AMC7812B datasheet(38/92 Pages) TAOS

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2N3904

D+

D-

2N3906

D+

D-

(b) PNP

(a) NPN

AMC7812B

SBAS625A – SEPTEMBER 2013 – REVISED SEPTEMBER 2013

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Filtering

Figure 88(a) and Figure 88(b) show the connection of recommended NPN or PNP transistors, respectively.

Remote junction temperature sensors are usually implemented in a noisy environment. Noise is most often

created by fast digital signals, and can corrupt measurements. The AMC7812B has a built-in 65-kHz filter on the

D+ and D– inputs to minimize the effects of noise. However, a bypass capacitor placed differentially across the

inputs of the remote temperature sensor can make the application more robust against unwanted coupled

signals. If filtering is required, the capacitance between D+ and D– should be limited to 330 pF or less for

optimum measurement performance. This capacitance includes any cable capacitance between the remote

temperature sensor and the device.

Figure 88. Remote Temperature Sensor Using Transistor

Series Resistance Cancellation

Parasitic resistance (in series with the remote diode) to the D+ and D– inputs of the device is caused by a variety

of factors, including printed circuit board (PCB) trace resistance and trace length. This series resistance appears

as a temperature offset in the remote sensor temperature measurement, and causes more than 0.45°C error per

ohm. The device implements a technology to automatically cancel out the effect of this series resistance, thus

providing a more accurate result without requiring user characterization of this resistance. With this technology,

the device is able to reduce the effects of series resistance to typically less than 0.0075°C per ohm. The

resistance cancellation is disabled when the RC bit in the temperature configuration register is cleared ('0').

Reading Temperature Data

Temperature is always read as 12-bit data. When the conversion finishes, the temperature is sent to the

corresponding temperature-data register. However, if a data transfer is in progress between the temperature-data

Conversion Time

The conversion time depends on the type of sensor and configuration, as shown in Table 4.

Table 4. Conversion Times

MONITORING

PROGRAMMABLE

TEMPERATURE SENSOR

CYCLE TIME (ms)

DELAY RANGE (s)

Local sensor is active, remote sensors are disabled or in power-down

0.48 to 3.84

One remote sensor is active and RC = 0, local sensor and one remote sensor are disabled

1.40 to 11.2

or in power-down

One remote sensor is active and RC = 1, local sensor and one remote sensor are disabled

2.97 to 23.8

or in power-down

One remote sensor and local sensor are active and RC = 0, one remote sensor is disabled

1.89 to 15.1

or in power-down

One remote sensor and local sensor are active and RC = 1, one remote sensor is disabled

108

3.45 to 27.65

or in power-down

Two remote sensors are active and RC = 0, local sensor is disabled or in power-down

2.81 to 22.5

Two remote sensors are active and RC = 1, local sensor is disabled or in power-down

186

5.95 to 47.6

All sensors are active and RC is '0'

103

3.92 to 26.38

All sensors are active and RC is '1'

201

6.43 to 51.45

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