ADT7483AARQZ-REEL Datasheet ADT7483AARQZ-R7, ADT7483AARQZ, ADT7483AARQZ-REEL | P7-P9

ADT7483A

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Theory of Operation

The ADT7483A is a local and 2 remote temperature

sensor and over/under temperature alarm. When the

ADT7483A is operating normally, the on-board ADC

operates in a freerunning mode. The analog input

multiplexer alternately selects either the on-chip

temperature sensor or one of the remote temperature sensors

to measure its local temperature. The ADC digitizes these

signals, and the results are stored in the local, Remote 1, and

Remote 2 temperature value registers.

The local and remote measurement results are compared

with the corresponding high, low, and THERM

temperature

limits stored in on-chip registers. Out-of-limit comparisons

generate flags that are stored in the status register. A result

that exceeds the high temperature limit, the low temperature

limit, or a remote diode open circuit causes the ALERT

output to assert low. Likewise, exceeding THERM

temperature limits causes the THERM output to assert low.

The ALERT

output can be reprogrammed as a second

THERM

output.

The limit registers can be programmed, and the device

controlled and configured, via the serial SMBus. The

contents of any register can also be read back via the SMBus.

Control and configuration functions consist of:

 Switching the Device between Normal Operation and

Standby Mode

 Selecting the Temperature Measurement Scale

 Masking or Enabling the ALERT Output

 Switching Pin 13 between ALERT and THERM2

 Selecting the Conversion Rate

Temperature Measurement Method

A simple method of measuring temperature is to exploit

the negative temperature coefficient of a diode, measuring

the baseemitter voltage (V

) of a transistor, operated at

constant current. Unfortunately, this technique requires

calibration to null the effect of the absolute value of V

which varies from device to device. The technique used in

the ADT7483A is to measure the change in V

when the

device is operated at two different currents.

Figure 14 shows the input signal conditioning used to

measure the output of a remote temperature sensor. This

figure shows the remote sensor as a substrate transistor, but

it could equally be a discrete transistor. If a discrete

transistor is used, the collector is not grounded and should

be linked to the base. To prevent ground noise interfering

with the measurement, the more negative terminal of the

sensor is not referenced to ground but is biased above ground

by an internal diode at the D− input. C1 can be optionally

added as a noise filter (recommended maximum value

1,000 pF).

To measure DV

, the operating current through the sensor

is switched among two related currents, I and N  I. The

currents through the temperature diode are switched

between I and N  I, giving DV

. The temperature is then

calculated using the DV

measurement.

The resulting DV

waveforms pass through a 65 kHz

low-pass filter to remove noise and then to a

chopper-stabilized amplifier. This amplifies and rectifies the

waveform to produce a dc voltage proportional to DV

The ADC digitizes this voltage and produces a temperature

measurement. To reduce the effects of noise, digital filtering

is performed by averaging the results of 16 measurement

cycles for low conversion rates. At rates of 16, 32, and

64 conversions/second, no digital averaging takes place.

Signal conditioning and measurement of the local

temperature sensor is performed in the same manner.

Figure 14. Input Signal Conditioning

LOW-PASS FILTER

= 65 kHz

REMOTE

SENSING

TRANSISTOR

BIAS

DIODE

D+

D−

BIAS

IN  I

OUT+

OUT−

To ADC

C1*

*CAPACITOR C1 IS OPTIONAL. IT IS ONLY NECESSARY IN NOISY ENVIRONMENTS. C1 = 1,000 pF MAX

Temperature Measurement Results

The results of the local and remote temperature

measurements are stored in the local and remote temperature

value registers and are compared with limits programmed

into the local and remote high and low limit registers.

The local temperature measurement is an 8-bit

measurement with 1C resolution. The remote temperature

measurements are 10-bit measurements, with eight MSBs

stored in one register and two LSBs stored in another

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Table 6. REGISTER ADDRESS FOR

THE TEMPERATURE VALUES

Temperature

Channel

MSBs

LSBs

Local 0x00 N/A

Remote 1 0x01 0x10 (2 MSBs)

Remote 2 0x30 0x33 (2 MSBs)

By setting Bit 3 of the Configuration 1 Register to 1, the

Remote 2 temperature values can be read from the following

Remote 2, MSBs = 0x01

Remote 2, LSBs = 0x10

The above is true only when Bit 3 of the Configuration 1

needs to be switched back to 0.

Only the two MSBs in the remote temperature low byte

are used. This gives the remote temperature measurement a

resolution of 0.25C. Table 7 shows the data format for the

remote temperature low byte.

Table 7. EXTENDED TEMPERATURE RESOLUTION

(REMOTE TEMPERATURE LOW BYTE)

Extended Resolution

Remote Temperature

Low Byte

0.00C 0 000 0000

0.25C 0 100 0000

0.50C 1 000 0000

0.75C 1 100 0000

When reading the full remote temperature value, both the

high and low byte, the two registers should be read LSB first

and then the MSB. This is because reading the LSB will

cause the MSB to be locked until it is read, guaranteeing that

the two values read are a result of the same temperature

measurement.

Temperature Measurement Range

The temperature measurement range for both local and

remote measurements is, by default, 0C to 127C.

However, the ADT7483A can be operated using an

extended temperature range from −64C to +191C. This

means, the ADT7483A can measure the full temperature

range of a remote thermal diode, from −55C to +150C. The

user can switch between these two temperature ranges by

setting or clearing Bit 2 in the Configuration 1 register. A

valid result is available in the next measurement cycle after

changing the temperature range.

In extended temperature mode, the upper and lower

temperatures that can be measured by the ADT7483A are

limited by the remote diode selection. The temperature

registers themselves can have values from −64C to +191C.

However, most temperature sensing diodes have a

maximum temperature range of −55C to +150C.

Note that although both local and remote temperature

measurements can be made while the part is in extended

temperature mode, the ADT7483A should not be exposed to

temperatures greater than those specified in theAbsolute

Maximum Ratings section. Further, the device is only

guaranteed to operate as specified at ambient temperatures

from −40C to +120C.

Temperature Data Format

The ADT7483A has two temperature data formats. When

the temperature measurement range is from 0C to 127C

(default), the temperature data format for both local and

remote temperature results is binary. When the

measurement range is in extended mode, an offset binary

data format is used for both local and remote results.

Temperature values in the offset binary data format are

offset by +64. Examples of temperatures in both data

formats are shown in Table 8.

Table 8. TEMPERATURE DATA FORMAT

(LOCAL AND REMOTE TEMPERATURE HIGH BYTE)

Temperature Binary

Offset Binary

(Note 1)

−55C 0 000 0000

(Note 2)

0 000 1001

0C 0 000 0000 0 100 0000

+1C 0 000 0001 0 100 0001

+10C 0 000 1010 0 100 1010

+25C 0 001 1001 0 101 1001

+50C 0 011 0010 0 111 0010

+75C 0 100 1011 1 000 1011

+100C 0 110 0100 1 010 0100

+125C 0 111 1101 1 011 1101

+127C 0 111 1111 1 011 1111

+150C 0 111 1111

(Note 3)

1 101 0110

1. Offset binary scale temperature values are offset by +64.

2. Binary scale temperature measurement returns 0 for all

temperatures < 0C.

3. Binary scale temperature measurement returns 127 for all

temperatures > 127C.

The user may switch between measurement ranges at any

time. Switching the range also switches the data format. The

next temperature result following the switching is reported

back to the register in the new format. However, the contents

of the limit registers do not change. It is up to the user to

ensure that when the data format changes, the limit registers

are reprogrammed as necessary (for more information, see

the Limit Registers section).

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Registers

The registers in the ADT7483A are eight bits wide. These

registers are used to store the results of remote and local

temperature measurements, and high and low temperature

limits, and to configure and control the device. A description

of these registers is provided in this section.

Address Pointer Register

The address pointer register does not have, nor does it

require, an address because the first byte of every write

operation is automatically written to this register. The data

in this first byte always contains the address of another

pointer register. It is to this other register address that the

second byte of a write operation is written, or to which a

subsequent read operation is performed.

The power-on default value of the address pointer register

is 0x00, so if a read operation is performed immediately after

power-on without first writing to the address pointer, the

value of the local temperature will be returned, since its

Temperature Value Registers

The ADT7483A has five registers to store the results of

local and remote temperature measurements. These

registers can only be written to by the ADC and can be read

by the user over the SMBus.

 The local temperature value register is at Address 0x00

 The Remote 1 temperature value high byte register is at

Address 0x01, with the Remote 1 low byte register at

Address 0x10

 The Remote 2 temperature value high byte register is at

Address 0x30, with the Remote 2 low byte register at

Address 0x33

 The Remote 2 temperature values can be read from

Address 0x01 for the high byte and Address 0x10 for

the low byte if Bit 3 of Configuration Register 1 is set

to 1

 To read the Remote 1 temperature values, Bit 3 of

Configuration Register 1 should be set to 0

 The power-on default for all five registers is 0x00

Table 9. CONFIGURATION 1 REGISTER (READ ADDRESS = 0x03, WRITE ADDRESS = 0x09)

Bit Mnemonic Function

7 Mask Setting this bit to 1 masks all ALERTs on the ALERT pin. Default = 0 = ALERT enabled. This applies only if

Pin 13 is configured as ALERT

, otherwise it has no effect.

6 Mon/STBY Setting this bit to 1 places the ADT7483A in standby mode, that is, suspends all temperature measurements

(ADC). The SMBus remains active and values can be written to, and read from, the registers. THERM

and

ALERT are also active in standby mode. Changes made to the limit registers in standby mode that affect the

THERM or ALERT outputs will cause these signals to be updated. Default = 0 = temperature monitoring

enabled.

5 AL/TH This bit selects the function of Pin 13. Default = 0 = ALERT. Setting this bit to 1 configures Pin 13 as the

THERM2

pin.

4 Reserved Reserved for future use.

3 Remote 1/

Remote 2

Setting this bit to 1 enables the user to read the Remote 2 values from the Remote 1 registers.

Default = 0 = Remote 1 temperature values and limits are read from these registers. This bit is not lockable.

2 Tem p

Range

Setting this bit to 1 enables the extended temperature measurement range (−50C to +150C).

Default = 0 = 0C to +127C.

1 Mask R1 Setting this bit to 1 masks ALERTs due to the Remote 1 temperature exceeding a programmed limit. Default = 0.

0 Mask R2 Setting this bit to 1 masks ALERTs due to the Remote 2 temperature exceeding a programmed limit. Default = 0.

Table 10. CONFIGURATION 2 REGISTER (ADDRESS = 0x24)

Bit Mnemonic Function

7 Lock Bit Setting this bit to 1 locks all lockable registers to their current values. This prevents settings being tampered

with until the device is powered down. Default = 0.

<6:0> Res Reserved for future use.

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P20

ADT7483AARQZ-REEL

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Manufacturer:

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SENSOR DIGITAL 0C-127C 16QSOP

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