EL8170 Datasheet, PDF (13/14 Pages) Intersil Corporation – Micropower, Single Supply, Rail-to-Rail Input-Output Instrumentation Amplifiers

EL8170, EL8173
Gain Error and Accuracy
The EL8173 has a Gain Error, E_G, of 0.2% typical. The
EL8170 has an E_G of 0.3% typical. The gain error indicated
in the “Electrical Specifications” table on page 2 is the
inherent gain error of the EL8170 and EL8173 and does not
include the gain error contributed by the resistors. There is
an additional gain error due to the tolerance of the resistors
used. The resulting non-ideal transfer function effectively
becomes Equation 4:
V_OUT
=
⎛
⎜1
⎝
+
R^-R----_G^-F--_{⎠⎟⎞}
× [1 – (E_RG + E_RF + E_G)] × V_IN
(EQ. 4)
Where:
E_RG = Tolerance of R_G
E_RF= Tolerance of R_F
E_G = Gain Error of the EL8170 or EL8173
The term [1 - (E_RG + E_RF + E_G)] is the deviation from the
theoretical gain. Thus, (E_RG + E_RF + E_G) is the total gain
error. For example, if 1% resistors are used for the EL8170,
the total gain error would be as shown in Equation 5:
= ±(E_RG + E_RF + E_G(typical))
= ±(0.01 + 0.01 + 0.003)
= ±2.3%
(EQ. 5)
Power Dissipation
It is possible to exceed the +150°C maximum junction
temperatures under certain load and power-supply
conditions. It is therefore important to calculate the
maximum junction temperature (T_JMAX) for all applications
to determine if power supply voltages, load conditions, or
package type need to be modified to remain in the safe
operating area. These parameters are related in Equation 6:
T_JMAX = T_MAX + (θ_JAxPD_MAXTOTAL)
(EQ. 6)
where:
• P_DMAXTOTAL is the sum of the maximum power
dissipation of each amplifier in the package (PD_MAX)
• PD_MAX for each amplifier can be calculated as shown in
Equation 7:
PD_MAX
=
2*V_S × I_SMAX + (V_S
-
V_OUTMAX
)
×
V_{-----O----U----T----M-----A----X--}
R_{L (EQ.}
7)
where:
• T_MAX = Maximum ambient temperature
• θ_JA = Thermal resistance of the package
• PD_MAX = Maximum power dissipation of 1 amplifier
• V_S = Supply voltage (Magnitude of V₊ and V_-)
• I_MAX = Maximum supply current of 1 amplifier
• V_OUTMAX = Maximum output voltage swing of the
application
• R_L = Load resistance
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13
FN7490.6
August 31, 2009