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PDF G768D Data sheet ( Hoja de datos )
| Número de pieza | G768D | |
| Descripción | Two Remote Temperature Sensors and One Fan Controller | |
| Fabricantes | GMT | |
| Logotipo |  |
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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
1
1 page  
Global Mixed-mode Technology Inc.
Pin Description
G768D
PIN NAME
FUNCTION
1 FANVCC Output connected to VCC of fan.
2,15 VCC Supply Voltage Input, 4.5V to 5.5V. Bypass to GND with a 0.1µF capacitor.
Combined Current Source and A/D Positive Input for remote-diode channel 1. Do not leave DXP1 floating;
3 DXP1 tie DXP1 to DXN if no remote diode on channel 1 is used. Place a 2200pF capacitor between DXP1 and
DXN for noise filtering.
Combined Current Sink and A/D Negative Input. DXN is common negative node of both remote diodes on
4
DXN
channel 1 and 2. The traces of DXP1-DXN and DXP2-DXN pairs should be routed independently. The
common DXN should be connected together as close as possible to the IC. DXN is internally connected to
the GND pin for signal ground use.
Combined Current Source and A/D Positive Input for remote-diode channel 2. Do not leave DXP2 floating;
5 DXP2 tie DXP2 to DXN if no remote diode on channel 2 is used. Place a 2200pF capacitor between DXP2 and
DXN for noise filtering.
6 RESET RESET Output remains low while VCC is below the reset threshold, and for 340ms after VCC rises above
the reset threshold.
7 DGND Digital Ground.
8 AGND Analog Ground.
9 CLK 32.768KHz clock input for fan controller.
10 FG Fan pulse input.
11 ALERT SMBus Alert (interrupt) Output, open drain.
12 SMBDATA SMBus Serial-Data Input / Output, open drain.
13 NC
14 SMBCLK SMBus Serial-Clock Input.
16 TH_SHUT Thermal Shutdown Output, push-pull output.
Detailed Description
The G768D (patents pending) is a 3-in-1 IC. It consists
of one temperature sensor, 1 fan speed controller and
provides system-reset function.
The temperature sensor is designed to work in con-
junction with an external micro-controller (µC) or other
intelligence in thermostatic, process-control, or moni-
toring applications. The µC is typically a powerman-
agement or keyboard controller, generating SMBus se-
rial commands by "bit-banging" general-purpose in-
put-output (GPIO) pins or via a dedicated SMBus inter-
face block.
Essentially a 12-bit serial analog-to-digital converter
(ADC) with a sophisticated front end, the G768D con-
tains a switched current source, a multiplexer, an ADC,
an SMBus interface, one fan controller, a reset circuit
and associated control logic (Figure 1).
Temperature data from the ADC is loaded into two
data registers, where it is automatically compared with
data previously stored in four over/under-temperature
alarm registers.
ADC and Multiplexer
The ADC is an averaging type that integrates over a
60ms period (each channel, typical).
The multiplexer automatically steers bias currents
through two remote diodes, measures their forward
voltages, and computes their temperatures. All chan-
nels are converted automatically once the conversion
process has started, either in free-running or sin-
gle-shot mode. If one of the two channels is not used,
the device still performs all measurements, and the
user can simply ignore the results of the unused
channel. If the remote diode channel is unused, tie
DXPx to DXN rather than leaving the pins open.
The DXN input is internally connected to the ground
node inside the chip to set up the analog to digital
(A/D) inputs for a differential measurement. The
worst-case DXP-DXN differential input voltage range
is 0.25V to 0.95V.
Excess resistance in series with the remote diode causes
about +1/2°C error per ohm. Likewise, 200µV of offset
voltage forced on DXP-DXN causes about 1°C error.
Ver: 1.2
Apr 03, 2002
TEL: 886-3-5788833
http://www.gmt.com.tw
5
5 Page 
Global Mixed-mode Technology Inc.
G768D
If the remote channel is shorted (DXP to DXN or DXP
to GND), the ADC reads 0000 0000 so as not to trip
either the THIGH or TLOW alarms at their POR set-
tings. In applications that are never subjected to 0°C in
normal operation, a 0000 0000 result can be checked
to indicate a fault condition in which DXP is acciden-
tally short circuited. Similarly, if DXP is short circuited
to VCC, the ADC reads +127°C for both channels, and
the device alarms.
ALERT Interrupts
The ALERT interrupt output signal is latched and can
only be cleared by reading the Alert Response ad-
dress. Interrupts are generated in response to THIGH
and TLOW comparisons and when the remote diode is
disconnected (for continuity fault detection). The in-
terrupt does not halt automatic conversions; new tem-
perature data continues to be available over the SMBus
interface after ALERT is asserted. The interrupt output
rupt output pin is open-drain so that device can share
a common interrupt line. The interrupt rate can never
exceed the conversion rate.
The interface responds to the SMBus Alert Response
address, an interrupt pointer return-address feature
(see Alert Response Address section). Prior to taking
corrective action, always check to ensure that an in-
terrupt is valid by reading the current temperature.
Alert Response Address
The SMBus Alert Response interrupt pointer provides
quick fault identification for simple slave devices that
lack the complex, expensive logic needed to be a bus
master. Upon receiving an ALERT interrupt signal, the
host master can broadcast a Receive Byte transmission
to the Alert Response slave address (0001 100). Then
any slave device that generated an interrupt attempts to
identify itself by putting its own address on the bus.
Table 4. Command-Byte Bit Assignments
REGISTER
RRTE2
RRTE1
RSL
RCL
RCRA
RRHI2
RRLS2
RRHI1
RRLS1
WCA
WCRW
WRHA2
WRLN2
WRHA1
WRLN1
OSHT
SET_CNT1
ACT_CNT1
FAN_STA1
TMAX1
THYST1
TMAX2
THYST2
TCRIT1
TCRIT2
COMMAND
00h
01h
02h
03h
04h
05h
06h
07h
08h
09h
0Ah
0Bh
0Ch
0Dh
0Eh
0Fh
10h
11h
12h
31h
32h
33h
34h
35h
36h
POR STATE
FUNCTION
0000 0000b Read 2nd remote temperature: returns latest temperature
0000 0000b Read 1st remote temperature: returns latest temperature
N/A Read status byte (flags, busy signal)
0000 0000b Read configuration byte
0000 0010b Read conversion rate byte
0111 1111b (127) Read 2nd remote THIGH limit
1100 1001b(-55) Read 2nd remote TLOW limit
0111 1111b (127) Read 1st remote THIGH limit
1100 1001b (-55) Read 1st remote TLOW limit
N/A Write configuration byte
N/A Write conversion rate byte
N/A Write 2nd remote THIGH limit
N/A Write 2nd remote TLOW limit
N/A Write 1st remote THIGH limit
N/A Write 1st remote TLOW limit
N/A One-shot command (use send-byte format)
1111 1111b Write 1st fan programmed speed register
1111 1111b Read 1st fan actual speed register
10b Read 1st fan status register
0100 0110b (70) 1st remote TMAX
0011 1100b (60) 1st remote THYST
0100 0110b (70) 2nd remote TMAX
0011 1100b (60) 2nd remote THYST
0110 1100b (108) Critical temperature for 1st remote temperaure sensor
0101 1000b (88) Critical temperature for 2nd remote temperaure sensor
Ver: 1.2
Apr 03, 2002
TEL: 886-3-5788833
http://www.gmt.com.tw
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet G768D.PDF ] | |
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