FAN4010 Fairchild Semiconductor, FAN4010 Datasheet - Page 7

• Manufacturer Part Number: FAN4010
• Description: The FAN4010 is a high-side current sense amplifier designed for battery-powered systems
• Manufacturer: Fairchild Semiconductor

© 2007 Fairchild Semiconductor Corporation
FAN4010 Rev. 1.0.5
V
Application Information
Detailed Description
The FAN4010 measures the voltage drop (V
across an external sense resistor located in the high
voltage side of the circuit. V
linear current via an internal operational amplifier and
precision 100Ω resistor. The value of this current is
V
I
output voltage proportional to the current flowing to
the load.
Use the following equations to scale a load current to
an output voltage:
V
V
Selecting R
Selection of R
racy and allowable voltage loss. Although the FAN4010
is optimized for high accuracy with low V
larger R
ever, larger values of R
drop, reducing the effective voltage available to the load.
This can be troublesome in low-voltage applications.
Because of this, the maximum expected load current
and allowable load voltage should be well understood.
Although higher values of V
should be chosen to satisfy the following condition:
10mV < V
For low-cost applications where accuracy is not as
important, a portion of the printed circuit board (PCB)
trace can be used as an R
shows an example of this configuration. The resistivity
of a 0.1 inch wide trace of two-ounce copper is about
30mΩ/ft. Unfortunately, the resistance temperature
coefficient is relatively large (approximately 0.4% / C),
so systems with a wide temperature range may need
OUT
OUT
SENSE
SENSE
OUT
R
pin to an external resistor R
OUT
= 0.01 x V
/100Ω (internal). Output current flows from the
SENSE
= I
SENSE
Load
Figure 12. Functional Circuit
SENSE
3
SENSE
value provides additional accuracy. How-
• R
SENSE
I
OUT
< 200mV
SENSE
is a balance between desired accu-
x R
100
SENSE
OUT
Load
SENSE
V
SENSE
IN
SENSE
create a larger voltage
R
6
1
sense
can be used, R
OUT
resistor. Figure 13
is converted to a
to generate an
SENSE
V
V
sense
+
-
IN
values, a
SENSE
SENSE
R
(1)
(2)
(3)
Load
)
7
to compensate for this effect. Additionally, self heating
due to load currents introduces a nonlinearity error.
Care must be taken not to exceed the maximum power
dissipation of the copper trace.
Selecting R
R
ge required for the particular downstream application.
For example, if the output of the FAN4010 is intended
to drive an analog-to-digital convertor (ADC), R
should be chosen such that the expected full-scale
output current produces an input voltage that matches
the input range of the ADC. For instance, if expected
loading current ranges from 0 to 1A, a R
of 1Ω produces an output current that ranges from 0 to
10mA. If the input voltage range of the ADC is 0 to 2V,
a R
The input voltage and full-scale output current (I
FS
output range. To ensure sufficient operating head-
room, choose:
V
Output current accuracy for the recommended V
levels between 10mV and 200mV are typically much
better than 1%. As a result, the absolute output volta-
ge accuracy is dependent upon the precision of the
output resistor.
Make sure the input impedance of the circuit con-
nected to V
accurate V
Since the FAN4010 provides a trans-impedance func-
tion, it is ideal for applications involving current rather
than voltage sensing.
(R
IN
OUT
) needs to be taken into account when setting up the
OUT
OUT
- V
V
OUT
can be chosen to obtain the output voltage ran-
SENSE
Figure 13. Using PCB Trace for R
value of 200Ω should be used.
• I
0.3in COPPER
OUT_FS
OUT
OUT
INPUT
OUT
- (R
R
OUT
values.
1
2
3
is much higher than R
) such that
OUT
V
NC
I
OUT
IN
• I
0.1in COPPER
OUT_FS
R
SENSE
) > 1.6V
Load
GND
NC
5
6
4
0.3in COPPER
LOAD
OUT
SENSE
SENSE
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to ensure
resistor
SENSE
OUT_
OUT
(4)