MAX1299CEAE+【PDF 16/20 页】IC TEMP SENS W/ADC 16-SSOP

收藏本站

您好，
买卖IC网欢迎您。
请登录
免费注册

买卖IC网

Sheet目录42

12页 13页 14页 15页 [16页]17页 18页 19页 20页

12-Bit Serial-Output Temperature Sensors

with 5-Channel ADC

16 ______________________________________________________________________________________

Place the MAX1298/MAX1299 in a low-current power-

down state between conversions to conserve power.

Select standby, standby-plus, or shutdown through bits

PM1 and PM0 of the initialization byte (Table 4).

The MAX1298/MAX1299 assume the shutdown power

mode when V

is first applied.

Standby Mode

Standby mode turns off the MAX1298/MAX1299 ADC,

internal clock, and reference buffer amplifier. Special

circuitry for temperature conversions is also deactivat-

ed. Wake-up time is limited by the reference buffer

amplifier and the associated bypass capacitor (see

Internal Reference). When an external reference is

used, wake-up time is 0.1ms.

Standby-Plus Mode

Standby-plus mode is similar to the standby mode, but

the internal reference output buffer remains active to

shorten the wake-up time to 0.1ms for internal refer-

ence mode. When using an external reference, stand-

by-plus mode is equivalent to standby mode.

Shutdown Mode

Shutdown mode turns off all functions other than start-

up circuitry, thereby reducing typical supply current to

2礎. Data registers are cleared. Use this power mode

when interconversion times are no less than 5ms.

Monitoring V

This mode of operation samples and converts the sup-

ply voltage, V

/4, which is internally generated. The

reference voltage must be larger than V

/8 for the

operation to work properly. From the result of a conver-

sion (CODE), CODE = 256 V

/ V

REF

Temperature Measurements

The MAX1298/MAX1299 perform temperature measure-

ments with internal or external diode-connected transis-

tors through a three-step process. First, the diode bias

current changes from 31.6礎 to 10礎 to produce a

temperature-dependent bias voltage difference, which

is amplified by a factor of 20 and converted to digital

format. Second, the bias current changes from 31.6礎

to 100礎, and the bias voltage difference is similarly

amplified by a factor of 20 and converted to digital for-

mat. Third, the intermediate results are subtracted to

achieve a digital output that is proportional to absolute

temperature in degrees Kelvin.

The reference voltage used in conjunction with tempera-

ture measurements is derived from the internal reference

source to ensure that 1LSB corresponds to 1/8 of a

degree. To convert to degrees Celsius, subtract 273.15

from the temperature inferred from the ADC output.

Temperature measurements require a conversion time

of 2.2ms.

Shield Output Buffer

The MAX1298/MAX1299 provide a shield output buffer

voltage at SHO that is approximately 0.6V (one diode

drop) above V

/2. When performing temperature

measurements with an external diode, use this voltage

to suppress error-producing leakage currents (see

Remote Diode Shielding). Figure 7 shows the SHO out-

put circuit.

Applications Information

Remote Diode Selection

Temperature accuracy depends on having a good-

quality, diode-connected small-signal transistor.

Accuracy has been experimentally verified for 2N3904

devices. CPUs and other ICs having on-board temper-

ature-sensing diodes can also be monitored if the

diode connections are uncommitted.

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

resistance less than 100&. Tight specifications for for-

ward current gain (+50 to +150, for example) indicate

that the manufacturer has good process controls and

that the devices have consistent V

characteristics.

(See Table 6 for recommended devices.)

For heatsink mounting, the 500-32BT02-000 thermal

sensor from Fenwal Electronics is a good choice. This

device consists of a diode-connected transistor, an alu-

minum plate with screw hole, and twisted-pair cable

(Fenwal Inc., Milford MA, 508-478-6000).

Table 4. Power-Mode Selection

PM1

PM0

MODE

Shutdown

Standby-plus

Standby

Normal operation

礎

SHO

Figure 7. SHO Output Circuit

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

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