Datasheet

LM95231
www.ti.com SNIS139E –FEBRUARY 2005–REVISED MARCH 2013
FUNCTIONAL DESCRIPTION
The LM95231 is a digital sensor that can sense the temperature of 3 thermal zones using a sigma-delta analog-
to-digital converter. It can measure its local die temperature and the temperature of two external transistor
junctions using a ΔV
be
temperature sensing method. The LM95231 can support two external transistor types, a
Pentium 4 processor on 90nm process thermal diode or a 2N3904 diode connected transistor. The transistor
type is register programmable and does not require software intervention after initialization. The LM95231 has an
advanced input stage using Texas Instruments' TruTherm technology that reduces the spread in non-ideality
found in Pentium 4 processors on 90nm process. Internal analog filtering has been included in the thermal diode
input stage thus minimizing the need for external thermal diode filter capacitors. In addition a digital filter has
been added. These noise immunity improvements in the analog input stage along with the digital filtering will
allow longer trace tracks or cabling to the thermal diode than previous thermal diode sensor devices.
The 2-wire serial interface, of the LM95231, is compatible with SMBus 2.0 and I2C. Please see the SMBus 2.0
specification for a detailed description of the differences between the I2C bus and SMBus.
The temperature conversion rate is programmable to allow the user to optimize the current consumption of the
LM95231 to the system requirements. The LM95231 can be placed in shutdown to minimize power consumption
when temperature data is not required. While in shutdown, a 1-shot conversion mode allows system control of
the conversion rate for ultimate flexibility.
The remote diode temperature resolution is variable and depends on whether the digital filter is activated. When
the digital filter is active the resolution is thirteen bits and is programmable to 13-bits unsigned or 12-bits plus
sign, with a least-significant-bit (LSb) weight for both resolutions of 0.03125°C. When the digital filter is inactive
the resolution is eleven bits and is programmable to 11-bits unsigned or 10-bits plus sign, with a least-significant-
bit (LSb) weight for both resolutions of 0.125°C. The unsigned resolution allows the remote diodes to sense
temperatures above 127°C. Local temperature resolution is not programmable and is always 9-bits plus sign and
has a 0.25°C LSb.
The LM95231 remote diode temperature accuracy will be trimmed for the thermal diode of a Pentium 4 processor
on 90nm process or a 2N3904 transistor and the accuracy will be ensured only when using either of these diodes
when selected appropriately. TruTherm mode should be enabled when measuring a Pentium 4 processor on
90nm process and disabled when measuring a 2N3904 transistor. Enabling TruTherm mode with a 2N3904
transistor connected may produce unexpected temperature readings.
Diode fault detection circuitry in the LM95231 can detect the presence of a remote diode: whether D+ is shorted
to V
DD
, D- or ground, or whether D+ is floating.
The LM95231 register set has an 8-bit data structure and includes:
1. Most-Significant-Byte (MSB) Local Temperature Register
2. Least-Significant-Byte (LSB) Local Temperature Register
3. MSB Remote Temperature 1 Register
4. LSB Remote Temperature 1 Register
5. MSB Remote Temperature 2 Register
6. LSB Remote Temperature 2 Register
7. Status Register: busy, diode fault
8. Configuration Register: resolution control, conversion rate control, standby control
9. Remote Diode Filter Setting
10. Remote Diode Model Select
11. Remote Diode TruTherm Mode Control
12. 1-shot Register
13. Manufacturer ID
14. Revision ID
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