ak4182 AKM Semiconductor, Inc., ak4182 Datasheet - Page 10

• Manufacturer Part Number: ak4182
• Description: Touch Screen Controllers
• Manufacturer: AKM Semiconductor, Inc.

ASAHI KASEI
Equation <1> describes the forward characteristics of the diode.
i
the ambient temperature can be predicted by knowing this voltage.
As the AK4182 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>
(i
T ° C = ( ∆ Vbe * q)/(k * ln N) – 273
T ° C = 2.573 × 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
MS0411-E-00
D
The diode characteristic is approximately shown as a diode junction voltage. That is theoretically proportional to the temperature;
D2
=I
Temperature Measurement
0
/ i
exp(v
D1
) = exp {(v
I
q : 1.602189×10
k : 1.38054×10
v
T: absolute temperature K
∆ Vbe = V (91 x I) – V (I)
D
0
D
: reverse saturation current
/V
D
: voltage across diode
/ln (i
T
) ( V
3
D
× ∆ Vbe – 273
(91 x I)
/I
T
0
)
= kT/q)
- v
-23
-19
(I)
(Boltzmann’s constant)
(electron charge)
)/V
T
<2>
} N = (i
iD1
= I
D2
TEMP0
<1>
/ i
Figure 5 Temperature Measurement
D1
) = 91 (ratio of the current)
Temp.
Sensor
10
TEMP1
iD2
= 91 x I
2005/08
[AK4182]