The MAX253 is a monolithic oscillator/power-driver 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.
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 DC supply and can deliver up to 1 W of isolated power. The device includes a CMOS oscillator, a pair of N‑channel power switches, and a shutdown (SD) pin for low‑power mode.
The document provides absolute maximum ratings, electrical characteristics, pin descriptions, and recommended component selections such as transformers, diodes, and capacitors. Typical application circuits for isolated RS‑485 and RS‑232 interfaces are shown, along with layout guidelines for high‑voltage isolation and noise immunity.
| Supply voltage range | 5 V or 3.3 V DC |
|---|---|
| Shutdown supply current | 0.4 µA |
| Switch on‑resistance (typical) | 1.5 Ω |
| Maximum isolated output power | 1 W |
| Maximum output switch current per switch | 200 mA |
The MAX253 can be powered from either a 5 V or a 3.3 V DC supply.
The shutdown supply current is 0.4 µA.
The MAX253 can provide up to 1 W of isolated power.