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G771 Datasheet(PDF) 5 Page - Global Mixed-mode Technology Inc

Part No. G771
Description  Two Remote Temperature Sensors with SMBus Serial Interface and System Reset Circuit
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Maker  GMT [Global Mixed-mode Technology Inc]
Homepage  http://www.gmt.com.tw
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G771 Datasheet(HTML) 5 Page - Global Mixed-mode Technology Inc

 
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Ver 0.2 Preliminary
Dec 11, 2001
TEL: 886-3-5788833
http://www.gmt.com.tw
5
G771
Global Mixed-mode Technology Inc.
Detailed Description
The G771 (patents pending) consists of two tempera-
ture sensors, one on-chip temperature sensor and
provides system-reset function.
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 G771 con-
tains a switched current source, a multiplexer, an ADC,
an SMBus interface, 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 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 chan-
nel. 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.
Fig 1. Functional Diagram
DXP2
THERMAL SHUTDOWN
LOGIC
CONTROL
LOGIC
SMBUS
REGISTERS
MUX
ADC
RESET
CIRCUIT
TH_SHUT
SMBCLK
SMBDATA
ALERT
RESET
V
CC
+
+
DXP1
DXN
+
INTERNAL GROUND
V
CC
DXP2
THERMAL SHUTDOWN
LOGIC
CONTROL
LOGIC
SMBUS
REGISTERS
MUX
ADC
RESET
CIRCUIT
TH_SHUT
SMBCLK
SMBDATA
ALERT
RESET
V
CC
+
+
DXP1
DXN
+
INTERNAL GROUND
V
CC


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