Page 1
Global Mixed-mode Technology Inc.
G768B
Remote/Local Temperature Sensor, 2 Fan Controllers
with SMBus Serial Interface and System Reset Circuit
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 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
G768B
1
OUT1
2
Vcc
3
DXP1
DXN
4
DXP2
5
RESET
GND
GND
6
7
8
16
OUT2
15
Vcc
14
SMBCLK
13
FG2
12
SMBDATA
11
ALERT
10
FG1
9
CLK
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 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.
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 capacitor per channel. It determines the current fan
speed based on the fan rotation pulses and an externally supplied clock.
(To be continued)
Ordering Information
PART* TEMP. RANGE PIN-PACKAGE
G768B -10°C to +85°C 16SSOP
Ver 1.3
Oct 28, 2002
16Pin SSOP
TEL: 886-3-5788833
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1
Page 2
Global Mixed-mode Technology Inc.
It uses pulse width modulation (PWM) 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 G768B also turns on the fans by hardware
watchdog system. The fan controller would fully turn
on both fans when one 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
10µF
10µF
IN
IN
OUT1
OUT1
G768B
The G768B 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 4.38V.
The G768B is available in a small, 16-pin SSOP surface-mount package.
OUT2
OUT2
supply voltage declines below a preset
CC
has risen above the reset threshold. The G768B
CC
RESET output. The reset com-
10µF
10µF
IN
IN
CC
.
FAN1
FAN1
2N3904
2N3904
2N3904
2N3904
RESET
RESET
µP
µP
FG
FG
10µF
10µF
2200pF
2200pF
2200pF
2200pF
FG1
FG1
V
V
CC
CC
DXP1
DXP1
DXN
DXN
DXP2
DXP2
RESET
RESET
G768B
G768B
SMBDATA
SMBDATA
FG2
FG2
V
V
SMBCLK
SMBCLK
ALERT
ALERT
CLK
CLK
FAN2
FAN2
FG
FG
10µF
10µF
CC
CC
10k EACH
10k EACH
SMBCLK
SMBCLK
SMBDATA
SMBDATA
INTERRUPT TO µC
INTERRUPT TO µC
CLOCK 32.768kHz
CLOCK 32.768kHz
Ver 1.3
Oct 28, 2002
GND
GND
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Absolute Maximum Ratings
Vcc to GND……………….………….…….-0.3V to +6V
DXP1, DXP2 to GND……………0.3V to (Vcc + 0.3V)
DXN to GND…………………………...-0.3V to +0.8V
SMBCLK, SMBDATA,
SMBDATA,
DXN Current……………………………..…………±1mA
ESD Protection (SMBCLK, SMBDATA,
Global Mixed-mode Technology Inc.
ESD Protection (other pins, human body
model).2000V
Continuous Power Dissipation (T
(de-rate 8.30mW/°C above +70°C)…….………667mW
Operating Temperature Range………-10°C to +85°C
Junction Temperature…………………....+150°C
Storage temperature Range…………..-65°C to +165°C
Lead Temperature (soldering,10sec)………….+300°C
ALERT
ALERT
to GND.-0.3V to +6V
Current…………-1mA to +50mA
ALERT
, hu-
G768B
= +70°C) SSOP
A
man body model)….…………………………….4000V
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.
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 Both fans’ speed = 0rpm 2 5 µA
MOSFET on resistance Each channel 0.2 0.25 Ω
Short-circuit current limit Each channel 0.5 A
Input logic low VIL 0.8 V
Input logic high VIH 2.4 V
Average Output current Each channel 350 mA
FG input Positive-going threshold voltage VCC=5V 1.8 V
FG input Negative-going threshold voltage VCC=5V 0.7 V
FG input Hysteresis voltage VCC=5V 1.1 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 Vcc or
GND
Auto-convert mode, average
measured over 4sec. Logic
inputs forced to Vcc or GND
= +60°C to +100°C -3.5 3.5 °C
A
SMBus static 3 10
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
Ver 1.3
Oct 28, 2002
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Page 4
Electrical Characteristics
Global Mixed-mode Technology Inc.
(continued)
G768B
(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
ALERT Output High Leakage Current ALERT forced to 5.5V
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 Rising-Edge Time
SMBus Data-Hold Time t
SMBCLK Falling Edge to SMBus
Data-Valid Time
ALERT , SMBDATA forced to 0.4V
, 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
RESET
Output Voltage Low
Output Voltage High
Note 1: Guaranteed but not 100% tested.
V
OL
V
OH
V
CC=VTH
I
SOURCE
min I
V
CC>VTH
=3.2mA
SINK
max
=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 G768B
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 1.3
Oct 28, 2002
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Global Mixed-mode Technology Inc.
Pin Description
PIN NAME FUNCTION
1 OUT1 PWM output, connect to fan 1
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
7,8 GND Ground
9 CLK Clock input for fan speed measurement.
10 FG1 Fan1 pulse input.
11
12 SMBDATA SMBus Serial-Data Input / Output, open drain.
13 FG2 Fan2 pulse input.
14 SMBCLK SMBus Serial-Clock Input.
16 OUT2 PWM output, connect to fan 2.
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 240ms after VCC rises above
G768B
Detailed Description
The G768B (patents pending) is a 4-in-1 IC. It consists
of one temperature sensor, 2 fan speed controllers
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 power-management
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 G768B contains a switched current source, a multiplexer, an ADC,
an SMBus interface, 2 fan controllers, 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), with excellent
noise rejection.
The multiplexer automatically steers bias currents
through the remote and local 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 three 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 1.3
Oct 28, 2002
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Global Mixed-mode Technology Inc.
OUT1
V
V
CC
CC
DXP1
DXP1
DXP2
DXP2
DXN
DXN
INTERNAL GROUND
INTERNAL GROUND
OUT1
FG1
FG1
FAN CONTROL
FAN CONTROL
CONTROL
CONTROL
+
+
+
+
MUX
MUX
+
+
LOGIC
LOGIC
G768B
CLK
CLK
OUT2
FAN CONTROL
FAN CONTROL
SMBUS
SMBUS
REGISTERS
REGISTERS
+
+
ADC
ADC
RESET
RESET
CIRCUIT
CIRCUIT
OUT2
FG2
FG2
SMBCLK
SMBCLK
SMBDATA
SMBDATA
ALERT
ALERT
RESET
RESET
Fig 1. Functional Diagram
A/D Conversion Sequence
If a Start command is written (or generated automatically in the free-running auto-convert mode), all three
channels are converted, and the results of all 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 G768B 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.
Thermal Mass and Self-Heating
Thermal mass can seriously degrade the G768B's
effective accuracy. The thermal time constant of the
SSOP-16 package is about 140sec in still air. For the
G768B 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.
Self-heating can significantly affect the measurement
accuracy. Remote-sensor self-heating due to the diode current source is negligible. For the local diode,
the worst-case error occurs when auto converting at
the fastest rate and simultaneously sinking maximum
current at the ALERT output, and both fans are working at low speeds.
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).
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Oct 28, 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
high-accuracy 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 G768B 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
Ver 1.3
Oct 28, 2002
G768B
errors are swamped out.
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 G768B 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 0.1F Vcc bypass
capacitors close to the G768B.
GND
GND
DXP1
DXP1
DXN
DXN
DXN
DXN
DXP2
DXP2
Fig 2(a) Connect the common DXN as close as
possible to the DXN pin on IC.
GND
GNDGND
10 MILS
10 MILS
10 MILS
10 MILS
DXP
DXPDXP
DXN
DXNDXN
GND
GNDGND
Fig 2 (b) Recommended DXP/DXN PC
7
DXP1
DXP1
DXN
DXN
G768B
G768B
DXP2
DXP2
GND
GND
Chip Boundary
Chip Boundary
10 MILS
10 MILS
MINIMUM
MINIMUM
10 MILS
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.
Global Mixed-mode Technology Inc.
G768B
N = (CLK x 30) / (rpm x P)
N : Count Number
P : FG pulses number per revolution of fan.
For CLK = 32768Hz, P = 2
N = 491520 / rpm
⇒
For CLK = 16384Hz, P = 2
N = 245762 / rpm
⇒
Some selected count numbers are shown below
Table 2. Count numbers for P=2
rpm CLK=32768Hz CLK=16384Hz
968 --- 254
1935 254 127
2000 246 123
3000 164 82
4000 123 61
5000 98 49
6000 82 41
7000 70 35
8000 61 31
9000 55 27
10000 49 25
20000 25 12
30000 16 8
To stop the fan, program the fan speed register to 255. This
also makes the fan controller into power saving mode.
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 G768B 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
25µA due to the current consumed by the conversion
rate timer. In standby mode, supply current drops to
about 3µA. at very low supply voltages (under the
power-on-reset threshold).
Fan Controller
The fan speed is measured by counting the number of
the CLK pin period between the rising edges of two
fan speed pulses on FG pin. 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:
Controlling Fan at Lower Speed
For stably controlling fans at lower rotataion speed,
three schemes are recommended as below:
1.Use larger decoupling capacitors between
FAN_OUT 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 FAN_OUT would be too low for fan
to generate recognizable FG signals.
Using decouple capacitors on FAN_OUT 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 G768B is relatively immune to short duration
negative-going V
Typically, for the G768B, 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
CC
pin
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Global Mixed-mode Technology Inc.
Ensuring a Valid Reset Output Down to VCC = 0V
When V
falls below 1V, the G768B 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 Ps with Bi-directional Reset Pins
Ps with bi-directional reset pins (such as the Motorola
68HC11 series) can connect to the G768B reset out-
put. If, for example, the G768B
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 G768B
RESET output
and the µP reset I/O (Figure 4). Buffer the G768B
RESET output to other system components.
G768B
SMBus Digital Interface
From a software perspective, the G768B 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 G768B 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.
Benefits of Highly Accurate Reset Threshold
Most µP supervisor Ics have reset threshold voltages
between 5% and 10% below the value of nominal supply voltages. This ensures a reset will not occur within
5% of the nominal supply, but will occur when the supply is 10% below nominal.
When using Ics rated at only the nominal supply ±5%
this leaves a zone of uncertainty where the supply is
between 5% and 10% low, and where the reset may or
may not be asserted.
The G768B use highly accurate circuitry to ensure that
reset is asserted close to the 5% limit, and long before
the supply has declined to 10% below nominal.
V
V
CC
CC
G768B
G768B
RESET
RESET
R1
R1
100k
GND
GND
100k
BUFFERED RESET
BUFFERED RESET
TO OTHER SYSTEM
TO OTHER SYSTEM
COMPONENTS
COMPONENTS
V
V
CC
CC
G768B
G768B
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
Fig 3. RESET Valid to V
Ver 1.3
Oct 28, 2002
= Ground Circuit
CC
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Page 10
Write Byte Format
S Address WR
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
Command Byte:
Receive Byte Format
Data Byte:
Global Mixed-mode Technology Inc.
ACK Command ACK DATA ACK P
7 bits 8 bits 8 bits 1
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
S Address WR
7 bits 8 bits
sends command with no data usually used for one-shot command
S Address RD
7 bits 8 bits
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 P
ACK Data /// P
G768B
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
source, 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
CC
ALERT interrupt
Ver 1.3
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10
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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
and local channels, and 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.
, the ADC reads +127°C for both remote
CC
Interrupts
ALERT is asserted. The interrupt output
G768B
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
SET_CNT2 20h 1111 1111b Write 2nd fan programmed speed register
ACT_CNT2 21h 1111 1111b Read 2nd fan actual speed register
FAN_STA2 22h 10b Read 2nd fan status register
CHIP_TMP 30h 0000 0000b On-chip temperature
TMAX1 31h 0100 0110b (70) 1st r emote 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
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
Ver: 1.3
Oct 28, 2002
not generate an acknowledge and continues to hold the
ALERT
line low until serviced (implies that the host
interrupt input is level sensitive). Successful reading of
the alert response address clears the interrupt latch.
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Page 12
Command Byte Functions
The 8-bit command byte register (Table 4) is the master index that points to the various other registers
within the G768B. 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.
Thermal Configuration Byte Functions
The configuration byte register (Table 5) is used to
mask (disable) interrupts and to put the device in
software standby mode. The lower six bits are internally set to (XX1111), making them "don't care" bits.
Write
Global Mixed-mode Technology Inc.
G768B
zeros to these bits. This register's contents can be
read back over the serial interface.
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 RUN/STOP bit in the configuration
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.
ALERT interrupt latch
Table 5. Configuration-Byte Bit Assignments
BIT NAME POR STATE FUNCTION
7 (MSB) MASK 0
/ STOP
RUN
6
5-0 RFU 0 Reserved for future use
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.
ALERT interrupts when high.
Table 6. Status-Byte Bit Assignments
BIT NAME FUNCTION
7(MSB) BUSY A high indicates that the ADC is busy converting.
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)
0(LSB) RFU Reserved for future use (returns 0)
*These flags stay high until cleared by POR, or until the status byte register is read.
Table 7. Conversion-Rate Control Byte
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 (
µµµµ
A TYP, at Vcc = 5V)
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Table 8. RLTS and RRTE Temp Register Update Timing Chart
Global Mixed-mode Technology Inc.
G768B
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
N/A
TIME UNTIL RLTS AND
RRTE ARE UPDAT ED
156ms max
When current conversion is
complete (1-shot is ignored)
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 G768B 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
Ver: 1.3
Oct 28, 2002
ALERT inter-
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 registers (10h for fan 1,
20h for fan 2) are read/write registers. They contain
the count number of the desired fan speed. Power up
default is FFh.
Actual fan speed register
The actual fan speed registers (11h for fan 1, 21h for
fan 2) are 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 for fan1, 22h for fan 2)
are 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.
Watchdog for fan control
Four temperature threshold registers intervene the
control of fans. Both pin OUT1 and pin OUT2 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 both fans 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
G768B to be used in the occasion when system fails
and loses the fan control of G768B.
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Slave Addresses
The G768B 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 G768B also responds to the SMBus Alert Response
slave address (see the Alert Response Address section).
POR and UVLO
The G768B has a volatile memory. To prevent ambiguous power-supply conditions from corrupting the
Global Mixed-mode Technology Inc.
G768B
data in memory and causing erratic behavior, a POR
voltage detector monitors Vcc and clears the memory
if Vcc falls below 1.7V (typical, see Electrical Characteristics table). When power is first applied and Vcc
rises above 1.75V (typical), the logic blocks begin operating, although reads and writes at V
3V are not recommended. A second Vcc comparator,
the ADC UVLO comparator, prevents the ADC from
converting until there is sufficient headroom (Vcc =
2.8V typical).
levels below
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 re-
AB C
t
LOW
t
HIGH
DE
mote Receive Byte queries.
THIGH and TLOW registers are set to max and
min limits, respectively.
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 SMBData 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
t
SU:STO
t
BUF
SMBCLK
SMBCLK
SMBDATA
SMBDATA
AB
AB
t
t
LOW
LOW
t
t
SU:STAtHD:ST A
SU:STAtHD:ST A
t
t
HIGH
HIGH
CDEF
CDEF
t
t
SU:DAT
SU:DAT
G
G
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
Ver: 1.3
Oct 28, 2002
14
JK
HI
HI
JK
t
t
SU:STO
SU:STO
t
t
BUF
BUF
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Global Mixed-mode Technology Inc.
Package Information
°
7
(4X)
G768B
C
E1
E
L
D
θ
A2 A
y
e
b
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 li censes are implied and GMT In c. reserves the right at any time without notice to change said circuitry and specifications.
Ver: 1.3
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15
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