LTC6104 LINER [Linear Technology], LTC6104 Datasheet - Page 10

• Manufacturer Part Number: LTC6104
• Description: High Voltage, High Side, Bi-Directional Current Sense Amplifi er
• Manufacturer: LINER [Linear Technology]

LTC6104
APPLICATIONS INFORMATION
From the Electrical Characteristics of the LTC6104, the
output voltage range is 0.3V to 8V.
If the circuit that is driven by the output limits the maxi-
mum output voltage to ≈5V, to achieve maximum dynamic
range, V
1mA I
A standard 2.5V reference could be used in this example.
With I
range would equal 0.3V to 4.7V
V
V
that the output can swing above and below this point. It is
recommended that this is an accurate voltage reference.
Most voltage references will work in this application as
long as they are able to sink and source current. Make sure
that the device maintains the required voltage accuracy as
the current varies through its entire range.
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
voltage, bias current and fi nite gain in the amplifi er cause
additional errors.
10
REF
REF
R
V
V
V
REF
OUT
SENSE
OUT
Considerations
as shown in Figure 1, provides a positive offset so
OUT
OUT
=
OUT
–
=
.
0 3
= ±1mA and R
V
=
5
.
REF
V
R
should be 0.3V for –1mA I
2
+
S S ENSE
– .
mA
=
5 0 3
0 3
I
– .
OUT
2
V
I •
=
SENSE
•
=
R
2 35
OUT
.
OUT
2 65
.
k
= 2.2k, the output voltage
,
=
V
V
SENSE
•
OUT
R
R
OUT
IN
and 5V for
,
Output Error, E
Voltage, V
The DC offset voltage of the amplifi er adds directly to the
value of the sense voltage, V
error of the system and it limits the available dynamic
range. The section, Selection of External Current Sense
Resistor, provides details.
Output Error, E
I
The bias current I
internal op amp. I
Since I
For instance if I
error is 0.1mV.
Output Error, E
Gain, A
This error is inconsequential as the A
is very large.
Example:
If an I
Then, from the Electrical Characteristics of the
LTC6104:
B
–
E
E
E
R
G G ain
OUT(IBIAS)
OUT VOS
OUT IBIAS
SENSE
SENSE
B
(
(
OL
+
=
≈ I
, of the LTC6104 Amplifi er
R
OS
≈
R
OUT
range = (±1mA to ±1A) and
)
B
IN
)
–
V
I
=
≈ –R
SENSE MAX
=
SENSE MAX
OUT
OUT
= I
OUT
BIAS
V
R
=
OS
B
BIAS
OUT B
B
, Due to the Amplifi er DC Offset
, Due to the Bias Currents, I
, Due to the Finite DC Open-Loop
–
OUT
V
+
(
V
is 100nA and R
SENSE MAX
•
(
fl ows into the negative input.
fl ows into the positive input of the
OUT MAX
R
, if R
⎛
⎝ ⎜
R
• I
I
OUT
IN
)
(
+
)
BIAS
(
SENSE
=
•
R
SENSE
500
)
SENSE
R
)
1
IN
=
A
<< R
mV
. This is the dominant
500
OUT
–
3
IN
=
OL
V
I
mV
B
500 Ω
then:
is 1k, the output
–
I
of the LTC6104
SENSE
V
⎞
⎠ ⎟
OUT
=
m
6 6
B
=
+
and
3
1
A
V
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