MCP9902 datasheet(9/50 Pages) MICROCHIP

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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

the

lower

conversion

rates

(see

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

VDD

GND

VDD = 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

210

000

1/16

000

1/8

001

1/4

001

1/2

010

011

4 (default)

011

100

101

Bh - Fh

All others

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