adm1027 Analog Devices, Inc., adm1027 Datasheet - Page 11

• Manufacturer Part Number: adm1027
• Description: Dbcool? Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

5. Once the ADM1027 has responded to the alert response
SMBus Timeout
The ADM1027 includes an SMBus timeout feature. If there is
no SMBus activity for a minimum of 15 ms and a maximum of
35 ms, the ADM1027 assumes that the bus is locked and releases
the bus. This prevents the device from locking or holding the
SMBus expecting data. Some SMBus controllers cannot handle
the SMBus timeout feature, so it can be disabled.
CONFIGURATION REGISTER 1 – Register 0x40
<6> TODIS = 0; SMBus timeout enabled (default)
<6> TODIS = 1; SMBus timeout disabled
VOLTAGE MEASUREMENT INPUTS
The ADM1027 has four external voltage measurement channels.
It can also measure its own supply voltage, V
Pins 20 to 23 are dedicated to measuring 5 V, 12 V, 2.5 V supplies
and the processor core voltage V
V
pin (Pin 4). Setting Bit 7 of Configuration Register 1 (Reg. 0x40)
allows a 5 V supply to power the ADM1027 and be measured
without overranging the V
input can be used to monitor a chipset supply voltage in com-
puter systems.
ANALOG-TO-DIGITAL CONVERTER
All analog inputs are multiplexed into the on-chip, successive
approximation, analog-to-digital converter. This has a resolu-
tion of 10 bits. The basic input range is 0 V to 2.25 V, but the
inputs have built-in attenuators to allow measurement of 2.5 V,
3.3 V, 5 V, 12 V and the processor core voltage V
any external components. To allow for the tolerance of these
supply voltages, the ADC produces an output of 3/4 full scale
(768 decimal or 300 hex) for the nominal input voltage, and so
has adequate headroom to cope with overvoltages.
INPUT CIRCUITRY
The internal structure for the analog inputs is shown in Figure 12.
Each input circuit consists of an input protection diode, an
attenuator, and a capacitor to form a first order low-pass filter
that gives the input immunity to high frequency noise.
VOLTAGE MEASUREMENT REGISTERS
Reg. 0x20 2.5 V Reading = 0x00 default
Reg. 0x21 V
Reg. 0x22 V
Reg. 0x23 5 V Reading = 0x00 default
Reg. 0x24 12 V Reading = 0x00 default
REV. A
CC
address, the master must read the status registers and the
SMBALERT will only be cleared if the error condition has
gone away.
supply voltage measurement is carried out through the V
CCP
CC
Reading = 0x00 default
Reading = 0x00 default
CC
measurement channel. The 2.5 V
CCP
(0 V to 3 V input). The
CC
.
CCP
, without
CC
–11–
VOLTAGE MEASUREMENT LIMIT REGISTERS
Associated with each voltage measurement channel are high and
low limit registers. Exceeding the programmed high or low limit
causes the appropriate status bit to be set. Exceeding either limit
can also generate SMBALERT interrupts.
Reg. 0x44 2.5 V Low Limit = 0x00 default
Reg. 0x45 2.5 V High Limit = 0xFF default
Reg. 0x46 V
Reg. 0x47 V
Reg. 0x48 V
Reg. 0x49 V
Reg. 0x4A 5 V Low Limit = 0x00 default
Reg. 0x4B 5 V High Limit = 0xFF default
Reg. 0x4C 12 V Low Limit = 0x00 default
Reg. 0x4D 12 V High Limit = 0xFF default
Table II shows the input ranges of the analog inputs and output
codes of the 10-bit A/D converter.
When the ADC is running, it samples and converts a voltage
input in 711 ms, and averages 16 conversions to reduce noise.
Therefore a measurement on any input takes nominally 11.38 ms.
V
3.3V
2.5V
12V
CCPIN
Figure 12. Structure of Analog Inputs
CCP
CCP
CC
CC
5V
IN
IN
IN
IN
Low Limit = 0x00 default
High Limit = 0xFF default
Low Limit = 0x00 default
High Limit = 0xFF default
120k
93k
68k
45k
35k
105k
20k
47k
71k
94k
30pF
30pF
30pF
30pF
35pF
ADM1027
MUX