G768BF_技术文档

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troller with SMBus Serial Interface and System Reset

Circuit

Features

General Description

^ꢀMeasures Two Remote Temperatures

^ꢀNo Calibration Required

The G768D contains a precise digital thermometer, a

fan controller, and a system-reset circuit.

^ꢀ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%

Except for one less fan controller, G768D is backward

compatible with G768B. G768D has 2 more functions,

fan-failure detection and programmable thermal shut-

down signal.

The thermometer reports the temperature of 2 remote

sensors. The remote sensors are diode-connected

transistors typically

a

low-cost, easily mounted

2N3904 NPN type that replace conventional thermis-

tors or thermocouples. Remote accuracy is ±5°C for

multiple transistor manufacturers, with no calibration

needed. The remote channel can also measure the die

temperature of other ICs, such as microprocessors,

that contain an on-chip, diode-connected transistor.

^ꢀ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

The 2-wire serial interface accepts standard System

Management Bus (SMBus^TM) Write Byte, Read Byte,

Send Byte, and Receive Byte commands to program

the alarm thresholds and to read temperature data.

The data format is 7 bits plus sign, with each bit cor-

responding to 1°C, in two’s-complement format.

Measurements can be done automatically and

autonomously, with the conversion rate programmed

by the user or programmed to operate in a single-shot

mode. The adjustable rate allows the user to control

the supply-current drain.

^ꢀ340ms Typical Power-On Reset Pulse Width

RESET Output

^ꢀGuaranteed RESET Valid to V_CC=1V

^ꢀPower Supply Transient Immunity

^ꢀNo External Components needed for reset

function

^ꢀSmall, 16-Pin SSOP Package

Applications

^ꢀDesktop and Notebook

^ꢀCentral Office Computers

^ꢀTelecom Equipment

^ꢀSmart Battery Packs

^ꢀTest and Measurement

^ꢀLAN Servers

G768D also contains a fan speed controller. It connects

directly to the fans and performs closed-loop control of

the fan speed independently. The only external compo-

nent required is a 10µF capacitor per channel. It deter-

mines the current fan speed based on the fan rotation

pulses and an externally supplied 32.768KHz clock.

^ꢀMulti-Chip Modules

^ꢀIndustrial Controls

Pin Configuration

Ordering Information

G768D

PART NUMBER TEMP. RANGE PIN-PACKAGE

G768D

-55°C to +125°C

16SSOP

1

2

3

4

5

FANVCC

Vcc

TH_SHUT

Vcc

16

15

DXP1

14

13

12

11

SMBCLK

NC

DXN

SMBDATA

DXP2

6

7

8

ALERT

RESET

DGND

10 FG

CLK

9

AGND

16Pin SSOP

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G768D

It uses LDO method and an on-chip MOSFET to con-

trol the fan speed to ±2% of the programmed speed.

The G768D also contains a microprocessor (µP) su-

pervisory circuit used to monitor the power supplies in

µP and digital systems. They provide excellent circuit

reliability and low cost by eliminating external compo-

nents and adjustments when used with 5V-powered

circuits. This circuit asserts a reset signal whenever

the V_CCsupply voltage declines below a preset

threshold, keeping it asserted for at least 140ms after

V_CChas risen above the reset threshold. The G768D

The desired fan speed is also programmed via

SMBus^TM. The actual fan speed and fan status can be

read via the SMBus^TM. Short-circuit protection is im-

plemented 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 hard-

ware watchdog system. The fan controller would fully

turn on the fan when any of the following conditions

happens.

has an active-low RESET output. The reset com-

parator is designed to ignore fast transients on V_CC.

Reset threshold of this circuit is set to 4.4V typical.

The G768D is available in a small, 16-pin SSOP sur-

face-mount package.

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

TH_SHUT

FANVCC

1µF

FAN1

FG

VCC

10µF

10k EACH

G768D

SMBCLK

DXP1

DXN

SMBDATA

ALERT

2200pF

2N3904

INTERRUPT TO µC

CLK

CLOCK 32.768kHz

DXP2

2200pF

2N3904

RESET

µP

GND

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G768D

Absolute Maximum Ratings

V_CCto GND……………….………….…….-0.3V to +6V

DXP1, DXP2 to GND……………0.3V to (V_CC+ 0.3V)

DXN to GND……………………………...-0.3V to +0.8V

man body model)….……….………….……..….….2000V

ESD Protection (other pins, human body model)…2000V

Continuous Power Dissipation (T_A= +70°C) SSOP

(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

CLK , FG, S MB CLK , S MB DA TA , ALERT to

GND.……………………….…….………...-0.3V to +6V

SMBDATA, ALERT Current…………...-1mA to +50mA

DXN Current………………………………………±1mA

ESD Protection (SMBCLK, SMBDATA, ALERT , hu-

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 opera-

tional sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may

affect device reliability.

Electrical Characteristics

(V_CC= + 5V, T_A= 60°C, unless otherwise noted.)

PARAMETER

Temperature Sensor

Temperature Resolution (Note 1)

Temperature Error, Remote Diode (Notes 2

and 3)

CONDITIONS

MIN TYP MAX UNITS

Monotonicity guaranteed

8

Bits

°C

T_R= 0°C to +125°C

T_R= 60°C to +100°C

-5

-3

5

3

Temperature Error, Local Diode

(Notes 1 and 2)

Including long-term drift

T_A= +60°C to +100°C

-3

3

°C

Supply-Voltage Range

4.5

5

5.5

V

mV

V

Under-voltage Lockout Threshold

Under-voltage Lockout Hysteresis

Power-On Reset Threshold

POR Threshold Hysteresis

V_CCinput, disables A/D conversion, rising edge

V_CC, falling edge

2.6 2.8 2.95

50

1.0 1.7 2.5

50

mV

SMBus static

Hardware or software

standby, SMBCLK at 10kHz

3

10

Logic inputs forced to V_CCor

GND

Standby Supply Current

µA

200

Auto-convert mode, average 0.25 conv/sec

250 300

300 350

Average Operating Supply Current

µA

measured over 4sec. Logic

2.0 conv/sec

inputs forced to V_CCor GND

Conversion Time

Conversion Rate Timing Error

From stop bit to conversion complete (all channels)

Auto-convert mode

94 125 156

ms

%

-25

25

High level

DXP forced to 1.5V

120 160 200

Remote-Diode Source Current

µA

Low level

15

20

25

Fan Controller

Supply voltage

Shutdown current

MOSFET on resistance

Short-circuit current limit

Input logic low

V_CC

4.5

5

2

5.5

5

V

µA

Ω

Fan speed = 0rpm

0.2 0.25

0.5

A

V

KHz

mA

V

VIL

VIH

CLK

0.7.

Input logic high

Clock frequency

1.0

32.768

FANVCC over-current trig

FANVCC current limit

FG input Positive-going threshold voltage

FG input Negative-going threshold voltage

FG input Hysteresis voltage

600

500

V_CC=5V

1

0.7

0.3

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G768D

(continued)

Electrical Characteristics

(V_CC= + 5V, T_A= 60°C, unless otherwise noted.)

PARAMETER

CONDITIONS

MIN TYP MAX UNITS

SMBus Interface

Logic Input High Voltage

Logic Input Low Voltage

Logic Output Low Sink Current

ALERT Output High Leakage Current ALERT forced to 5.5V

Logic Input Current

SMBus Input Capacitance

SMBus Clock Frequency

SMBCLK Clock Low Time

SMBCLK Clock High Time

SMBus Start-Condition Setup Time

SMBus Repeated Start-Condition

Setup Time

SMBCLK, SMBDATA; V_CC= 4.5V to 5.5V

ALERT , SMBDATA forced to 0.4V

2.4

6

V

0.8

mA

µA

pF

KHz

µs

ns

1

2

Logic inputs forced to V_CCor GND

SMBCLK, SMBDATA

(Note 4)

t_LOW, 10% to 10% points

t_HIGH, 90% to 90% points

-2

5

DC

4.7

4

4.7

500

100

t_{SU : STA ,}90% to 90% points

SMBus Start-Condition Hold Time

SMBus Start-Condition Setup Time

SMBus Data Valid to SMBCLK Rising- t_{SU: DAT ,}10% or 90% of SMBDATA to 10% of

Edge Time

t_{HD: STA ,}10% of SMBDATA to 90% of SMBCLK

t_{SD: STO ,}90% of SMBDATA to 10% of SMBDATA

4

800

µs

ns

SMBCLK

SMBus Data-Hold Time

SMBCLK Falling Edge to SMBus

Data-Valid Time

t_{HD : DAT}(Note 5)

Master clocking in data

0

µs

1

(continued)

Electrical Characteristics

(V_CC=full range, T_A= 60°C, unless otherwise noted.)

PARAMETER

Reset Threshold

Reset Active Timeout Period

RESET Output Voltage Low

RESET Output Voltage High

SYMBOL

CONDITIONS

MIN TYP MAX UNITS

V_TH

4.2

4.4

4.5

V

ms

V

340

V

_CC=V_THmin, I_SINK=3.2mA

_CC>V_THmax, I_SOURCE=5.0mA

V_OL

V_OH

0.4

V_CC-1.5

V

Note 1: Guaranteed but not 100% tested.

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 tem-

perature range. See Table3.

Note 3: A remote diode is any diode-connected transistor from Table1. T_Ris the junction temperature of the re-

mote diode. See Remote Diode Selection for remote diode forward voltage requirements.

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.

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G768D

Pin Description

1

NAME

FUNCTION

FANVCC Output connected to V_CCof fan.

2,15

V_CC

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;

tie DXP1 to DXN if no remote diode on channel 1 is used. Place a 2200pF capacitor between DXP1 and

DXN for noise filtering.

3

DXP1

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.

4

DXN

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 Output remains low while V_CCis below the reset threshold, and for 340ms after V_CCrises above

the reset threshold.

5

6

DXP2

RESET

7

8

9

10

11

12

13

14

16

DGND

AGND

CLK

FG

ALERT

Digital Ground.

Analog Ground.

32.768KHz clock input for fan controller.

Fan pulse input.

SMBus Alert (interrupt) Output, open drain.

SMBDATA SMBus Serial-Data Input / Output, open drain.

NC

SMBCLK SMBus Serial-Clock Input.

TH_SHUT Thermal Shutdown Output, push-pull output.

Detailed Description

ADC and Multiplexer

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 ADC is an averaging type that integrates over a

60ms period (each channel, typical).

The multiplexer automatically steers bias currents

through two remote diodes, measures their forward

voltages, and computes their temperatures. All chan-

nels are converted automatically once the conversion

process has started, either in free-running or sin-

gle-shot mode. If one of the two channels is not used,

the device still performs all measurements, and the

user can simply ignore the results of the unused

channel. If the remote diode channel is unused, tie

DXPx to DXN rather than leaving the pins open.

The temperature sensor is designed to work in con-

junction with an external micro-controller (µC) or other

intelligence in thermostatic, process-control, or moni-

toring applications. The µC is typically a powerman-

agement or keyboard controller, generating SMBus se-

rial commands by "bit-banging" general-purpose in-

put-output (GPIO) pins or via a dedicated SMBus inter-

face block.

Essentially a 12-bit serial analog-to-digital converter

(ADC) with a sophisticated front end, the G768D con-

tains a switched current source, a multiplexer, an ADC,

an SMBus interface, one fan controller, a reset circuit

and associated control logic (Figure 1).

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.

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.

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.

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G768D

FANVCC

THERMAL SHUTDOWN

LOGIC

TH_SHUT

FAN CONTROL

FG

V_CC

CLK

SMBCLK

SMBDATA

ALERT

SMBUS

CONTROL

LOGIC

REGISTERS

DXP1

DXP2

DXN

+

RESET

+

ADC

MUX

CIRCUIT

RESET

INTERNAL GROUND

Fig 1. Functional Diagram

Thermal Mass and Self-Heating

A/D Conversion Sequence

If a Start command is written (or generated automati-

cally in the free-running auto-convert mode), both two

channels are converted, and the results of both meas-

urements are available after the end of conversion. A

BUSY status bit in the status byte shows that the de-

vice is actually performing a new conversion; however,

even if the ADC is busy, the results of the previous

conversion are always available.

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, im-

proves the situation. Take care to account for thermal

gradients between the heat source and the sen-

sor ,and ensure that stray air current across the sen-

sor package do not interfere with measurement accu-

racy.

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 tempera-

Table 1. Remote-Sensor Transistor Manufacturers

MANUFACTURER

Philips

MODEL NUMBER

PMBS 3904

ture-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 ex-

pected 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.

Motorola (USA)

National Semiconductor (USA)

MMBT3904

Note:Transistors must be diode-connected (base short

-ed to collector).

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G768D

ADC Noise Filtering

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 practi-

cal.

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.

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.

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 ca-

pacitance. Higher capacitance than 3300pF introduces

errors due to the rise time of the switched current

source.

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 con-

necting to GND.

Nearly all noise sources tested cause the ADC meas-

urements 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

^ꢀ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 V_CCbypass

capacitors close to the G768D.

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.

GND

DXP1

DXN

DXP1

DXN

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.

G768D

DXN

DXP2

GND

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.

Chip Boundary

^ꢀFig 2(a) Connect the common DXN as close as

possible to the DXN pin on IC.

Route the 2 pairs of DXP1-DXN and DXP2-DXN

traces independently (Figure 2a). Connect the com-

mon DXN as close as possible to the DXN pin on IC

(Figure 2a).

GND

10 MILS

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.

10 MILS

DXP

DXN

GND

MINIMUM

10 MILS

Route through as few vias and crossunders as possi-

ble 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 ther-

mocouples 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.

Fig 2 (b) Recommended DXP/DXN PC

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G768D

Twisted Pair and Shielded Cables

N: Count Number

For remote-sensor distances longer than 8 in., or in

particularly noisy environments, a twisted pair is rec-

ommended. Its practical length is 6 feet to 12feet (typi-

cal) 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.

P: FG pulses number per revolution

P=1 ⇒ N = 983040 / rpm

P=2 ⇒ N = 491520 / rpm

P=4 ⇒ N = 245762 / rpm

Some selected count number for P=2 are listed below.

Table 2.

Rpm

3000

4000

5000

6000

7000

8000

9000

10000

20000

30000

N

164

123

98

82

70

61

55

49

25

Excess capacitance at DX_limits practical remote

sensor distances (see Typical Operating Characteris-

tics), 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.

16

Low-Power Standby Mode

To stop the fan, program the fan speed register to 255. This

also makes the fan controller enter power saving 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 mem-

ory, and the SMB interface is alive and listening for

reads and writes. This is valid for temperature sensor

only.

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.

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 con-

version rate reduces the average supply current (see

Typical Operating Characteristics). In between con-

versions, the instantaneous supply current is about

200µA due to the current consumed by the system

resetting circuit.

Reset Immunity Negative-Going V_CCTransients

In addition to issuing a reset to the microprocessor (µP)

during power-up, power-down, and brownout condi-

tions, the G768D is relatively immune to short duration

negative-going V_CCtransients (glitches).

Typically, for the G768D, a V_CCtransient that goes

100mV below the reset threshold and lasts 20µs or

less will not cause a reset pulse. A 0.1µF bypass ca-

pacitor mounted as close as possible to the V_CCpin

provides additional transient immunity.

Fan Controller

Since the fan speed is measured by counting the num-

ber 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 writ-

ing the corresponding count number. The count num-

ber is given by:

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G768D

Ensuring a Valid Reset Output Down to V_CC= 0V

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 con-

trol 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.

When V_CCfalls below 1V, the G768D RESET output

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_CCbe-

low 1V. However, in applications where RESET must

be valid down to 0V, adding a pull-down resistor to

RESET causes any stray leakage currents to flow to

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 regis-

ter 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 re-

ported as +100°C.

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 Mo-

torola 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, indeter-

minate 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.

BUFFERED RESET

BUFFER

V_CC

TO OTHER SYSTEM

COMPONENTS

V_CC

G768D

µP

RESET

4.7k

G768D

RESET

R1

100k

GND

Fig 4. Interfacing to µPs with Bi-directional Reset I/O

Fig 3 RESET Valid to V_CC= Ground Circuit

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G768D

Write Byte Format

S

Address

7 bits

WR

ACK

Command

ACK

DATA

8 bits

ACK

P

1

8 bits

Slave Address: equivalent to chip-select line of a 3-wire interface

Command Byte: selects, which register you, are writing to

Data Byte: data goes into the register set by the command byte (to set thresholds, configuration masks, and

sampling rate)

Read Byte Format

S

Address WR

ACK

Command ACK

S

Address

7 bits

RD ACK DATA

///

P

7 bits

8 bits

Slave Address: equivalent to chip- select line

Command Byte: selects, which register you, are reading from

Slave Address: repeated due to change in data-flow direction

Data byte: reads from the register set by the command byte

Send Byte Format

S

Address

WR

ACK

Command

8 bits

ACK

///

P

7 bits

Command Byte: sends command with no data usually used for one-shot command

Receive Byte Format

S

Address

RD

ACK

Data

8 bits

7 bits

Data Byte: reads data from the register commanded by the last Read Byte or Write

Byte transmission; also used for SMBus Alert Response return address

S = Start condition Shaded = Slave transmission P = Stop condition /// = Not acknowledged

Fig 5. SMBus Protocols

Table 3. Data Format (Twos-Complement)

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-

ROUND

TEMP.

(°C)

DIGITAL OUTPUT

DATA BITS

TEMP.

(°C)

SIGN

MSB

111

001

000

111

110

100

011

LSB

+130.00

+127.00

+126.50

+126.00

+25.25

+0.50

+127

+126

+25

+1

0

1

1111

1110

1001

0001

0000

1111

0111

0110

1001

1111

sponding alarm threshold value, an ALERT interrupt

is asserted.

The power-on-reset (POR) state of both THIGH regis-

ters is full scale (0111 1111, or +127°C). The POR

state of both TLOW registers is 1100 1001 or -55°C.

+0.25

+0

Diode Fault Alarm

+0.00

+0

There is a continuity fault detector at DXP that detects

whether the remote diode has an open-circuit condi-

tion. 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_CC-1V (typical) due to the diode current 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.

-0.25

+0

-0.50

+0

-0.75

-1

-1.00

-1

-25.00

-25.50

-54.75

-55.00

-65.00

-70.00

-25

-55

-65

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G768D

If the remote channel is shorted (DXP to DXN or DXP

to GND), the ADC reads 0000 0000 so as not to trip

either the THIGH or TLOW alarms at their POR set-

tings. In applications that are never subjected to 0°C in

normal operation, a 0000 0000 result can be checked

to indicate a fault condition in which DXP is acciden-

tally short circuited. Similarly, if DXP is short circuited

to V_CC, the ADC reads +127°C for both channels, and

the device alarms.

rupt output pin is open-drain so that device can share

a common interrupt line. The interrupt rate can never

exceed the conversion rate.

The interface responds to the SMBus Alert Response

address, an interrupt pointer return-address feature

(see Alert Response Address section). Prior to taking

corrective action, always check to ensure that an in-

terrupt is valid by reading the current temperature.

Alert Response Address

ALERT Interrupts

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

The ALERT interrupt output signal is latched and can

only be cleared by reading the Alert Response ad-

dress. Interrupts are generated in response to THIGH

and TLOW comparisons and when the remote diode is

disconnected (for continuity fault detection). The in-

terrupt does not halt automatic conversions; new tem-

perature data continues to be available over the SMBus

master. Upon receiving an ALERT interrupt signal, the

host master can broadcast a Receive Byte transmission

to the Alert Response slave address (0001 100). Then

any slave device that generated an interrupt attempts to

identify itself by putting its own address on the bus.

interface after ALERT is asserted. The interrupt output

Table 4. Command-Byte Bit Assignments

REGISTER

RRTE2

RRTE1

RSL

RCL

RCRA

COMMAND

00h

POR STATE

0000 0000b

N/A

0000 0000b

0000 0010b

FUNCTION

Read 2nd remote temperature: returns latest temperature

Read 1st remote temperature: returns latest temperature

Read status byte (flags, busy signal)

Read configuration byte

01h

02h

03h

04h

Read conversion rate byte

RRHI2

RRLS2

RRHI1

RRLS1

WCA

05h

06h

07h

08h

0111 1111b (127) Read 2nd remote THIGH limit

1100 1001b(-55) Read 2nd remote TLOW limit

0111 1111b (127) Read 1st remote THIGH limit

1100 1001b (-55) Read 1st remote TLOW limit

09h

N/A

Write configuration byte

Write conversion rate byte

WCRW

WRHA2

WRLN2

WRHA1

WRLN1

OSHT

SET_CNT1

ACT_CNT1

FAN_STA1

TMAX1

THYST1

TMAX2

THYST2

TCRIT1

TCRIT2

0Ah

0Bh

0Ch

0Dh

0Eh

0Fh

10h

11h

12h

31h

32h

N/A

Write 2nd remote THIGH limit

Write 2nd remote TLOW limit

Write 1st remote THIGH limit

Write 1st remote TLOW limit

One-shot command (use send-byte format)

Write 1st fan programmed speed register

Read 1st fan actual speed register

Read 1st fan status register

N/A

1111 1111b

10b

0100 0110b (70) 1st remote TMAX

0011 1100b (60) 1st remote THYST

0100 0110b (70) 2nd remote TMAX

33h

34h

35h

36h

0011 1100b (60) 2nd remote THYST

0110 1100b (108) Critical temperature for 1^stremote temperaure sensor

0101 1000b (88) Critical temperature for 2^ndremote temperaure sensor

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G768D

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

Bit 6 (RUN/STOP) is to put the device in software

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.

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 re-

sponse address clears the interrupt latch.

Thermal Status Byte Functions

Command Byte Functions

The thermal status byte register (02h) (Table 6) indi-

cates 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 8-bit command byte register (Table 4) is the mas-

ter 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

the fault persists. Note that the ALERT interrupt latch

is not automatically cleared when the status flag bit is

cleared.

(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.

When reading the status byte, you must check for in-

ternal 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 configura-

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.

Configuration Byte Functions

The configuration byte register contents are listed in

table 5. Bit 7(MASK) is used to mask ALERT interrupt.

Table 5. Configuration-Byte Bit Assignments

BIT

NAME

POR STATE

FUNCTION

7 (MSB)

MASK

0

Masks all ALERT interrupts when high.

Standby mode control bit. If high, the device immediately stops converting and en-

ters standby mode. If low, the device converts in either one-shot or timer mode.

Validation of the fan failure detection. If high, activated. If low, disable.

Validation of the fault queue function of thermal shutdown.

6

RUN / STOP

0

5

4

DET_FAN

EN_TH_SHUT

0

1

Fault Queue. Number of faults necessary to detect before setting TH_SHUT output

to avoid false tripping due to noise.

3-0

FQ_TH_SHUT

0010b

Table 6. Number of Faults assigned by FQ_TH_SHUT

FQ_TH_SHUT

0000b

Number of Faults

FQ_TH_SHUT

1000b

Number of Faults

1

9

0001b

0010b

0011b

0100b

0101b

0110b

0111b

2

1001b

1010b

1011b

1100b

1101b

1110b

1111b

10

11

12

13

14

15

16

3(Power-up default)

4

5

6

7

8

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G768D

Table 7. Status-Byte Bit Assignments

BIT

7(MSB)

NAME

BUSY

FUNCTION

A high indicates that the ADC is busy converting.

6

5

4

3

2

1

RHIGH2*

RLOW2*

RHIGH1*

RLOW1*

OPEN*

A high indicates that the 2^nddiode high-temperature alarm has activated.

A high indicates that the 2^nddiode low-temperature alarm has activated.

A high indicates that the 1^stdiode high-temperature alarm has activated.

A high indicates that the 1^stdiode low-temperature alarm has activated.

A high indicates a remote-diode continuity (open-circuit) fault.

Reserved for future use (returns 0)

RFU

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

CONVERSION

Temperature Sensor Average

DATA

RATE (Hz)

Supply Current (µA TYP, at V_CC= 5V)

00h

01h

02h

03h

04h

0.0625

0.125

0.25

0.5

1

30

33

35

48

70

05h

06h

07h

2

4

8

RFU

128

225

425

-

08h to FFh

Table 9. RLTS and RRTE Temp Register Update Timing Chart

OPERATING

MODE

Auto-Convert

CONVERSION

INITIATED BY:

Power-on reset

NEW CONVERSION RATE

TIME UNTIL RLTS AND

RRTE ARE UPDATED

156ms max

(CHANGED VIA WRITE TO CRW)

N/A (0.25Hz)

1-shot command, while idling

between automatic conversions

1-shot command that occurs

during a conversion

Auto-Convert

N/A

156ms max

When current conversion is

complete (1-shot is ignored)

Auto-Convert

Rate timer

0.0625Hz

0.125Hz

0.25Hz

0.5Hz

1Hz

2Hz

4Hz

8Hz

N/A

20sec

10sec

5sec

2.5sec

1.25sec

625ms

312.5ms

237.5ms

156ms

Software Standby RUN/STOP bit

Software Standby 1-shot command

N/A

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G768D

Watchdog for fan control

To check for internal bus collisions, read the status

byte. If the least significant seven bits are ones, dis-

card the data and read the status byte again. The

status bits LHIGH, LLOW, RHIGH, and RLOW are

refreshed on the SMBus clock edge immediately fol-

lowing 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

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 Be-

sides, 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.

conversion, so OPEN data is lost. The ALERT inter-

rupt latch is independent of the status byte register, so

no false alerts are generated by an internal bus colli-

sion.

Slave Addresses

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 (espe-

cially 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 es-

tablish the trend direction.

The G768D appears to the SMBus as one device hav-

ing 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 Re-

sponse slave address (see the Alert Response Ad-

dress section).

POR and UVLO

The G768D has a volatile memory. To prevent am-

biguous power-supply conditions from corrupting the

data in memory and causing erratic behavior, a POR

voltage detector monitors V_CCand clears the memory

if V_CCfalls below 1.7V (typical, see Electrical

Characteristics table). When power is first applied and

V_CCrises above 1.75V (typical), the logic blocks begin

operating, although reads and writes at V_CClevels

below 3V are not recommended. A second V_CC

comparator, the ADC UVLO comparator, prevents the

ADC from converting until there is sufficient headroom

(V_CC= 2.8V typical).

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 avail-

able one total conversion time (125ms nominal, 156ms

maximum) after initiating a conversion, whether con-

version is initiated via the RUN/STOP bit, one-shot

command, or initial power-up. Changing the conver-

sion rate can also affect the delay until new results are

available. See Table 8.

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-

mote Receive Byte queries.

^ꢀTHIGH and TLOW registers are set to max and

min limits, respectively

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.

Detection On fan Failure

Setting bit 5 (DET_FAN) of CONFIGURATION-BYTE

register with logic 1 activates the detection of fan fail-

ure. G768D detects fan failure via FG pin. G768D de-

fines 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.

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.

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.

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G768D

Thermal Shutdown Signal

same mechanism is duplicated for DX2. There fore,

either one of DX1, DX2 continuously over their re-

spective Tcrit, the TH_SHUT will assert logic high to

indicate a thermal shutdown event.

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

G

D

E

H

I

J

K

M

A

B

C

F

L

t_HIGH

t_LOW

SMBCLK

SMBDATA

t_HD:DAT

t_BUF

t_SU:STO

t_SU:STAt_HD:STA

t_SU:DAT

Figure 6. SMBus Write Timing Diagram

A = start condition

H = LSB of data clocked into slave

I = slave pulls SMBDATA line low

J = acknowledge clocked into master

K = acknowledge clocked pulse

L = stop condition data executed by slave

M = new start condition

B = MSB of address clocked into slave

C = LSB of address clocked into slave

D = R / W bit clocked into slave

E = slave pulls SMB Data line low

F = acknowledge bit clocked into master

G = MSB of data clocked into slave

A

B

G

J

K

C

D

E

F

H

I

t_HIGH

t_LOW

SMBCLK

SMBDATA

t_BUF

t_SU:STO

t_SU:STAt_HD:STA

t_SU:DAT

Figure 7. SMBus Read Timing Diagram

A = start condition

G = MSB of data clocked into master

H = LSB of data clocked into master

I = acknowledge clocked pulse

J = stop condition

B = MSB of address clocked into slave

C = LSB of address clocked into slave

D = R / W bit clocked into slave

E = slave pulls SMBDATA line low

F =acknowledge bit clocked into master

K= new start condition

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Package Information

G768D

C

E1

E

L

D

θ

7 °

(4X)

A2

A1

A

e

y

b

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

4.Controlling dimension is millimeter converted inch dimensions are not necessarily exact.

DIMENSION IN MM

DIMENSION IN INCH

SYMBOLS

MIN

1.35

0.10

-----

0.20

0.19

4.80

5.80

3.80

-----

0.40

-----

0º

NOM

1.60

-----

1.45

0.25

-----

0.64

-----

MAX

1.75

0.25

-----

0.30

0.25

5.00

6.20

4.00

-----

MIN

0.053

0.004

-----

0.008

0.007

0.189

0.228

0.150

-----

NOM

0.064

-----

MAX

0.069

0.010

-----

0.012

0.010

0.197

0.244

0.157

-----

A

A1

A2

b

C

D

E

E1

e

L

y

θ

0.057

0.010

-----

0.025

-----

1.27

0.10

8º

0.016

-----

0º

0.050

0.004

8º

Taping Specification

Feed Direction

Typical SSOP Package Orientation

GMT Inc. does 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.

TEL: 886-3-5788833

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型号：	G768BF
厂家：	GLOBAL MIXED-MODE TECHNOLOGY INC
描述：	暂无描述风扇传感器温度传感器复位电路控制器
文件：	总16页 (文件大小：343K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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