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Current-mode PWM controllers

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article image Compatible with UC2842/UCC2842 and UC2844/UCC2844.

MAXIM Integrated Products, represented in Australia by Arrow Electronics has released the MAX5071A/MAX5071B single-ended, current-mode PWM controllers for isolated telecom dc-dc or universal offline-input ac-dc power supplies.

These devices are pin-compatible with the industry standard multisourced UC2842/UCC2842 and UC2844/UCC2844 family of products. The feedback FB pin is replaced with a bidirectional SYNC input pin. This allows designers to upgrade existing power supply designs for higher performance with minimal component changes.

The bidirectional synchronisation input on the MAX5071A/MAX5071B allows multiple power supplies to operate at the same frequency. This eliminates beat frequencies caused by power supplies operating at varying frequencies. The bidirectional synchronisation pin is an input/output pin that outputs synchronising pulses and can also accept synchronisation signals from an external source or from other MAX5071A/MAX5071B devices. The SYNC input pins of multiple MAX5071A/MAX5071B devices can be connected together, with all devices synchronising to the device with the highest frequency.

The switching frequency is externally programmable from 20kHz to 1MHz. The timing-capacitor discharge current is trimmed to ±5%. This allows the maximum duty cycle to be set accurately, avoiding transformer saturation. The maximum duty cycles for the MAX5071A and MAX5071B are 100% and 50%, respectively. In addition, the switching frequency is trimmed for ±7% accuracy while the current-limit threshold and start/stop voltages are trimmed to ±5% accuracy. The devices' 60ns cycle-by-cycle current limit propagation delay allows a fast response to output short circuit.

Startup current is typically 35μA. This allows the use of a high-value startup resistor, reducing power dissipation in the start-up resistor in standby mode. The size and value of the start-up capacitor are also reduced. The MAX5071A/MAX5071B gate-driver outputs are capable of sourcing 2A and sinking 1A. Both devices include overtemperature shutdown.

Rated for operation from -40°C to 125°C temperature range, the MAX5071A and MAX5071B are available in 8-pin SO and 8-pin microMAX packages.

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