MAX6641AUB92+【PDF 5/17 页】IC TEMP MONITOR SMBUS 10UMAX

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Detailed Description

The MAX6641 temperature sensor and fan controller

accurately measures the temperature of its own die

and the temperature of a remote pn junction. The

device reports temperature values in digital form using

a 2-wire serial interface. The remote pn junction is typi-

cally the emitter-base junction of a common-collector

pnp on a CPU, FPGA, or ASIC. The MAX6641 operates

from supply voltages of 3.0V to 5.5V and consumes

500礎 of supply current. The temperature data controls

a PWM output signal to adjust the speed of a cooling

fan. The device also features an over-temperature

alarm output to generate interrupts, throttle signals, or

shut down signals.

SMBus Digital Interface

From a software perspective, the MAX6641 appears as

a set of byte-wide registers that contain temperature

data, alarm threshold values, and control bits. A stan-

dard SMBus-compatible 2-wire serial interface is used

to read temperature data and write control bits and

alarm threshold data. These devices respond to the

same SMBus slave address for access to all functions.

The MAX6641 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 when using the shorter protocols in

multimaster systems, as a second master could over-

write the command byte without informing the first mas-

ter. The MAX6641 has four different slave addresses

available; therefore, a maximum of four MAX6641

devices can share the same bus.

Temperature data within the 0癈 to +255癈 range can

be read from the read external temperature register

(00h). Temperature data within the 0癈 to +125癈 range

can be read from the read internal temperature register

(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 are clipped to 00h.

Table 1 details the register address and function,

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

reset (POR) state. See Tables 15 for all other register

functions and the Register Descriptions section. Figure 4

is the MAX6641 block diagram.

SMBus-Compatible Temperature Monitor with

Automatic PWM Fan-Speed Controller

_______________________________________________________________________________________ 5

NAME

FUNCTION

1, 6

I.C.

Internally Connected. Must be connected to GND.

DXN

Combined Remote-Diode Cathode Connection and A/D Negative Input. Connect the cathode of the

remote-diode-connected transistor to DXN.

DXP

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

DXP to the anode of a remote-diode-connected temperature-sensing transistor. DO NOT LEAVE

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

and DXN for noise filtering.

GND

Ground

Active-Low, Open-Drain, Over-Temperature Output. Use OT as an interrupt, a system shutdown

signal, or to control clock throttling. OT can be pulled up to 5.5V, regardless of the voltage on V

OT is high impedance when V

= 0.

SMBCLK

SMBus Serial-Clock Input. SMBCLK can be pulled up to 5.5V, regardless of V

. Open drain.

SMBCLK is high impedance when V

= 0.

SMBDATA

SMBus Serial-Data Input/Output. SMBDATA can be pulled up to 5.5V, regardless of V

. Open drain.

SMBDATA is high impedance when V

= 0.

Positive Supply. Bypass with a 0.1礔 capacitor to GND.

PWMOUT

PWM Output to Fan Power Transistor. Connect PWMOUT to the gate of a MOSFET or the base of a

bipolar transistor to drive the fans power supply with a PWM waveform. Alternatively, the PWM output

can be connected to the PWM input of a fan with direct speed-control capability, or it can be

converted to a DC voltage for driving the fans power supply. PWMOUT requires a pullup resistor. The

pullup resistor can be connected to a voltage supply up to 5.5V, regardless of V

Pin Description

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