AMC1306E05_017 Datasheet, PDF (31/38 Pages) Texas Instruments – Small, High-Precision, Reinforced Isolated Delta-Sigma Modulators with High CMTI

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AMC1306E05, AMC1306E25, AMC1306M05, AMC1306M25
SBAS734A – MARCH 2017 – REVISED JULY 2017
This additional series resistor (R3') influences the gain error of the circuit. The effect can be calculated using
Equation 5 with R5 = R5' = 50 kΩ and R4 = R4' = 2.5 kΩ (for the AMC1306x05) or 12.5 kΩ (for the
AMC1306x25).
E _G(%)
§
¨©¹
R4
R4' R3
'
·
¸¹
u
100%
(5)
9.2.2.3 Application Curve
Figure 60 shows the dependency of the input bias current on the common-mode voltage at the input of the
AMC1306.
60
40
20
0
-20
-40
-60
AMC1306x25
AMC1306x05
-80
-0.5 0 0.5 1 1.5 2 2.5 3 3.5
V_CM (V)
D005
Figure 60. Input Bias Current vs Common-Mode Input Voltage
9.2.3 Do's and Don'ts
Do not leave the inputs of the AMC1306 unconnected (floating) when the device is powered up. If both modulator
inputs are left floating, the input bias current drives these inputs to the output common-mode of the analog front-
end of approximately 2 V. If that voltage is above the specified input common-mode range, the front gain
diminishes and the modulator outputs a bitstream resembling a zero input differential voltage.
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