2015-2016 Microchip Technology Inc. DS20005382C-page 9
MCP9902/3/4
4.0 FUNCTIONAL DESCRIPTION
Thermal management is performed in cooperation
with a host device. This consists of the host reading
the temperature data of both the external and internal
temperature diodes of the MCP9902/3/4 and using
that data to control the speed of one or more fans.
The MCP9902/3/4 has two levels of monitoring. The
first provides a maskable ALERT
signal to the host
when the measured temperatures exceed user pro-
grammable limits. This allows the MCP9902/3/4 to be
used as an independent thermal watchdog to warn the
host of temperature hot spots without direct control by
the host. The second level of monitoring provides a
non-maskable interrupt on the THERM
output if the
measured temperatures meet or exceed a second pro-
grammable limit.
Figure 4-1 shows a system level block diagram of the
MCP9902/3/4.
FIGURE 4-1: MCP9902/3/4 System
Diagram.
4.1 Power States
The MCP9902/3/4 has two modes of operation:
• Active (Run) - In this mode of operation, the ADC
is converting on all temperature channels at the
programmed conversion rate. The temperature
data is updated at the end of every conversion
and the limits are checked. In Active mode, writing
to the one-shot register will do nothing.
• Standby (Stop) - In this mode of operation, the
majority of circuitry is powered down to reduce
supply current. The temperature data is not
updated and the limits are not checked. In this
mode of operation, the SMBus is fully active and
the part will return requested data. Writing to the
one-shot register will enable the device to update
all temperature channels. Once all the channels
are updated, the device will return to the Standby
mode.
4.2 Conversion Rates
The MCP9902/3/4 may be configured for different con-
version rates based on the system requirements. The
default conversion rate is 4 conversions per second.
Other available conversion rates are shown in Table 4-1.
4.3 Dynamic Averaging
Dynamic averaging allows the MCP9902/3/4 to
measure the external diode channel for an extended
time based on the selected conversion rate. This
functionality can be disabled for increased power
savings at the lower conversion rates (see
Register 5-6). When dynamic averaging is enabled,
the device will automatically adjust the sampling and
measurement time for the external diode channels.
This allows the device to average 2x or 16x longer
than the normal 11 bit operation (nominally 21 ms per
channel) while still maintaining the selected
conversion rate. The benefits of dynamic averaging
are improved noise rejection due to the longer
integration time as well as less random variation of the
temperature measurement.
When enabled, the dynamic averaging applies when a
one-shot command is issued. The device will perform
the desired averaging during the one-shot operation
according to the selected conversion rate.
When enabled, the dynamic averaging will affect the
typical supply current based on the chosen conversion
rate as shown in the power supply characteristics in
Table 1.2 "DC Characteristics".
CPU/GPU
MCP990X
Host
DP1
DN1
SMDATA
Thermal
Junction
SMCLK
SMBus
Interface
THERM/ADDR
ALERT
Power
Control
V
DD
GND
V
DD
= 3.3V
3.3V – 5V
DN2/
DP3
DP2/
DN3
Optional
Anti-parallel
diode
MCP9903/4 only
TABLE 4-1: CONVERSION RATE
CONV<3:0>
Conversions/
Second
HEX 3210
0h 0000 1/16
1h 0001 1/8
2h 0010 1/4
3h 0011 1/2
4h 0100 1
5h 0101 2
6h 0110 4 (default)
7h 0111 8
8h 1000 16
9h 1001 32
Ah 1010 64
Bh - Fh All others 1
