AM452 – Voltage-to-current transducer IC

with a differential input

Analog Microelectronics GmbH

An der Fahrt 13, D – 55124 Mainz

February 2008 - Rev 1.2 - Page 18/21

Phone: +49 (0)6131/91 073-0

Fax:

+49 (0)6131/91 073-30

Internet: http://www.analogmicro.de

Email: info@analogmicro.de

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

R1 = 74.48kΩ

R2 = 10kΩ

R3 = 89.7kΩ

R4 = 5kΩ

R5 = 39Ω

RL = 0...900Ω

C1 = 2.2µF

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. ISET may only be 3.9mA. In this example and if VREF = 5V Equation (9) yields the

following:

4

3

4

0

2

R

R

R

R

V

I

REF

SET

+

⋅

=

= 3,9mA =

Ω

+

Ω

⋅

Ω

k

R

k

V

5

5

66

5

3

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.

V

BG

AM452

OP2

1

OP2 als Spannungsreferenz

verschaltet

2

V

CVREF

R

6

R

7

µP

Figure 9: OP2 as a voltage reference

V

BG

AM452

OP2

1

R

S

OP2 als Stromquelle

verschaltet

2

I

S

Figure 8: OP2 as a constant current source