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G768B Datasheet(PDF) 5 Page - List of Unclassifed Manufacturers

Part No. G768B
Description  Remote/Local Temperature Sensor, 2 Fan Controllers with SMBus Serial Interface and System Reset Circuit
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G768B Datasheet(HTML) 5 Page - List of Unclassifed Manufacturers

 
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Ver 1.3
Oct 28, 2002
TEL: 886-3-5788833
http://www.gmt.com.tw
5
G768B
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.
3
DXP1
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.
4
DXN
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.
5
DXP2
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.
6
RESET
RESET
Output remains low while VCC is below the reset threshold, and for 240ms after VCC rises above
the reset threshold.
7,8
GND
Ground
9
CLK
Clock input for fan speed measurement.
10
FG1
Fan1 pulse input.
11
ALERT
SMBus Alert (interrupt) Output, open drain.
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.
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 conjunc-
tion with an external micro-controller (µC) or other intel-
ligence in thermostatic, process-control, or monitoring
applications. The µC is typically a power-management
or keyboard controller, generating SMBus serial com-
mands 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 con-
tains 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 con-
version 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.


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