2
AN1480.2
July 18, 2011
Multiplying the ISL28133 input offset voltage by the amplifier
gain allows the input offset error to be expressed as a percent of
full scale output voltage.
Using the Evaluation Board
The evaluation board has separate connections for the amplifier
power supply, an output zero reference (V
REF
),and the current
sense terminals. The correct inter-connection between the I-
SENSE terminals and the V
REF
terminals are needed to
implement the different types of current sense configurations.
The I-SENSE + and I-SENSE - connections to the measured circuit
determine the polarity of the amplifier output voltage.
Establishing a current flow from the I-SENSE + to I-SENSE -
causes the output voltage to increase in proportion to the input
current. Reversing the I-SENSE current flow reverses the output
polarity.
The voltage applied to the V
REF
pin defines the amplifier output
zero current level, and must be between 0V and +5V. For
bi-directional current sensing, a reference midway between the
ground and the supply voltage will maximize the output span. For
example, a V
REF
= +2.5V would be the best choice for +5V power
supply. The jumper selectable internal voltage divider is provided
for this internal reference. The +2.5V will establish an output
current scale setting 0A = +2.5V, but the accuracy is determined
by the voltage divider accuracy (0.1% resistors on the evaluation
board). Connecting the jumper to the external reference position
enables an external reference source to be used.
Figure 2 shows the connections to implement a high side,
bi-directional current sense with the ability to monitor the
charging current. Figure 3 shows the connection for
uni-directional ground referenced current sensing. The ISL28133
maintains precision performance from rail-to-rail making
precision ground-side sensing possible.
V
OS Total
(
)
3e 10
R14 R9
×
R14 R9
+
-------------------------
×
–
⎝
⎠
⎛
⎞
8
μ
V
+
=
(EQ. 4)
V
OS Total
(
)
3e 10 4950
×
–
(
)
=
8
μ
V
9.5
μ
V
=
+
(EQ. 5)
% F.S. Error
V
OS
×
R14
R9
-----------
⎝
⎠
⎛
⎞
2.5V
±
-------------------------------------
=
0.038%
±
=
(EQ. 6)
FIGURE 1. ISL28133 DIFFERENTIAL CURRENT SENSE AMPLIFIER
I-SENSE+
R1
DNP
R2
DNP
R3
0.1
R4
DNP
R5
DNP
R7
10
Ω
R6
10
Ω
D2
C9
1nF
C7
1nF
C8
10nF
R9
4.99k
R8
4.99k
D3B
D4B
R10A, B
1M
R12A, B
1M
JUMPER
EXT
REFERENCE
V
S
/2
REFERENCE
D3A
D4A
C20
OPEN
R11
499k
R14
499k
3
4
5
2
1
ISL28133
+
-
V+
V-
C4
1nF
R13
0
C2
4.7µF
C10
OPEN
D1
5.6V
GND
R15
100
I
SENSE
OUT
V
REF
V
S
1.65V TO +5.5V
I-SENSE-
Application Note 1480
