ADT7516 datasheet(25/44 Pages) AD

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ADT7516/ADT7517/ADT7519

Rev. B | Page 25 of 44

FUNCTIONAL DESCRIPTION—MEASUREMENT

Temperature Sensor

The ADT7516/ADT7517/ADT7519 contain an ADC with

special input signal conditioning to enable operation with

external and on-chip diode temperature sensors. When the

ADT7516/ADT7517/ADT7519 operate in single-channel mode,

the ADC continually processes the measurement taken on one

channel only. This channel is preselected by Bits[C0:C2] in the

Control Configuration 2 register (Address 0x19). When in

round robin mode, the analog input multiplexer sequentially

selects the VDD input channel, the on-chip temperature sensor

to measure its internal temperature, either the external tempera-

ture sensor or AIN1 and AIN2, AIN3, and then AIN4. These

signals are digitized by the ADC and the results are stored in

the various value registers.

The measured results from the temperature sensors are com-

pared with the internal and external THIGH and TLOW limits.

These temperature limits are stored in on-chip registers. If the

temperature limits are not masked, any out-of-limit comparisons

generate flags that are stored in the Interrupt Status 1 register.

One or more out-of-limit results cause the INT/INT output to

pull either high or low depending on the output polarity setting.

Theoretically, the temperature measuring circuit can measure

temperatures from −128°C to +127°C with a resolution of

0.25°C. However, temperatures outside TA are outside the

guaranteed operating temperature range of the device.

Temperature measurement from −128°C to +127°C is possible

using an external sensor.

Temperature measurement is initiated by three methods. The

first method is applicable when the part is in single-channel

measurement mode. The temperature is measured 16 times and

internally averaged to reduce noise. In single-channel mode, the

part is continuously monitoring the selected channel, that is, as

soon as one measurement is taken another one is started on the

same channel. The total time to measure a temperature channel

with the ADC operating at slow speed is typically 11.4 ms

(712 μs × 16) for the internal temperature sensor and 24.22 ms

(1.51 ms × 16) for the external temperature sensor. The new

temperature value is stored in two 8-bit registers and is ready

for reading by the I2C or SPI interface. The user has the option

of disabling the averaging by setting Bit 5 in the Control

Configuration 2 register (Address 0x19). The ADT7516/

ADT7517/ADT7519 default on power-up is with averaging

enabled.

The second method is applicable when the part is in round

robin measurement mode. The part measures both the internal

and external temperature sensors as it cycles through all

possible measurement channels. The two temperature channels

are measured each time the part runs a round robin sequence.

In round robin mode, the part is continuously measuring all

channels.

Temperature measurement is also initiated after every read or

write to the part when the part is in either single-channel

measurement mode or round robin measurement mode.

Once serial communication has started, any conversion in

progress stops and the ADC resets. Conversion restarts

immediately after the serial communication has finished. The

temperature measurement proceeds normally as described above.

VDD Monitoring

The ADT7516/ADT7517/ADT7519 also have the ability to

monitor their own power supply. The part measures the voltage

on its VDD pin to a resolution of 10 bits. The resulting value is

stored in two 8-bit registers; the two LSBs are stored in register

Address 0x03 and the eight MSBs are stored in register

Address 0x06. This allows the option of doing just a 1-byte read

if 10-bit resolution is not important. The measured result is

compared with the VHIGH and VLOW limits. If the VDD interrupt is

not masked, any out-of-limit comparison generates a flag in the

Interrupt Status 2 register and one or more out-of-limit results

cause the INT/INT output to pull either high or low, depending

on the output polarity setting.

Measuring the voltage on the VDD pin is regarded as monitoring

a channel along with the internal, external, and AIN channels.

The user can select the VDD channel for single-channel

measurement by setting Bit C4 = 1 and setting Bits[C0:C2] to all

0s in the Control Configuration 2 register.

When measuring the VDD value, the reference for the ADC is

sourced from the internal reference. Table 8 shows the data

format. As the maximum measurable VDD voltage is 7 V,

internal scaling is performed on the VDD voltage to match the

2.28 V internal reference value. Following is an example of how

the transfer function works:

VDD = 5 V

ADC Reference = 2.28 V

1 LSB = ADC Reference/210

= 2.28/1024

= 2.226 mV

Scale Factor = Full-Scale VCC/ADC Reference

= 7/2.28

= 3.07

Conversion Result = VDD/(Scale Factor × LSB size)

= 5/(3.07 × 2.226 mV)

= 0x2DC

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