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ADT7516 Datasheet(PDF) 19 Page - Analog Devices

Part No. ADT7516
Description  SPI/I2C Compatible, Temperature Sensor, Four Channel ADC and Quad Voltage Output DAC
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Maker  AD [Analog Devices]
Homepage  http://www.analog.com
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ADT7516 Datasheet(HTML) 19 Page - Analog Devices

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ADT7516/ADT7517/ADT7519
Rev. A | Page 19 of 44
THEORY OF OPERATION
Directly after the power-up calibration routine, the ADT7516/
ADT7517/ADT7519 go into idle mode. In this mode, the
devices are not performing any measurements and are fully
powered up. All four DAC outputs are at 0 V.
To begin monitoring, write to the Control Configuration 1
register (Address 18h) and set Bit C0 = 1. The ADT7516/
ADT7517/ADT7519 go into their power-up default measure-
ment mode, which is round robin. The devices proceed to take
measurements on the VDD channel, internal temperature sensor
channel, external temperature sensor channel, or AIN1 and
AIN2, AIN3, and finally AIN4. Once they finish taking
measurements on the AIN4 channel, the devices immediately
loop back to start taking measurements on the VDD channel and
repeats the same cycle as before. This loop continues until the
monitoring is stopped by resetting Bit C0 of the Control
Configuration 1 register to 0.
It is also possible to continue monitoring as well as switching to
single-channel mode by writing to the Control Configuration 2
register (Address 19h) and setting Bit C4 = 1. Further explana-
tion of the single-channel and round robin measurement modes
is given in later sections. All measurement channels have
averaging enabled on them on power-up. Averaging forces the
devices to take an average of 16 readings before giving a final
measured result. To disable averaging and consequently
decrease the conversion time by a factor of 16, set Bit C5 = 1 in
the Control Configuration 2 register.
There are four single-ended analog input channels on the
ADT7516/ADT7517/ADT7519: AIN1 to AIN4. AIN1 and AIN2
are multiplexed with the external temperature sensor terminals
D+ and D–. Bits C1 and C2 of the Control Configuration 1
register (Address 18h) are used to select between AIN1/AIN2
and the external temperature sensor. The input range on the
analog input channels is dependent on whether the ADC
reference used is the internal VREF or VDD. To meet linearity
specifications, it is recommended that the maximum VDD value
is 5 V. Bit C4 of the Control Configuration 3 register is used to
select between the internal reference or VDD as the analog inputs’
ADC reference.
Controlling the DAC outputs can be done by writing to the
DACs’ MSB and LSB registers (Addresses 10h to 17h). The
power-up default setting is to have a low going pulse on the
LDAC pin (Pin 9) controlling the updating of the DAC outputs
from the DAC registers. Alternatively, one can configure the
updating of the DAC outputs to be controlled by means other
than the LDAC pin by setting Bit C3 = 1 of the Control
Configuration 3 register (Address 1Ah). The DAC Configur-
ation register (Address 1Bh) and the LDAC Configuration
register (Address 1Ch) can now be used to control the DAC
updating. These two registers also control the output range of
the DACs and selecting between the internal or external refer-
ence. DAC A and DAC B outputs can be configured to give a
voltage output proportional to the temperature of the internal
and external temperature sensors, respectively.
The dual serial interface defaults to the I2C protocol on power-
up. To select and lock in the SPI protocol, follow the selection
process as described in the Serial Interface Selection section.
The I2C protocol cannot be locked in, while the SPI protocol
is automatically locked in on selection. The interface can be
switched back to be I2C on selection when the device is powered
off and on. When using I2C, the CS pin should be tied to either
VDD or GND.
There are a number of different operating modes on the
ADT7516/ADT7517/ADT7519 devices and all of them can be
controlled by the configuration registers. These features consist
of enabling and disabling interrupts, polarity of the INT/INT
pin, enabling and disabling the averaging on the measurement
channels SMBus timeout and software reset.
POWER-UP CALIBRATION
It is recommended that no communication to the part be ini-
tiated until approximately 5 ms after VDD has settled to within
10% of its final value. It is generally accepted that most systems
take a maximum of 50 ms to power up. Power-up time is
directly related to the amount of decoupling on the voltage
supply line.
During the 5 ms after VDD has settled, the part is performing a
calibration routine. Any communication to the device during
calibration will interrupt this routine, and could cause erro-
neous temperature measurements. If it is not possible to have
VDD at its nominal value by the time 50 ms has elapsed or if
communication to the device has started prior to VDD settling, it
is recommended that a measurement be taken on the VDD chan-
nel before a temperature measurement is taken. The VDD
measurement is used to calibrate out any temperature measure-
ment error due to different supply voltage values.
CONVERSION SPEED
The internal oscillator circuit used by the ADC has the capa-
bility to output two different clock frequencies. This means that
the ADC is capable of running at two different speeds when
doing a conversion on a measurement channel. Thus, the time
taken to perform a conversion on a channel can be reduced by
setting Bit C0 of the Control Configuration 3 register (Address
1Ah). This increases the ADC clock speed from 1.4 kHz to
22 kHz. At the higher clock speed, the analog filters on the D+
and D– input pins (external temperature sensor) are switched
off. This is why the power-up default setting is to have the ADC
working at the slow speed. The typical times for fast and slow
ADC speeds are given in the specifications.


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