PRODUCT SPECIFICATION
FMS2701
2
P
Architectural Overview
Overall operation of the FMS2701 is controlled by the
SMBus which sets register values and interrupt masking.
Four sensing inputs are monitored:
1. Remote temperature diode voltage
2. Ambient temperature sensing diode voltage
3. Remote 3.3 volt power supply voltage
4. Local 3.3 volt power supply
Following comparisons against either preset or programma-
ble thresholds, the following hardware outputs are set:
1. Master reset
2. Auxiliary reset
3. Temperature trip point violated (THERM)
4. Interrupt (INT)
Also set are the following register bits:
1. GPI active (General Purpose Input)
2. Remote Temperature limit exceeded
3. THERM input asserted
4. Remote diode fault
Fan Speed control voltage, FAN_SPD is set in the range
0–2.5V by loading the D/A Register through the SMBus.
External THERM = L forces FAN_SPD = 2.5V. A Master
Reset clears the D/A Register.
Temperature Channel
There are two temperature sense inputs: one for remote sens-
ing; the other for measuring ambient temperature. Both
inputs utilize the thermal variation of the voltage drop across
a diode, to derive the diode temperature.
Instead of sensing the change in V
D
at one current, which is
approximately –2mV/°C, V
D
is sampled at two currents
(I
MAX
= 10 and I
MIN
= 100 μA) to cancel out common error
voltages. Difference voltage between the two currents is
proportional to absolute temperature:
Where:
n = PN junction ideality factor, typically 1.0065 for the
Pentium II thermal diode. Nominal diode sensitivity is
199.7 μV/°C.
Following the A/D converter is a DSP block which averages
digitized temperature over several samples.
Upper and lower temperature limits are loaded into the limit
registers. If a limit is violated, an interrupt is generated. Remote
diode open or short circuit fault condition is also sensed.
Power Supply Voltage Monitors
Two Voltage Monitors operating over a 1.0 to 3.8 volt
supply range, sense VCC3 and VCC3AUX voltages. If
input VCC3 < 2.93 volt or master reset input, MR = L, then
RST= L until 140 msec after sensing the fault condition.
If the FMS2701 supply, VCC3AUX < 2.93 volt, AUXRST = L
until 140 msec. after sensing the fault condition, and the main
reset RST = L until 180 msec. after AUXRST is cleared.
When AUXRST = L, internal reset, INTRST =L. AUXRST
is bi-directional, accepting a hard reset input.
SMBus Interface
FMS2701 Registers are accessed through the SMBus inter-
face located at the address 0x2C + n; where n = 0, 1, 2
depending upon the state of ADD, a tri-level input. Within
the FMS2701, registers are accessed through an 8-bit bus.
Addressable Memory
Within the FMS2701, there are three sections of addressable
memory which implement the following functions.
Command Register (5 locations)
Configuration
Interrupt status
Interrupt mask
Interrupt status mirror
Extended function
Read only RAM (2 locations)
Company ID
Revision No.
Value RAM (13 locations)
Diode temperature, °C
THERM temperature trip points, °C
INT temperature limits, °C
Analog output D/A converter
Write accessible locations have default values that may be
overridden by programming through the SMBus interface.
q
nkT
V
D
ln
I
MAX
I
MIN
=