GMT G768D Datasheet

Global Mixed-mode Technology Inc.

G768D

Two Remote Temperature Sensors and One Fan Con­troller with SMBus Serial Interface and System Reset
Circuit

Features

Measures Two Remote Temperatures

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No Calibration Required

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SMBus 2-Wire Serial Interface

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Programmable Under/Over-temperature Alarms

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Programmable Thermal Shutdown Signal

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Supports SMBus Alert Response

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Accuracy: ±5°C (-40°C to + 125°C, remote)

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±3°C (+60°C to + 100°C, remote)

+4.5V to +5.5V Supply Range

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Fan speed control range: 3,000 to 30,000 rpm

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Fan speed accuracy: ±2%

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Built-in MOSFET switch

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Internal current-limit and over-temperature

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protection for fan control
Watchdog for fan control

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Alarm for fan failure

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Precision Monitoring of 5V Power-Supply

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Voltage
340ms Typical Power-On Reset Pulse Width

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RESET Output

Guaranteed RESET Valid to VCC=1V

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Power Supply Transient Immunity

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No External Components needed for reset

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function

Small, 16-Pin SSOP Package

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Applications

Desktop and Notebook

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Central Office Computers

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Telecom Equipment

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Smart Battery Packs

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Test and Measurement

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LAN Servers

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Multi-Chip Modules

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Industrial Controls

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Pin Configuration

General Description

The G768D contains a precise digital thermometer, a
fan controller, and a system-reset circuit.

Except for one less fan controller, G768D is backward
compatible with G768B. G768D has 2 more functions,
fan-failure detection and programmable thermal shut­down signal.

The thermometer reports the temperature of 2 remote
sensors. The remote sensors are diode-connected
transistors typically a low-cost, easily mounted
2N3904 NPN type that replace conventional thermis­tors or thermocouples. Remote accuracy is ±5°C for
multiple transistor manufacturers, with no calibration
needed. The remote channel can also measure the die
temperature of other ICs, such as microprocessors,
that contain an on-chip, diode-connected transistor.

The 2-wire serial interface accepts standard System
Management Bus (SMBus

TM

) Write Byte, Read Byte,
Send Byte, and Receive Byte commands to program
the alarm thresholds and to read temperature data.
The data format is 7 bits plus sign, with each bit cor­responding to 1°C, in two’s-complement format.
Measurements can be done automatically and
autonomously, with the conversion rate programmed
by the user or programmed to operate in a single-shot
mode. The adjustable rate allows the user to control
the supply-current drain.

G768D also contains a fan speed controller. It connects
directly to the fans and performs closed-loop control of
the fan speed independently. The only external compo­nent required is a 10µF capacitor per channel. It deter­mines the current fan speed based on the fan rotation
pulses and an externally supplied 32.768KHz clock.

Ordering Information

Vcc

DXP1

DXN

DXP2

RESET

DGND

AGND

1

2

3

4

5

6

7

8

FANVCC

Ver: 1.2

Apr 03, 2002

G768D

16Pin SSOP

16

15

14

13

12

11

10

9

TH_SHUT

Vcc

SMBCLK

NC

SMBDATA

ALERT

FG

CLK

PART NUMBER TEMP. RANGE PIN-PACKAGE

G768D -55°C to +125°C 16SSOP

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Global Mixed-mode Technology Inc.

It uses LDO method and an on-chip MOSFET to con­trol the fan speed to ±2% of the programmed speed.

The desired fan speed is also programmed via
SMBus
read via the SMBus

TM

. The actual fan speed and fan status can be

TM

. Short-circuit protection is im­plemented to prevent damages to the fan and this IC
itself. The accepted frequency of fan rotation pulses is
100~1000Hz, which corresponds to 3,000 to 30,000
rpm for a typical fan that produces two pulses per
revolution. The G768D also turns on the fans by hard­ware watchdog system. The fan controller would fully
turn on the fan when any of the following conditions
happens.

1. when either of the remote temperature is higher than
its own T

MAX

.

2.when either of these two remote diodes is open.

3.when both remote diodes are short.

Typical Operating Circuit

IN

FAN1

FAN1

IN

1µF

1µF

FANVCC

FANVCC

G768D

The G768D also contains a microprocessor (µP) su­pervisory circuit used to monitor the power supplies in
µP and digital systems. They provide excellent circuit
reliability and low cost by eliminating external compo­nents and adjustments when used with 5V-powered
circuits. This circuit asserts a reset signal whenever
the V
threshold, keeping it asserted for at least 140ms after
V

has an active-low
parator is designed to ignore fast transients on V
Reset threshold of this circuit is set to 4.4V typical.

The G768D is available in a small, 16-pin SSOP sur­face-mount package.

TH_SHUT

TH_SHUT

supply voltage declines below a preset

CC

has risen above the reset threshold. The G768D

CC

RESET output. The reset com-

CC

.

2N3904

2N3904

2N3904

2N3904

RESET

RESET

µP

µP

FG

FG

2200pF

2200pF

2200pF

2200pF

FG

FG

DXP1

DXP1

DXN

DXN

DXP2

DXP2

RESET

RESET

GND

GND

G768D

G768D

SMBDATA

SMBDATA

VCC

VCC

SMBCLK

SMBCLK

ALERT

ALERT

CLK

CLK

10µF

10µF

CLOCK 32.768kHz

CLOCK 32.768kHz

10k EACH

10k EACH

SMBCLK

SMBCLK

SMBDATA

SMBDATA

INTERRUPT TO µC

INTERRUPT TO µC

Ver: 1.2

Apr 03, 2002

TEL: [phone]

http://www.gmt.com.tw

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Global Mixed-mode Technology Inc.

G768D

Absolute Maximum Ratings

VCC to GND……………….………….…….-0.3V to +6V
DXP1, DXP2 to GND……………0.3V to (V

+ 0.3V)

CC

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

CLK, FG, SMBCLK, SMBDATA,

ALERT

to

GND.……………………….…….………...-0.3V to +6V

SMBDATA,

ALERT

Current…………...-1mA to +50mA

DXN Current………………………………………±1mA

ESD Protection (SMBCLK, SMBDATA,

Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are
stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the opera­tional sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may
affect device reliability.

ALERT

, hu-

man body model)….……….………….……..….….2000V
ESD Protection (other pins, human body model)…2000V
Continuous Power Dissipation (T

= +70°C) SSOP

A

(de-rate 8.30mW/°C above +70°C)…………667mW
Operating Temperature Range…-55°C to +125°C

Junction Temperature………………....+150°C

Storage temperature Range………-65°C to +165°C
Lead Temperature (soldering, 10sec)……….+300°C

Electrical Characteristics

(VCC = + 5V, TA = 60°C, unless otherwise noted.)

PARAMETER CONDITIONS MIN TYP MAX UNITS

Temperature Sensor

Temperature Resolution (Note 1) Monotonicity guaranteed 8 Bits

Temperature Error, Remote Diode (Notes 2
and 3)

Temperature Error, Local Diode
(Notes 1 and 2)

Supply-Voltage Range 4.5 5 5.5 V

Under-voltage Lockout Threshold VCC input, disables A/D conversion, rising edge 2.6 2.8 2.95 V

Under-voltage Lockout Hysteresis 50 mV

Power-On Reset Threshold VCC, falling edge 1.0 1.7 2.5 V

POR Threshold Hysteresis 50 mV

Standby Supply Current

Average Operating Supply Current

Conversion Time From stop bit to conversion complete (all channels) 94 125 156 ms

Conversion Rate Timing Error Auto-convert mode -25 25 %

Remote-Diode Source Current DXP forced to 1.5V

Fan Controller

Supply voltage VCC 4.5 5 5.5 V

Shutdown current Fan speed = 0rpm 2 5 µA

MOSFET on resistance 0.2 0.25

Short-circuit current limit 0.5 A

Input logic low VIL 0.7. V

Input logic high VIH 1.0 V

Clock frequency CLK 32.768 KHz

FANVCC over-current trig 600 mA

FANVCC current limit 500 mA

FG input Positive-going threshold voltage VCC=5V 1 V

FG input Negative-going threshold voltage VCC=5V 0.7 V

FG input Hysteresis voltage VCC=5V 0.3 V

TR = 0°C to +125°C -5 5

= 60°C to +100°C -3 3

T

R

Including long-term drift T

Logic inputs forced to V
GND

Auto-convert mode, average
measured over 4sec. Logic
inputs forced to V

or GND

CC

CC

= +60°C to +100°C -3 3 °C

A

SMBus static 3 10

or

Hardware or software
standby, SMBCLK at 10kHz

0.25 conv/sec 250 300

2.0 conv/sec 300 350

High level 120 160 200

Low level 15 20 25

200

°C

µA

µA

µA

Ω

Ver: 1.2

Apr 03, 2002

3

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Electrical Characteristics

Global Mixed-mode Technology Inc.

(continued)

G768D

(VCC = + 5V, TA = 60°C, unless otherwise noted.)

PARAMETER CONDITIONS MIN TYP MAX UNITS

SMBus Interface

Logic Input High Voltage SMBCLK, SMBDATA; VCC = 4.5V to 5.5V 2.4 V

Logic Input Low Voltage SMBCLK, SMBDATA; VCC = 4.5V to 5.5V 0.8 V

Logic Output Low Sink Current

Output High Leakage Current

ALERT

Logic Input Current Logic inputs forced to VCC or GND -2 2 µA

SMBus Input Capacitance SMBCLK, SMBDATA 5 pF

SMBus Clock Frequency (Note 4) DC 100 KHz

SMBCLK Clock Low Time t

SMBCLK Clock High Time t

SMBus Start-Condition Setup Time 4.7 µs

SMBus Repeated Start-Condition
Setup Time

SMBus Start-Condition Hold Time t

SMBus Start-Condition Setup Time t

SMBus Data Valid to SMBCLK Rising­Edge Time

SMBus Data-Hold Time t

SMBCLK Falling Edge to SMBus
Data-Valid Time

ALERT , SMBDATA forced to 0.4V

forced to 5.5V

ALERT

, 10% to 10% points 4.7 µs

LOW

, 90% to 90% points 4 µs

HIGH

t

t
SMBCLK

Master clocking in data 1 µs

90% to 90% points 500 ns

SU : STA ,

10% of SMBDATA to 90% of SMBCLK 4 µs

HD: STA ,

90% of SMBDATA to 10% of SMBDATA 4 µs

SD: STO ,

10% or 90% of SMBDATA to 10% of

SU: DAT ,

(Note 5) 0 µs

HD : DAT

6 mA

1 µA

800 ns

(continued)

Electrical Characteristics

(VCC =full range, TA= 60°C, unless otherwise noted.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Reset Threshold VTH 4.2 4.4 4.5 V

Reset Active Timeout Period 340 ms

RESET

Output Voltage Low

RESET

Output Voltage High

Note 1: Guaranteed but not 100% tested.

V

V

OL

V

V

OH

CC=VTH

CC>VTH

min, I

max, I

=3.2mA

SINK

SOURCE

=5.0mA

0.4 V

-1.5 V

V

CC

Note 2: Quantization error is not included in specifications for temperature accuracy. For example, if the G768D

device temperature is exactly +66.7°C, or +68°C (due to the quantization error plus the +1/2°C offset
used for rounding up) and still be within the guaranteed ±3°C error limits for the +60°C to +100°C tem­perature range. See Table3.

Note 3: A remote diode is any diode-connected transistor from Table1. T

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

is the junction temperature of the re-

R

Note 4: The SMBus logic block is a static design that works with clock frequencies down to DC. While slow op-

eration is possible, it violates the 10kHz minimum clock frequency and SMBus specifications, and may
monopolize the bus.

Note 5: Note that a transition must internally provide at least a hold time in order to bridge the undefined region

(300ns max) of SMBCLK's falling edge.

Ver: 1.2

Apr 03, 2002

TEL: [phone]

http://www.gmt.com.tw

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Pin Description

PIN NAME FUNCTION

1 FANVCC Output connected to VCC of fan.

2,15 VCC Supply Voltage Input, 4.5V to 5.5V. Bypass to GND with a 0.1µF capacitor.

Combined Current Source and A/D Positive Input for remote-diode channel 1. Do not leave DXP1 floating;

3 DXP1

4 DXN

5 DXP2

RESET

6

7 DGND Digital Ground.

8 AGND Analog Ground.

9 CLK 32.768KHz clock input for fan controller.

10 FG Fan pulse input.

11

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

13 NC

14 SMBCLK SMBus Serial-Clock Input.

16 TH_SHUT Thermal Shutdown Output, push-pull output.

ALERT

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

Combined Current Sink and A/D Negative Input. DXN is common negative node of both remote diodes on
channel 1 and 2. The traces of DXP1-DXN and DXP2-DXN pairs should be routed independently. The
common DXN should be connected together as close as possible to the IC. DXN is internally connected to
the GND pin for signal ground use.

Combined Current Source and A/D Positive Input for remote-diode channel 2. Do not leave DXP2 floating;
tie DXP2 to DXN if no remote diode on channel 2 is used. Place a 2200pF capacitor between DXP2 and
DXN for noise filtering.

RESET

the reset threshold.

SMBus Alert (interrupt) Output, open drain.

Output remains low while VCC is below the reset threshold, and for 340ms after VCC rises above

G768D

Detailed Description

The G768D (patents pending) is a 3-in-1 IC. It consists
of one temperature sensor, 1 fan speed controller and
provides system-reset function.

The temperature sensor is designed to work in con­junction with an external micro-controller (µC) or other
intelligence in thermostatic, process-control, or moni­toring applications. The µC is typically a powerman­agement or keyboard controller, generating SMBus se­rial commands by "bit-banging" general-purpose in­put-output (GPIO) pins or via a dedicated SMBus inter­face block.

Essentially a 12-bit serial analog-to-digital converter
(ADC) with a sophisticated front end, the G768D con­tains a switched current source, a multiplexer, an ADC,
an SMBus interface, one fan controller, a reset circuit
and associated control logic (Figure 1).

Temperature data from the ADC is loaded into two
data registers, where it is automatically compared with
data previously stored in four over/under-temperature
alarm registers.

ADC and Multiplexer

The ADC is an averaging type that integrates over a
60ms period (each channel, typical).

The multiplexer automatically steers bias currents
through two remote diodes, measures their forward
voltages, and computes their temperatures. All chan­nels are converted automatically once the conversion
process has started, either in free-running or sin­gle-shot mode. If one of the two channels is not used,
the device still performs all measurements, and the
user can simply ignore the results of the unused
channel. If the remote diode channel is unused, tie
DXPx to DXN rather than leaving the pins open.

The DXN input is internally connected to the ground
node inside the chip to set up the analog to digital
(A/D) inputs for a differential measurement. The
worst-case DXP-DXN differential input voltage range
is 0.25V to 0.95V.

Excess resistance in series with the remote diode causes
about +1/2°C error per ohm. Likewise, 200µV of offset
voltage forced on DXP-DXN causes about 1°C error.

Ver: 1.2

Apr 03, 2002

5

TEL: [phone]

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