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 7/21

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

Fax:

+49 (0)6131/91 073-30

Internet: http://www.analogmicro.de

Email: info@analogmicro.de

BOUNDARY CONDITIONS

Parameter

Symbol

Conditions

Min.

Typ.

Max.

Unit

Sense Resistor

R0

IOUTFS = 20mA

16

27

38

Ω

R0

c = 20mA/IOUTFS

c

⋅ 16

c

⋅ 27

c

⋅ 38

Ω

Stabilization Resistor

R5

IOUTFS = 20mA

35

40

45

Ω

R5

c = 20mA/IOUTFS

c

⋅ 35

c

⋅ 40

c

⋅ 45

Ω

Load Resistance

RL

Only for 3-wire operation

0

600

Ω

Sum Gain Resistors

R1 + R2

20

200

k

Ω

Sum Offset Resistors

R3 + R4

20

200

k

Ω

Sum IA Offset Resistor

R6 + R7

20

200

k

Ω

VREF Capacitance

C1

Min. value for Tamb 85°C

1.9

2.2

5.0

µF

Output Capacitance

C2

Only for 2-wire operation

90

100

250

nF

D1 Breakdown Voltage

VBR

35

50

V

T1 Forward Current Gain

βF

e.g. BCX54/55/56

50

150

Table 2: Boundary conditions

NB: In 2-wire operation and with the connected resistors capacitance C2 acts as a low pass

filter with a time constant of τ = RL C2.

V

BG

13

IA

5

14

11

10

8

16

12

15

Voltage Reference

1

7

OP1

Ground

I

OUT

R

1

R

2

C

1

R

0

T

1

D

1

R

5

3

4

2

AM452

OP2

V

ZA

V

IN+

V

IN-

R

3

R

4

V

OP

G

SET

V

C VREF

V

SET

V

REF

V

S

V

CVSET

V

REF

R

6

R

7

G

SET

G

VI

V/I Converter

G

VI

9

SET Stage

ZERO Stage

GND

Figure 2: Block diagram of AM452 (3-wire version).

Figure 2 shows AM452 as

a 3-wire application where

output current IOUT min >

0mA is set using the

instrumentation amplifier

(with a negative offset at

the IA input) and the SET

stage. The gain on the

maximum output current

is adjusted using OP1.