50

60

70

80

90

100

ALERT

THERM Limit

THERM Limit - Hysteresis

High Temperature Limit

THERM

110

120

130

140

150

Temperature Conversion Complete

Time

Measured

Temperature

ALERT output

serviced by master

50

60

70

80

90

100

THERM2

THERM Limit

THERM Limit - Hysteresis

THERM

110

120

130

140

150

Temperature Conversion Complete

Time

Measured

Temperature

THERM2 Limit

THERM2 Limit - Hysteresis

TMP451

SBOS686A – JUNE 2013 – REVISED DECEMBER 2014

www.ti.com

7.3.6

ALERT and THERM Functions

The operation of the ALERT (pin 6) and THERM (pin 4) interrupts is shown in Figure 13. The operation of the

THERM (pin 4) and THERM2 (pin 6) interrupts is shown in Figure 14.

Figure 13. ALERT and THERM Interrupt Operation

Figure 14. THERM and THERM2 Interrupt

Operation

The hysteresis value is stored in the THERM hysteresis register. The value of the CONAL[2:0] bits in the

consecutive ALERT register determines the number of limit violations before the ALERT pin is tripped. The

default value is 000b and corresponds to one violation, 001b programs two consecutive violations, 011b

programs three consecutive violations, and 111b programs four consecutive violations. This provides additional

filtering for the ALERT pin state.

7.4 Device Functional Modes

7.4.1 Shutdown Mode (SD)

The TMP451 shutdown mode enables the user to save maximum power by shutting down all device circuitry

other than the serial interface, reducing current consumption to typically less than 3

μA; see Figure 11. Shutdown

mode is enabled when the SD bit (bit 6) of the configuration register is high; the device shuts down after the

current conversion is finished. When the SD bit is low, the device maintains a continuous-conversion state.

7.4.2 One-shot Mode

When the TMP451 device is in shutdown mode (SD = 1 in the configuration register), a single conversion is

started by writing any value to the one-shot start register, pointer address 0Fh. This write operation starts one

conversion and comparison cycle on both the local and the remote sensors. The TMP451 device returns to

shutdown mode when the cycle completes. The value of the data sent in the write command is irrelevant and is

not stored by the TMP451 device.

7.5 Programming

7.5.1 Serial Interface

The TMP451 device operates only as a slave device on either the two-wire bus or the SMBus. Connections to

either bus are made using the open-drain I/O lines, SDA and SCL. The SDA and SCL pins feature integrated

spike suppression filters and Schmitt triggers to minimize the effects of input spikes and bus noise. The TMP451

device supports the transmission protocol for fast (1 kHz to 400 kHz) and high-speed (1 kHz to 2.5 MHz) modes.

All data bytes are transmitted MSB first.

12

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