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

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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.
MAX253: Typical Operating Circuit MAX253: Typical Operating Circuit Enlarge+

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


  • 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
Part NumberVIN
Driver Output Resistance
Package/PinsOper. Temp.
minmaxmaxmaxSee Notes
MAX253 2.5640.2Push-Pull3500.45
SOIC (N)/8
-55 to +125
-40 to +85
0 to +70
$1.49 @1k
See All Transformer Drivers (6)
Pricing Notes:
This pricing is BUDGETARY, for comparing similar parts. Prices are in U.S. dollars and subject to change. Quantity pricing may vary substantially and international prices may differ due to local duties, taxes, fees, and exchange rates. For volume-specific and version-specific prices and delivery, please see the price and availability page or contact an authorized distributor.

Tools & Models

  • MAX253 Macromodel
  • Device   Fab Process   Technology   Sample size   Rejects   FIT at 25°C   FIT at 55°C  

    Note : The failure rates are summarized by technology and mapped to the associated material part numbers. The failure rates are highly dependent on the number of units tested.

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