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Global Mixed-mode Technology Inc.
G768D
Two Remote Temperature Sensors and One Fan Controller 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 shutdown 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 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 corresponding 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 component required is a 10µF capacitor per channel. It determines the current fan speed based on the fan rotation
pulses and an externally supplied 32.768KHz clock.
Ordering Information
Vcc
DXP1
DXN
DXP2
RESET
DGND
AGND
1
2
3
4
5
6
7
8
FANVCC
Ver: 1.2
Apr 03, 2002
G768D
16Pin SSOP
16
15
14
13
12
11
10
9
TH_SHUT
Vcc
SMBCLK
NC
SMBDATA
ALERT
FG
CLK
PART NUMBER TEMP. RANGE PIN-PACKAGE
G768D -55°C to +125°C 16SSOP
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Global Mixed-mode Technology Inc.
It uses LDO method and an on-chip MOSFET to control the fan speed to ±2% of the programmed speed.
The desired fan speed is also programmed via
SMBus
read via the SMBus
TM
. The actual fan speed and fan status can be
TM
. Short-circuit protection is implemented to prevent damages to the fan and this IC
itself. The accepted frequency of fan rotation pulses is
100~1000Hz, which corresponds to 3,000 to 30,000
rpm for a typical fan that produces two pulses per
revolution. The G768D also turns on the fans by hardware watchdog system. The fan controller would fully
turn on the fan when any of the following conditions
happens.
1. when either of the remote temperature is higher than
its own T
MAX
.
2.when either of these two remote diodes is open.
3.when both remote diodes are short.
Typical Operating Circuit
IN
FAN1
FAN1
IN
1µF
1µF
FANVCC
FANVCC
G768D
The G768D also contains a microprocessor (µP) supervisory circuit used to monitor the power supplies in
µP and digital systems. They provide excellent circuit
reliability and low cost by eliminating external components and adjustments when used with 5V-powered
circuits. This circuit asserts a reset signal whenever
the V
threshold, keeping it asserted for at least 140ms after
V
has an active-low
parator is designed to ignore fast transients on V
Reset threshold of this circuit is set to 4.4V typical.
The G768D is available in a small, 16-pin SSOP surface-mount package.
TH_SHUT
TH_SHUT
supply voltage declines below a preset
CC
has risen above the reset threshold. The G768D
CC
RESET output. The reset com-
CC
.
2N3904
2N3904
2N3904
2N3904
RESET
RESET
µP
µP
FG
FG
2200pF
2200pF
2200pF
2200pF
FG
FG
DXP1
DXP1
DXN
DXN
DXP2
DXP2
RESET
RESET
GND
GND
G768D
G768D
SMBDATA
SMBDATA
VCC
VCC
SMBCLK
SMBCLK
ALERT
ALERT
CLK
CLK
10µF
10µF
CLOCK 32.768kHz
CLOCK 32.768kHz
10k EACH
10k EACH
SMBCLK
SMBCLK
SMBDATA
SMBDATA
INTERRUPT TO µC
INTERRUPT TO µC
Ver: 1.2
Apr 03, 2002
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Global Mixed-mode Technology Inc.
G768D
Absolute Maximum Ratings
VCC to GND……………….………….…….-0.3V to +6V
DXP1, DXP2 to GND……………0.3V to (V
+ 0.3V)
CC
DXN to GND……………………………...-0.3V to +0.8V
CLK, FG, SMBCLK, SMBDATA,
ALERT
to
GND.……………………….…….………...-0.3V to +6V
SMBDATA,
ALERT
Current…………...-1mA to +50mA
DXN Current………………………………………±1mA
ESD Protection (SMBCLK, SMBDATA,
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are
stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may
affect device reliability.
ALERT
, hu-
man body model)….……….………….……..….….2000V
ESD Protection (other pins, human body model)…2000V
Continuous Power Dissipation (T
= +70°C) SSOP
A
(de-rate 8.30mW/°C above +70°C)…………667mW
Operating Temperature Range…-55°C to +125°C
Junction Temperature………………....+150°C
Storage temperature Range………-65°C to +165°C
Lead Temperature (soldering, 10sec)……….+300°C
Electrical Characteristics
(VCC = + 5V, TA = 60°C, unless otherwise noted.)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Temperature Sensor
Temperature Resolution (Note 1) Monotonicity guaranteed 8 Bits
Temperature Error, Remote Diode (Notes 2
and 3)
Temperature Error, Local Diode
(Notes 1 and 2)
Supply-Voltage Range 4.5 5 5.5 V
Under-voltage Lockout Threshold VCC input, disables A/D conversion, rising edge 2.6 2.8 2.95 V
Under-voltage Lockout Hysteresis 50 mV
Power-On Reset Threshold VCC, falling edge 1.0 1.7 2.5 V
POR Threshold Hysteresis 50 mV
Standby Supply Current
Average Operating Supply Current
Conversion Time From stop bit to conversion complete (all channels) 94 125 156 ms
Conversion Rate Timing Error Auto-convert mode -25 25 %
Remote-Diode Source Current DXP forced to 1.5V
Fan Controller
Supply voltage VCC 4.5 5 5.5 V
Shutdown current Fan speed = 0rpm 2 5 µA
MOSFET on resistance 0.2 0.25
Short-circuit current limit 0.5 A
Input logic low VIL 0.7. V
Input logic high VIH 1.0 V
Clock frequency CLK 32.768 KHz
FANVCC over-current trig 600 mA
FANVCC current limit 500 mA
FG input Positive-going threshold voltage VCC=5V 1 V
FG input Negative-going threshold voltage VCC=5V 0.7 V
FG input Hysteresis voltage VCC=5V 0.3 V
TR = 0°C to +125°C -5 5
= 60°C to +100°C -3 3
T
R
Including long-term drift T
Logic inputs forced to V
GND
Auto-convert mode, average
measured over 4sec. Logic
inputs forced to V
or GND
CC
CC
= +60°C to +100°C -3 3 °C
A
SMBus static 3 10
or
Hardware or software
standby, SMBCLK at 10kHz
0.25 conv/sec 250 300
2.0 conv/sec 300 350
High level 120 160 200
Low level 15 20 25
200
°C
µA
µA
µA
Ω
Ver: 1.2
Apr 03, 2002
3
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Page 4
Electrical Characteristics
Global Mixed-mode Technology Inc.
(continued)
G768D
(VCC = + 5V, TA = 60°C, unless otherwise noted.)
PARAMETER CONDITIONS MIN TYP MAX UNITS
SMBus Interface
Logic Input High Voltage SMBCLK, SMBDATA; VCC = 4.5V to 5.5V 2.4 V
Logic Input Low Voltage SMBCLK, SMBDATA; VCC = 4.5V to 5.5V 0.8 V
Logic Output Low Sink Current
Output High Leakage Current
ALERT
Logic Input Current Logic inputs forced to VCC or GND -2 2 µA
SMBus Input Capacitance SMBCLK, SMBDATA 5 pF
SMBus Clock Frequency (Note 4) DC 100 KHz
SMBCLK Clock Low Time t
SMBCLK Clock High Time t
SMBus Start-Condition Setup Time 4.7 µs
SMBus Repeated Start-Condition
Setup Time
SMBus Start-Condition Hold Time t
SMBus Start-Condition Setup Time t
SMBus Data Valid to SMBCLK RisingEdge Time
SMBus Data-Hold Time t
SMBCLK Falling Edge to SMBus
Data-Valid Time
ALERT , SMBDATA forced to 0.4V
forced to 5.5V
ALERT
, 10% to 10% points 4.7 µs
LOW
, 90% to 90% points 4 µs
HIGH
t
t
SMBCLK
Master clocking in data 1 µs
90% to 90% points 500 ns
SU : STA ,
10% of SMBDATA to 90% of SMBCLK 4 µs
HD: STA ,
90% of SMBDATA to 10% of SMBDATA 4 µs
SD: STO ,
10% or 90% of SMBDATA to 10% of
SU: DAT ,
(Note 5) 0 µs
HD : DAT
6 mA
1 µA
800 ns
(continued)
Electrical Characteristics
(VCC =full range, TA= 60°C, unless otherwise noted.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Reset Threshold VTH 4.2 4.4 4.5 V
Reset Active Timeout Period 340 ms
RESET
Output Voltage Low
RESET
Output Voltage High
Note 1: Guaranteed but not 100% tested.
V
V
OL
V
V
OH
CC=VTH
CC>VTH
min, I
max, I
=3.2mA
SINK
SOURCE
=5.0mA
0.4 V
-1.5 V
V
CC
Note 2: Quantization error is not included in specifications for temperature accuracy. For example, if the G768D
device temperature is exactly +66.7°C, or +68°C (due to the quantization error plus the +1/2°C offset
used for rounding up) and still be within the guaranteed ±3°C error limits for the +60°C to +100°C temperature range. See Table3.
Note 3: A remote diode is any diode-connected transistor from Table1. T
mote diode. See Remote Diode Selection for remote diode forward voltage requirements.
is the junction temperature of the re-
R
Note 4: The SMBus logic block is a static design that works with clock frequencies down to DC. While slow op-
eration is possible, it violates the 10kHz minimum clock frequency and SMBus specifications, and may
monopolize the bus.
Note 5: Note that a transition must internally provide at least a hold time in order to bridge the undefined region
(300ns max) of SMBCLK's falling edge.
Ver: 1.2
Apr 03, 2002
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Global Mixed-mode Technology Inc.
Pin Description
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
4 DXN
5 DXP2
RESET
6
7 DGND Digital Ground.
8 AGND Analog Ground.
9 CLK 32.768KHz clock input for fan controller.
10 FG Fan pulse input.
11
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.
ALERT
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
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;
tie DXP2 to DXN if no remote diode on channel 2 is used. Place a 2200pF capacitor between DXP2 and
DXN for noise filtering.
RESET
the reset threshold.
SMBus Alert (interrupt) Output, open drain.
Output remains low while VCC is below the reset threshold, and for 340ms after VCC rises above
G768D
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 conjunction with an external micro-controller (µC) or other
intelligence in thermostatic, process-control, or monitoring applications. The µC is typically a powermanagement or keyboard controller, generating SMBus serial commands by "bit-banging" general-purpose input-output (GPIO) pins or via a dedicated SMBus interface block.
Essentially a 12-bit serial analog-to-digital converter
(ADC) with a sophisticated front end, the G768D contains 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 channels are converted automatically once the conversion
process has started, either in free-running or single-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
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Page 6
DXP1
DXP1
DXP2
DXP2
DXN
DXN
Global Mixed-mode Technology Inc.
FANVCC
V
V
CC
CC
INTERNAL GROUND
INTERNAL GROUND
V
V
CC
CC
FANVCC
FG
FG
CLK
CLK
FAN CONTROL
FAN CONTROL
CONTROL
CONTROL
+
+
+
+
MUX
MUX
LOGIC
LOGIC
+
+
Fig 1. Functional Diagram
A/D Conversion Sequence
If a Start command is written (or generated automatically in the free-running auto-convert mode), both two
channels are converted, and the results of both measurements are available after the end of conversion. A
BUSY status bit in the status byte shows that the device is actually performing a new conversion; however,
even if the ADC is busy, the results of the previous
conversion are always available.
Remote-Diode Selection
Temperature accuracy depends on having a
good-quality, diode-connected small-signal transistor.
Accuracy has been experimentally verified for all of
the devices listed in Table 1. The G768D can also
directly measure the die temperature of CPUs and
other integrated circuits having on-board temperature-sensing diodes. The transistor must be a
small-signal type with a relatively high forward voltage;
otherwise, the A/D input voltage range can be violated.
The forward voltage must be greater than 0.25V at
10µA; check to ensure this is true at the highest expected temperature. The forward voltage must be less
than 0.95V at 200A; check to ensure this is true at the
lowest expected temperature. Large power transistors
don't work at all. Also, ensure that the base resistance
is less than 100Ω. Tight specifications for forward
current gain (+50 to +150, for example) indicate that
the manufacturer has good process controls and that
the devices have consistent VBE characteristics.
G768D
THERMAL SHUTDOWN
THERMAL SHUTDOWN
LOGIC
LOGIC
SMBUS
SMBUS
REGISTERS
REGISTERS
RESET
ADC
ADC
RESET
CIRCUIT
CIRCUIT
Thermal Mass and Self-Heating
Thermal mass can seriously degrade the G768D's
effective accuracy. The thermal time constant of the
SSOP-16 package is about 140sec in still air. For the
G768D junction temperature to settle to within +1°C
after a sudden +100°C change requires about five
time constants or 12 minutes. The use of smaller
packages for remote sensors, such as SOT23s, improves the situation. Take care to account for thermal
gradients between the heat source and the sensor ,and ensure that stray air current across the sensor package do not interfere with measurement accuracy.
Table 1. Remote-Sensor Transistor Manufacturers
MANUFACTURER MODEL NUMBER
Philips PMBS 3904
Motorola (USA) MMBT3904
National Semiconductor (USA) MMBT3904
Note:Transistors must be diode-connected (base short
-ed to collector).
TH_SHUT
TH_SHUT
SMBCLK
SMBCLK
SMBDATA
SMBDATA
ALERT
ALERT
RESET
RESET
Ver: 1.2
Apr 03, 2002
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Global Mixed-mode Technology Inc.
ADC Noise Filtering
The ADC is an integrating type with inherently good
noise rejection, especially of low-frequency signals
such as 60Hz/120Hz power-supply hum. Micro-power
operation places constraints on high-frequency noise
rejection; therefore, careful PC board layout and
proper external noise filtering are required for highaccuracy remote measurements in electrically noisy
environments.
High-frequency EMI is best filtered at DXP and DXN
with an external 2200pF capacitor. This value can be
increased to about 3300pF(max), including cable capacitance. Higher capacitance than 3300pF introduces
errors due to the rise time of the switched current
source.
Nearly all noise sources tested cause the ADC measurements to be higher than the actual temperature,
typically by +1°C to 10°C, depending on the frequency
and amplitude (see Typical Operating Characteristics).
PC Board Layout
Place the G768D as close as practical to the remote
diode. In a noisy environment, such as a computer
motherboard, this distance can be 4 in. to 8 in. (typical)
or more as long as the worst noise sources (such as
CRTs, clock generators, memory buses, and ISA/PCI
buses) are avoided.
Do not route the DXP-DXN lines next to the deflection
coils of a CRT. Also, do not route the traces across a
fast memory bus, which can easily introduce +30°C
error, even with good filtering, Otherwise, most noise
sources are fairly benign.
Route the DXP and DXN traces in parallel and in close
proximity to each other, away from any high-voltage
traces such as +12VDC. Leakage currents from PC
board contamination must be dealt with carefully,
since a 20MΩ leakage path from DXP to ground
causes about +1°C error.
Route the 2 pairs of DXP1-DXN and DXP2-DXN
traces independently (Figure 2a). Connect the common DXN as close as possible to the DXN pin on IC
(Figure 2a).
Connect guard traces to GND on either side of the
DXP-DXN traces (Figure 2b). With guard traces in place,
routing near high-voltage traces is no longer an issue.
Route through as few vias and crossunders as possible to minimize copper/solder thermocouple effects.
When introducing a thermocouple, make sure that
both the DXP and the DXN paths have matching
thermocouples. In general, PC board- induced thermocouples are not a serious problem, A copper-solder
thermocouple exhibits 3µV/°C, and it takes about
200µV of voltage error at DXP-DXN to cause a +1°C
measurement error. So, most parasitic thermocouple
errors are swamped out.
Ver: 1.2
Apr 03, 2002
G768D
Use wide traces. Narrow ones are more inductive and
tend to pick up radiated noise. The 10 mil widths and
spacing recommended on Figure 2 aren't absolutely
necessary (as they offer only a minor improvement in
leakage and noise), but try to use them where practical.
Keep in mind that copper can't be used as an EMI
shield, and only ferrous materials such as steelwork
will. Placing a copper ground plane between the
DXP-DXN traces and traces carrying high-frequency
noise signals do not help reduce EMI.
PC Board Layout Checklist
Place the G768D close to a remote diode.
Keep traces away from high voltages (+12V bus).
Keep traces away from fast data buses and CRTs.
Use recommended trace widths and spacing.
Place a ground plane under the traces
Use guard traces flanking DXP and DXN and connecting to GND.
Route two DXPx-DXN pairs independently
Connect the common DXN as close as possible to
the DXN pin on IC.
Place the noise filter and the 0.1µF VCC bypass
capacitors close to the G768D.
GND
DXP1
DXN
DXN
DXP2
Fig 2(a) Connect the common DXN as close as
possible to the DXN pin on IC.
GND
10 MILS
10 MILS
DXP
DXN
GND
Fig 2 (b) Recommended DXP/DXN PC
7
DXP1
DXN
G768D
DXP2
GND
Chip Boundary
10 MILS
MINIMUM
10 MILS
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Twisted Pair and Shielded Cables
For remote-sensor distances longer than 8 in., or in
particularly noisy environments, a twisted pair is recommended. Its practical length is 6 feet to 12feet (typical) before noise becomes a problem, as tested in a
noisy electronics laboratory. For longer distances, the
best solution is a shielded twisted pair like that used
for audio microphones. Connect the twisted pair to
DXP and DXN and the shield to GND, and leave the
shield's remote end unterminated.
Excess capacitance at DX_limits practical remote
sensor distances (see Typical Operating Characteristics), For very long cable runs, the cable's parasitic
capacitance often provides noise filtering, so the
2200pF capacitor can often be removed or reduced in
value. Cable resistance also affects remote-sensor
accuracy; 1Ω series resistance introduces about + 1°C
error.
Low-Power Standby Mode
Standby mode disables the ADC and reduces the
supply-current drain to less than 10µA. Enter standby
mode via the RUN/STOP bit in the configuration byte
register. In standby mode, all data is retained in memory, and the SMB interface is alive and listening for
reads and writes. This is valid for temperature sensor
only.
Standby mode is not a shutdown mode. With activity
on the SMBus, extra supply current is drawn (see
Typical Operating Characteristics). In software
standby mode, the G768D can be forced to perform
temperature measurement via the one-shot command,
despite the RUN/STOP bit being high.
Supply-current drain during the 125ms conversion
period is always about 500µA. Slowing down the conversion rate reduces the average supply current (see
Typical Operating Characteristics). In between conversions, the instantaneous supply current is about
200µA due to the current consumed by the system
resetting circuit.
Fan Controller
Since the fan speed is measured by counting the number of 32.768KHz cycles between the rising edges of
two fan speed pulses. In this way, we are actually
measuring the period of the fan speed. To avoid the
cost of doing division to obtain the speed, this count
number, N, is used in the PWM control algorithm, thus,
the desired fan speed should be programmed by writing the corresponding count number. The count number is given by:
Global Mixed-mode Technology Inc.
G768D
N: Count Number
P: FG pulses number per revolution
P=1 ⇒ N = 983040 / rpm
P=2 ⇒ N = 491520 / rpm
P=4 ⇒ N = 245762 / rpm
CC
.
pin
Some selected count number for P=2 are listed below
Table 2.
Rpm N
3000 164
4000 123
5000 98
6000 82
7000 70
8000 61
9000 55
10000 49
20000 25
30000 16
To stop the fan, program the fan speed register to 255. This
also makes the fan controller enter power saving mode.
Controlling Fan at Lower Speed
For stably controlling fans at lower rotation speed,
three schemes are recommended as below:
1.Use larger decoupling capacitors between FANVCC
and GND.
2.Shunt a capacitor of 1µF-2µF on FG pin to GND.
3.Use fans with open-collector FG outputs.
When controlling fans under lower rotation speed, the
output voltage of FANVCC would be too low for fan to
generate recognizable FG signals.
Using decouple capacitors on FANVCC and FG is to
increase the SNR on FG pins. While using fans with
open-collector FG outputs can thoroughly solve the
problem, because the logic high level of FG would be
fixed to 5V.
Reset Immunity Negative-Going V
In addition to issuing a reset to the microprocessor (µP)
during power-up, power-down, and brownout conditions, the G768D is relatively immune to short duration
negative-going V
Typically, for the G768D, a V
100mV below the reset threshold and lasts 20µs or
less will not cause a reset pulse. A 0.1µF bypass capacitor mounted as close as possible to the V
provides additional transient immunity.
transients (glitches).
CC
Transients
CC
transient that goes
CC
Ver: 1.2
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Global Mixed-mode Technology Inc.
Ensuring a Valid Reset Output Down to VCC = 0V
When V
falls below 1V, the G768D RESET output
CC
no longer sinks current-it becomes an open circuit.
Therefore, high-impedance CMOS logic inputs con-
nected to
RESET can drift to undetermined voltages.
This presents no problem in most applications, since
most µP and other circuitry is inoperative with V
low 1V. However, in applications where
RESET must
CC
be-
be valid down to 0V, adding a pull-down resistor to
RESET causes any stray leakage currents to flow to
ground, holding
RESET low (Figure 3). R1's value is
not critical; 100kΩ is large enough not to load
RESET and small enough to pull RESET to ground.
Interfacing to µPs with Bi-directional Reset Pins
A µP with bi-directional reset pins (such as the Motorola 68HC11 series) can connect to the G768D reset
output. If, for example, the G768D
RESET output is
asserted high and the µP wants to pull it low, indeterminate logic levels may result. To correct this, connect
a 4.7kΩ resistor between the G768D
RESET output
and the µP reset I/O (Figure 4). Buffer the G768D
RESET output to other system components.
G768D
SMBus Digital Interface
From a software perspective, the G768D appears as a
set of byte-wide registers that contain temperature
data, alarm threshold values, fan speed data, or control bits, A standard SMBus 2-wire serial interface is
used to read temperature data and write control bits
and alarm threshold data. Each A/D and fan control
channel within the device responds to the same
SMBus slave address for normal reads and writes.
The G768D employs four standard SMBus protocols:
Write Byte, Read Byte, Send Byte, and Receive Byte
(Figure 5). The shorter Receive Byte protocol allows
quicker transfers, provided that the correct data register was previously selected by a Read Byte instruction.
Use caution with the shorter protocols in multi-master
systems, since a second master could over-write the
command byte without informing the first master.
The temperature data format is 7bits plus sign in
twos-complement form for each channel, with each
data bit representing 1°C (Table3), transmitted MSB
first. Measurements are offset by +1/2°C to minimize
internal rounding errors; for example, +99.6°C is reported as +100°C.
V
CC
G768D
RESET
GND
Fig 3 RESET Valid to V
R1
100k
= Ground Circuit
CC
BUFFERED RESET
BUFFERED RESET
TO OTHER SYSTEM
TO OTHER SYSTEM
COMPONENTS
COMPONENTS
V
V
CC
CC
G768D
G768D
RESET
RESET
GND
GND
4.7k
4.7k
BUFFER
BUFFER
RESET
RESET
V
V
µP
µP
GND
GND
CC
CC
Fig 4. Interfacing to µPs with Bi-directional Reset I/O
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Global Mixed-mode Technology Inc.
G768D
Write Byte Format
S Address WR
7 bits 8 bits 8 bits 1
Slave Address:
Command Byte:
Data Byte:
Read Byte Format
S Address WR
7 bits 8 bits 7 bits 8 bits
Slave Address:
Command Byte:
Slave Address:
Data byte:
Send Byte Format
S Address WR
7 bits 8 bits
Command Byte:
Receive Byte Format
S Address RD
7 bits 8 bits
Data Byte:
equivalent to chip-select line of a 3-wire interface
selects, which register you, are writing to
data goes into the register set by the command byte (to set thresholds, configuration masks, and
sampling rate)
equivalent to chip- select line
selects, which register you, are reading from
repeated due to change in data-flow direction
reads from the register set by the command byte
sends command with no data usually used for one-shot command
reads data from the register commanded by the last Read Byte or Write
Byte transmission; also used for SMBus Alert Response return address
ACK Command ACK S Address RD ACK DATA /// P
ACK Command ACK DATA ACK P
ACK Command ACK P
ACK Data /// P
S = Start condition Shaded = Slave transmission P = Stop condition /// = Not acknowledged
Fig 5. SMBus Protocols
Table 3. Data Format (Twos-Complement)
TEMP.
(
C)
°°°°
+130.00 +127 0 111 1111
+127.00 +127 0 111 1111
+126.50 +127 0 111 1111
+126.00 +126 0 111 1110
+25.25 +25 0 001 1001
+0.50 +1 0 000 0001
+0.25 +0 0 000 0000
+0.00 +0 0 000 0000
-0.25 +0 0 000 0000
-0.50 +0 0 000 0000
-0.75 -1 1 111 1111
-1.00 -1 1 111 1111
-25.00 -25 1 110 0111
-25.50 -25 1 110 0110
-54.75 -55 1 100 1001
-55.00 -55 1 100 1001
-65.00 -65 1 011 1111
-70.00 -65 1 011 1111
ROUND
TEMP.
(
C)
°°°°
DIGITAL OUTPUT
DATA BITS
SIGN MSB LSB
Alarm Threshold Registers
Four registers store alarm threshold data, with
high-temperature (THIGH) and low-temperature
(TLOW) registers for each A/D channel. If either
measured temperature equals or exceeds the corre-
sponding alarm threshold value, an
is asserted.
The power-on-reset (POR) state of both THIGH registers is full scale (0111 1111, or +127°C). The POR
state of both TLOW registers is 1100 1001 or -55°C.
Diode Fault Alarm
There is a continuity fault detector at DXP that detects
whether the remote diode has an open-circuit condition. At the beginning of each conversion, the diode
fault is checked, and the status byte is updated. This
fault detector is a simple voltage detector; if DXP rises
above V
a fault is detected. Note that the diode fault isn't
checked until a conversion is initiated, so immediately
after power-on reset the status byte indicates no fault
is present, even if the diode path is broken.
-1V (typical) due to the diode current source,
CC
ALERT interrupt
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Page 11
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 settings. 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 accidentally short circuited. Similarly, if DXP is short circuited
to V
, the ADC reads +127°C for both channels, and
CC
the device alarms.
ALERT
The
ALERT interrupt output signal is latched and can
only be cleared by reading the Alert Response address. Interrupts are generated in response to THIGH
and TLOW comparisons and when the remote diode is
disconnected (for continuity fault detection). The interrupt does not halt automatic conversions; new temperature data continues to be available over the SMBus
interface after
Table 4. Command-Byte Bit Assignments
Global Mixed-mode Technology Inc.
Interrupts
ALERT is asserted. The interrupt output
G768D
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 interrupt 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
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.
ALERT interrupt signal, the
REGISTER COMMAND POR STATE FUNCTION
RRTE2 00h 0000 0000b Read 2nd remote temperature: returns latest temperature
RRTE1 01h 0000 0000b Read 1st remote temperature: returns latest temperature
RSL 02h N/A Read status byte (flags, busy signal)
RCL 03h 0000 0000b Read configuration byte
RCRA 04h 0000 0010b Read conversion rate byte
RRHI2 05h 0111 1111b (127) Read 2nd remote THIGH limit
RRLS2 06h 1100 1001b(-55) Read 2nd remote TLOW limit
RRHI1 07h 0111 1111b (127) Read 1st remote THIGH limit
RRLS1 08h 1100 1001b (-55) Read 1st remote TLOW limit
WCA 09h N/A Write configuration byte
WCRW 0Ah N/A Write conversion rate byte
WRHA2 0Bh N/A Write 2nd remote THIGH limit
WRLN2 0Ch N/A Write 2nd remote TLOW limit
WRHA1 0Dh N/A Write 1st remote THIGH limit
WRLN1 0Eh N/A Write 1st remote TLOW limit
OSHT 0Fh N/A One-shot command (use send-byte format)
SET_CNT1 10h 1111 1111b Write 1st fan programmed speed register
ACT_CNT1 11h 1111 1111b Read 1st fan actual speed register
FAN_STA1 12h 10b Read 1st fan status register
TMAX1 31h 0100 0110b (70) 1st remote TMAX
THYST1 32h 0011 1100b (60) 1st remote THYST
TMAX2 33h 0100 0110b (70) 2nd remote TMAX
THYST2 34h 0011 1100b (60) 2nd remote THYST
TCRIT1 35h 0110 1100b (108) Cri ti cal temperature for 1st remote temperaure sensor
TCRIT2 36h 0101 1000b (88) Cri ti cal temperature for 2nd remote temperaure sensor
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The Alert Response can activate several different slave
devices simultaneously, similar to the SMBus General
Call. If more than one slave attempts to respond, bus
arbitration rules apply, and the device with the lower
address code wins. The losing device does not generate
an acknowledge and continues to hold the
low until serviced (implies that the host interrupt input is
level sensitive). Successful reading of the alert response address clears the interrupt latch.
Command Byte Functions
The 8-bit command byte register (Table 4) is the master index that points to the various other registers
within the G768D. The register's POR state is 0000
0000, so that a Receive Byte transmission (a protocol
that lacks the command byte) that occurs immediately
after POR returns the current local temperature data.
The one-shot command immediately forces a new
conversion cycle to begin. In software standby mode
(
RUN /STOP bit = high), a new conversion is begun,
after which the device returns to standby mode. If a
conversion is in progress when a one-shot command
is received in auto-convert mode (RUN/STOP bit = low)
between conversions, a new conversion begins, the
conversion rate timer is reset, and the next automatic
conversion takes place after a full delay elapses.
Configuration Byte Functions
The configuration byte register contents are listed in
table 5. Bit 7(MASK) is used to mask
Global Mixed-mode Technology Inc.
ALERT
ALERT
line
interrupt.
G768D
Bit 6 (
standby mode. Setting bit 5 (DET_FAN) with logic 1
can activate the detection of fan failure. Logic 1 in bit 4
(EN_TH_SHUT) makes thermal shutdown function
valid and logic 0 disables this function and keep
TH_SHUT pin low. Bit 3~0 forms thermal shutdown
fault queue. The number of faults these bits decided
are listed in table 6.
Thermal Status Byte Functions
The thermal status byte register (02h) (Table 6) indicates which (if any) temperature thresholds have been
exceeded. This byte also indicates whether or not the
ADC is converting and whether there is an open circuit
in the remote diode DXPx-DXN path. After POR, the
normal state of all the flag bits is zero, assuming none
of the alarm conditions are present. The status byte is
cleared by any successful read of the status, unless
the fault persists. Note that the
is not automatically cleared when the status flag bit is
cleared.
When reading the status byte, you must check for internal bus collisions caused by asynchronous ADC
timing, or else disable the ADC prior to reading the
status byte (via the
tion byte). In one-shot mode, read the status byte only
after the conversion is complete, which is 150ms max
after the one-shot conversion is commanded.
RUN /STOP) is to put the device in software
ALERT interrupt latch
RUN /STOP bit in the configura-
Table 5. Configuration-Byte Bit Assignments
BIT NAME POR STATE FUNCTION
7 (MSB) MASK 0
/ STOP
RUN
6
5 DET_FAN 0 Validation of the fan failure detection. If high, activated. If low, disable.
4 EN_TH_SHUT 1 Validation of the fault queue function of thermal shutdown.
3-0 FQ_TH_SHUT 0010b
Table 6. Number of Faults assigned by FQ_TH_SHUT
FQ_TH_SHUT Number of Faults FQ_TH_SHUT Number of Faults
0000b 1 1000b 9
0001b 2 1001b 10
0010b 3(Power-up default) 1010b 11
0011b 4 1011b 12
0100b 5 1100b 13
0101b 6 1101b 14
0110b 7 1110b 15
0111b 8 1111b 16
0
Masks all
Standby mode control bit. If high, the device immediately stops converting and enters standby mode. If low, the device converts in either one-shot or timer mode.
Fault Queue. Number of faults necessary to detect before setting TH_SHUT output
to avoid false tripping due to noise.
ALERT interrupts when high.
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Table 7. Status-Byte Bit Assignments
7(MSB) BUSY A high indicates that the ADC is busy converting.
0(LSB) FAN_FAIL* A high indicates that the fan failure alarm has activated.
*These flags stay high until cleared by POR, or until the status byte register is read.
Table 8. Conversion-Rate Control Byte
Global Mixed-mode Technology Inc.
BIT NAME FUNCTION
6 RHIGH2* A high indicates that the 2nd diode high-temperature alarm has activated.
5 RLOW2* A high indicates that the 2nd diode low-temperature alarm has activated.
4 RHIGH1* A high indicates that the 1st diode high-temperature alarm has activated.
3 RLOW1* A high indicates that the 1st diode low-temperature alarm has activated.
2 OPEN* A high indicates a remote-diode continuity (open-circuit) fault.
1 RFU Reserved for future use (returns 0)
G768D
DATA
00h 0.0625 30
01h 0.125 33
02h 0.25 35
03h 0.5 48
04h 1 70
05h 2 128
06h 4 225
07h 8 425
08h to FFh RFU -
CONVERSION
RATE (Hz)
Temperature Sensor Average
Supply Current (µA TYP, at V
= 5V)
CC
Table 9. RLTS and RRTE Temp Register Update Timing Chart
OPERATING
MODE
Auto-Convert Power-on reset N/A (0.25Hz) 156ms max
Auto-Convert
Auto-Convert
Auto-Convert Rate timer 0.0625Hz 20sec
Auto-Convert Rate timer 0.125Hz 10sec
Auto-Convert Rate timer 0.25Hz 5sec
Auto-Convert Rate timer 0.5Hz 2.5sec
Auto-Convert Rate timer 1Hz 1.25sec
Auto-Convert Rate timer 2Hz 625ms
Auto-Convert Rate timer 4Hz 312.5ms
Auto-Convert
Software Standby RUN/STOP bit N/A 156ms
Software Standby 1-shot command N/A 156ms
1-shot command, while idling
between automatic conversions
1-shot command that occurs
during a conversion
Rate timer 8Hz 237.5ms
CONVERSION
INITIATED BY:
NEW CONVERSION RATE
(CHANGED VIA WRITE TO CRW)
N/A 156ms max
N/A
TIME UNTIL RLTS AND
RRTE ARE UPDAT ED
When current conversion is
complete (1-shot is ignored)
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To check for internal bus collisions, read the status
byte. If the least significant seven bits are ones, discard the data and read the status byte again. The
status bits LHIGH, LLOW, RHIGH, and RLOW are
refreshed on the SMBus clock edge immediately following the stop condition, so there is no danger of
losing temperature-related status data as a result of
an internal bus collision. The OPEN status bit (diode
continuity fault) is only refreshed at the beginning of a
conversion, so OPEN data is lost. The
rupt latch is independent of the status byte register, so
no false alerts are generated by an internal bus collision.
When auto-converting, if the THIGH and TLOW limits
are close together, it's possible for both high-temp and
low-temp status bits to be set, depending on the
amount of time between status read operations (especially when converting at the fastest rate). In these
circumstances, it's best not to rely on the status bits to
indicate reversals in long-term temperature changes
and instead use a current temperature reading to establish the trend direction.
Temperature Conversion Rate Byte
The conversion rate register (Table 7) programs the
time interval between conversions in free running
auto-convert mode. This variable rate control reduces
the supply current in portable-equipment applications.
The conversion rate byte's POR state is 02h (0.25Hz).
The G768D looks only at the 3 LSB bits of this register,
so the upper 5 bits are "don't care" bits, which should
be set to zero. The conversion rate tolerance is ±25%
at any rate setting.
Valid A/D conversion results for all channels are available one total conversion time (125ms nominal, 156ms
maximum) after initiating a conversion, whether conversion is initiated via the RUN/STOP bit, one-shot
command, or initial power-up. Changing the conversion rate can also affect the delay until new results are
available. See Table 8.
Programmed fan speed register
The programmed fan speed register 10h is read / write
register. They contain the count number of the desired
fan speed. Power up default is FFh.
Actual fan speed register
The actual fan speed register 11h is read only. They
contain the count number of the actual fan speed.
Power up default is FFh.
Fan status register
The fan status registers 12h is read only. Its bit 0 is set
to 1 when the actual fan speed is ±20% outside the
desired speed. Its bit 1 is set to 1 when fan speed is
below 1920 rpm. Power up default is 0000_0010b.
Global Mixed-mode Technology Inc.
ALERT inter-
G768D
Watchdog for fan control
Four temperature threshold registers intervene the
control of fan. Pin FANVCC go high when one of the
remote temperature, DX1 and DX2, rises above the
respective TMAX. The control is not released until
both temperature values drop below their THYST Besides, the fan controller also fully turns on the fan
when either of the two remote diodes is open or both
are short.
The power-up default values for TMAX and THYST
are +70°C and +60°C, respectively. This allows the
G768D to be used in the occasion when system fails
and loses the fan control of G768D.
Slave Addresses
The G768D appears to the SMBus as one device having a common address for all the ADC and fan control
channels. The device address is fixed to be 7Ah for
write and 7Bh for read.
The G768D also responds to the SMBus Alert Response slave address (see the Alert Response Address section).
POR and UVLO
The G768D has a volatile memory. To prevent ambiguous power-supply conditions from corrupting the
data in memory and causing erratic behavior, a POR
voltage detector monitors V
if V
falls below 1.7V (typical, see Electrical
CC
CC
Characteristics table). When power is first applied and
V
rises above 1.75V (typical), the logic blocks begin
CC
operating, although reads and writes at V
below 3V are not recommended. A second V
comparator, the ADC UVLO comparator, prevents the
ADC from converting until there is sufficient headroom
(V
= 2.8V typical).
CC
Power-Up Defaults:
Interrupt latch is cleared.
ADC begins auto /converting at a 0.25Hz rate.
Command byte is set to 00h to facilitate quick remote Receive Byte queries.
THIGH and TLOW registers are set to max and
min limits, respectively
Detection On fan Failure
Setting bit 5 (DET_FAN) of CONFIGURATION-BYTE
register with logic 1 activates the detection of fan failure. G768D detects fan failure via FG pin. G768D defines fan failure as no transition on FG pin for about
0.5sec or the fan measurement result is 255 counts for
consecutive 8 times, it takes about 0.25sec. Once fan
failure is detected the ALERT# will be set to logic low
and the bit 0 (FAN_FAIL) of STATUS-BYTE will be set
to logic high.
To clear the ALERT# signal caused by fan failure, the
DET_FAN bit should be set to 0 then issue an ARA
command on serial bus.
and clears the memory
levels
CC
CC
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Thermal Shutdown Signal
When the temperature of DX1 reaches or exceeds
the Tcrit1 threshold consecutively for the times
equal to the number of faults of the FQ_TH_SHUT
registers, TH_SHUT pin becomes logic high. The
Global Mixed-mode Technology Inc.
G768D
same mechanism is duplicated for DX2. There fore,
either one of DX1, DX2 continuously over their respective Tcrit, the TH_SHUT will assert logic high to
indicate a thermal shutdown event.
AB C
t
LOW
t
HIGH
DE
F
G
HIJ KLM
SMBCLK
SMBDATA
t
SU:STAtHD:STA
t
SU:DAT
t
HD:DAT
Figure 6. SMBus Write Timing Diagram
A = start condition H = LSB of data clocked into slave
B = MSB of address clocked into slave I = slave pulls SMBDATA line low
C = LSB of address clocked into slave J = acknowledge clocked into master
D = R / W bit clocked into slave K = acknowledge clocked pulse
E = slave pulls SMB Data line low L = stop condition data executed by slave
F = acknowledge bit clocked into master M = new start condition
G = MSB of data clocked into slave
AB
AB
t
t
LOW
LOW
t
t
HIGH
HIGH
CDEF
CDEF
G
G
HI
HI
t
t
BUF
SU:STO
JK
JK
SMBCLK
SMBCLK
SMBDATA
SMBDATA
t
t
SU:STAtHD:ST A
SU:STAtHD:ST A
t
t
SU:DAT
SU:DAT
Figure 7. SMBus Read Timing Diagram
A = start condition
B = MSB of address clocked into slave
C = LSB of address clocked into slave
D = R /
W bit clocked into slave
G = MSB of data clocked into master
H = LSB of data clocked into master
I = acknowledge clocked pulse
J = stop condition
E = slave pulls SMBDATA line low K= new start condition
F =acknowledge bit clocked into master
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Apr 03, 2002
15
t
t
t
t
SU:STO
SU:STO
BUF
BUF
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Global Mixed-mode Technology Inc.
Package Information
7
°
(4X)
G768D
C
E1
E
L
D
θ
A2 A
y
b
e
A1
Note:
1. Package body sizes exclude mold flash and gate burrs
2. Dimension L is measured in gage plane
3. Tolerance 0.10mm unless other wise specified
Controlling dimension is millimeter converted inch dimensions are not necessarily exact.
4.
SYMBOLS
A 1.35 1.60 1.75 0.053 0.064 0.069
A1 0.10 ----- 0.25 0.004 ----- 0.010
A2 ----- 1.45 ----- ----- 0.057 -----
b 0.20 0.25 0.30 0.008 0.010 0.012
C 0.19 ----- 0.25 0.007 ----- 0.010
D 4.80 ----- 5.00 0.189 ----- 0.197
E 5.80 ----- 6.20 0.228 ----- 0.244
E1 3.80 ----- 4.00 0.150 ----- 0.157
e ----- 0.64 ----- ----- 0.025 -----
L 0.40 ----- 1.27 0.016 ----- 0.050
y ----- ----- 0.10 ----- ----- 0.004
θ
MIN NOM MAX MIN NOM MAX
0º ----- 8º 0º ----- 8º
DIMENSION IN MM DIMENSION IN INCH
Taping Specification
Feed Direction
Feed Direction
Typical SSOP Package Orientation
Typical SSOP Package Orientation
GMT Inc. d oes not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and GMT Inc. reserves the right at any time without notice to change said circuitry and specifications.
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