Electronic Design

IC Provides Precise Digital Control Of Analog Supplies

For high-availability server and communications applications, Linear Technology's LTC2970 enables precise voltage control and I2C power-system monitoring in systems that use simple voltage-regulator chips. The LTC2970 uses a seven-channel, 14-bit delta-sigma analog-to-digital converter (ADC) to measure supply voltages, load currents, or internal die temperature. The ADC output is available via I2C for system monitoring. A "dash-1" version of the LTC2970 adds a tracking feature so the I2C bus can sequence multiple supplies.

Precision control comes from a pair of voltage-buffered, 8-bit IDACs (current-output digital-to-analog converters)—one for programming the output voltage of each dc-dc converter. Each IDAC provides a controlled current to a precision resistor. Full-scale current output and resistance then define the maximum regulated voltage.

The chip monitors the voltage of each external supply and compares it to a target value stored in a servo register. After each conversion, the IDAC output is incremented or decremented by 1 or held, whichever brings or keeps the measured voltage closer to the targeted servo value. This one-bit-per-iteration mode, "soft-connect," minimizes power-supply transients. It also is useful for power-supply margining.

A "hard connect" mode bypasses the soft-connect algorithm. Hard connects are used in systems that have calculated or measured an acceptable voltage at which to connect the IDAC's output to the regulator's feedback node. The IDACs also have a "servo-on-fault" mode in which the IDAC is only stepped when the output voltage drifts outside of a user-programmable window. A point-of-load ground reference for the IDAC outputs minimizes errors that would otherwise occur in power systems that experience ground bounce.

Pricing for the LTC2970 and LTC2970-1 starts at $3.99 each in 1000-piece lots.

Linear Technology

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