The MAX253 is a monolithic oscillator/power-driver, specifically designed to provide isolated power for an isolated RS-485 or RS-232 data interface. It 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.
The MAX253 is a monolithic oscillator/power‑driver designed to provide isolated power for RS‑485 or RS‑232 data interfaces. It drives a center‑tapped transformer primary from a 5 V or 3.3 V supply and can deliver up to 1 W of isolated output power. The device includes a CMOS oscillator, a toggle flip‑flop, and two N‑channel power switches with break‑before‑make action.
Key features include a pin‑selectable switching frequency (350 kHz or 200 kHz), low‑current shutdown mode (0.4 µA), and availability in 8‑pin DIP, SO, and uMAX packages. The datasheet provides absolute maximum ratings, electrical characteristics, typical operating curves, and recommended external components such as diodes and filter capacitors.
| Supply Voltage (VCC) | 0.3 V to +7 V |
|---|---|
| Operating Temperature Range | -55 °C to +125 °C |
| Pin‑Selectable Frequency | 350 kHz or 200 kHz |
| Low‑Current Shutdown Mode | 0.4 µA |
| Package Types | 8‑Pin DIP, SO, uMAX |
The device operates from 0.3 V up to +7 V supply voltage.
The frequency is set by the FS pin: 350 kHz when FS is high, or 200 kHz when FS is low.
In shutdown mode the device draws only 0.4 µA.
The MAX253 is offered in 8‑pin DIP, SO, and uMAX packages.