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 12/21

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

Fax:

+49 (0)6131/91 073-30

Internet: http://www.analogmicro.de

Email: info@analogmicro.de

Selecting the supply voltage

"System" supply voltage VS needed to operate AM452 is dependent on the selected mode of

operation. The word "system" here refers to the IC plus its external circuitry.

When using current output pin 8 (IOUT) in conjunction with the external transistor VS is

dependent on the relevant load resistor RL used by the application. The following is then

applicable to the minimum system supply voltage VS:

min

max

CC

L

OUT

S

V

R

I

V

+

≥

(7)

Here, IOUTmax stands for the maximum output current and VCCmin for the minimum IC supply

voltage which is dependent on the selected reference voltage:

V

1

min

+

≥

REF

CC

V

V

(8)

For the 3-wire version the load resistance is limited to RLmax = 600Ω due to the condition:

VOUT max = 12V @ VCC ≥ 18V.

Equation 7 is also valid for the 2-wire version; here, however, the RLmax = 600Ω limitation

does not apply. Here, load resistor RLmax = 900Ω when VS = 24V.

Setting the offset and output current range for VIN = 0

When adjusting AM452 a preset should first be made. To this end the offset of the output

current is compensated for, in which the two IA inputs are first short-circuited (VIN = 0) and

then both set to a permitted potential (c.f. CMIR in ELECTRICAL SPECIFICATIONS). With

the short-circuit at the input the following is derived from Equations (3) and (4) when the

voltage divider from R3 and R4 is taken into account for reference voltage VREF (see Figure 2,

for example):

V

S [V]

R

L [Ω]

6

35

V

CCmin = 6V

R

Lmax

= 600Ω

I

OUTmax = 20mA

18

R

VV

I

L

SCCmin

OUTmax

≤

−

24

12

600

Operating range

0

300

0

Figure 5: Working range in conjunction with the load

resistor in 3-wire operation

In Equation (7) of Figure 5

the ohmic resistance of

power supply lines RR is not

taken into consideration. This

is entered as an additive

quantity (IOUT max RR) to the

calculation of VS in Equation

(7).