1W Primary-Side Transformer H-Bridge Driver for Isolated Supplies

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 flip-flop to ensure 50% duty cycle to each of the switches. Internal delays are arranged to ensure break-before-make 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.

Applications

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

* 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