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AD7415 Datasheet(PDF) 13 Page - Analog Devices |
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AD7415 Datasheet(HTML) 13 Page - Analog Devices |
13 / 20 page 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 register to set the active polarity of the ALERT output. The 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 register. It is reset when a write operation to the configuration register sets D3 to 1 or when the temperature falls below the 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 register. 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 register is set to 1. 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. |
Similar Part No. - AD7415_15 |
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Similar Description - AD7415_15 |
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