Two Remote Temperature Sensors and One Fan Con-
troller with SMBus Serial Interface and System Reset
Circuit
Ver: 1.4
May 23, 2003
TEL: 886-3-5788833
http://www.gmt.com.tw
1
G768D
Global Mixed-mode Technology Inc.
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 V
CC
=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 (SMBus
TM
) 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
ORDER NUMBER
TEMP. RANGE
PACKAGE
G768D
-55°C to +125°C
SSOP-16L
RESET
SMBDATA
1
2
3
4
5
6
7
8
FANVCC
Vcc
DXP1
DXN
DXP2
DGND
AGND
16
15
14
13
12
11
10
9
TH_SHUT
SMBCLK
NC
ALERT
FG
CLK
SSOP-16L
Vcc
G768D