LM99EVAL National Semiconductor, LM99EVAL Datasheet - Page 10

• Manufacturer Part Number: LM99EVAL
• Description: BOARD EVALUATION LM99
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM99EVAL

• Sensor Type: Temperature
• Sensing Range: 0°C ~ 125°C
• Interface: SMBus (2-Wire/I²C)
• Sensitivity: ±1°C
• Voltage - Supply: 3 V ~ 3.6 V
• Embedded: No
• Utilized Ic / Part: LM99
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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1.0 Functional Description
Remote temperature data is represented by an 11-bit, two’s
complement word with an LSB (Least Significant Bit) equal
Local Temperature data is represented by an 8-bit, two’s
complement byte with an LSB (Least Significant Bit)
equal to 1˚C:
1.7 OPEN-DRAIN OUTPUTS
The SMBData, ALERT and T_CRIT_A outputs are open-
drain outputs and do not have internal pull-ups. A “high” level
will not be observed on these pins until pull-up current is
provided by some external source, typically a pull-up resis-
tor. Choice of resistor value depends on many system fac-
tors but, in general, the pull-up resistor should be as large as
possible. This will minimize any internal temperature reading
errors due to internal heating of the LM99. The maximum
resistance of the pull-up to provide a 2.1V high level, based
on LM99 specification for High Level Output Current with the
supply voltage at 3.0V, is 82 kΩ (5%) or 88.7 kΩ (1%).
Output is 11-bit two’s complement word. LSB = 0.125 ˚C.
Temperature
Actual Remote Diode
+125˚C
+25˚C
−25˚C
−55˚C
Local
+1˚C
−1˚C
Actual Remote Diode
T_Crit Setpoint,˚C
0˚C
Temperature,˚C
126
120
125
126
130
135
140
0001 1001
0000 0001
0000 0000
1100 1001
0111 1101
1110 0111
1111 1111
Binary
Digital Output
Actual vs. LM99 Remote Temperature Conversion
Factory-Programmed
Remote T_CRIT High
Temperature Register, ˚C
LM99 Remote Diode
Setpoint, ˚C
Actual vs. Remote T_Crit Setpoint
+110
(Continued)
+104
+109
+110
+114
+119
+124
Hex
7Dh
FFh
E7h
C9h
19h
01h
00h
10
Binary Remote T_CRIT High
to 0.125˚C. The data format is a left justified 16-bit word
available in two 8-bit registers:
1.8 DIODE FAULT DETECTION
The LM99 is equipped with operational circuitry designed to
detect fault conditions concerning the remote diode. In the
event that the D+ pin is detected as shorted to V
floating, the Remote Temperature High Byte (RTHB) register
is loaded with +127˚C, the Remote Temperature Low Byte
(RTLB) register is loaded with 0, and the OPEN bit (D2) in
the status register is set. As a result, if the Remote T_CRIT
setpoint register (RCS) is set to a value less than +127˚C the
ALERT and T_Crit output pins will be pulled low, if the Alert
Mask and T_Crit Mask are disabled. If the Remote HIGH
Setpoint High Byte Register (RHSHB) is set to a value less
than +127˚C then ALERT will be pulled low, if the Alert Mask
is disabled. The OPEN bit itself will not trigger and ALERT.
In the event that the D+ pin is shorted to ground or D−, the
Remote Temperature High Byte (RTHB) register is loaded
with −128˚C (1000 0000) and the OPEN bit (D2) in the status
register will not be set. Since operating the LM99 at −128˚C
is beyond it’s operational limits, this temperature reading
represents this shorted fault condition. If the value in the
Remote Low Setpoint High Byte Register (RLSHB) is more
than −128˚C and the Alert Mask is disabled, ALERT will be
pulled low.
Remote diode temperature sensors that have been previ-
ously released and are competitive with the LM99 output a
code of 0˚C if the external diode is short-circuited. This
change is an improvement that allows a reading of 0˚C to be
truly interpreted as a genuine 0˚C reading and not a fault
condition.
Remote Temperature Register
Binary Results in LM99
Setpoint Value
0110 1000 0000 0000
0110 1101 0000 0000
0110 1110 0000 0000
0111 0010 0010 0000
0111 1100 0000 0000
0111 0111 0000 0000
0110 1110
Hex Remote T_CRIT
High Setpoint Value
Temperature
Hex Remote
Register
71h
6D00h
6800h
7100h
7200h
7700h
7200h
DD
or