lm96163cisdx-1 National Semiconductor Corporation, lm96163cisdx-1 Datasheet - Page 9

• Manufacturer Part Number: lm96163cisdx-1
• Description: Remote Diode Digital Temperature Sensor With Integrated Fan Control And Trutherm Bjt Transistor Beta Compensation Technology
• Manufacturer: National Semiconductor Corporation

1.0 Functional Description
The LM96163 Remote Diode Temperature Sensor with Inte-
grated Fan Control incorporates a ΔV
sensor utilizing a Local or Remote diode and a 10-bit plus sign
ΔΣ ADC (Delta-Sigma Analog-to-Digital Converter). The
LM96163 includes TruTherm BJT beta compensation tech-
nology that allows precision temperature sensing of remote
diodes found in sub-micron processes. The pulse-width mod-
ulated (PWM) open-drain output, with a pull-up resistor, is
driven by a 12-point temperature to duty cycle look-up table
(LUT) and can directly drive a PWM input of a 4-pin fan in
order to modulate it's speed enabling optimum system acous-
tic performance. The LM96163 LUT fan control algorithm also
includes a smoothing function that allows the PWM duty cycle
to gradually change over a programmed time interval when
switching from one level to the next in the LUT. When running
at a frequency of 22.5kHz the PWM output resolution is
0.39%. The LM96163 includes a TACH input that can mea-
sure the speed of a fan using the pulses from a 3 or 4 pin fan’s
tachometer output. The LM96163 includes a smart-tach mea-
surement mode to accommodate the corrupted tachometer
pulses when using switching transistor power drive to modu-
late the fan speed. The LM96163 has an ALERT open-drain
output that will be pulled low when the measured temperature
exceeds certain programmed limits when enabled. Details
are contained in the sections below.
The LM96163's two-wire interface is compatible with the SM-
Bus Specification 2.0 . For more information the reader is
directed to www.smbus.org.
In the LM96163 digital comparators are used to compare the
measured Local Temperature (LT) to the Local High Setpoint
user-programmable temperature limit register. The measured
Remote Temperature (RT) is digitally compared to the Re-
mote High Setpoint (RHS), the Remote Low Setpoint (RLS),
and the Remote T_CRIT Setpoint (RCS) user-programmable
temperature limits. An ALERT output will occur when the
measured temperature is: (1) higher than either the High Set-
point or the T_CRIT Setpoint, or (2) lower than the Low
Setpoint. The ALERT Mask register allows the user to prevent
the generation of these ALERT outputs. A TCRIT output will
occur when the measured temperature is higher than the
T_CRIT Setpoint.
The TCRIT function and the look-up table temperature hys-
teresis can be set separately. The hysteresis value associat-
ed with the TCRIT output is set in the Remote T_CRIT
Hysteresis Register. The value associated with the look-up
table function is set in the Lookup Table Hysteresis Register.
The LM96163 may be placed in a low power Standby mode
by setting the Standby bit found in the Configuration Register.
In the Standby mode continuous conversions are stopped. In
Standby mode the user may choose to allow the PWM output
signal to continue, or not, by programming the PWM Disable
in Standby bit in the Configuration Register.
The Local Temperature reading and setpoint data registers
are 8-bits wide. The format of the 11-bit remote temperature
data is a 16-bit left justified word. Two 8-bit registers, high and
low bytes, are provided for each setpoint as well as the tem-
perature reading. A digital filter may be invoked for remote
temperature readings that increases the resolution from 11-
bits to 13-bits. The temperature readings are also available in
an unsigned format allowing resolution above 127°C. Two
Remote Temperature Offset (RTO) Registers: High Byte and
Low Byte (RTOHB and RTOLB) may be used to correct the
temperature readings by adding or subtracting a fixed value
based on a different non-ideality factor and series resistance
BE
-based temperature
9
of the thermal diode if different from the thermal diode found
in the Intel processors on 45 nm process. See section 3.4
DIODE NON-IDEALITY.
1.2 ALERT and TCRIT OUTPUTS
In this section we will address the ALERT and TCRIT active-
low open-drain output functions. When the ALERT Mask bit
in the Configuration register is written as zero the ALERT in-
terrupts are enabled.
The LM96163's ALERT pin is versatile and can produce three
different methods of use to best serve the system designer:
(1) as a temperature comparator (2) as a temperature-based
interrupt flag, and (3) as part of an SMBus ALERT System.
The three methods of use are further described below. The
ALERT and interrupt methods are different only in how the
user interacts with the LM96163.
The remote temperature (RT) reading is associated with a
T_CRIT Setpoint Register, and both local and remote tem-
perature (LT and RT) readings are associated with a HIGH
setpoint register (LHS and RHS). The RT is also associated
with a LOW setpoint register (RLS). At the end of every tem-
perature reading a digital comparison determines whether
that reading is above its HIGH or T_CRIT setpoint or below
its LOW setpoint. If so, the corresponding bit in the ALERT
Status Register is set. If the ALERT mask bit is low, any bit
set in the ALERT Status Register, with the exception of Busy
or RDFA, will cause the ALERT output to be pulled low. Any
temperature conversion that is out of the limits defined in the
temperature setpoint registers will trigger an ALERT. Addi-
tionally, the ALERT Mask Bit must be cleared to trigger an
ALERT in all modes.
The format of the Remote High limit and T_CRIT limit com-
parison is programmable. The USF bit found in the Enhanced
Configuration register controls whether comparisons use a
signed or unsigned format. The temperature format used for
Remote High and T_CRIT limit comparisons is +255.875 °C
to -256 °C.
The three different ALERT modes and TCRIT function will be
discussed in the following sections.
1.2.1 ALERT Output as a Temperature Comparator
When the LM96163 is used in a system in which does not
require temperature-based interrupts, the ALERT output
could be used as a temperature comparator. In this mode,
once the condition that triggered the ALERT to go low is no
longer present, the ALERT is negated (Figure 1). For exam-
ple, if the ALERT output was activated by the comparison of
LT > LHS, when this condition is no longer true, the ALERT
will return HIGH. This mode allows operation without software
intervention, once all registers are configured during set-up.
In order for the ALERT to be used as a temperature com-
parator, the Comparator Mode bit in the Remote Diode Tem-
perature Filter and Comparator Mode Register must be
asserted. This is not the power-on default state.
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