Datasheet

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SBAS265G − OCTOBER 2002 − REVISED JANUARY 2008
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13
The second mode does not require a test temperature
calibration, but uses a two-measurement method to eliminate
the need for absolute temperature calibration and for
achieving 2°C accuracy. This mode requires a second
conversion with an address of A2 = 1, A1 = 1, and A0 = 1,
with a 91 times larger current. The voltage difference
between the first and second conversion using 91 times the
bias current is represented by Equation (1):
DV +
kT
q
@ In(N)
where:
N is the current ratio = 91.
k = Boltzmann’s constant = 1.3807 × 10
−23
J/K
(joules/kelvins).
q = the electron charge = 1.6022 × 10
–19
C (coulombs).
T = the temperature in kelvins (K).
This method can provide improved absolute temperature
measurement, but at a lower resolution of 1.6°C/LSB. The
resulting equation that solves for T is:
T +
q @ DV
k @ In(N)
where:
∆V = V
BE
(TEMP1) − V
BE
(TEMP0) (in mV)
∴
T = 2.573 ⋅ ∆V (in K)
or T = 2.573 ⋅ ∆V – 273 (in °C)
NOTE: The bias current for each diode temperature
measurement is only on for 3 clock cycles (during the
acquisition mode) and, therefore, does not add any
noticeable increase in power, especially if the temperature
measurement only occurs occasionally.
BATTERY MEASUREMENT
An added feature of the TSC2046 is the ability to monitor the
battery voltage on the other side of the voltage regulator
(DC/DC converter), as shown in Figure 7. The battery
voltage can vary from 0V to 6V, while maintaining the voltage
to the TSC2046 at 2.7V, 3.3V, etc. The input voltage (V
BAT
)
is divided down by 4 so that a 5.5V battery voltage is
represented as 1.375V to the ADC. This simplifies the
multiplexer and control logic. In order to minimize the power
consumption, the divider is only on during the sampling
period when A2 = 0, A1 = 1, and A0 = 0 (see Table 1 for the
relationship between the control bits and configuration of the
TSC2046).
+V
CC
V
BAT
7.5k
Ω
2.5k
Ω
DC/DC
Converter
Battery
0.5V
to
5.5V
0.125V to 1.375V
2.7V
+
ADC
Figure 7. Battery Measurement Functional Block
Diagram
(1)
(2)