SE95_7

© NXP B.V. 2009. All rights reserved.

Product data sheet

Rev. 07 — 2 September 2009

4 of 27

NXP Semiconductors

SE95

Ultra high accuracy digital temperature sensor and thermal watchdog

7.

Functional description

7.1 General operation

The SE95 uses the on-chip band gap sensor to measure the device temperature with a

resolution of 0.03125

°C and stores the 13-bit two’s complement digital data, resulting

from 13-bit analog to digital conversion, into register Temp. Register Temp can be read at

conversion in progress during the read operation.

The device can be set to operate in either mode: normal or shutdown mode. In normal

operation mode, by default, the temperature-to-digital conversion is executed every

100 ms and register Temp is updated at the end of each conversion. In shutdown mode,

the device becomes idle, data conversion is disabled and register Temp holds the latest

can be performed. The device operation mode is controlled by programming bit

SHUTDOWN of register Conf. The temperature conversion is initiated when the device is

powered up or returned to normal mode from shutdown mode.

In addition, at the end of each conversion in normal mode, the temperature data (or Temp)

in register Temp is automatically compared with the overtemperature shutdown threshold

data (or Tos) stored in register Tos, and the hysteresis data (or Thyst) stored in register

Thyst, in order to set the state of the device OS output accordingly. The registers Tos and

Thyst are write/read capable, and both operate with 9-bit two’s complement digital data.

To match with this 9-bit operation, register Temp uses only the 9 MSB bits of its 13-bit data

for the comparison.

The device temperature conversion rate is programmable and can be chosen to be one of

the four values: 0.125, 1.0, 10, and 30 conversions/s. The default conversion rate is

10 conversions/s. Furthermore, the conversion rate is selected by programming bits

RATEVAL[1:0] of register Conf as shown in Table 6. Note that the average supply current

as well as the device power consumption increase with the conversion rate.

The way that the OS output responds to the comparison operation depends upon the OS

operation mode selected by configuration bit OS_COMP_INT, and the user-defined fault

queue defined by configuration bits OS_F_QUE[1:0].

In OS comparator mode, the OS output behaves like a thermostat. It becomes active

Reading the device registers or putting the device into shutdown mode does not change

the state of the OS output. The OS output in this case can be used to control cooling fans

or thermal switches.

A1

6

user-defined address bit 1 digital input

A0

7

user-defined address bit 0 digital input

8

supply voltage

Table 2.

Symbol

Pin

Description