 with a linear regulator, a center-tapped transformer, optocouplers, and the appropriate Maxim interface product. The MAX253 consists of an RC oscillator followed by a toggle flip-flop, which generates two 50% duty-cycle square waves, out-of-phase at half the oscillator frequency. These two signals drive the groundreferenced output switches. Internal delays ensure break-before-make action between the two switches. Ground SD for normal operation. When high, SD disables all internal circuitry, including the oscillator and both power switches. Pulling FS low reduces the oscillator frequency and lowers the supply current. FS includes a weak pull-up, so it will be set to the highfrequency state if not connected.

Applications

• Isolated RS-485/RS-232 Power-Supply
• Transformer Driver
• High Noise-Immunity Communications Interface
• Isolated and/or High-Voltage Power Supplies
• Bridge Ground Differentials
• Medical Equipment
• Process Control

Key features

• Simple Power-Supply Transformer Driver Design for Isolated RS-485/RS-232 Data-Interface Applications
• Single 5V or 3.3V Supply
• Low-Current Shutdown Mode: 0.4μA
• Pin-Selectable Frequency: 350kHz or 200kHz
• 8-Pin DIP, SO, and μMAX Packages Take Minimal Board Space