Datasheet
LM95221
www.ti.com
SNIS134B –MAY 2004–REVISED MARCH 2013
Table 6. Remote Temperature MSB (Read Only Address 11h, 12h) 10 bit plus sign format
(1)
:
BIT D7 D6 D5 D4 D3 D2 D1 D0
Value SIGN 64 32 16 8 4 2 1
(1) Temperature Data: LSb = 1°C.
Table 7. Remote Temperature MSB (Read Only Address 11h, 12h) 11-bit unsigned format
(1)
:
BIT D7 D6 D5 D4 D3 D2 D1 D0
Value 128 64 32 16 8 4 2 1
(1)
Table 8. Remote Temperature LSB(Read Only Address 21, 22h) 10-bit plus sign or 11-bit unsigned binary
formats
(1)
:
BIT D7 D6 D5 D4 D3 D2 D1 D0
Value 0.5 0.25 0.125 0 0 0 0 0
(1) Temperature Data: LSb = 0.125°C.
For data synchronization purposes, the MSB register should be read first if the user wants to read both MSB and
LSB registers. The LSB will be locked after the MSB is read. The LSB will be unlocked after being read. If the
user reads MSBs consecutively, each time the MSB is read, the LSB associated with that temperature will be
locked in and override the previous LSB value locked-in.
MANUFACTURERS ID REGISTER
(Read Address FEh) The default value is 01h.
DIE REVISION CODE REGISTER
(Read Address FFh) Value to be determined. This register will increment by 1 every time there is a revision to
the die by Texas Instruments.
Applications Hints
The LM95221 can be applied easily in the same way as other integrated-circuit temperature sensors, and its
remote diode sensing capability allows it to be used in new ways as well. It can be soldered to a printed circuit
board, and because the path of best thermal conductivity is between the die and the pins, its temperature will
effectively be that of the printed circuit board lands and traces soldered to the LM95221's pins. This presumes
that the ambient air temperature is almost the same as the surface temperature of the printed circuit board; if the
air temperature is much higher or lower than the surface temperature, the actual temperature of the LM95221 die
will be at an intermediate temperature between the surface and air temperatures. Again, the primary thermal
conduction path is through the leads, so the circuit board temperature will contribute to the die temperature much
more strongly than will the air temperature.
To measure temperature external to the LM95221's die, use a remote diode. This diode can be located on the
die of a target IC, allowing measurement of the IC's temperature, independent of the LM95221's temperature.
The LM95221 has been optimized to measure the remote thermal diode with a non-ideality of 1.008 and a series
resistance of 2.7Ω. The thermal diode on the Pentium 4 processor on the 90 nm process has a typical non-
ideality of 1.011 and a typical series resistance of 3.33Ω. Therefore, when measuring this thermal diode with the
LM95221 a typical offset of +1.5°C will be observed. This offset can be compensated for easily by subracting
1.5°C from the LM95221's readings. A discrete diode can also be used to sense the temperature of external
objects or ambient air. Remember that a discrete diode's temperature will be affected, and often dominated, by
the temperature of its leads.
Most silicon diodes do not lend themselves well to this application. It is recommended that a 2N3904 transistor
base emitter junction be used with the collector tied to the base.
When measuring a diode-connected 2N3904, with an LM95221, an offset of -3.25°C will be observed. This offset
can simply be added to the LM95221's reading:
T
2N3904
= T
LM95221
+ 3.25°C (1)
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