ADT6401/ADT6402

Rev. 0 | Page 9 of 12

THEORY OF OPERATION

CIRCUIT INFORMATION

The ADT6401/ADT6402 are 11-bit digital temperature sensors

sensor generates a voltage precisely proportional to absolute

temperature, which 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 pin-selectable trip level. The output trip pin

is activated if the temperature measured is greater than, or less

than, the pin-selectable trip level. Overall accuracy for the

ADT6401/ ADT6402 is ±6°C (maximum) 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 ADT6401 has active

low, open-drain output structures that can sink current. The

ADT6402 has active high, push-pull output structures that can

sink and source current. On power-up, the output becomes

active when the first conversion is completed, which 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 11 bits of effective

accuracy in an extremely compact circuit.

CONVERTER DETAILS

The Σ-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.

PIN-SELECTABLE TRIP POINT AND HYSTERESIS

The temperature trip point and hysteresis values for the

ADT6401/ADT6402 are selected using Pin S0, Pin S1, and

or left floating. The ADT6401/ADT6402 decode the inputs on

S0, S1, and S2 to determine the temperature trip point and

hysteresis value, as outlined in Table 4.

The ADT6401 overtemperature/undertemperature output is

intended to interface to reset inputs of microprocessors. The

ADT6402 is intended for driving circuits of applications, such

as fan control circuits.

Table 4. Selecting Trip Points and Hysteresis1

S2

S1

S0

Temperature

Trip Point

Hysteresis

0

0

0

+45°C

2°C

0

0

1

+55°C

2°C

0

0

Float

+65°C

2°C

0

1

0

+75°C

2°C

0

1

1

+85°C

2°C

0

0

Float

+95°C

2°C

0

Float

0

+105°C

2°C

0

Float

1

+115°C

2°C

1

Float

Float

+55°C

10°C

1

0

0

+65°C

10°C

1

0

1

+75°C

10°C

1

0

Float

+85°C

10°C

1

1

0

+95°C

10°C

1

1

1

+105°C

10°C

1

1

Float

+115°C

10°C

1

Float

0

+5°C

2°C

1

Float

1

−5°C

2°C

1

Float

Float

−15°C

2°C

Float

0

0

−25°C

2°C

Float

0

1

−35°C

2°C

Float

0

Float

−45°C

2°C

Float

1

0

+5°C

10°C

Float

1

1

−5°C

10°C

Float

1

Float

−15°C

10°C

Float

Float

0

−25°C

10°C

Float

Float

1

−35°C

10°C

Float

Float

Float

−45°C

10°C