參數(shù)資料
型號(hào)： MAX1359BCTL-T
廠商： MAXIM INTEGRATED PRODUCTS INC
元件分類： 模擬信號(hào)調(diào)理
英文描述： SPECIALTY ANALOG CIRCUIT, QCC40
封裝： 6 X 6 MM, 0.80 MM HEIGHT, MO220, TQFN-40
文件頁(yè)數(shù)： 27/74頁(yè)
文件大?。?/td> 1214K
代理商： MAX1359BCTL-T
MAX1358/MAX1359/MAX1360
16-Bit Data-Acquisition Systems with ADC, DACs,
UPIOs, RTC, Voltage Monitors, and Temp Sensor
______________________________________________________________________________________
33
ambient is negligible. For the four and eight measure-
ment methods, the ratio of currents used in the diode
calculations is precisely known since the ADC mea-
sures the resulting voltage across the same sense
resistor. See Figure 15 for a block diagram of the tem-
perature sensor.
Two-Current Method
For the two-current method, currents I1 and I2 are
passed through a p-n junction. This requires two VBE
measurements. Temperature measurements can be
performed using I1 and I2.
where k is Boltzman’s constant. A four-measurement
procedure is adopted to improve accuracy by precisely
measuring the ratio of I1 and I2:
1) Current I1 is driven through the diode and the series
resistor R, and the voltage across the diode is mea-
sured as VBE1.
2) For the same current, the voltage across the diode
and R is measured as V1.
3) Repeat steps 1 and 2 with I2. I1 is typically 4A and
I2 is typically 60A (see Table 22).
Since only four integer numbers are accessible from the
ADC conversions at a certain voltage reference, the previ-
ous equation can be represented in the following manner:
where NV1, NV2, NVBE1, and NVBE2 are the measure-
ment results in integer format and VREF is the reference
voltage used in the ADC measurements.
Four-Current Method
The four-current method is used to account for the
diode series resistance and trace resistance. The four
currents are defined as follows; I1, I2, M1I1, and M2I2. If
the currents are selected so (M1 - 1)I1 = (M2 - 1)I2, the
effect of the series resistance is eliminated from the
temperature measurements. For the currents I1 = 4A
and I2 = 60A, the factors are selected as M1 = 16 and
M2 = 2. This results in the currents I3 = M1I1 = 64A
and I4 = M2I2 = 120A (typ). As in the case of the two-
current method, two measurements per current are
used to improve accuracy by precisely measuring the
values of the currents.
1) Current I1 is driven through the diode and the series
resistor R, and the voltage is measured across the
diode using the ADC as NVBE1.
2) For the same current, the voltage across the diode and
the series resistor is measured by the ADC as NV1.
3) Repeat steps 1 and 2 with I2, I3, and I4.
The measured temperature is defined as follows:
where VREF is the reference voltage used and:
External Temperature Sensor
For an external temperature sensor, either the two-cur-
rent or four-current method can be used. Connect an
external diode (such as 2N3904 or 2N3906) between
pins AIN1 and AGND (or AIN2 and AGND). Connect a
sense resistor R between AIN1 and AIN2. Maximize R
so the IR drop plus VBE of the p-n junction [(R x
60A)+VBE] is the smaller of the ADC reference voltage
or (AVDD - 400mV). The same procedure as the internal
temperature sensor can be used for the external tem-
perature sensor, by routing the currents to AIN1 (or
AIN2) (see Table 21).
For the two-current method, if the external diode’s
series resistance (RS) is known, then the temperature
measurement can be corrected as shown below:
Temperature-Sensor Calibration
To account for various error sources during the temper-
ature measurement, the internal temperature sensor is
calibrated at the factory. The calibrated temperature
equation is shown below:
TA = g x TMEAS + b
where g and b are the gain and offset calibration val-
ues, respectively. These calibration values are avail-
able for reading from the TEMP_CAL register.
Voltage Reference and Buffer
An internal 1.25V bandgap reference has a buffer with
a selectable 1.0V/V, 1.638V/V, or 2.0V/V gain, resulting
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