Global Mixed-mode Technology Inc.
G7921
Three Remote Temperature Sensors and One Fan
Controllers with SMBus Serial Interface and System
Reset Circuit
Features
General Description
Measures Three Remote Temperatures
The G7921 contains 3 precise digital thermometers,
one fan controllers, hardware and software thermal
shutdown, and a system-reset circuit.
Adjustable Offset for Each Sensor via SMBus
Accuracy: ±1°C (+ 60°C to + 100°C)
±3°C (- 10°C to + 120°C)
The thermometers report the temperature of 3 remote
sensors. The remote sensors are diode-connected tran-
sistors typically a low-cost, easily mounted 2N3904 NPN
type or the diode built-in in CPU. Remote accuracy is
±1°C for multiple transistor manufacturer. The G7921
also support offset adjust function via SMBus to fix the
error due to different CPU diode or parasitic resistors.
+4.5V to +5.5V Supply Range
Programmable Hardware Thermal Shutdown
for Sensor 2 and Programmable Software
Thermal Shutdown for Sensor 1, 3.
SMBus 2-Wire Serial Interface With Writting
Protection Function.
Alert Signal for Diode Fault, Fan Fail, and Fan
Out of Control
The 2-wire serial interface accepts standard System
Management Bus (SMBusTM) Write Byte, Read Byte,
Send Byte, and Receive Byte commands. The SMBus
address is 7ah for write and 7bh for read, and sup-
ports writting protection function by command 20h to
prevent error behavior of µP.
Supports SMBus Alert Response
Fan Drivers Using Linear Control Algorithm
with Built-in MOSFET
Closed Loop Speed Control and programmable
8 Bits Open Loop Voltage Control for Fan1
Wide speed control range for Fan1, Accuracy
within 2%, when SET_CNT1 > 50
Internal Current- limit and Over-temperature
Protection for the Fan
G7921 contains one fan controllers. FAN1 controller
performs closed-loop and open-loop control. G7921
determines the current fan speed based on the FG
inputs and an externally supplied 32.768KHz clock.
The driving ability of FAN1 is 500mA. G7921 also pro-
vide ALERT for fan fail and out of control event.
Reset Function Precision Monitoring of 5V
Power-Supply Voltage
Measure Thermal Diode with Transistor Model
Support 45nm, 65nm and 90nm CPU thermal
diode
The G7921 provides hardware and software thermal
shutdown. The hardware thermal shutdown is for the
sensor 2. The trigger point is set by external resistors.
The trigger points of software thermal shutdown are
set via SMBus. If thermal shutdown event occurs,
20-Pin SSOP Package
Applications
THERM pin outputs low.
Desktop and Notebook
Central Office Computers
Telecom Equipment
Smart Battery Packs
Industrial Controls
LAN Servers
The G7921 contains a microprocessor (µP) supervi-
sory circuit used to monitor the power supplies in µP
and digital systems. Reset threshold is set to 4.38V
typical.
Pin Configuration
Ordering Information
G7921
ORDER
NUMBER
TEMP.
RANGE
20
DVCC
FAN1
RESET
1
2
3
4
5
6
7
MARKING
PACKAGE
19 N.C.
18 SCL
G7921SF1U
G7921
-55°C to +125°C
SSOP-20
THERM_SET
FG1
Note: SF: SSOP-20
1: Bonding Code
U: Tape & Reel
DGND
17
16
SDA
DGND
VCC
ALERT
CLK
15
14
DXP1
13 THERM
12 DXN3
11 DXP3
DXN1
DXP2
8
9
SMBusTM is a trademark of Intel Corp.
SGND2 10
SSOP-20
TEL: 886-3-5788833
http://www.gmt.com.tw
Ver: 0.3
Jan 30, 2008
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