MAX6678AEP92+【PDF 6/19 页】IC TEMP MONITOR 2CH PWM 20-QSOP

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SMBus Digital Interface

From a software perspective, the MAX6678 appears as a

set of byte-wide registers. This device uses a standard

SMBus 2-wire/I

C-compatible serial interface to access

the internal registers. The MAX6678 has four different

slave addresses available; therefore, a maximum of four

MAX6678 devices can share the same bus.

The MAX6678 employs four standard SMBus protocols:

write byte, read byte, send byte, and receive byte

(Figures 1, 2, and 3). The shorter receive byte protocol

allows quicker transfers, provided that the correct data

tion. Use caution with the shorter protocols in multimaster

systems, since a second master could overwrite the

command byte without informing the first master.

Temperature data can be read from registers 00h and

01h. The temperature data format for these registers is

8 bits, with the LSB representing 1癈 (Table 1) and the

MSB representing +128癈. The MSB is transmitted first.

All values below 0癈 clip to 00h.

Table 2 details the register address and function, whether

they can be read or written to, and the power-on reset

(POR) state. See Tables 26 for all other register functions

and the Register Descriptions section.

Temperature Reading

The MAX6678 contains two external temperature mea-

surement inputs to measure the die temperature of CPUs

or other ICs having on-chip temperature-sensing diodes,

or discrete diode-connected transistors as shown in the

Typical Operating Circuits. For best accuracy, the dis-

crete diode-connected transistor should be a small-signal

device with its collector and base connected together.

The on-chip ADC converts the sensed temperature and

outputs the temperature data in the format shown in Table

1. Temperature channel 2 can be used to measure either

a remote thermal diode or the internal temperature of the

MAX6678. Bit D1 of register 02h (Table 2) selects local or

remote sensing for temperature channel 2 (1 = local). The

temperature measurement resolution is 1癈 for both local

and remote temperatures. The temperature accuracy is

within ?癈 for remote temperature measurements from

+60癈 to +100癈.

2-Channel Temperature Monitor with Dual Automatic

PWM Fan-Speed Controller and Five GPIOs

6 _______________________________________________________________________________________

Write Byte Format

Read Byte Format

Send Byte Format

Receive Byte Format

Slave address: equiva-

lent to chip-select line of

a 3-wire interface

Command byte: selects which

Data byte: data goes into the register

set by the command byte (to set

thresholds, configuration masks, and

sampling rate)

Slave address: equivalent

to chip-select line

Command byte: selects

which register you are

reading from

Slave address: repeated

due to change in data-

flow direction

Data byte: reads from

the register set by the

command byte

Command byte: sends com-

mand with no data, usually

used for one-shot command

Data byte: reads data from

the register commanded

by the last read byte or

write byte transmission;

also used for SMBus alert

response return address

S = Start condition

Shaded = Slave transmission

P = Stop condition

/// = Not acknowledged

Figure 1. SMBus Protocols

ADDRESS

ACK

DATA

///

7 bits

8 bits

ACK

COMMAND

ACK

8 bits

ADDRESS

7 bits

ACK

DATA

8 bits

ACK

COMMAND

8 bits

ACK

ADDRESS

7 bits

ADDRESS

ACK

COMMAND

ACK

ADDRESS

7 bits

8 bits

7 bits

ACK

DATA

8 bits

///

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