PWM controller boosts PSU efficiency

A dual-ended PWM controller features low power consumption and high speed that makes it ideal for designing compact high-power isolated offline and telecomms power supplies.

New from Semtech, the SC4806 is a dual-ended pulsewidth modulation (PWM) controller that features low power consumption and high speed that makes it ideal for designing compact high-power isolated offline and telecomms power supplies.

The SC4806 has very low 90uA startup current and can be configured in either current mode or voltage mode.

The controller can operate in peak current mode or in voltage mode by programming the slope compensation using a single external resistor.

Operating in voltage mode feed forward allows fast line transient response and eliminates the need for current sensing elements.

The current mode control simplifies the loop dynamics and reduces transformer saturation problems in full-bridge and push-pull topologies.

The SC4806 contains all of the control circuitry required for isolated applications where a secondary side error amplifier is used.

Operating from telecomms power rails (36 to 76V), the SC4806 can be used to design highly efficient, high current push-pull, half-bridge or full-bridge isolated power convertors.

The SC4806 can be programmed using an external RC circuit to 1MHz operating frequency.

The two outputs operate 180-degrees out-of-phase and run at half the frequency.

The controller also features SYNC that allows the oscillator to synchronise its clock to an external source.

The SC4806 utilises a unique oscillator that allows two SC4806 devices to be synchronised to provide automatic out-of-phase (biphase) switching, minimising input and output current ripple and reducing the stress on, and size of input/output filter components.

The SC4806 features two levels of undervoltage lockout (UVLO) programmable through an external resistor divider.

An additional programmable soft start feature allows for a controlled system startup.

"The SC4806 is the ultimate versatile PWM controller", said Ven Shan, Vice President of Marketing for Semtech's Power Management Products.

"The feature set is augmented by a small package size, high operating frequency and high integration that can deliver high power density to isolated DC to DC convertor designs for the networking, telecom and server markets".

The SC4806 has built-in pulse-by-pulse current limiting and auto-restart overcurrent protection in both current and voltage modes.

Each SC4806 has a two-channel half-bridge power circuit, with the flexibility to combine two devices in a full bridge design for systems needing up to 1000W of power.

This capability comes with programmable dead time between the two outputs that can be adjusted depending on the size of the timing components.

The turn-on threshold of this device is 7.9V typically, matching the common bias voltage for synchronous-rectifier drives.

The SC4806 extends Semtech's SC4800-series family of dual-ended PWM power controllers.

The part is packaged in a small MLPQ-12 package that is lead-free, and complies with the European Union's RoHS Directive to meet worldwide environmental and regulatory requirements.

The SC4806 is available immediately in production quantities and is priced at $1.50 each in 1000-piece lots.

The order code for the device is SC4806MLTRT.

Semtech offers comprehensive design assistance, including field- and factory-based support.

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