lt6107mps5-trpbf Linear Technology Corporation, lt6107mps5-trpbf Datasheet - Page 8

• Manufacturer Part Number: lt6107mps5-trpbf
• Description: High Temperature High Side Current Sense Amp In Sot-23
• Manufacturer: Linear Technology Corporation

Selection of External Input Resistor, R
R
while limiting the output current to 1mA. In addition, the
maximum value for R
the largest expected sense voltage gives I
the maximum output dynamic range is available. Output
dynamic range is limited by both the maximum allowed
output current and the maximum allowed output voltage,
as well as the minimum practical output signal. If less
dynamic range is required, then R
accordingly, reducing the maximum output current and
power dissipation. If low sense currents must be resolved
accurately in a system that has a very wide dynamic range,
a smaller R
be used if the maximum current is limited in another way,
such as with a Schottky diode across R
This will reduce the high current measurement accuracy
by limiting the result, while increasing the low current
measurement resolution.
LT6107
APPLICATIONS INFORMATION
by orders of magnitude. A sense resistor with integrated
Kelvin sense terminals will give the best results. Figure 2
illustrates the recommended method.
8
Figure 3. Shunt Diode Limits Maximum Input Voltage to Allow
Better Low Input Resolution Without Overranging
Figure 2. Kelvin Input Connection Preserves Accuracy with
Large Load Currents
IN
should be chosen to allow the required resolution
R
SENSE
LOAD
V
IN
+
than the maximum current spec allows may
R
IN
+IN
V
–
R
LT6107
SENSE
IN
LOAD
+
is 500Ω. By setting R
V
+
6107 F03
–
D
SENSE
–IN
OUT
V
+
IN
6107 F02
can be increased
IN
R
SENSE
OUT
OUT
V
OUT
= 1mA, then
IN
(Figure 3).
such that
This approach can be helpful in cases where occasional
bursts of high currents can be ignored.
Care should be taken when designing the board layout for
R
connect resistances will increase the effective R
causing a gain error.
Selection of External Output Resistor, R
The output resistor, R
rent is converted to voltage. V
In choosing an output resistor, the maximum output volt-
age must fi rst be considered. If the following circuit is a
buffer or ADC with limited input range, then R
chosen so that I
maximum input range of this circuit.
In addition, the output impedance is determined by R
the circuit to be driven has high enough input impedance,
then almost any useful output impedance will be accept-
able. However, if the driven circuit has relatively low input
impedance, or draws spikes of current such as an ADC
might do, then a lower R
to preserve the accuracy of the output. As an example, if
the input impedance of the driven circuit is 100 times R
then the accuracy of V
Error Sources
The current sense system uses an amplifi er and resistors
to apply gain and level shift the result. The output is then
dependent on the characteristics of the amplifi er, such as
gain and input offset, as well as resistor matching.
Ideally, the circuit output is:
In this case, the only error is due to resistor mismatch,
which provides an error in gain only. However, offset volt-
age and bias current cause additional errors.
IN
V
V
, especially for small R
OUT
OUT
=
=
=
I I
I
V
OUT
OUT
SENSE
•
•
OUT(MAX)
R
R
R
OUT
•
OUT
OUT
R
OUT
R
OUT
OUT
IN
•
+
OUT
•
100
101
, determines how the output cur-
R
R
• R
;
will be reduced by 1% since:
IN DRIVEN
IN DRIVEN
IN
value may be required in order
V
(
(
OUT
SENSE
=
values. All trace and inter-
OUT
0 99
.
is less than the allowed
is simply I
)
)
=
•
R
I
OUT
SENSE
OUT
•
R
OUT
OUT
OUT
•
I
SENSE
IN
must be
• R
value,
OUT
OUT
OUT
6107fb
. If
.
,