SI8540-B-FSR Silicon Laboratories Inc, SI8540-B-FSR Datasheet - Page 8

• Manufacturer Part Number: SI8540-B-FSR
• Description: IC CURRENT SENSOR AMP 8SOIC
• Manufacturer: Silicon Laboratories Inc

Specifications of SI8540-B-FSR

• Amplifier Type: Current Sense
• Number Of Circuits: 1
• Current - Supply: 90µA
• Current - Output / Channel: 10mA
• Voltage - Supply, Single/dual (±): 5 V ~ 36 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Output Type: -
• -3db Bandwidth: -
• Slew Rate: -
• Gain Bandwidth Product: -
• Current - Input Bias: -
• Voltage - Input Offset: -

Si8540
3.1.1. Selecting R
Selecting R
dissipate less power while higher values maximize accuracy. In general, it is best to choose a relatively high value
for R
should be able to dissipate the heat from its power loss; otherwise, its value may drift or it may fail open, possibly
causing a large differential voltage across RG1 and RG2 that may damage the device. In most applications,
R
measured (low inductance metal film resistors are recommended). Also, note that the Si8540 requires at least
3.5 V of voltage headroom between the voltage at pin RG1 and pin OUT. This voltage headroom decreases as
R
equation:
R
Where:
V
V
I
3.1.2. Selecting RG1 and RG2
The values of resistors R
same value, and resulting current gain is equal to R
The minimum value of R
between the internal current sense amp input and the sense resistor (approximately 0.2 ). As the value of R
reduced, the input resistance becomes a larger portion of the total gain-setting resistance. This gain error can be
compensated by trimming R
following equation:
R
Where:
R
V
Note that for a given value of V
current at the OUT pin. This causes additional power to be dissipated in R
reduce efficiency. Note also that mismatches in the currents passing R
full scale error.
This error can be reduced by lowering the values of R
be reduced by increasing the value of R
3.1.3. Choosing R
R
determined by R
that it drives. This input impedance should be much larger than R
degraded. A good guideline for choosing the value of R
(V
8
LOAD
SENSE
SENSE
SENSEmax
SOURCE
OUTmax
Gmax
Gmax
SENSEmax
OUT
OUTfullscale
SENSE
is the current passing through R
must be chosen to generate the required full-scale output voltage at the full scale I
= (V
is the largest value for RG1 and RG2
should have low inductance to reduce the impact of any high-frequency components in the current being
increases. A good guideline for determining the maximum value for R
is the full-scale output voltage at the OUT pin
is the high-side voltage
SENSEmax
SENSE
in applications where the measured current is small. For higher current applications, the sense resistor
is the value of V
= (V
x R
SOURCE
G1
G
) / (I
involves making the best trade-off between power efficiency and accuracy. Low R
SENSE
OUT
, R
/ 1.5 mA)
G2
LOAD
, and R
– V
G
G1
is determined by the maximum current at the OUT pin (1.5 mA) and by the resistance
x R
SENSE
OUTmax
G
and R
or R
SENSE
SENSE
SENSE
OUT
at maximum I
G2
– 3.5 V)/I
)
. The upper limit of R
. A good guideline for determining the maximum value for R
SENSE
, a decrease of the R
determine the sense amp current-gain. These two resistors must have the
SENSE
LOAD
measured by the Si8540
.
LOAD
SENSE
Rev. 1.1
G1
OUT
, R
/ R
OUT
G2
is shown in the following equation:
G
G
resistor values causes a corresponding increase in
and/or lowering their tolerances. This error can also
is determined by the input impedance of the device
(where R
OUT
G1
; otherwise, measurement accuracy will be
G
and R
= R
OUT
G1
G2
rather than in the load, which can
= R
SENSE
(IOS) together with R
G2
).
is shown in the following
OUT
, which, in turn, is
G
is shown in the
SENSE
G
affect the
values
G
is