HV7801 데이터 시트보기 (PDF) - Supertex Inc
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HV7801 Datasheet PDF : 5 Pages
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HV7801
Sense Resistor Considerations
Transient Protection
Limit the sense resistor voltage to 500mV during normal
operating conditions. Limit the power dissipation in the sense
resistor to suit the application; a high sense voltage benefits
accuracy, but increases power dissipation.
Add a protection resistor (RP) in series with the LOAD pin
if VSENSE can exceed 5V in a positive sense or 600mV in a
negative sense, whether in a steady state or in transient
conditions.
Consider the use of Kelvin connections for applications
where considerable voltage drops may occur in the PCB
traces. A layout pattern which minimizes voltage across the
sense lines is shown below.
- + VSENSE
A large VSENSE may occur during system startup or shutdown
due to the charging and discharging of bulk storage
capacitors. VSENSE may be large due to fault conditions, such
as a short circuit condition, or a broken or missing sense
resistor.
An internal 5V Zener diode with a current rating of 10mA
protects the sense amplifier inputs. The block diagram
shows the orientation of this diode. The Zener diode provides
clamping at 5V for a positive VSENSE and at 600mV for a
negative VSENSE.
R SENSE
IN LOAD
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.
A trace or component inductance of just 10nH contributes
an impedance of 6.2mΩ at 100kHz, which constitutes a 6%
error when using a 100mΩ sense resistor.
Under worst case conditions, limit the Zener current to 10mA.
A 100kΩ resistor limits the maximum Zener diode current to
4.5mA when VSENSE is 450V, whether positive or negative.
Note that the protection resistor may affect the bandwidth.
The resistor forms an RC network with the trace and pin
capacitance at the LOAD pin. A capacitance of 5pF results
in a time constant of 500ns.
The protection resistor may cause an offset voltage due
to bias current at the LOAD input. Under worst case bias
current, a 100kΩ protection resistor could cause an offset
of 100µV or 0.2% of full scale. Note that the bias current
is nominally zero as the LOAD is a high impedance CMOS
input.
Pin Description
Pin #
Pin Name
1
LOAD
2
NC
3
IN
4
GND
5
OUT
Description
Sense amplifier input. High impedance input with Zener diode protection. Add an external
protection resistor in series with LOAD if VSENSE exceeds the range of -600mV to +5V.
No connect. This pin must be left floating for proper operation.
Sense amplifier input and supply.
Supply return.
Output with a nominal output resistance of 16.5kΩ. Preservation of accuracy may require
an external buffer amplifier to prevent excessive loading.
4
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