HV7800 Просмотр технического описания (PDF) - Supertex Inc
Номер в каталоге
Компоненты Описание
производитель
HV7800 Datasheet PDF : 7 Pages
| |||
Block Diagram
VSENSE
ISENSE
RSENSE
RP (optional)
IN
LOAD
RA
HV7800
Principle of Operation
The operational amplifier and MOSFET force the voltage
across RA to track VSENSE within the limit of the offset voltage
of the opamp, i.e. VRA = VSENSE.
The current through RA returns to ground through RB. RA and
RB are integrated, exhibiting tight matching and excellent
tracking. By design, RA and RB have the same resistance.
Consequently, VRA is equal to VRB, resulting in a voltage gain
of 1.
Bias
Circuits
OUT Pin Loading Effects
Note that the OUT pin has a typical output resistance of
3.6kΩ. Loading the output causes the voltage gain to drop
and rise/fall time to increase.
VOUT
OUT
RB
HV7800
GND
For example, assuming an output resistance of 3.6kΩ, the
load resistance should exceed 3.6MΩ in order to limit the
drop in gain to 1 part in 1000.
Again assuming an output resistance of 3.6kΩ, capacitive
loading of 30pF results in a response pole with a time
constant of 100ns, not yet high enough to materially affect
the output rise and fall time (about 700ns).
Application Information
General
The HV7800 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.
The part typically performs the measurement of line or
load current for overcurrent protection, metering or current
regulation.
Sense Resistor Considerations
Choose a sense resistor that will not exceed 500mV during
normal operating conditions. Limit the power dissipation in
the sense resistor to whatever is practical; a high sense
voltage benefits accuracy, but increases power dissipation.
Consider the use of Kelvin connections for applications
where considerable voltage drops may occur in the PCB
traces that carry the current to be measured to the sense
resistor. A layout pattern that minimizes voltage across the
sense lines is shown below.
High side current sensing, as opposed to ground referenced
or low side current sensing, is desirable or required when:
+ VSENSE -
►► The current to be measured does not flow in a circuit
associated with ground.
►► The measurement at ground level can lead to ambiguity
due to changes in the grounding arrangement during
field use.
►► Introduction of a sense resistor in the system ground
is undesirable due to issues with safety, EMI, or signal
degradation caused by common impedance coupling.
IN LOAD
RSENSE
Choose a low inductance type sense resistor if preservation of
bandwidth is important. The use of Kelvin connections helps
by excluding the inductive voltage drop across the traces
leading to the sense resistor. The inductive voltage drop may
be substantial when operating at high frequencies.
Doc.# DSFP-HV7800
A062813
Supertex inc.
5
www.supertex.com
Share Link: 