Rainbow Electronics DS1857 - Manual (Page 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 CC ,
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.
PIN BALL NAME FUNCTION
1 B2 SDA 2-Wire Serial Data Interface. This pin is for serial data transfer to and from the device.
2 A2 SCL 2-Wire Serial Clock Interface. The serial clock input is used to clock data into and out of the device.
3 C3 A0 Address Input. The address input pins specify the 2-wire address of the device (when ADFIX = 0).
4 A1 A1 Address Input. The address input pins specify the 2-wire address of the device (when ADFIX = 0).
5 B1 A2 Address Input. The address input pins specify the 2-wire address of the device (when ADFIX = 0).
6 C2 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).
7 C1 GND Supply Ground
8 D1 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 ).
9 D3 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
CC , 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
CC , or go below ground.
14 B4 L1 Low-End Resistor 1 Terminal
15 A4 H1 High-End Resistor 1 Terminal.
16 A3 V
CC
Supply Voltage
Pin Descriptions