Datasheet AD7414, AD7415 (Analog Devices) - 13

Data Sheet AD7414/ AD7415 SMBUS ALERT OPERATING MODES
The AD7414 ALERT output is an SMBus interrupt line for
Mode 1
devices that want to trade their ability to master for an extra This is the power-on default mode of the AD7414/AD7415. In pin. The AD7414 is a slave-only device and uses the SMBus this mode, the AD7414/AD7415 does a temperature conversion ALERT to signal to the host device that it wants to talk. The every 800 ms and then partially powers down until the next SMBus ALERT on the AD7414 is used as an overtemperature conversion occurs. indicator. If a one-shot operation (setting D2 of the configuration register The ALERT pin has an open-drain configuration that allows the to a 1) is performed between automatic conversions, a conver- ALERT outputs of several AD7414s to be wire-AND’ed together sion is initiated right after the write operation. After this when the ALERT pin is active low. Use D4 of the configuration conversion, the part returns to performing a conversion every register to set the active polarity of the ALERT output. The 800 ms. power-up default is active low. The ALERT function can be Depending on where a serial port access occurs during a disabled or enabled by setting D5 of the configuration register conversion, that conversion might be aborted. If the conversion to 1 or 0, respectively. is completed before the part recognizes a serial port access, the The host device can process the ALERT interrupt and temperature register is updated with the new conversion. If the simultaneously access all SMBus ALERT devices through the conversion is completed after the part recognizes a serial port alert response address. Only the device that pulled the ALERT access, the internal logic prevents the temperature register from low acknowledges the Alert Response Address (ARA). If more being updated, because corrupt data could be read. than one device pulls the ALERT pin low, the highest priority A temperature conversion can start anytime during a serial port (lowest address) device wins communication rights via standard access (other than a one-shot operation), but the result of that I2C arbitration during the slave address transfer. conversion is loaded into the temperature register only if the The ALERT output becomes active when the value in the temper- serial port access is not active at the end of the conversion. ature value register exceeds the value in the THIGH register. It is
Mode 2
reset when a write operation to the configuration register sets D3 to 1 or when the temperature falls below the value stored in The only other mode in which the AD7414/AD7415 operates is the T the full power-down mode. This mode is usually used when LOW register. temperature measurements are required at a very slow rate. The The ALERT output requires an external pull-up resistor. This power consumption of the part can be greatly reduced in this can be connected to a voltage different from VDD, provided the mode by writing to the part to go to a full power-down. Full maximum voltage rating of the ALERT output pin is not power-down is initiated right after D7 of the configuration exceeded. The value of the pull-up resistor depends on the register is set to 1. application, but it should be as large as possible to avoid excessive sink currents at the ALERT output, which can heat the When a temperature measurement is required, a write chip and affect the temperature reading. 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).
POWER-ON DEFAULTS
The power-up takes approximately 4 s. The part then performs The AD7414/AD7415 always power up with these defaults: a conversion and is returned to full power-down. The Address pointer register pointing to the temperature value temperature value can be read in the full power-down mode, register. because the serial interface is still powered up. 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. Rev. G | Page 13 of 19 Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION FUNCTIONAL BLOCK DIAGRAM PRODUCT HIGHLIGHTS TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ESD CAUTION PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS THEORY OF OPERATION CIRCUIT INFORMATION FUNCTIONAL DESCRIPTION MEASUREMENT TECHNIQUE TEMPERATURE DATA FORMAT INTERNAL REGISTER STRUCTURE ADDRESS POINTER REGISTER CONFIGURATION REGISTER (ADDRESS 0x01) TEMPERATURE VALUE REGISTER (ADDRESS 0x00) AD7414 THIGH REGISTER (ADDRESS 0X02) AD7414 TLOW REGISTER (ADDRESS 0x03) SERIAL INTERFACE SERIAL BUS ADDRESS WRITE MODE Writing to the Address Pointer Register for a Subsequent Read Writing a Single Byte of Data to the Configuration Register, THIGH Register, or TLOW Register READ MODE SMBUS ALERT POWER-ON DEFAULTS OPERATING MODES Mode 1 Mode 2 POWER VS. THROUGHPUT Mode 1 Mode 2 MOUNTING THE AD7414/AD7415 SUPPLY DECOUPLING TEMPERATURE ACCURACY VS. SUPPLY TYPICAL TEMPERATURE ERROR GRAPH OUTLINE DIMENSIONS ORDERING GUIDE