[AK4185]

Equation <1> describes the forward characteristics of the diode.

( )

T

D

V

V

0

D

e

I

i

⋅

=

>

<

=

1

)

q

kT

V

(

T

q: 1.602189

k: 1.38054

T: absolute temperature K

The diode characteristic is approximately shown as a diode junction voltage. That is theoretically to the temperature; the

ambient temperature can be predicated by knowing this voltage.

Temp.

Sensor

TEMP0

TEMP1

I

80

1

Figure 6. Temperature Measurement

As the AK4185 has two different fixed current circuits and a diode (temperature sensor), the temperature can be measured

by using two different methods.

The first method needs two conversions, but can derive the temperature directly without knowing the voltage at a specific

temperature.

From equation <1>

()

()

⎪⎭

⎪

⎬

⎫

⎪⎩

⎪

⎨

⎧

−

=

=

⎟⎟

⎟

⎟

⎠

⎞

⎜⎜

⎜

⎜

⎝

⎛

=

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

T

V

)

80

(

V

1

V

D0

D1

e

80

80

I

1

I

i

i

273

)

80

(

In

k

q

V

T

be

]

C

[

−

⋅

Δ

=

⋅

°

() ( )

80

V

1

V

−

=

Δ

273

V

10

648

.

2

T

be

3

]

C

[

−

Δ

×

×

=

°

The second method needs only one conversion as the following equation, but requires knowing the junction voltage at the

specific temperature.

>

<

⎟

⎠

⎞

⎜

⎝

⎛

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

=

⋅

2

In

V

q

k

T

0

I

D

i

D

MS0954-E-05

2010/10

- 11 -