AM460 datasheet(9/18 Pages) AME

9 / 18 page

Industrial Converter and Protector IC

AM460

analog microelectronics

April 2003

9/18

In 2-wire operation the IC ground is "virtual" (floating), as with a constant load resistance the supply voltage of

the device VCC changes according to the current. As a rule, the following equation applies to 2-wire operation:

()

OUT

−

(4)

The reason for this is that in 2-wire operation the IC is connected in series to the actual load resistor RL. This is

illustrated in Figure 3.

In 3-wire operation VCC = VS, as the IC ground is connected to the ground of the system.

Setting the voltage gain using the voltage output

Using amplifier stages OP1 and OP3 for signal conditioning the overall gain can be set by selecting suitable ex-

ternal resistors R1 and R2. The transfer function for the output voltage is calculated by multiplying Equations 1

and 2 as follows:

GAIN

INP

OUT

⋅

(5)

with GGAIN = 1 + R1/R2 and GOP = 2.2.

Setting the output current range using the current output

When using amplification stage OP1 together with the V/I converter for signal conditioning the offset of the

output current should first be compensated for by suitable selection of resistors R3 and R4. To this end the OP1

input must be connected to ground (VINP = 0). With the short circuit at the input and by connecting up V/I con-

verter pin VSET as shown in Figure 2 the values of the output current according to Equation 3 are as follows:

()

REF

SET

INDAI

OUT

⋅

(6)

and thus for the ratio of the resistors R3/R4:

−

SET

REF

(7)

The output current area is set in conjunction with the selection of external resistors R1 and R2 (or fine adjustment

with R0 ). With Equations 1 and 3 the following is calculated for output current IOUT :

SET

GAIN

INP

OUT

with

GAIN

(8)

Selecting the supply voltage

System supply voltage VS needed to operate AM460 is dependent on the selected mode of operation.

• When using voltage output pin VOUT the minimum V

S needed for operation is determined by the maximum

output voltage VOUTmax required by the application. This is expressed as follows:

max +

≥

OUT

(9)

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