SE97_7 © NXP B.V. 2010. All rights reserved.
Product data sheet Rev. 07 — 29 January 2010 8 of 55
NXP Semiconductors
SE97
DDR memory module temp sensor with integrated SPD, 3.3 V
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
register (CONFIG). The interrupt mode or comparator mode is selected using CONFIG[0],
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 8
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]). 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]).
• Advisory note:
– NXP device: After power-up, bit 3 (1) and bit 2 or bit 0 (leave as 0 or 1) can be set
at the same time (e.g., in same byte) but once bit 3 is set (1) then changing bit 2 or
bit 0 has no effect on the device operation.
– Competitor device: Does not require that bit 3 be cleared (e.g., set back to (0))
before changing bit 2 or bit 0.
– Work-around: In order to change bit 2 or bit 0 once bit 3 (1) is set, bit 3 (0) must be
cleared in one byte and then change bit 2 or bit 0 and reset bit 3 (1) in the next
byte.
– SE97B will allow bit 2 or bit 0 to be changed even if bit 3 is set.
If the device enters Shutdown mode (CONFIG[8]) with asserted EVENT
output, the output
remains asserted during shutdown.
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 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.
