PWM buck controllers change voltage on the fly

Synchronous, pulse-width modulation (PWM) buck controllers have integrated voltage-transitioning switches for "on-the-fly" voltage output changes and voltage margining.

Semtech has announced the SC471(A) and SC475A synchronous, pulse-width modulation (PWM) buck controllers with integrated voltage-transitioning switches for "on-the-fly" voltage output changes and voltage margining.

The SC471(A) has two FET switches to allow the output to change dynamically between up to four different levels.

The SC471(A) can be used as a voltage-margining controller for function and reliability testing of a system at upper and lower power-supply voltage limits.

The device can also be used with graphics processors or microprocessors requiring more than two input voltage levels for normal operation and for sleep modes.

The SC475A controller has one FET switch to dynamically change the output voltage for processors that require a different voltage for normal operation and for sleep mode.

The power-good output is blanked during output voltage transitions to eliminate the potential for glitches.

Both high-efficiency devices have a constant on-time topology for a fast transient response requiring less output capacitance than competing fixed-frequency convertors.

The devices also include Semtech's patent-pending Smart Power-Save mode for protecting the downstream device from high voltage levels due to leakage or load dump.

Semtech's Smart-Drive circuitry is built into both devices to reduce electromagnetic interference with a two-stage technique for turning on the FET.

The first stage slowly turns on voltage to the FET to prevent ringing, before switching to a faster voltage level increase to maximise efficiency.

The reduced EMI levels from this approach contribute to a system-wide effort to reduce EMI levels to pass FCC regulations.

"The SC471(A) and SC475A were developed to address the space constraints of graphics cards as well as to enable voltage margining, an essential technique needed to ensure robust system performance", says Ramesh Balasubramaniam, Marketing Manager for Semtech's Power Management Division.

"These devices also improve EMI performance due to Semtech's proprietary SmartDrive technology, which helps create compliance with environmental regulations".

The SC471(A) and SC475A have extensive power protection, including programmable current limit, output overvoltage protection, input undervoltage lockout and overtemperature protection.

Both devices have a battery input range of 3 to 25V, and an output range of 0.75 to 5.25V as well as an above average output voltage accuracy at +/-0.85%.

The SC471(A) and SC475A are both packaged in 3 x 3mm MLP packages for mobile applications.

The devices are RoHS/WEEE compliant to meet worldwide regulatory standards.

The SC471 (order code: SC471MLTRT) and SC471(A) (order code: SC471AMLTRT) are available immediately in production quantities and priced at US $0.86 each in 1,000-piece lots.

The SC475 (order code: SC475MLTRT) and SC475A (order code: SC475AMLTRT) are available immediately in production quantities and priced at $0.79 each in 1,000-piece lots.

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