41594B datasheet(123/372 Pages) MICROCHIP

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Preliminary

DS41594B-page 123

PIC12LF1840T48A

15.0 TEMPERATURE INDICATOR

MODULE

This family of devices is equipped with a temperature

circuit designed to measure the operating temperature

of the silicon die. The circuit’s range of operating

temperature falls between -40°C and +85°C. The

output is a voltage that is proportional to the device

temperature. The output of the temperature indicator is

internally connected to the device ADC.

The circuit may be used as a temperature threshold

detector or a more accurate temperature indicator,

depending on the level of calibration performed. A one-

point calibration allows the circuit to indicate a

temperature closely surrounding that point. A two-point

calibration allows the circuit to sense the entire range

of temperature more accurately. Reference Application

Note AN1333, “Use and Calibration of the Internal

Temperature Indicator” (DS01333) for more details

regarding the calibration process.

15.1

Circuit Operation

Figure 15-1 shows a simplified block diagram of the

temperature circuit. The proportional voltage output is

achieved by measuring the forward voltage drop across

multiple silicon junctions.

Equation 15-1 describes the output characteristics of

the temperature indicator.

EQUATION 15-1:

VOUT RANGES

The temperature sense circuit is integrated with the

Fixed

Voltage

Reference

(FVR)

module.

See

Section 14.0 “Fixed Voltage Reference (FVR)” for

more information.

The circuit is enabled by setting the TSEN bit of the

FVRCON register. When disabled, the circuit draws no

current.

The circuit operates in either high or low range. The high

range, selected by setting the TSRNG bit of the

FVRCON register, provides a wider output voltage. This

provides more resolution over the temperature range,

but may be less consistent from part to part. This range

requires a higher bias voltage to operate and thus, a

higher VDD is needed.

The low range is selected by clearing the TSRNG bit of

the FVRCON register. The low range generates a lower

voltage drop and thus, a lower bias voltage is needed to

operate the circuit. The low range is provided for low

voltage operation.

FIGURE 15-1:

TEMPERATURE CIRCUIT

DIAGRAM

15.2

Minimum Operating VDD vs.

Minimum Sensing Temperature

When the temperature circuit is operated in low range,

the device may be operated at any operating voltage

that is within specifications.

When the temperature circuit is operated in high range,

the device operating voltage, VDD, must be high

enough to ensure that the temperature circuit is cor-

rectly biased.

Table 15-1 shows the recommended minimum VDD vs.

range setting.

TABLE 15-1:

RECOMMENDED VDD VS.

RANGE

15.3

Temperature Output

The output of the circuit is measured using the internal

Analog-to-Digital Converter. Channel 29 is reserved for

the temperature circuit output. Refer to Section 16.0

“Analog-to-Digital Converter (ADC) Module” for

detailed information.

15.3.1

ACQUISITION TIME

The user must wait at least 200

sec when the ADC

input multiplexer is switched to the temperature indica-

tor output. This wait time is also required between

sequential conversions of the temperature indicator

output voltage.

High Range: VOUT = VDD - 4VT

Low Range: VOUT = VDD - 2VT

Min. VDD, TSRNG = 1

Min. VDD, TSRNG = 0

3.6V

1.8V

TSEN

ADC

MUX

TSRNG

VDD

ADC

CHS bits

(ADCON0 register)

VOUT

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