SE97BTP,547【PDF 7/53 页】IC TEMP SENSOR DIMM 8HWSON

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Sheet目录46

3页 4页 5页 6页 [7页]8页 9页 10页 11页

SE97B_1

Product data sheet

Rev. 01 27 January 2010

7 of 53

NXP Semiconductors

SE97B

DDR memory module temp sensor with integrated SPD

7.3 EVENT

output condition

The EVENT

output indicates conditions such as the temperature crossing a predefined

boundary. The EVENT

modes are very configurable and selected using the configuration

using either TCRIT/UPPER/LOWER or TCRIT only temperature bands (CONFIG[2]) as

modified by hysteresis (CONFIG[10:9]). The UPPER/LOWER (CONFIG[6]) and TCRIT

(CONFIG[7]) bands can be locked. Figure 4

shows an example of the measured

temperature versus time, with the corresponding behavior of the EVENT

output in each of

these modes.

Upon device power-up, the default condition for the EVENT

output is high-impedance to

prevent spurious or unwanted alarms, but can be later enabled (CONFIG[3]). CONFIG[3]

does not have to be cleared (e.g., set back to (0)) before changing CONFIG[2] or

CONFIG[0]. EVENT

output polarity can be set to active HIGH or active LOW

(CONFIG[1]). EVENT

status can be read (CONFIG[4]) and cleared (CONFIG[5]).

If the EVENT

output is enabled (CONFIG[3] = 1) and the part is switched between

Interrupt mode and Comparator mode or vice versa, the EVENT

output may glitch during

the change.

If the device enters Shutdown mode (CONFIG[8]) with asserted EVENT

output, the output

either de-asserts (default) or remains asserted (frozen) depending on SMBUS[4].

7.3.1 EVENT

pin output voltage levels and resistor sizing

The EVENT

open-drain output is typically pulled up to a voltage level from 0.9 V to 3.6 V

with an external pull-up resistor, but there is no real lower limit on the pull-up voltage for

the EVENT

pin since it is simply an open-drain NMOS pull-down output. It could be pulled

up to 0.1 V and would not affect the output. From the system perspective, there will be a

practical limit. That limit will be the voltage necessary for the device monitoring the

interrupt pin to detect a HIGH on its input. A possible practical limit for a CMOS input

would be 0.4 V. Another thing to consider is the value of the pull-up resistor. When a low

supply voltage is applied to the drain (through the pull-up resistor) it is important to use a

higher value pull-up resistor, to allow a larger maximum signal swing on the EVENT

pin.

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