SE95U,025 Datasheet SE95U,025, SE95D,112, SE95D,118 | P4-P6

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

any time by a controller on the I

C-bus. Reading temperature data does not affect the

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

result; however, the device I

C-bus interface is still active and register write/read operation

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

when the temperature exceeds T

, and is reset when the temperature drops below T

hyst

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. Pin description

…continued

Symbol Pin Description

Product data sheet Rev. 07 — 2 September 2009 5 of 27

NXP Semiconductors

SE95

Ultra high accuracy digital temperature sensor and thermal watchdog

In OS interrupt mode, the OS output is used for thermal interruption. When the device is

powered-up, the OS output is ﬁrst activated only when Temp exceeds T

; then it remains

active indeﬁnitely until being reset by a read of any register. Once the OS output has been

activated by crossing T

and then reset, it can be activated again only when Temp drops

below T

hyst

; then again, it remains active indeﬁnitely until being reset by a read of any

trip, reset,

hyst

trip, reset, T

hyst

trip, reset, and etc. Putting the device into shutdown

mode also resets the OS output.

In both cases, comparator mode and interrupt mode, the OS output is activated only if a

number of consecutive faults, deﬁned by the device fault queue, has been met. The fault

queue is programmable and stored in bits OS_F_QUE[1:0], of register Conf. Also, the OS

output active state is selectable as HIGH or LOW by setting accordingly the bit OS_POL

of register Conf.

At power-up, the device is put into normal operation mode, register Tos is set to 80 °C,

to 1. The data reading of register Temp is not available until the ﬁrst conversion is

completed in about 33 ms.

The OS response to the temperature is illustrated in Figure 4.

(1) OS is reset by either reading register or putting the device in shutdown mode. Assumed that the

fault queue is met at each T

and T

hyst

crossing point.

Fig 4. OS response to temperature

001aad623

(1) (1) (1)

hyst

OS RESET

OS ACTIVE

OS RESET

OS ACTIVE

OS output in comparator mode

OS output in interrupt mode

reading temperature limits

Product data sheet Rev. 07 — 2 September 2009 6 of 27

NXP Semiconductors

SE95

Ultra high accuracy digital temperature sensor and thermal watchdog

7.2 OS output and polarity

The OS output is an open-drain output and its state represents results of the device

watchdog operation as described in Section 7.1. In order to observe this output state, an

external pull-up resistor is needed. The resistor should be as large as possible, up to

200 kΩ, to minimize the Temp reading error due to internal heating by the high OS sinking

current.

The OS output active state can be selected as HIGH or LOW by programming bit

OS_POL of register Conf: setting bit OS_POL to logic 1 selects OS active HIGH and

setting to logic 0 sets OS active LOW. At power-up, bit OS_POL is equal to logic 0 and the

OS active state is LOW.

7.3 OS comparator and interrupt modes

As described in Section 7.1, the OS output responds to the result of the comparison

between register Temp data and the programmed limits, in registers Tos and Thyst, in

different ways depending on the selected OS mode: OS comparator or OS interrupt. The

OS mode is selected by programming bit OS_COMP_INT of register Conf: setting bit

OS_COMP_INT to logic 1 selects the OS interrupt mode, and setting to logic 0 selects the

OS comparator mode. At power-up, bit OS_COMP_INT is equal to logic 0 and the OS

comparator is selected.

The main difference between the two modes is that in OS comparator mode, the OS

output becomes active when Temp has exceeded T

and reset when Temp has dropped

below T

hyst

, reading a register or putting the device into shutdown mode does not change

the state of the OS output; while in OS interrupt mode, once it has been activated either

by exceeding T

or dropping below T

hyst

, the OS output will remain active indeﬁnitely until

reading a register or putting the device into shutdown mode occurs, then the OS output is

reset.

Temperature limits T

and T

hyst

must be selected so that T

> T

hyst

. Otherwise, the OS

output state will be undeﬁned.

7.4 OS fault queue

Fault queue is deﬁned as the number of faults that must occur consecutively to activate

the OS output. It is provided to avoid false tripping due to noise. Because faults are

determined at the end of data conversions, fault queue is also deﬁned as the number of

consecutive conversions returning a temperature trip. The value of fault queue is

selectable by programming the two bits OS_F_QUE[1:0] in register Conf. Notice that the

programmed data and the fault queue value are not the same. Table 3 shows the

one-to-one relationship between them. At power-up, fault queue data = 00 and fault queue

value = 1.

Table 3. Fault queue table

Fault queue data Fault queue value

OS_F_QUE[1] OS_F_QUE[0] Decimal

001

012

104

116

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P24 P25-P27

SE95U,025

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SENSOR DIGITAL -55C-125C DIE

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