Rainbow-electronics MAX6673 Manual de usuario descargar pdf (Pagina 4)

Detailed Description

The MAX6672/MAX6673 are low-current (60µA, typ),

local temperature sensors ideal for interfacing with µCs

or µPs. The MAX6672/MAX6673 convert their own tem-

perature into a ratiometric PWM output. The square-

wave output waveform time ratio contains the

temperature information. The output is a square wave

with a nominal frequency of 1.4kHz at +25°C. The tem-

perature is obtained with the following formula:

Temperature (°C) = -200

(0.85 - t

/ t

)

+ (425

/ t

) - 273

Where t

is a fixed value and t

is modulated with the

temperature. Table 1 lists time ratio vs. temperature.

For temperatures greater than +50°C, the temperature

error is primarily first order and the following equation

can be used:

Temperature (°C) = (425

/ t

) - 273

The MAX6673 has a push-pull output. The rise and fall

times of the MAX6673 output are negligible with

respect to the period; therefore, errors caused by

capacitive loading are minimized.

The output load capacitance should be minimized in

MAX6672 applications because the sourcing current is

set by the pullup resistor. If the output capacitance

becomes too large, unequal rise and fall times distort

the pulse width, thus delivering inaccurate readings.

Applications Information

Pulse-Width Modulation

Interfacing with a µC

The Typical Application Circuit shows the MAX6672/

MAX6673 interfaced with a µC. In this example, the

MAX6672/MAX6673 convert the ambient temperature

to a PWM waveform. The µC reads the temperature by

measuring the t

and t

periods in software and hard-

ware. The only timing requirements are that the clock

frequency used for timing measurements is stable and

084121620

THERMAL RESPONSE

IN STIRRED OIL BATH

MAX6672 toc10

TIME (s)

TEMPERATURE (°C)

100

TRANSITION FROM +25°C AIR

TO +100°C STIRRED OIL BATH

-50 0-25 25 50 75 100 125

OUTPUT SINK CURRENT

vs. TEMPERATURE

MAX6672 toc11

TEMPERATURE (°C)

SINK CURRENT (mA)

= 0.4V

= 3.3V

= 5V

1.0

0.5

2.0

1.5

2.5

3.0

-50 0-25 25 50 75 100 125

MAX6673 OUTPUT SOURCE CURRENT

vs. TEMPERATURE

MAX6672 toc12

TEMPERATURE (°C)

SOURCE CURRENT (mA)

= V

- 0.5V

= 3.3V

= 5V

MAX6672/MAX6673

PWM Output Temperature Sensors

in SC70 Packages

4 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

= 3.3V, T

= +25°C, unless otherwise noted.)

PIN NAME FUNCTION

1 DOUT Digital Output Pin. PWM output, open-drain output (MAX6672), or push-pull output (MAX6673).

2 N.C. No Connection. Not internally connected.

3, 4 GND Pin 3 and Pin 4 must be tied together and connected to ground.

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

Pin Description

1 2 3 4 5 6

MAX6672/MAX6673 1

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Rainbow-electronics MAX6673 Manual de usuario Pagina 4

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