Detailed Description

The MAX6615/MAX6616 accurately monitor two tem-

perature channels, either the internal die temperature

and the temperature of an external thermistor, or the

temperatures of two external thermistors. They report

temperature values in digital form using a 2-wire

MAX6616 operate from a supply voltage range of 3.0V

to 5.5V and consume 500µA (typ) of supply current.

The temperature data controls the duty cycles of two

PWM output signals that are used to adjust the speed

of a cooling fan. They also feature an overtemperature

alarm output to generate interrupts, throttle signals, or

shutdown signals.

The MAX6616 also includes six GPIO input/outputs to

provide additional flexibility. The GPIO0 power-up state

is set by connecting the GPIO PRESET input to ground

SMBus Digital Interface

From a software perspective, the MAX6615/MAX6616

appear as a set of byte-wide registers. Their devices use

to access the internal registers. The MAX6615/MAX6616

have nine different slave addresses available; therefore, a

maximum of nine MAX6615/MAX6616 devices can share

the same bus.

The MAX6615/MAX6616 employ four standard SMBus

protocols: write byte, read byte, send byte, and receive

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

col allows quicker transfers, provided that the correct

data register was previously selected by a read byte

instruction. Use caution with the shorter protocols in mul-

timaster 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

MSB representing 128°C. The MSB is transmitted first.

All values below 0°C clip to 00h.

Table 3 details the register address and function, whether

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

Dual-Channel Temperature Monitors and

Fan-Speed Controllers with Thermistor Inputs

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 REGISTER YOU ARE

WRITING TO

DATA BYTE: DATA GOES INTO THE REG-

ISTER 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: REPEAT-

ED 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

S

ADDRESS

RD

ACK

DATA

///

P

—

7 BITS

—

—

8 BITS

—

—

WR

S

ACK

COMMAND

ACK

P

—

—

—

8 BITS

—

—

ADDRESS

7 BITS

P

1

ACK

—

DATA

8 BITS

ACK

—

COMMAND

8 BITS

ACK

—

WR

—

ADDRESS

7 BITS

S

—

S

ADDRESS

WR

ACK

COMMAND

ACK

S

ADDRESS

7 BITS

—

—

8 BITS

—

—

7 BITS

—

RD

—

ACK

—

DATA

8 BITS

///

—

P

—

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