Supertex inc.
Supertex inc.
1235 Bordeaux Drive, Sunnyvale, CA 94089
Tel: (408) 222-8888
FAX: (408) 222-4895
www.supertex.com
1
NR031306
HV7800
Initial Release
Features
450V Maximum supply voltage
Voltage output device
1% Typical gain accuracy
500mV Maximum V
SENSE
Fast response: 700ns rise and fall time
50A Quiescent current (max.)
Applications
LED driver current monitor
SMPS current monitor
Battery current monitor
Motor controls
General Description
The HV7800 is a high side current monitor IC, which
senses the voltage across an external current sense
resistor located in the power or "high" side of the circuit
and translates this voltage to a ground referenced circuit
at a gain of one.
The HV7800 has a wide operating range of 3V-450VDC,
which enables its use in DC power systems of 12V/24V/
48V, and in AC systems operating at voltages from 85VAC
to 265VAC.
The fast response time of the HV7800 allows use of this
current monitor in the feedback loop of a switching power
supply or in LED driver applications.
Typical Application Circuit
High Side Current Monitor
1
5
4
2
3
R
SENSE
V
OUT
= I
LOAD
R
SENSE
400VDC Input
HV7800
V
SENSE
LOAD
I
LOAD
2
NR031306
HV7800
Ordering Information
DEVICE
Package Options
HV7800K1-G
5-Lead SOT-23
-G indicates package is RoHS compliant (`Green')
Absolute Maximum Ratings
Symbol
Parameter
Min
Typ
Max
Units
Conditions
ESD Characteristics, IN, LOAD
ESD
Human body model
-
2.0
-
kV
1.5k, 100pF
Supply
V
IN
Supply voltage
10
-
450
V
---
I
Q
Quiescent supply current
10
-
50
A
V
IN
= 400V, V
SENSE
= 0mV
Input and Output Characteristics
I
LOAD
Input current to LOAD pin
-1.0
-
1.0
nA
V
SENSE
= 500mV
R
OUT
OUT pin output resistance
2.60
3.30
4.0
k
---
V
OUT
Output Voltage
0
-
5.0
mV
V
SENSE
= 0mV
94
106
V
SENSE
= 100mV
193
207
V
SENSE
= 200mV
490
510
V
SENSE
= 500mV
Dynamic Characteristics
t
RISE
Output rise time, 10% to 90%
-
700
-
ns
V
SENSE
step 0mV to 500mV
t
FALL
Output fall time, 90% to 10%
-
700
-
ns
V
SENSE
step 500mV to 0mV
Electrical Characteristics
(Voltages referenced to GND, V
IN
= 10V, T
A
= 25C, unless otherwise noted. Values of parameters marked with a apply over the full temperature range.)
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent
damage to the device. These are stress ratings only, and functional operation of the device
at these or any other conditions beyond those indicated in the operational sections of the
specifi cations is not implied. Exposure to absolute maximum rating conditions for extended
periods may affect device reliability.
1
Limited by package dissipation.
Parameter
Value
IN
-0.5V
to
+450V
LOAD
-0.5V to +450V
OUT
-0.5V
to
+10V
Operating Ambient Temperature
1
-40C
to
+85C
Operating Junction Temperature
-40C to +125C
Storage Temperature
-65C to +150C
SOT23-5 Package Thermal Resistance
260 K/W
Pinout
IN
LOAD
OUT
GND
HV7800K1
1
5
4
2
3
N/C
3
NR031306
HV7800
Typical Performance Characteristics
160
120
40
0
-40
10m
0.1
10
100
1K
10K
100K
1M
10M
Frequency (Hz)
CMRR (dB)
80
1.0
1.0M
10m
0.1
10
100
1K
10K
100K
1M
10M
1
Frequency (Hz)
0
-20
-40
-60
Gain (dB)
2
4
6
8
10
12
0
0.1
0.2
0.3
0.4
0.5
V
SENSE
,
V
OUT
(V)
time (s)
V
SENSE
= 5mV-500mV
Common Mode Rejection Ratio
vs Frequency
Gain
vs Frequency
Step Response
(5.0mV to 500mV)
Output Characteristics
(V
OUT
vs V
IN
)
2
4
6
8
10
0
0.1
0.2
0.3
0.4
0.5
V
OUT
V
o
ltage(V)
V
IN
Voltage(V)
0
V
SENSE
= 500mV
V
SENSE
= 400mV
V
SENSE
= 300mV
V
SENSE
= 200mV
V
SENSE
= 100mV
4
NR031306
HV7800
Pin Description
Block Diagram
5
4
1
3
LOAD
I
LOAD
R
SENSE
IN
OUT
R
B
GND
BIAS
CKTS
R
A
Pin
Name
Description
1
LOAD
This pin is an input sense pin that connects to the negative (-) side of sense resistor, R
SENSE
. The
negative side denotes the system load end of the sense resistor.
2
N/C
No Connection
3
IN
Positive supply. Input voltage range is 3.0 to 450V. This pin is an input sense pin that connects to
the positive (+) side of sense resistor, R
SENSE
.
4
GND
This pin is connected to the GND or return of the system.
5
OUT
Output Voltage referenced to GND terminal. The voltage at OUT will be equal to V
SENSE
. The output
impedance of this pin is typically 3.3 k.
IN
LOAD
OUT
GND
HV7800K1
1
5
4
2
3
N/C
5
NR031306
HV7800
Application Information
General
The HV7800 offers high side current sensing featuring
accuracy, small size, low component count, low power
consumption, ease of use and low cost. The input voltage
rating of 450V extends the use to off-line applications.
The HV7800 allows measurement of line or load current
for purpose of overcurrent protection, current metering and
current regulation.
High side current sensing, as opposed to ground or low-side
sensing, is desirable or required when:
The current to be measured does not fl ow in a circuit
associated with ground.
The addition of resistance in the grounding system
will cause issues with safety, EMI, or will lead to
signal degradation due to common impedance
coupling.
Principle of Operation
The operational amplifi er and associated MOSFET, as
shown in the block diagram, force a current through resistor
R
A
such that V
RA
is equal to V
SENSE
. The current through R
A
fl ows to ground through R
B
and develops an output voltage
V
OUT
, which is equal to V
SENSE
, given that R
A
and R
B
have
equal resistance.
Note that the output is not buffered, having an output
resistance of 3.3k nominal. Loading of the output will affect
gain accuracy and / or bandwidth.
Assume in the following that R
OUT
= 4k.
To limit gain error to say 1 part in 1000, the external load
impedance should exceed 4M.
Capacitive loading forms a load pole. The break frequency
follows from:
where
E.g. let R
LOAD
=
and C
LOAD
= 1nF, then the load pole is
located at 38.8kHz, giving rise and fall times of 8.8us.
Sense Resistor Considerations
The choice of value of the sense resistor entails a trade-
off between power dissipation from the sense resistor and
accuracy. Power dissipation from the sense resistor is
equal to (V
SENSE
I
LOAD
). It is generally desirable to maximize
V
SENSE
to enhace accuracy, but not to the extent that power
dissipation from the sense resistor becomes objectionable.
Consider the use of Kelvin connections for applications with
a large load current. A typical layout pattern, which minimizes
voltage drops across the sense lines is shown below:
V
SENSE
Preservation of bandwidth requires careful attention to trace
layout and choice of sense resistor. Note that the resistance
of the sense resistor is typically small, and that both the
impedence of printed circuit board traces and the equivalent
series inductance of the sense resistance can be a major part
of the total sense/impedence at high frequency operation.
An inductance of just 1nH contributes an impedence of 3m
at 500kHz.
f
=
1
2
=
(
)
R
R
C
B
LOAD
LOAD
//
HV7800
R
OUT
= 3.3k 30%
I
LOAD
R
SENSE
C
LOAD
R
LOAD
IN
LOAD
GND
OUT
Sense
Resistor
Supertex inc.
1235 Bordeaux Drive, Sunnyvale, CA 94089
TEL: (408) 222-8888 / FAX: (408) 222-4895
www.supertex.com
2006 Supertex inc. All rights reserved. Unauthorized use or reproduction is prohibited.
Supertex inc.
does not recommend the use of its products in life support applications, and will not knowingly sell its products for use in such applications, unless it receives an adequate
"product liability indemnification insurance agreement". Supertex does not assume responsibility for use of devices described and limits its liability to the replacement of the devices
determined defective due to workmanship. No responsibility is assumed for possible omissions or inaccuracies. Circuitry and specifications are subject to change without notice. For the latest
product specifications, refer to the Supertex website: http//www.supertex.com.
6
Doc.# DSFP - HV7800
NR031306
HV7800
Protection of the LOAD input
In situations where the sense voltage can signifi cantly
exceed 500mV, the LOAD input to the differential amplifi er
should be protected by the addition of a protection resistor
and two diodes as shown below:
An excessive sense voltage might occur when line or load
current is signifi cantly larger during the startup or shutdown
event, or during overcurrent or short circuit events. A large
differential voltage can also exist if the sense resistor fails
open, or is inadvertently not installed.
HV7800
IN
LOAD
GND
OUT
R
PROTECT
R
SENSE
I
SURGE
Top View
Front View
Side View
All dimensions are in millimeters
Legend: min
max
0.30
0.55
0.09
0.20
0.90
1.45
0.30
0.50
0.00
0.15
0.90
1.30
0.95ref
1.90ref
2.60
3.00
2.80
3.05
1.50
1.75
Pin 1
5-Lead SOT-23 (K1) Package Outline
(The package drawing(s) in this data sheet may not refl ect the most current specifi cations. For the latest package outline informa-
tion go to
http://www.supertex.com/packaging.html
.)
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