REV. A

AD22151

–5–

to self-heating as a function of power dissipation. Second, pack-

age stress effect alters the specific operating parameters of the

gain compensation, particularly the specific crossover tempera-

ture of TC1, TC3 (

±10∞C).

CONFIGURATION AND COMPONENT SELECTION

There are three areas of sensor operation that require external

component selection: temperature compensation (R1), signal

gain (R2 and R3), and offset (R4).

Temperature

If the internal gain compensation is used, an external resistor is

required to complete the gain TC circuit at Pin 3. A number of

factors contribute to the value of this resistor:

a. The intrinsic Hall cell sensitivity TC

950 ppm.

b. Package induced stress variation in a.

±150 ppm.

c. Specific field TC

–200 ppm (Alnico), –2000 ppm

(Ferrite), 0 ppm (electromagnet), and so on.

d. R1, TC.

The final value of target compensation also dictates the use of

either Pin 1 or Pin 2. Pin 1 is provided to allow for large nega-

tive field TC devices such as ferrite magnets; thus, R1 would be

connected to Pins 1 and 3.

Pin 2 uses an internal resistive TC to optimize smaller field

coefficients such as Alnico down to 0 ppm coefficients when

only the sensor gain TC itself is dominant. Because the TC of

R1 itself will also affect the compensation, a low TC resistor

(

±50 ppm) is recommended.

Figures 10 and 11 indicate R1 resistor values and their associ-

ated effectiveness for Pins 1 and 2, respectively. Note that the

indicated drift response in both cases incorporates the intrinsic

For example, the AD22151 sensor is to be used in conjunction

with an Alnico material permanent magnet. The TC of such mag-

nets is

–200 ppm (see Figures 5 and 6). Figure 11 indicates

that a compensating drift of 200 ppm at Pin 3 requires a nomi-

nal value of R1 = 18 k

W (assuming negligible drift of R1 itself).

R1 – k

3500

3000

1000

2500

1500

2000

05

10

20

25

500

0

15

30

Figure 10. Drift Compensation (Pins 1 and 3) vs.

Typical Resistor Value R1

R1 – k

800

600

–200

400

0

200

05

10

20

25

–400

–600

15

30

35

40

45

50

Figure 11. Drift Compensation (Pins 2 and 3) vs.

Typical Resistor Value R1

GAIN AND OFFSET

The operation of the AD22151 can be bipolar (i.e., 0 Gauss =

Zero Gauss point at some other potential (i.e., 0.25 V).

The gain of the sensor can be set by the appropriate R2 and R3

resistor values (see Figure 1) such that:

Gin

R

R

mV G

a

=+

¥

1

3

2

04

./

(1)

However, if an offset is required to position the quiescent out-

put at some other voltage, the gain relationship is modified to:

Gin

R

RR

mV G

a

1

3

24

04

./

(2)

The offset that R4 introduces is:

Offset

R

RR

VV

CC

OUT

=+

+

1

3

24

–

(3)

the sensor is approximately 0.4 mV/Gauss. If a sensitivity of

6 mV/Gauss is required with a quiescent output voltage of 1 V,

the calculations below apply (see Figure 2).

A value would be selected for R3 that complied with the various

considerations of current and power dissipation, trim ranges (if

applicable), and so on. For the purpose of example, assume a

value of 85 k

W.

To achieve a quiescent offset of 1 V requires a value for R4 as:

V

V

CC

CC

2

1

0 375

Ê

ËÁ

ˆ

¯˜

=

–

.

(4)

Thus:

R

k

kk

4

85

0 375

85

141 666

= ÊËÁ

ˆ

¯˜

=

W

WW

.

–.

(5)

The gain required would be 6/0.4 (mV/Gauss) = 15.