G768 View Datasheet(PDF) - Unspecified
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G768 Datasheet PDF : 15 Pages
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Global Mixed-mode Technology Inc.
Table 8. RLTS and RRTE Temp Register Update Timing Chart
OPERATING
MODE
CONVERSION
INITIATED BY:
NEW CONVERSION RATE
(CHANGED VIA WRITE TO CRW)
Auto-Convert
Power-on reset
N/A (0.25Hz)
Auto-Convert
1-shot command, while idling N/A
between automatic conversions
Auto-Convert
1-shot command that occurs
during a conversion
N/A
Auto-Convert
Rate timer
0.0625Hz
Auto-Convert
Rate timer
0.125Hz
Auto-Convert
Rate timer
0.25Hz
Auto-Convert
Rate timer
0.5Hz
Auto-Convert
Rate timer
1Hz
Auto-Convert
Rate timer
2Hz
Auto-Convert
Rate timer
4Hz
Auto-Convert
Rate timer
8Hz
Software Standby RUN/STOP bit
N/A
Software Standby 1-shot command
N/A
G768B
TIME UNTIL RLTS AND
RRTE ARE UPDATED
156ms max
156ms max
When current conversion is
complete (1-shot is ignored)
20sec
10sec
5sec
2.5sec
1.25sec
625ms
312.5ms
237.5ms
156ms
156ms
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
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.
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.
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 G768B 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
156ms maximum) after initiating a conversion, whether
conversion 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.
Programmed fan speed register
The programmed fan speed registers (10h for fan 1,
20h for fan 2) are read/write registers. They contain
the count number of the desired fan speed. Power up
default is FFh.
Actual fan speed register
The actual fan speed registers (11h for fan 1, 21h for
fan 2) are 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 for fan1, 22h for fan 2)
are 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.
Watchdog for fan control
Four temperature threshold registers intervene the
control of fans. Both pin OUT1 and pin OUT2 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. Besides, the fan controller also fully turns
on both fans 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
G768B to be used in the occasion when system fails
and loses the fan control of G768B.
Ver: 1.3
Oct 28, 2002
TEL: 886-3-5788833
http://www.gmt.com.tw
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