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ADT6501 Datasheet(PDF) 8 Page - Analog Devices

Part No. ADT6501
Description  Low Cost, 2.7 V to 5.5 V, Micropower Temperature Switches in SOT-23
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Manufacturer  AD [Analog Devices]
Direct Link  http://www.analog.com
Logo AD - Analog Devices

ADT6501 Datasheet(HTML) 8 Page - Analog Devices

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Preliminary Technical Data
ADT6501/ADT6502/ADT6503/ADT6504
Rev. PrA | Page 8 of 16
THEORY OF OPERATION
CIRCUIT INFORMATION
The ADT6501/ADT6502/ADT6503/ADT6504 are 12-bit digital
temperature sensors with the 12th bit acting as the sign bit. An on-
board temperature sensor generates a voltage precisely
proportional to absolute temperature that is compared to an
internal voltage reference and input to a precision digital
modulator. The 12-bit output from the modulator is input into a
digital comparator where it is compared with a factory set trip
level. The output trip pin is activated if the temperature measured
is greater than the factory set trip level. Overall accuracy for the
ADT650x family is ±6°C from −45°C to +115°C.
The on-board temperature sensor has excellent accuracy and
linearity over the entire rated temperature range without needing
correction or calibration by the user. The ADT6501/ADT6503
have active-low, open-drain output structures that can only sink
current. The ADT6502/ADT6504 have active-high, push-pull
output structures that can sink and source current. On power-up,
the output cannot become active until the first conversion is
completed. This typically takes 30 ms.
The sensor output is digitized by a first-order, ∑-Δ modulator,
also known as the charge balance type analog-to-digital
converter (ADC). This type of converter utilizes time-domain
oversampling and a high accuracy comparator to deliver 12 bits
of effective accuracy in an extremely compact circuit.
CONVERTER DETAILS
The ∑-Δ modulator consists of an input sampler, a summing
network, an integrator, a comparator, and a 1-bit digital-to-
analog converter (DAC). Similar to the voltage-to-frequency
converter, this architecture creates a negative feedback loop and
minimizes the integrator output by changing the duty cycle of
the comparator output in response to input voltage changes.
The comparator samples the output of the integrator at a much
higher rate than the input sampling frequency; this is called
oversampling. Oversampling spreads the quantization noise
over a much wider band than that of the input signal, improving
overall noise performance and increasing accuracy.
Σ-Δ MODULATOR
INTEGRATOR
COMPARATOR
1-BIT
DAC
LPF DIGITAL
FILTER
CLOCK
GENERATOR
VOLTAGE REF
AND VPTAT
TEMPERATURE
VALUE
REGISTER
1-BIT
12-BIT
+
Figure 14. First-Order
∑-Δ Modulator
The modulated output of the comparator is encoded using a
circuit technique that results in SMBus/I2C temperature data.
FACTORY PROGRAMMED THRESHOLD RANGE
The ADT6501/ADT6502/ADT6503/ADT6504 are available
with factory set threshold levels ranging from −45°C to +115°C
in 10°C. The ADT6501/ADT6503 outputs are intended to
interface to reset inputs of microprocessors. The
ADT6502/ADT6504 are intended for driving circuits of
applications, such as fan control circuits. Table 4 lists the
available temperature threshold ranges.
Table 4. Factory Set Temperature Threshold Ranges
Device
Threshold (TTH) Range
ADT6501
+35°C < TTH < +115°C
ADT6502
+35°C < TTH < +115°C
ADT6503
−45°C < TTH < +15°C
ADT6504
−45°C < TTH < +15°C
HYSTERESIS INPUT
The HYST pin is used to select a temperature hysteresis of 2°C
or 10°C. If the HYST pin is connected to VCC then a hysteresis
of 10°C is selected or if the HYST pin is connected to GND then
a hysteresis of 2°C is selected. The HYST pin should not be left
floating. Hysteresis prevents oscillation on the output pin when
the temperature is approaching the trip point, after it activates.
For example, if the temperature trip is 45°C and the hysteresis
selected is 10°C, the temperature would have to go as low as
35°C before the output deactivates.


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