G768 datasheet(13/15 Pages) ETC

13 / 15 page

Ver: 1.3

Oct 28, 2002

TEL: 886-3-5788833

http://www.gmt.com.tw

G768B

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)

TIME UNTIL RLTS AND

RRTE ARE UPDATED

Auto-Convert

Power-on reset

N/A (0.25Hz)

156ms max

Auto-Convert

1-shot command, while idling

between automatic conversions

N/A

156ms max

Auto-Convert

1-shot command that occurs

during a conversion

N/A

When current conversion is

complete (1-shot is ignored)

Auto-Convert

Rate timer

0.0625Hz

20sec

Auto-Convert

Rate timer

0.125Hz

10sec

Auto-Convert

Rate timer

0.25Hz

5sec

Auto-Convert

Rate timer

0.5Hz

2.5sec

Auto-Convert

Rate timer

1Hz

1.25sec

Auto-Convert

Rate timer

2Hz

625ms

Auto-Convert

Rate timer

4Hz

312.5ms

Auto-Convert

Rate timer

8Hz

237.5ms

Software Standby RUN/STOP bit

N/A

156ms

Software Standby 1-shot command

N/A

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.

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