Global Mixed-mode Technology Inc.
G781
POR AND UVLO
Operation of The THERMFunction
The G781 has a volatile memory. To prevent ambiguous
power-supply conditions from corrupting the data in
memory and causing erratic behavior, a POR voltage
detector monitors VCC and clears the memory if VCC
falls below 1.7V (typical, see Electrical Characteristics
table). When power is first applied and VCC rises above
1.7V (typical), the logic blocks begin operating, although
reads and writes at VCC levels below 3V are not recom-
mended. A second VCC comparator, the ADC UVLO
comparator, prevents the ADC from converting until there
is sufficient headroom (VCC= 2.8V typical).
A local and remote THERM limit can be programmed
into the G781 to set the temperature limit above which
the THERM pin asserts low and the bit 1, of status
byte will be set to 1 corresponding to remote and local
over temperature. These two bits won’t be cleared to 0
by reading status byte it the over temperature condi-
tion remain. A hysteresis value is provided by writing
the register 21h to set the temperature threshold to
release the THERM pin alarm state, The releasing
temperature is the value of register 19h, 20h minus the
value in register 21h. The format of register 21h is 2’s
ALERT Fault Queue
complement. The THERM signal is open drain and
requires a pull-up resistor to power supply.
To suppress unwanted ALERTtriggering the G781 em-
bedded a fault queue function. The ALERT won’t as-
sert until consecutive out of limit measurements have
reached the queue number. The mapping of fault
queue register (ALERTFQ, 22h) value to fault queue
number is shown in the Table 9.
Table 9. Alert Fault Queue
ALERTFQ
FAULT QUEUE NUMBER
VALUE
XXXX000X
XXXX001X
XXXX010X
XXXX011X
XXXX100X
XXXX101X
XXXX110X
XXXX111X
1
2
3
3
4
4
4
4
Ver: 1.0
Oct 02, 2002
TEL: 886-3-5788833
http://www.gmt.com.tw
12
ETC [ ETC ]
