AD7414 datasheet(13/20 Pages) AD

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AD7414/AD7415

Rev. F | Page 13 of 20

SMBUS ALERT

The AD7414 ALERT output is an SMBus interrupt line for

devices that want to trade their ability to master for an extra

pin. The AD7414 is a slave-only device and uses the SMBus

ALERT to signal to the host device that it wants to talk. The

SMBus ALERT on the AD7414 is used as an overtemperature

indicator.

The ALERT pin has an open-drain configuration that allows the

ALERT outputs of several AD7414s to be wire-AND’ed together

when the ALERT pin is active low. Use D4 of the configuration

power-up default is active low. The ALERT function can be

disabled or enabled by setting D5 of the configuration register

to 1 or 0, respectively.

The host device can process the ALERT interrupt and

simultaneously access all SMBus ALERT devices through the

alert response address. Only the device that pulled the ALERT

low acknowledges the Alert Response Address (ARA). If more

than one device pulls the ALERT pin low, the highest priority

(lowest address) device wins communication rights via standard

I2C arbitration during the slave address transfer.

The ALERT output becomes active when the value in the

temperature value register exceeds the value in the THIGH

value stored in the TLOW register.

The ALERT output requires an external pull-up resistor. This

can be connected to a voltage different from VDD, provided the

maximum voltage rating of the ALERT output pin is not

exceeded. The value of the pull-up resistor depends on the

application, but it should be as large as possible to avoid

excessive sink currents at the ALERT output, which can heat the

chip and affect the temperature reading.

POWER-ON DEFAULTS

The AD7414/AD7415 always power up with these defaults:

Address pointer register pointing to the temperature value

THIGH register loaded with 7Fh.

TLOW register loaded with 80h.

Configuration register loaded with 40h.

Note that the AD7415 does not have any THIGH or TLOW registers.

OPERATING MODES

Mode 1

This is the power-on default mode of the AD7414/AD7415. In

this mode, the AD7414/AD7415 does a temperature conversion

every 800 ms and then partially powers down until the next

conversion occurs.

If a one-shot operation (setting D2 of the configuration register

to a 1) is performed between automatic conversions, a conver-

sion is initiated right after the write operation. After this

conversion, the part returns to performing a conversion every

800 ms.

Depending on where a serial port access occurs during a

conversion, that conversion might be aborted. If the conversion

is completed before the part recognizes a serial port access, the

temperature register is updated with the new conversion. If the

conversion is completed after the part recognizes a serial port

access, the internal logic prevents the temperature register from

being updated, because corrupt data could be read.

A temperature conversion can start anytime during a serial port

access (other than a one-shot operation), but the result of that

conversion is loaded into the temperature register only if the

serial port access is not active at the end of the conversion.

Mode 2

The only other mode in which the AD7414/AD7415 operates is

the full power-down mode. This mode is usually used when

temperature measurements are required at a very slow rate. The

power consumption of the part can be greatly reduced in this

mode by writing to the part to go to a full power-down. Full

power-down is initiated right after D7 of the configuration

When a temperature measurement is required, a write

operation can be performed to power up the part and put it into

one-shot mode (setting D2 of the configuration register to a 1).

The power-up takes approximately 4 μs. The part then performs

a conversion and is returned to full power-down. The

temperature value can be read in the full power-down mode,

because the serial interface is still powered up.

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