REV.-A
2.9.3
Temperature
Detector
Circuit
When
the
power
switch
is off, battery
power
consumption
is minimized
by
optinizing the refresh
current according
to
ambient temperatures. The ambient temperature is sensed
by
a
thermistor
and fed
to
channel ANO
of
the A-O converter
which
detects the reference temperatures.
2.9.3.1
Circuit
Operations
Fig.
2-91
shows
the temperature
detector
circuit, including the sensing section. The reference
voltage
(VRF)
is adjusted
to
+2.0V
by VR2. Thus, the potential
at
point
(A) is given
as
follows,
be-
cause
of
the voltage divider
circuit
consisting
of
R76 and
Rlll
:
RlllVx
VRF
= -R-7-6-+-R-l-l-l-
Vx=
VRE(R76+Rlll)
Rlll
C
K
C
5
5 C
o L
o I
(ID)UPD
7001
~
2
ERT
COJR56JAA
Fig. 2-91
Temperature
Detector
Circuit
Vx
= 2 (34.8 x
10
3
+
100
x
10
3
)
100
x
10
3
=
2.696
(V)
Potential
at
point
(A)
010
MA
153
RS8
10K
GND
The potential (A) is also applied
to
the voltage divider circuit consisting
of
R86 and the
thermistor
TH 1,
which
is the temperature sensor. The potential at the
junction
of
R86 and TH 1, VTH,
which
is supplied
to
channel ANO, is therefore represented by the
following
expression:
VTH = R (TH1)·
2.696
R86 + R (TH1)
where the
thermister
resistance R
(TH
1) has the
following
temperature characteristic:
R
(TH
1) =
56
K exp 4.3 (
0.27~2
+ t -
0.2~82
) [t:
DC]
As
the temperature rises, the
thermister
resistance decreases, causing the voltage supply
to
the
ANO channel (VTH)
to
be lowered.
2-89
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