MAX6664AEE+T【PDF 8/24 页】IC TEMP MON FAN CNTRL 16-QSOP

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The MAX6663 resets its INT output and some of the

status bits in the status register after responding to an

alert response address; however, if the error condition

that caused the interrupt is still present, INT is reassert-

ed on the next monitoring cycle. INT is maskable to

allow full control of ALERT conditions.

Temperature Measurement

The MAX6653/MAX6663/MAX6664 contain on-chip tem-

perature sensors to sense their own die (local) tempera-

tures. These devices can also measure remote

temperatures such as 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

Tables 3 and 4. The temperature measurement resolution

is 0.125癈 for both local and remote temperatures. The

temperature accuracy is within ?癈 for remote tempera-

ture measurements from +60癈 to +100癈.

The Local Temperature Offset (0Dh) and Remote

Temperature Offset (0Eh) registers allow the measured

temperature to be increased or decreased by a fixed

value to compensate for errors due to variations in diode

resistance and ideality factor (see the Remote Diode

Considerations section). The reported temperature is the

measured temperature plus the correction value. Both the

measured temperature and the reported value are limited

by the sensors temperature range. For example, if a

remote thermal diode is being measured and its tempera-

ture is 135癈, the measured temperature is the maximum

value of 127.875癈. If the remote offset value is set to -

10癈, the reported value is 117.875癈, not 125癈.

The temperature conversion rate is programmable using

bits [4:2] of the fan filter register (23h) as shown in Table 5.

The DXN input is biased at 0.65V above ground by an

internal diode to set up the analog-to-digital inputs for a

differential measurement. The worst-case DXP-DXN dif-

ferential input voltage range is from 0.25V to 0.95V.

Excess resistance in series with the remote diode caus-

es about 0.5癈 error per ohm. Likewise, a 200礦 offset

voltage forced on DXP-DXN causes about 1癈 error.

High-frequency EMI is best filtered at DXP and DXN with

an external 2200pF capacitor. This value can be

increased to about 3300pF, including cable capacitance.

Capacitance higher than 3300pF introduces errors due to

the rise time of the switched current source.

Temperature Monitors and

PWM Fan Controllers

8 _______________________________________________________________________________________

Figure 3. SMBus Read Timing Diagram

SMBCLK

E F

I J

SMBDATA

SU:STA

HD:STA

LOW

HIGH

SU:DAT

HD:DAT

SU:STO

BUF

F = ACKNOWLEDGE BIT CLOCKED INTO MASTER

G = MSB OF DATA CLOCKED INTO MASTER

H = LSB OF DATA CLOCKED INTO MASTER

I = MASTER PULLS DATA LINE LOW

J = ACKNOWLEDGE CLOCKED INTO SLAVE

K = ACKNOWLEDGE CLEAR PULSE

L = STOP CONDITION, EXECUTED BY SLAVE

M = NEW START CONDITION

A = START CONDITION

B = MSB OF ADDRESS CLOCKED INTO SLAVE

C = LSB OF ADDRESS CLOCKED INTO SLAVE

D = R/W BIT CLOCKED INTO SLAVE

E = SLAVE PULLS SMBDATA LINE LOW

Table 3. Temperature Data High Byte Format

TEMP (?/SPAN>C)

DIGITAL

OUTPUT (癈)

DIGITAL OUTPUT

(BINARY)

130.00

+127

0111 1111

127.00

+127

0111 1111

126.00

+126

0111 1110

25.25

+25

0001 1001

0.50

0000 0000

0.00

0000 0000

-1

1111 1111

-125

1000 0011

-128

1000 0000

Diode fault

(short or open)

1000 0000

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