GMT G768B Datasheet

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: [phone]

http://www.gmt.com.tw

1

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

TEL: [phone]

http://www.gmt.com.tw

2

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

3

TEL: [phone]

http://www.gmt.com.tw

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

TEL: [phone]

http://www.gmt.com.tw

4

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

5

TEL: [phone]

http://www.gmt.com.tw