Rainbow-electronics DS1857 Manual do Utilizador descarregar pdf (Página 7)

DS1857

Dual Temperature-Controlled Resistors with

External Temperature Input and Monitors

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Detailed Description

The user can read the registers that monitor the V

MON1, MON2, and temperature analog signals. After

each signal conversion, a corresponding bit is set that

can be monitored to verify that a conversion has

occurred. The signals also have alarm flags that notify

the user when the signals go above or below the user-

defined value. Interrupts can also be set for each signal.

The position values of each resistor can be indepen-

dently programmed. The user can assign a unique

value to each resistor for every 2°C increment over the

-40°C to +102°C range. Both resistors can also be put

in a high-impedance mode using the RHIZ pin.

An external temperature sense input, EXTTMP, con-

verts an analog voltage into a digital value that repre-

sents temperature. Its scale is defined by +10mV/°C

gain and +500mV offset at 0°C. This corresponds to the

characteristics of the LM50 temperature sensor. The

resistor look-up tables are stepped through according

to this temperature every 2°C from -40°C to +102°C.

BALL

NAME

FUNCTION

1B2SDA 2-Wire Serial Data Interface. This pin is for serial data transfer to and from the device.

2A2SCL 2-Wire Serial Clock Interface. The serial clock input is used to clock data into and out of the device.

3C3A0Address Input. The address input pins specify the 2-wire address of the device (when ADFIX = 0).

4A1A1Address Input. The address input pins specify the 2-wire address of the device (when ADFIX = 0).

5B1A2Address Input. The address input pins specify the 2-wire address of the device (when ADFIX = 0).

6C2

WPEN

Write Protect Enable. The device is not write protected if WPEN is connected to ground. This pin has

an internal pullup (R

WPEN

) (See Table 6).

7C1

GND

Supply Ground

8D1

RHIZ

Resistor Disable Input. When high, this signal places both resistors in an off state or high impedance

mode. When low, the resistors are on. This pin has an internal pullup (R

RHIZ

9D3

MON1

External Analog Input

10 D4

MON2

External Analog Input

11 C4

EXTTMP

External Temperature Input. This analog signal is converted into a digital value that represents a

temperature. The digitized value indexes through the look-up tables.

12 D2 L0

Low-End Resistor 0 Terminal. It is not required that the low-end terminals be connected to a potential

less than the high-end terminal of the corresponding resistor. Voltage applied to any of the resistor

terminals cannot exceed the power-supply voltage, V

, or go below ground.

13 B3 H0

High-End Resistor 0 Terminal. It is not required that the high-end terminals be connected to a

potential greater than the low-end terminal of the corresponding resistor. Voltage applied to any of the

resistor terminals cannot exceed the power-supply voltage, V

, or go below ground.

14 B4 L1 Low-End Resistor 1 Terminal

15 A4 H1 High-End Resistor 1 Terminal.

16 A3 V

Supply Voltage

Pin Descriptions

1 2 3 4 5 6 7 8 9 10 11 12 ... 21 22

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