AM452 Datasheet, PDF (18/21 Pages) Analog Microelectronics – Voltage-to-current transducer IC with a differential input

AM452 – Voltage-to-current transducer IC
with a differential input
By solving the above system of equations and taking the given defaults for the external
components into account, the following values are computed:
R₀ = 33Ω
R₃ = 89.7kΩ
R_L = 0...900Ω
R₁ = 74.48kΩ
R₄ = 5kΩ
C₁ = 2.2µF
R₂ = 10kΩ
R₅ = 39Ω
C₂ = 100nF
In the 2-wire application particular attention must be paid to the overall power consumption
which may not exceed a value of 4mA across the entire temperature range.
Here it is also possible to correct the offset output current using the voltage divider at the SET stage
input.
Offset compensation using a voltage divider at SET stage
The offset value of the output current can be adjusted at the SET pin (pin 16) via voltage
divider R₃ and R₄ (see Figure 7). If, due to internal offsets and parasites, the output current is
too great by 0.1mA, for example (4.1mA and 20.1mA), the current must be reduced by this
amount, i.e. I_SET may only be 3.9mA. In this example and if V_REF = 5V Equation (9) yields the
following:
I _SET
= ^VREF ⋅ ^R4
2R₀ R₃ + R₄
= 3,9mA =
5V _⋠5kΩ
66Ω R₃ + 5kΩ
Once R₃ has been put through the equation R₃ = 92.125kΩ instead of 89.7kΩ. The voltage at
SET (pin 16) is then just 257.4mV instead of 264mV and the output current has been reduced
by 0.1mA.
OP2 als Stromquelle
verschaltet
I_S
1
AM452
2
OP2
R_S
V_BG
V_{C VR EF}
OP2 als Spannungsreferenz
verschaltet
1
µP
R₆
AM452
2
R₇
OP2
V_BG
Figure 8: OP2 as a constant current source Figure 9: OP2 as a voltage reference
Analog Microelectronics GmbH
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February 2008 - Rev 1.2 - Page 18/21