LTC6102CDD LINER [Linear Technology], LTC6102CDD Datasheet - Page 11

• Manufacturer Part Number: LTC6102CDD
• Description: Precision Zero Drift Current Sense Amplifi er
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
must be chosen such that the max output voltage does
not exceed the LTC6102 max output voltage rating. If the
following circuit is a buffer or ADC with limited input range,
then R
than the allowed 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 output impedance will be acceptable.
However, if the driven circuit has relatively low input imped-
ance, or draws spikes of current, such as an ADC might
do, then a lower R
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.
Output Error, E
Voltage, V
The DC offset voltage of the amplifi er adds directly to the
value of the sense voltage, V
(3μV typ) and may be ignored for reasonable values of R
For very high dynamic range, this offset can be calibrated
in the system due to its extremely low drift.
E
V
OUT(VOS)
OUT
V
OUT
OUT
= V
must be chosen so that I
OS
=I
=I
SENSE
= V
OUT
OUT
OUT
OS
•
• R
, Due to the Amplifi er DC Offset
•
OUT
R
• (R
R
R
R
OUT
OUT
OUT
OUT
IN
OUT
value may be required in order to
OUT
+ R
•
• R
;V
will be reduced by 1% since:
100
101
/R
SENSE
SENSE
IN(DRIVEN)
IN(DRIVEN)
IN
)
= 0.99 •I
. This error is very small
= R
OUT(MAX)
SENSE
OUT
• R
•I
• R
SENSE
OUT
OUT
is less
OUT
OUT
IN
. If
,
.
Output Error, E
I
The input bias current of the LTC6102 is vanishingly small.
However, for very high resolution, or at high temperatures
where I
signifi cant.
The bias current I
internal op amp. I
Since I
For instance if I
error is –10μV.
Note that in applications where R
a voltage offset in R
I
R
external resistor R
shown in Figure 4. Under both conditions:
Adding R
range of the circuit. For less sensitive designs, R
not necessary.
B
B
IN
(+) and I
(–) and E
E
E
E
, the bias current error can be similarly reduced if an
R
OUT(IBIAS)
OUT(IBIAS)
OUT(IBIAS)
SENSE
B
LOAD
B
(+) ≈ I
V
+
increases due to leakage, the current may be
IN
B
OUT(IBIAS)
+
(–)
R
R
Figure 4. Second Input R Minimizes
Error Due to Input Bias Current
as described will maximize the dynamic
IN
IN
LTC6102/LTC6102HV
= R
≈ –R
= ± R
B
OUT
–
+
(–) = I
BIAS
+IN
V
–
OUT
B
B
, Due to the Bias Currents,
IN
(+) fl ows into the positive input of the
R
(–) fl ows into the negative input.
OUT
OUT
IN
LTC6102
(+) = (R
is 1nA and R
SENSE
((I
+
≈ 0. In applications where R
BIAS
=
R
• I
+
B
• I
IN
(+) • (R
–
BIAS
, if R
OS
–
R
that cancels the error due to
SENSE
IN
; I
–
OS
SENSE
– R
SENSE
SENSE
= I
SENSE
OUT
B
<< R
(+) – I
–INS
V
OUT
–INF
V
/R
REG
≈ R
+
6102 F04
is 10k, the output
) is connected as
IN
IN
IN
) – I
R
, I
B
OUT
then,
(–)
B
B
(+) causes
V
(–))
OUT
0.1μF
11
SENSE
IN
6102fb
+
is
<