ICs Simplify High-Side Current Measurements

Designers making in-circuit current measurements can avoid ground-reference problems by putting the sense resistor on the supply side of the load. However, high-side measurement components must deal with high common-mode voltages.

To make high-side differential measurements across a sense resistor, the HV7801 and HV7802 high-side current monitors from Supertex offer an 8- to 450-V input voltage range. They also provide 700-ns rise and fall times.

In the HV7802, I_OUT equals the drop across the sense resistor divided by R_A, which makes it easy to digitize the current as the drop across R_B with a simple instrumentation amplifier and analog-to-digital converter (ADC). The HV7802 also has a user-programmable voltage or transconductance gain (see the figure). The R_P protection resistor can be added if the drop across the sense resistor could exceed +5 or –0.6 V.

The HV7801 eliminates the variable-gain feature made possible by selecting values for R_A and R_B in the HV7802. It provides a fixed gain of five between the difference between the IN and LOAD pins and the OUT pin.

In 1000-unit quantities, the HV7801 costs $0.56, while the HV7802 is $0.62.

Supertex
www.supertex.com