AK4185 AKM [Asahi Kasei Microsystems], AK4185 Datasheet - Page 11

• Manufacturer Part Number: AK4185
• Manufacturer: AKM [Asahi Kasei Microsystems]

■
Equation <1> describes the forward characteristics of the diode.
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.
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>
The second method needs only one conversion as the following equation, but requires knowing the junction voltage at the
specific temperature.
MS0954-E-00
Temperature Measurement
i
T
D
⎛
⎜ ⎜
⎝
T
Δ
T
=
i
i
[
V
[
=
°
°
D1
D0
C
C
⎛
⎜ ⎜
⎝
be
I
]
]
0
⎞
⎟ ⎟
⎠
k
q
=
=
=
⋅
I
q: 1.602189×10
k: 1.38054×10
V
T: absolute temperature K
=
⎞
⎟ ⎟
⎠
0
e
Δ
. 2
: reverse saturation current
V
D
⋅
( )
⎛
⎜
⎜
⎜
⎜
⎝
: voltage across diode
V
V
V
In
648
( )
80
D
T
1
1
be
I
I
V
⎛
⎜
⎝
−
D
i
⋅
0 I
⎞
⎟
⎟
⎟
⎟
⎠
D
×
k
V
=
⎞
⎟
⎠
10
⋅
( )
80
In
80
(
3
q
V
-23
(
×
<
=
-19
80
T
(Boltzmann’s constant)
Δ
2
e
=
(electron charge)
)
V
⎧
⎪
⎨
⎪ ⎩
>
(
−
be
kT
q
V
273
I
( )
−
1
−
V
273
)
V
T
Figure 6. Temperature Measurement
(
80
)
)
<
⎫
⎪
⎬
⎪ ⎭
1
>
80
TEMP0
- 11 -
TEMP1
1
Temp.
Sensor
[AK4185]
2008/05