Global Mixed-mode Technology Inc.
G768D
Two Remote Temperature Sensors and One Fan Con-
troller 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
Fan speed control range: 3,000 to 30,000 rpm
Fan speed accuracy: ±2%
Built-in MOSFET switch
Internal current-limit and over-temperature
protection for fan control
Watchdog for fan control
Alarm for fan failure
Precision Monitoring of 5V Power-Supply
Voltage
340ms Typical 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
Pin Configuration
General Description
The G768D contains a precise digital thermometer, a
fan controller, and a system-reset circuit.
Except for one less fan controller, G768D is backward
compatible with G768B. G768D has 2 more functions,
fan-failure detection and programmable thermal shut-
down 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.
G768D also contains a fan speed controller. It connects
directly to the fans and performs closed-loop control of
the fan speed independently. The only external compo-
nent required is a 10µF capacitor per channel. It deter-
mines the current fan speed based on the fan rotation
pulses and an externally supplied 32.768KHz clock.
Ordering Information
FANVCC 1
Vcc 2
DXP1 3
DXN 4
DXP2 5
RESET 6
DGND 7
AGND 8
G768D
16 TH_SHUT
15 Vcc
14 SMBCLK
13 NC
12 SMBDATA
11 ALERT
10 FG
9 CLK
PART NUMBER TEMP. RANGE PIN-PACKAGE
G768D
-55°C to +125°C
16SSOP
16Pin SSOP
Ver: 1.2
Apr 03, 2002
TEL: 886-3-5788833
http://www.gmt.com.tw
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