MAX6643LBFAEE+【PDF 8/17 页】IC CTLR PWM FAN-SPEED 16QSOP

Applications Information

Figures 36 show various configurations.

Remote-Diode Considerations

When using an external thermal diode, temperature

accuracy depends upon having a good-quality, diode-

connected, small-signal transistor. Accuracy has been

experimentally verified for a variety of discrete small-

signal transistors, some of which are listed in Table 5.

The MAX6643/MAX6644/MAX6645 can also directly

measure the die temperature of CPUs and other ICs

with on-board temperature-sensing diodes.

The transistor must be a small-signal type with a rela-

tively high forward voltage. This ensures that the input

voltage is within the ADC input voltage range. The for-

ward voltage must be greater than 0.25V at 10礎 at the

highest expected temperature. The forward voltage

must be less than 0.95V at 100礎 at the lowest expect-

ed temperature. The base resistance has to be less

than 100? Tight specification of forward-current gain

(+50 to +150, for example) indicates that the manufac-

turer has good process control and that the devices

have consistent characteristics.

Effect of Ideality Factor

The accuracy of the remote temperature measurements

depends on the ideality factor (n) of the remote diode

(actually a transistor). The MAX6643/MAX6644/MAX6645

are optimized for n = 1.01, which is typical of many dis-

crete 2N3904 and 2N3906 transistors. It is also near the

ideality factors of many widely available CPUs, GPUs, and

FPGAs. However, any time a sense transistor with a differ-

ent ideality factor is used, the output data is different.

Fortunately, the difference is predictable. Assume a

remote-diode sensor designed for a nominal ideality fac-

tor n

NOMINAL

is used to measure the temperature of a

diode with a different ideality factor, n

1

. The measured

temperature T

M

can be corrected using:

where temperature is measured in Kelvin.

As mentioned above, the nominal ideality factor of the

MAX6643/MAX6644/MAX6645 is 1.01. As an example,

assume the MAX6643/MAX6644/MAX6645 are config-

ured with a CPU that has an ideality factor of 1.008. If

the diode has no series resistance, the measured data

is related to the real temperature as follows:

For a real temperature of +60癈 (333.15K), the mea-

sured temperature is 59.33癈 (332.49K), which is an

error of -0.66癈.

T

n

T

1.01

1.008

T

ACTUAL M

NOMINAL

1

M

=

?/DIV>

=

?/DIV>

=

(

)

.

1 00198

T T

n

M

ACTUAL

1

NOMINAL

=

?/DIV>

Automatic PWM Fan-Speed Controllers with

Overtemperature Output

8 _______________________________________________________________________________________

MANUFACTURER

MODEL NO.

Central Semiconductor (USA)

CMPT3906

Rohm Semiconductor (USA)

SST3906

Samsung (Korea)

KST3906-TF

Siemens (Germany)

SMBT3906

Table 5. Remote-Sensor Transistor

Manufacturers

OT2

OT1

T

OVERT

(癈)

L SUFFIX

0

60

0

High-Z

65

0

1

70

High-Z

0

75

High-Z

80

High-Z

1

85

1

0

90

1

High-Z

95

1

100

Table 4. Setting the Overtemperature

Thresholds (T

OVERT

) (MAX6643 and MAX6644)

Table 3. Configuring the FAN_IN_ Inputs with TACHSET

VDD

GND

UNCONNECTED

TACHSET

FAN_IN1

FAN_IN2

FAN_IN1

FAN_IN2

FAN_IN1

FAN_IN2

MAX6643

Tachometer

Do not connect

to GND

Do not connect

to GND

Disables fan-

failure detection

Disables fan-

failure detection

MAX6644

Tachometer

Current sense

Locked rotor

MAX6645

Tachometer

Current sense

Locked rotor

High-Z = high impedance

发布紧急采购，3分钟左右您将得到回复。

采购需求

(若只采购一条型号，填写一行即可)

*型号	*数量	厂商	批号	封装

添加更多采购

我的联系方式

*

采购需求

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

我的联系方式