AK4180VT AKM [Asahi Kasei Microsystems], AK4180VT Datasheet - Page 10

• Manufacturer Part Number: AK4180VT
• Description: Touch Screen Controller
• Manufacturer: AKM [Asahi Kasei Microsystems]

[ASAHI KASEI]
Equation <1> describes the forward characteristics of the diode.
i
ambient temperature can be predicted by knowing this voltage.
As the AK4180 has two different fixed current circuits and a diode, 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>
(i
T C = ( Vbe * q)/(k * ln N) – 273
T C = 2.63 10
The second method needs only one conversion as the following equation, but requires knowing the junction voltage at the specific
temperature.
T = (k/q)* v
<MS0195-E-01>
D
The diode characteristics is approximately showed As a diode junction voltage is theoretically proportional to the temperature, the
D2
=I
Temperature Measurement
/ i
0
exp(v
D1
) = exp{(v
I
q : 1.602189 10
k : 1.38054 10
v
T: absolute temperature K
D
0
D
Vbe = V(NI) – V(I)
/V
: reverse saturation current
D
: voltage across diode
/ln(i
T
3
) ( V
D
(NI)
/I
Vbe – 273
0
T
)
- v
= kT/q)
(I)
-23
)/V
-19
(Boltzmann’s constant)
(electron charge)
T
} N = (i
<2>
D2
/ i
I
D1
<1>
Figure 4 Temperature Measurement
) = 82 (ratio of the current)
TEMP0
10
Temp.
Sensor
TEMP0
82I
2003/02
[AK4180]