ADT7476 Analog Devices, Inc., ADT7476 Datasheet - Page 20

• Manufacturer Part Number: ADT7476
• Description: Dbcool Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

ADT7476
VID CODE MONITORING
The ADT7476 has five dedicated voltage ID (VID code) inputs.
These are digital inputs that can be read back through the VID
register (0x43) to determine the processor voltage required or
being used in the system. Five VID code inputs support VRM9.x
solutions. In addition, Pin 21 (12 V input) can be reconfigured as
a sixth VID input to satisfy future VRM requirements.
VID Code Register (0x43)
Bit 0 = VID0, reflects logic state of Pin 5.
Bit 1 = VID1, reflects logic state of Pin 6.
Bit 2 = VID2, reflects logic state of Pin 7.
Bit 3 = VID3, reflects logic state of Pin 8.
Bit 4 = VID4, reflects logic state of Pin 19.
Bit 5 = VID5, reconfigurable 12 V input. This bit reads 0 when
Pin 21 is configured as the 12 V input. This bit reflects the logic
state of Pin 21 when the pin is configured as VID5.
VID CODE INPUT THRESHOLD VOLTAGE
The switching threshold for the VID code inputs is approximately
1 V. To enable future compatibility, it is possible to reduce the
VID code input threshold to 0.6 V. Bit 6 (THLD) of the VID
register (0x43) controls the VID input threshold voltage.
VID Code Register (0x43)
Bit 6 THLD = 0, VID switching threshold = 1 V,
V
Bit 6 THLD = 1, VID switching threshold = 0.6 V,
V
Bit 7 VIDSEL = 0, Pin 21 functions as a 12 V measurement
input. Software can read this bit to determine that there are five
VID inputs being monitored. Bit 5 of Register 0x43 (VID5)
always reads back 0. Bit 0 of Status Register 2 (0x42) reflects
12 V out-of-limit measurements.
Bit 7 VIDSEL = 1, Pin 21 functions as the sixth VID code input
(VID5). Software can read this bit to determine that there are
six VID inputs being monitored. Bit 5 of Register 0x43 reflects
the logic state of Pin 21. Bit 0 of Status Register 2 (0x42) reflects
VID code changes.
Reconfiguring Pin 21 as VID5 Input
Pin 21 can be reconfigured as a sixth VID code input (VID5)
for VRM10 compatible systems. Because the pin is configured
as VID5, it is not possible to monitor a 12 V supply.
Bit 7 of the VID configuration register (0x43) determines the
function of Pin 21. System or BIOS software can read the state
of Bit 7 to determine whether the system is designed to monitor
12 V or is monitoring a sixth VID input.
VID CODE CHANGE DETECT FUNCTION
The ADT7476 has a VID code change detect function. When
Pin 21 is configured as the VID5 input, VID code changes are
OL
OL
< 0.8 V, V
< 0.4 V, V
IH
IH
> 1.7 V, V
> 0.8 V, V
MAX
MAX
= 3.3 V.
= 3.3 V.
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detected and reported back by the ADT7476. Bit 0 of Interrupt
Status Register 2 (0x42) is the 12 V/VC bit and denotes a VID
change when set. The VID code change bit is set when the logic
states on the VID inputs are different than they were 11 μs
previously. The change of VID code is used to generate an
SMBALERT interrupt. If an SMBALERT interrupt is not
required, Bit 0 of Interrupt Mask Register 2 (0x75), when set,
prevents SMBALERT s from occurring on VID code changes.
Interrupt Status Register 2 (0x42)
Bit 0 12 V/VC = 0, if Pin 21 is configured as VID5, Logic 0
denotes no change in VID code within the last 11 μs.
Bit 0 12 V/VC = 1, if Pin 21 is configured as VID5, Logic 1 means
that a change has occurred on the VID code inputs within the
last 11 μs. An SMBALERT is generated if this function is enabled.
PROGRAMMING THE GPIOS
The ADT7476 follows an upgrade path from the ADM1027 to
ADT7476. To maintain consistency between versions, it is
necessary to omit references to GPIO5. As a result, there are six
GPIOs as follows: GPIO0, GPIO1, GPIO2, GPIO3, GPIO4, and
GPIO6.
Setting Bit 4 of Configuration Register 5 (0x7C) to 1 enables
GPIO functionality. This turns all pins configured as VID
inputs into general-purpose outputs. Writing to the corres-
ponding VID bit in the VID register (0x43) sets the polarity for
the corresponding GPIO. GPIO6 can be programmed indepen-
dently as an input/output using Bits [3:2] of Configuration
Register 5 (0x7C).
TEMPERATURE MEASUREMENT METHOD
Local Temperature Measurement
The ADT7476 contains an on-chip band gap temperature
sensor whose output is digitized by the on-chip, 10-bit ADC.
The 8-bit MSB temperature data is stored in the temperature
registers (Register 0x25, Register 0x26, and Register 0x27).
Because both positive and negative temperatures can be
measured, the temperature data is stored in Offset 64 format or
twos complement format, as shown in Table 10 and Table 11.
Theoretically, the temperature sensor and ADC can measure
temperatures from −63°C to +127°C (or −61°C to +191°C in
the extended temperature range) with a resolution of 0.25°C.
However, this exceeds the operating temperature range of the
device, so local temperature measurements outside the ADT7476
operating temperature range are not possible.
Remote Temperature Measurement
The ADT7476 can measure the temperature of two remote
diode sensors or diode-connected transistors connected to
Pin 17 and Pin 18 or to Pin 15 and Pin 16.
The forward voltage of a diode or diode-connected transistor
operated at a constant current exhibits a negative temperature
coefficient of about −2 mV/°C. Unfortunately, the absolute