Detailed Description

The MAX6678 temperature sensor and fan controller

accurately measures the temperature of either two

remote pn junctions or one remote pn junction and its

own die. The device reports temperature values in digi-

tal form using a 2-wire serial interface. The remote pn

junction is typically the emitter-base junction of a com-

mon-collector pnp on a CPU, FPGA, or ASIC. The

MAX6678 operates from supply voltages of 3.0V to

5.5V and consumes 500µA (typ) of supply current. The

temperature data controls a PWM output signal to

adjust the speed of a cooling fan. The device also fea-

tures an overtemperature alarm output to generate

interrupts, throttle signals, or shutdown signals.

Five GPIO input/outputs provide additional flexibility.

The GPIO power-up states are set by connecting the

2-Channel Temperature Monitor with Dual Automatic

PWM Fan-Speed Controller and Five GPIOs

_______________________________________________________________________________________

5

Pin Description

PIN

THIN QFN

QSOP

NAME

DESCRIPTION

13

SMBDATA

SMBus Serial-Data Input/Output, Open Drain. Can be pulled up to 5.5V,

24

SMBCLK

3, 12, 13,

14, 16

5, 14, 15,

16, 18

GPIO0–GPIO4

Active-Low, Open-Drain GPIO Pins. Can be pulled up to 5.5V, regardless of

4, 9, 10,

11, 20

2, 6, 11,

12, 13

PRESET0–PRESET4

5, 7

7, 9

DXP1, DXP2

Combined Current Source and A/D Positive Input for Remote Diode. Connect to

anode of remote-diode-connected temperature-sensing transistor. Do not leave

floating; connect to DXN if no remote diode is used. Place a 2200pF capacitor

between DXP_ and DXN for noise filtering.

68

DXN

Combined Remote-Diode Cathode Input. Connect cathode of the remote-diode-

connected transistor to DXN.

810

GND

Ground. Connect to a clean ground reference.

15

17

OT

Active-Low, Open-Drain Over-Temperature Output. Typically used for system

17, 19

1, 19

PWMOUT1,

PWMOUT2

Open-Drain Output to Power Transistor Driving Fan. Connect to the gate of a

MOSFET or base of a transistor. PWMOUT_ requires a pullup resistor. The

pullup resistor can be connected to a supply voltage as high as 5.5V,

regardless of the MAX6678’s supply voltage.

18

20

TEMPERATURE

PROCESSING

BLOCK

PWM

GENERATOR

BLOCK

SMBus

INTERFACE

AND

REGISTERS

LOGIC

MAX6678

GND

SMBCLK

SMBDATA

DXN

DXP1

DXP2

PWMOUT1

PWMOUT2

OT

GPIO0

GPIO4

PRESET0

PRESET4

Block Diagram