参数资料
型号: TSC2300IPAGRG4
厂商: TEXAS INSTRUMENTS INC
元件分类: 消费家电
英文描述: SPECIALTY CONSUMER CIRCUIT, PQFP64
封装: GREEN, PLASTIC, TQFP-64
文件页数: 42/83页
文件大小: 1268K
代理商: TSC2300IPAGRG4
www.ti.com
X+
MUX
A/D
Converter
Temperature Select
TEMP1
TEMP2
°K +
q DV
k n(N)
(6)
DV + V I82 –V I1 (inmV)
(7)
N
°K + 2.573DV°K mV
°C + 2.573 DV(mV) * 273°K
(8)
TSC2300
SLAS372 — NOVEMBER 2002
In some applications, such as estimating remaining battery life or setting RAM refresh rate, a measurement of ambient
temperature is required. The temperature measurement technique used in the TSC2300 relies on the characteristics of
a semiconductor junction operating at a fixed current level. The forward diode voltage (VBE) has a well-defined
characteristic versus temperature. The ambient temperature can be predicted in applications by knowing the 25
°C
value of the VBE voltage and then monitoring the delta of that voltage as the temperature changes.
The TSC2300 offers two modes of temperature measurement. The first mode requires calibration at a known
temperature, but only requires a single reading to predict the ambient temperature. A diode, as shown in Figure 61, is
used during this measurement cycle. The voltage across this diode is typically 600 mV at +25
°C while conducting a
20-A current. The absolute value of this diode voltage can vary several millivolts, but the temperature coefficient (TC)
of this voltage is very consistent at -2.1 mV/
°C. During the final test of the end product, the diode voltage would be
measured by the TSC2300’s ADC at a known room temperature, and the corresponding digital code stored in system
memory, for calibration purposes by the user. The result is an equivalent temperature measurement resolution of
0.3
°C/LSB. This measurement of what is referred to as Temperature 1 is illustrated in Figure 62.
Figure 61. Functional Block Diagram of Temperature Measurement Mode.
The second mode does not require a test temperature calibration, but uses a two-measurement (differential) method to
eliminate the need for absolute temperature calibration, and achieves a 2
°C/LSB accuracy. This mode requires a
second conversion with a current 82 times larger than the first 20uA current. The voltage difference between the first
(TEMP1) and second (Temp2) conversion, using 82 times the bias current, is represented by kT/q ln (N), where N is
the current ratio = 82, k = Boltzmann’s constant (1.38054 x 10-23 electron volts/degree Kelvin), q = the electron charge
(1.602189 x 10-19 C), and T = the temperature in degrees Kelvin. This method can provide much improved absolute
temperature measurement without calibration, with resolution of 2
°C/LSB. The resultant equation for solving for °K is:
where
Temperature 2 measurement is illustrated in Figure 63.
47
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