National Drives Deeper Into Power IC Stronghold

Electronic News, August 17, 1998

The LM3812 and LM3813 current gauges feature a patented 4-milliohm internal lead frame resistor that produces claimed near-zero insertion losses, eliminating the need for external sense elements. Near-zero insertion losses from current flow measurements are particularly important when measuring currents in the ampere range.

The LM3812 senses current on the positive side of the load, while the LM3813 is used for low-side current sensing. Both devices measure current flow with claimed virtually zero insertion loss in the measurement line. In turn, they send a pulse width modulated (PWM) digital output directly to a microcontroller, indicating current magnitude and direction. PWM accuracy at room temperature is rated at +/-2 percent.

Venkatesh Shan, National's director of marketing for power management products, said, "National's solution simplifies the design, lowers cost, and eliminates measurement errors caused by amplifier offset as well as value tolerances of external resistors required by competing devices."

The voltage across the lead frame resistor is measured with a delta-sigma converter, then converted to a PWM output that is said by National to be universally compatible with all microcontrollers.

The LM3812FM and LM3813FM are currently available in 8-pin SOIC packages and are priced at $1.52 each when purchased in 1,000-unit lots. u