ak4181a AKM Semiconductor, Inc., ak4181a Datasheet - Page 10

• Manufacturer Part Number: ak4181a
• Description: Touch Screen Controller
• 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 AK4181A 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 = 2.63×10
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
MS0313-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(82I) – V(I)
D
0
D
: reverse saturation current
/V
D
: voltage across diode
/ln(i
T
3
) ( V
× ∆Vbe – 273
D
(NI)
/I
0
T
)
- v
= kT/q)
(I)
-23
)/V
-19
(Boltzmann’s constant)
(electron charge)
T
} N = (i
<2>
D2
/ i
I
D1
<1>
) = 82 (ratio of the current)
TEMP0
Figure 5 Temperature Measurement
10
Temp.
Sensor
TEMP1
82I
[AK4181A]
2004/06