LTC6101HV Linear Technology, LTC6101HV Datasheet - Page 9

• Manufacturer Part Number: LTC6101HV
• Description: High-Side Current Sense Amplifier
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
Useful Gain Configurations
Selection of External Current Sense Resistor
The external sense resistor, R
effect on the function of a current sensing system and
must be chosen with care.
First, the power dissipation in the resistor should be
considered. The system load current will cause both heat
and voltage loss in R
should be as small as possible while still providing the
input dynamic range required by the measurement. Note
that input dynamic range is the difference between the
maximum input signal and the minimum accurately repro-
duced signal, and is limited primarily by input DC offset of
the internal amplifier of the LTC6101. In addition, R
must be small enough that V
maximum input voltage specified by the LTC6101, even
under peak load conditions. As an example, an application
may require that the maximum sense voltage be 100mV.
If this application is expected to draw 2A at peak load,
R
Once the maximum R
mum sense resistor value will be set by the resolution or
dynamic range required. The minimum signal that can be
accurately represented by this sense amp is limited by the
input offset. As an example, the LTC6101B has a typical
input offset of 150µV. If the minimum current is 20mA, a
sense resistor of 7.5mΩ will set V
the same value as the input offset. A larger sense resistor
will reduce the error due to offset by increasing the sense
voltage for a given load current.
Choosing a 50mΩ R
range and provide a system that has 100mV across the
sense resistor at peak load (2A), while input offset causes
an error equivalent to only 3mA of load current.
Gain
100
SENSE
20
50
should be no more than 50mΩ.
499
200
100
R
IN
R
10k
10k
10k
OUT
U
SENSE
SENSE
SENSE
V
SENSE
U
. As a result, the sense resistor
value is determined, the mini-
250mV
100mV
50mV
at V
will maximize the dynamic
SENSE
OUT
SENSE
SENSE
= 5V
W
does not exceed the
, has a significant
to 150µV. This is
I
OUT
at V
500µA
500µA
500µA
U
OUT
SENSE
= 5V
Peak dissipation is 200mW. If a 5mΩ sense resistor is
employed, then the effective current error is 30mA, while
the peak sense voltage is reduced to 10mV at 2A, dissipat-
ing only 20mW.
The low offset and corresponding large dynamic range of
the LTC6101 make it more flexible than other solutions in
this respect. The 150µV typical offset gives 60dB of
dynamic range for a sense voltage that is limited to 150mV
max, and over 70dB of dynamic range if the rated input
maximum of 500mV is allowed.
Sense Resistor Connection
Kelvin connection of the IN
resistor should be used in all but the lowest power appli-
cations. Solder connections and PC board interconnec-
tions that carry high current can cause significant error in
measurement due to their relatively large resistances. One
10mm x 10mm square trace of one-ounce copper is
approximately 0.5mΩ. A 1mV error can be caused by as
little as 2A flowing through this small interconnect. This
will cause a 1% error in a 100mV signal. A 10A load current
in the same interconnect will cause a 5% error for the same
100mV signal. By isolating the sense traces from the high-
current paths, this error can be reduced by orders of
magnitude. A sense resistor with integrated Kelvin sense
terminals will give the best results. Figure 2 illustrates the
recommended method.
R
SENSE
LOAD
Figure 2. Kelvin Input Connection Preserves
Accuracy Despite Large Load Current
V
+
LTC6101/LTC6101HV
R
IN
4
2
LTC6101
+
–
and IN
–
+
inputs to the sense
6101 F02
3
5
1
R
OUT
V
OUT
6101fa
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