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TMP108

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SBOS663A – APRIL 2013 – REVISED SEPTEMBER 2019

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If multiple devices on the bus respond to the SMBus alert command, arbitration during the slave address portion

of the SMBus alert command determines which device clears its alert status first. If the TMP108 wins the

arbitration, its ALERT pin becomes inactive at the completion of the SMBus alert command. If the TMP108 loses

the arbitration, its ALERT pin remains active.

7.3.7 General Call

The TMP108 responds to a two-wire general call address (0000000) if the eighth bit is 0. The device

acknowledges the general call address and responds to commands in the second byte. If the second byte is

00000100, the TMP108 latches the status of the address pin, but does not reset. If the second byte is 00000110,

the TMP108 internal registers are reset to power-up values. The TMP108 does not support the general address

acquire command.

7.3.8 High-Speed (Hs) Mode

In order for the two-wire bus to operate at frequencies above 400 kHz, the master device must issue an SMBus

Hs-mode master code (00001xxx) as the first byte after a start condition to switch the bus to high-speed

operation. The TMP108 does not acknowledge this byte, but does switch its input filters on SDA and SCL and its

output filters on SDA to operate in Hs-mode, allowing transfers at up to 3.4 MHz. After the Hs-mode master code

has been issued, the master transmits a two-wire slave address to initiate a data-transfer operation. The bus

continues to operate in Hs-mode until a stop condition occurs on the bus. Upon receiving the stop condition, the

TMP108 switches the input and output filters back to fast-mode operation.

7.3.9 Timeout Function

The TMP108 resets the serial interface if SCL or SDA are held low for 28 ms (typical) between a start and stop

condition. If the TMP108 is pulled low, it releases the bus and then waits for a start condition. To avoid activating

the timeout function, it is necessary to maintain a communication speed of at least 1 kHz for the SCL operating

frequency.

7.4 Device Functional Modes

The mode bits, M1 and M0, can be set to three different modes: shutdown, one-shot, or continuous conversion.

7.4.1 Shutdown Mode (M1 = 0, M0 = 0)

Shutdown mode saves power by shutting down all device circuitry other than the serial interface, thus reducing

current consumption to typically less than 0.5 μA. Shutdown mode is enabled when M1 and M0 = 00. The device

shuts down when current conversion is completed.

7.4.2 One-Shot Mode (M1 = 0, M0 = 1)

The TMP108 features a one-shot temperature measurement mode. When the device is in shutdown mode,

writing a ‘01’ to the M1 and M0 bits starts a single temperature conversion. During the conversion, the M1 and

M0 bits reads 01. The device returns to the shutdown state at the completion of the single conversion. After the

conversion, the M1 and M0 bits read 00. This feature is useful for reducing the power consumption of the

TMP108 when continuous temperature monitoring is not required.

As a result of the short conversion time, the TMP108 can achieve a higher conversion rate. A single conversion

typically takes 27 ms and a read can take place in less than 20 μs. However, when using one-shot mode, 30 or

more conversions per second are possible.

7.4.3 Continuous Conversion Mode (M1 = 1)

When the TMP108 is in continuous conversion mode (M1 = 1), a single conversion is performed at a rate

determined by the conversion rate bits (CR1 and CR0 in the configuration register). The TMP108 performs a

single conversion, and then goes in standby and waits for the appropriate delay set by the CR1 and CR0 bits.

See Table 10 for CR1 and CR0 settings.