Remote/Local Temperature Sensor, 2 Fan Controllers
with SMBus Serial Interface and System Reset Circuit
Ver 1.3
Oct 28, 2002
TEL: 886-3-5788833
http://www.gmt.com.tw
1
G768B
Global Mixed-mode Technology Inc.
Features
Measures Two Remote and One Local
Temperatures
No Calibration Required
SMBus 2-Wire Serial Interface
Programmable Under/Over-temperature
Alarms
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
Constant Fan Speed Control
Built-in MOSFET switch
Internal short-circuit protection
PWM control for stable operation
Watchdog for fan control
Precision Monitoring of 5V Power-Supply
Voltage
140ms Min 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 G768B contains a precise digital thermometer, 2
fan controllers, and a system-reset circuit.
The G768B is backward compatible with G768, Except
that there is an additional watchdog function. This
function prevents fan from being out of control when
system fails.
The thermometer reports the temperature of 2 remote
sensors and its own package. The remote sensors are
diode-connected transistors typically a low-cost, easily
mounted 2N3904 NPN type that replace conventional
thermistors 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.
G768B also contains a 2-channel fan speed controller.
It connects directly to the fans and performs
closed-loop control of the fan speed independently.
The only external component required is a 10μF ca-
pacitor per channel. It determines the current fan
speed based on the fan rotation pulses and an exter-
nally supplied clock.
(To be continued)
Ordering Information
PART*
TEMP. RANGE
PIN-PACKAGE
G768B
-10°C to +85°C
16SSOP
RESET
SMBDATA
1
2
3
4
5
6
7
8
OUT1
Vcc
DXP1
DXN
DXP2
GND
GND
16
15
14
13
12
11
10
9
OUT2
SMBCLK
FG2
ALERT
FG1
CLK
16Pin SSOP
Vcc
G768B