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TMP05/TMP06

Rev. 0 | Page 13 of 28

THEORY OF OPERATION

CIRCUIT INFORMATION

The TMP05/TMP06 are monolithic temperature sensors that

generate a modulated serial digital output that varies in direct

proportion with the temperature of the device. An on-board

sensor generates a voltage precisely proportional to absolute

temperature, which is compared to an internal voltage reference

and is input to a precision digital modulator. The ratiometric

encoding format of the serial digital output is independent of

the clock drift errors common to most serial modulation

techniques such as voltage-to-frequency converters. Overall

accuracy for the A Grade is ±2°C from 0°C to +70°C, with

excellent transducer linearity. B Grade accuracy is ±1°C from

25°C to 70°C. The digital output of the TMP05 is CMOS/TTL

compatible, and is easily interfaced to the serial inputs of most

popular microprocessors. The open-drain output of the TMP06

is capable of sinking 5 mA.

The on-board temperature sensor has excellent accuracy and

linearity over the entire rated temperature range without

correction or calibration by the user.

The sensor output is digitized by a first-order Σ-∆ modulator,

also known as the charge balance type analog-to-digital

converter. This type of converter utilizes time-domain over-

sampling and a high accuracy comparator to deliver 12 bits of

effective accuracy in an extremely compact circuit.

CONVERTER DETAILS

The Σ-∆ modulator consists of an input sampler, a summing

network, an integrator, a comparator, and a 1-bit DAC. Similar

to the voltage-to-frequency converter, this architecture creates,

in effect, a negative feedback loop whose intent is to minimize

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, which 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-∆ MODULATOR

INTEGRATOR

COMPARATOR

1-BIT

DAC

DIGITAL

FILTER

CLOCK

GENERATOR

VOLTAGE REF

AND VPTAT

TMP05/TMP06

OUT

(SINGLE-BIT)

Figure 21. First-Order

Σ-∆ Modulator

The modulated output of the comparator is encoded using a

circuit technique that results in a serial digital signal with a

mark-space ratio format. This format is easily decoded by any

microprocessor into either °C or °F values, and is readily

transmitted or modulated over a single wire. More importantly,

this encoding method neatly avoids major error sources

common to other modulation techniques, because it is clock-

independent.

FUNCTIONAL DESCRIPTION

The output of the TMP05/TMP06 is a square wave with a

typical period of 116 ms at 25°C (CONV/IN pin is left floating).

The high period, TH, is constant, while the low period, TL, varies

with measured temperature. The output format for the nominal

conversion rate is readily decoded by the user as follows:

Temperature (°C) = 421 − (751 × (TH/TL))

(1)

Figure 22. TMP05/TMP06 Output Format

The time periods TH (high period) and TL (low period) are

values easily read by a microprocessor timer/counter port, with

the above calculations performed in software. Because both

periods are obtained consecutively using the same clock,

performing the division indicated in the previous formula

results in a ratiometric value that is independent of the exact

frequency or drift of either the originating clock of the TMP05/

TMP06 or the user’s counting clock.

OPERATING MODES

The user can program the TMP05/TMP06 to operate in three

different modes by configuring the FUNC pin on power-up as

either low, floating, or high.

Table 6. Operating Modes

FUNC Pin

Operating Mode

Low

One shot

Floating

Continuously converting

High

Daisy-chain

Continuously Converting Mode

In continuously converting mode, the TMP05/TMP06 continu-

ously output a square wave representing temperature. The

frequency at which this square wave is output is determined by

the state of the CONV/IN pin on power-up. Any change to the

state of the CONV/IN pin after power-up is not reflected in the

parts until the TMP05/TMP06 are powered down and back up.

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