Compact, 36V H-Bridge Transformer Driver for Isolated Supplies

The MAX22256/MAX22258 integrated primary-side controllers and H-bridge drivers for isolated power-supply circuits feature a precision on-board oscillator, protection circuitry, and internal MOSFETs to provide up to 650mARMS of current to the primary winding of a transformer. These devices feature an internal 450kHz (typ) oscillator and can also be driven by an external clock to synchronize multiple devices and control EMI. An internal flip-flop stage guarantees a fixed 50% duty-cycle to prevent DC current flow in the transformer as long as the clock period is constant.

The MAX22256/MAX22258 operate from a wide single-supply voltage range from 5V to 36V and include undervoltage lockout for controlled startup. Break-before-make switching is integrated to prevent cross-conduction of the H-bridge MOSFETs. A resistor-adjustable overcurrent limit allows primary-side limiting of load currents on the transformer’s secondary side and thermal shutdown circuitry provides additional protection against excessive power dissipation.

The MAX22256A features a 30ns (typ) dead time for conventional H-bridge switching topologies. The MAX22256B/C feature a fixed dead time of 60ns (typ) and 100ns (typ), respectively, and are optimized for the zero-voltage switching of an LLC topology. The MAX22258 features a resistor-programmable dead time and a synchronized clock output (CLKO).

Applications

* Isolated Motor Drive Gate Power Supply * Isolated +24V PLC Field Supply

* Simple, Flexible Design

* 5V to 36V Supply Range * Up to 91% Efficiency * Provides over 15W to Transformer * Undervoltage Lockout * Internal or External Clock Source * Synchronous Clock Output (MAX22258) * Programmable Overcurrent Threshold * 30ns to 200ns Adjustable Deadtime (MAX22258)

* Robust Integrated System Protection

* Fault Detection and Indication * Overcurrent Limiting up to 1A * Overtemperature Protection * Precision Internal Clock Source (±6%) Prevents Excessive Transformer Core Losses Due to Frequency Shift * Wide Temperature Range: -40°C to +125°C

* Space Savings

* Small 3mm x 3mm 10-Pin TDFN Package (MAX22256A/B/C) with 0.5mm Pitch * Small 4mm x 5mm 14-Pin TSSOP Package (MAX22258) with 0.65mm Pitch