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Global Mixed-mode Technology Inc.
G771
Two Remote Temperature Sensors with SMBus
Serial Interface and System Reset Circuit
Features
Measures Two Remote Temperatures
No Calibration Required
SMBus 2-Wire Serial Interface
Programmable Under/Over-temperature Alarms
Programmable Thermal Shutdown Signal
Supports SMBus Alert Response
Accuracy: ±5°C (-40°C to + 125°C, remote)
±3°C (+60°C to + 100°C, remote)
4.5V to 5.5V Supply Range
Precision Monitoring of 5V Power-Supply
Voltage
140ms Min Power-On Reset Pulse Width
RESET Output
Guaranteed RESET Valid to VCC=1V
Power Supply Transient Immunity
No External Components needed for reset
function
Small, 16-Pin SSOP Package
Applications
Desktop and Notebook
Central Office Computers
Telecom Equipment
Smart Battery Packs
Test and Measurement
LAN Servers
Multi-Chip Modules
Industrial Controls
General Description
The G771 contains a precise digital thermometer, a
system-reset circuit, and a programmable thermal
shutdown signal.
The thermometer reports the temperature of 2 remote
sensors. The remote sensors are diode-connected
transistors typically a low-cost, easily mounted
2N3904 NPN type that replace conventional thermis-
tors or thermocouples. Remote accuracy is ±5°C for
multiple transistor manufacturers, with no calibration
needed. The remote channel can also measure the die
temperature of other ICs, such as microprocessors,
that contain an on-chip, diode-connected transistor.
The 2-wire serial interface accepts standard System
Management Bus (SMBusTM) Write Byte, Read Byte,
Send Byte, and Receive Byte commands to program
the alarm thresholds and to read temperature data.
The data format is 7 bits plus sign, with each bit cor-
responding to 1°C, in two’s-complement format.
Measurements can be done automatically and
autonomously, with the conversion rate programmed
by the user or programmed to operate in a single-shot
mode. The adjustable rate allows the user to control
the supply-current drain.
Ordering Information
PART*
G771
TEMP. RANGE
-55°C to +125°C
PIN-PACKAGE
16SSOP
Pin Configuration
NC 1
Vcc 2
DXP1 3
DXN 4
DXP2 5
NC 6
DGND 7
AGND 8
G771
16 TH_SHUT(push-pull)
15 NC
14 SMBCLK
13 NC
12 SMBDATA
11 ALERT
10 NC
9 RESET
16Pin SSOP
Ver 0.2 Preliminary
Dec 11, 2001
TEL: 886-3-5788833
http://www.gmt.com.tw
1
Global Mixed-mode Technology Inc.
G771
The G771 also contains a microprocessor (µP) super-
visory circuit used to monitor the power supplies in µP
and digital systems. They provide excellent circuit re-
liability and low cost by eliminating external compo-
nents and adjustments when used with 5V-powered
circuits. This circuit asserts a reset signal whenever
the VCC supply voltage declines below a preset
threshold, keeping it asserted for at least 140ms after
VCC has risen above the reset threshold. The G771
has an active-low RESET output. The reset com-
parator is designed to ignore fast transients on VCC.
Reset threshold of this circuit is set to 4.38V.
When the temperature of DX1 reaches or exceeds
the Tcrit1 (SMBus 35h) threshold consecutively for
the times equal to the number of faults of the
FQ_TH_SHUT registers, TH_SHUT pin becomes
logic high. The same mechanism is duplicated for
DX2. Therefore, either one of DX1, DX2 continu-
ously over their respective Tcrit, the TH_SHUT will
assert logic high to indicate a thermal shutdown
event.
The G771’s SMBus device address is fixed to be 7Ah
for write and 7Bh for read.
The G771 is available in a small, 16-pin SSOP sur-
face-mount package.
Typical Operating Circuit
TH_SHUT
0.1µF
Vcc
0.1µF
Vcc
2N3904
DXP1
G771
SMBCLK
2200pF
DXN
SMBDATA
ALERT
2N3904
DXP2
2200pF
RESET
µP
RESET
GND
10k EACH
SMBCLK
SMBDATA
INTERRUPT TO µC
Ver 0.2 Preliminary
Dec 11, 2001
TEL: 886-3-5788833
http://www.gmt.com.tw
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