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, IOUT equals the drop
across the sense resistor divided by RA, which makes it easy to digitize the current as
the drop across RB with a simple instrumentation amplifier and analog-to-digital converter (ADC). The HV7802 also has a user-programmable voltage or transconductance
gain (). The RP 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 RA and RB 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