Ver: 2.4
May 23, 2003
TEL: 886-3-5788833
http://www.gmt.com.tw
5
G767
Global Mixed-mode Technology Inc.
Figure 1. Functional Diagram
A/D Conversion Sequence
If a Start command is written (or generated automati-
cally in the free-running auto-convert mode), both
channels are converted, and the results of both meas-
urements are available after the end of conversion. A
BUSY status bit in the status byte shows that the de-
vice is actually performing a new conversion; however,
even if the ADC is busy, the results of the previous
conversion are always available.
Remote-Diode Selection
Temperature
good-quality, diode-connected small-signal transistor.
Accuracy has been experimentally verified for all of the
devices listed in Table 1. The G767 can also directly
measure the die temperature of CPUs and other inte-
grated circuits having on-board temperature-sensing
diodes.
accuracy
depends
on
having
a
The transistor must be a small-signal type with a rela-
tively high forward voltage; otherwise, the A/D input
voltage range can be violated. The forward voltage
must be greater than 0.25V at 10μA; check to ensure
this is true at the highest expected temperature. The
forward voltage must be less than 0.95V at 100μA;
check to ensure this is true at the lowest expected
temperature. Large power transistors don’t work at all.
Also, ensure that the base resistance is less than
100
. Tight specifications for forward-current gain
(+50 to +150, for example) indicate that the manufac-
turer has good process controls and that the devices
have consistent VBE characteristics.
Thermal Mass and Self-Heating
Thermal mass can seriously degrade the G767’s ef-
fective accuracy. The thermal time constant of the
SSOP-16 package is about 140sec in still air. For the
G767 junction temperature to settle to within +1°C
after a sudden +100°C change requires about five
time constants or 12 minutes. The use of smaller
packages for remote sensors, such as SOT23s, im-
proves the situation. Take care to account for thermal
gradients between the heat source and the sensor,
and ensure that stray air currents across the sensor
package do not interfere with measurement accuracy.
V
CC
DXP
DXN
MUX
+
+
+
REMOTE
LOCAL
ADC
CONTROL
LOGIC
STBY ADD0 ADD1
ADDRESS
DECODER
SMBUS
7
SMBDATA
SMBCLK
READ WRITE
DIODE
FAULT
2
8
8
COMMAND BYTE
(INDEX) REGISTER
STATUS BYTE
REGISTER
CONFIGURATION
BYTE REGISTER
CONVERSION RATE
REGISTER
ALERT RESPONSE
ADDRESS REGISTER
8
8
LOCAL EMPERATURE
DATA REGISTER
HIGH-TEMPETATURE
THRESHOLD (LOCALT
HIGH
)
LOW-TEMPETATURE
THRESHOLD (LOCAL T
LOW
)
8
DIGITAL COMPARATOR
(LOCAL)
SELECTED VIA
SLAVE ADD = 0001 100
8
8
ALERT
Q
S
R
REMOTE TEMPERATURE
DATA REGISTER
HIGH-TEMPETATURE
THRESHOLD (REMOTE
HIGH
)
LOW-TEMPETATURE
THRESHOLD (REMOTE
LOW
)
DIGITAL COMPARATOR
(REMOTE)