HV7801
Block Diagram
Typical use is measurement of line or load current for purpose
of overcurrent protection, metering and current regulation.
VSENSE
ISENSE
High side current sensing, as opposed to ground referenced
or low side current sensing, is desirable or required when:
RSENSE
RP
(Optional,
see text)
► The current to be measured does not flow in a circuit
associated with ground.
IN
LOAD
► The measurement at ground level can lead to ambiguity
due to changes in the grounding arrangement during
field use.
RA
► The introduction of a sense resistor in the system ground
is undesirable due to issues with safety, EMI, or signal
degradation due to common impedance coupling.
Principle of Operation
Bias
Circuits
The operational amplifier and MOSFET forces the voltage
across RA to track VSENSE within the limit of the offset voltage
of the opamp, i.e. VRA = VSENSE
.
VOUT
OUT
The current through RA returns to ground through R .
RA and RB are integrated, exhibiting tight matching anBd
excellent tracking. By design, RB is five times larger than R .
Consequently, V is five times larger than VRA, thus resultinAg
in a voltage gainRoB f 5.
R
B
HV7801
GND
OUT Pin Loading Effects
Note that the OUT pin has an typical output resistance of
±6.5kΩ. Loading the output causes the voltage gain to drop
and rise/fall times to increase.
Application Information
For example, assuming output resistance is ±6.5kΩ, the load
resistance should exceed ±6.5MΩ in order to limit the drop in
gain to ± part in ±000.
General
Again assuming output resistance is ±6.5kΩ, capacitive
loading of 6pF results in a response pole with a time constant
of ±00ns, not high enough to materially affect the output rise
and fall times (about 700ns).
The HV780± high side current monitor IC features accurate
current sensing, small size, low component count, low power
consumption, exceptional input voltage range, ease of use
and low cost.
3
SUPERTEX [ Supertex, Inc ]
