Datasheet

© 2009 Microchip Technology Inc. DS22153C-page 33
MCP9843/98243
5.2.3.1 Comparator Mode
Comparator mode is selected using bit 0 of CONFIG. In
this mode, the Event output is asserted as active-high
or active-low using bit 1 of CONFIG. Figure 5-12 shows
the conditions that toggle the Event output.
If the device enters Shutdown mode with asserted
Event output, the output will de-assert. It will remain de-
asserted until the device enters Continuous Conver-
sion mode and after the first temperature conversion is
completed, t
CONV
. After the initial temperature conver-
sion, T
A
must satisfy the T
UPPER
or T
LOWER
boundary
conditions in order for Event output to be asserted.
Comparator mode is useful for thermostat-type
applications, such as turning on a cooling fan or
triggering a system shutdown when the temperature
exceeds a safe operating range.
5.2.3.2 Interrupt Mode
In the Interrupt mode, the Event output is asserted as
active-high or active-low (depending on the polarity
configuration) when T
A
drifts above or below T
UPPER
and T
LOWER
limits. The output is deasserted by setting
bit 5 (Interrupt Clear) of CONFIG. If the device enters
Shutdown mode with asserted Event output, the output
will de-assert. It will remain de-asserted until the device
enters Continuous Conversion mode and after the first
temperature conversion is completed, t
CONV
. If the inter-
rupt clear bit (Bit 5) is never set, then the Event output will
re-assert after the first temperature conversion.
In addition, if T
A
>= T
CRIT
the Event output is forced as
Comparator mode and asserts until T
A
< T
CRIT
- T
HYST
.
While the Event output is asserted, user must send Clear
Interrupt command (bit 5 of CONFIG) for Event output to
de-assert, when temperature drops below the critical
limit, T
A
< T
CRIT
- T
HYST
. Otherwise, Event output
remains asserted (see Figure 5-12 for graphical descrip-
tion). Switching from Interrupt mode to Comparator mode
also de-asserts Event output.
This mode is designed for interrupt driven microcontroller
based systems. The microcontroller receiving the
interrupt will have to acknowledge the interrupt by setting
bit 5 of CONFIG register from the MCP9843/98243.
5.2.4 TEMPERATURE RESOLUTION
The MCP9843/98243 device is capable of providing a
temperature data with 0.5°C to 0.0625°C resolution.
The Resolution can selected using the Resolution
register (Register 5-9) which is located in address
‘00001000’b. This address location is not specified in
JEDEC Standard JC42.4. However, it provides
additional flexibility while being functionally compatible
with JC42.4 and provide a 0.25°C resolution at 125 ms
(max.). The selected resolution can be read by user
using bit 4 and bit 3 of the Capability register
(Register 5-2). A 0.25°C resolution is set as POR
default by factory.
TABLE 5-2: TEMPERATURE
CONVERSION TIME
Resolution
t
CONV
(ms)
Samples/sec
(typical)
0.5°C 30 33
0.25°C
(Power-up default)
65 15
0.125°C 130 8
0.0625°C 260 4