G680H 查看數據表（PDF） - Global Mixed-mode Technology Inc
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G680H Datasheet PDF : 7 Pages
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Global Mixed-mode Technology Inc.
G680/G681
A value such as 1MΩ for RTOTAL is a reasonable value
because it draws minimum battery current but has no
measurable effect on accuracy.
When working with large resistors, a small amount of
leakage current can cause voltage offsets that
degrade system accuracy.
The maximum recommended total resistance from
VBAT to ground is 3MΩ.
V BATT
R1 604k
1%
R2
56k
1%
G 680/G 681
VCC
LTH
HTH
RESET
RESET
Once R3 is determined, the equation for VBAT (lo) can
be used to determine R2. A single lithium-ion cell
should not be discharged below 2.5V. Many applica-
tions limit the drain to 3.1V. Using 3.1V for the V BAT (lo)
threshold allows calculation of the two remaining re-
sistor values.
VBAT (lo) =3.1V = 1.245
1MΩ
R2+344k
R2 = 56kΩ
R1 = 1MΩ - R2 - R3
R 1=600kΩ
The accuracy of the resistors can be chosen based
upon the accuracy required by the system.
VCC
340k
R3
1%
VCC
G681
RESET
RPULL-UP
VCC
µP
RESET MOTOROLA
INPUT 68HCXX
Figure 2. Example Circuit
Once the desired trip points are determined, set the
VBAT(hi) threshold first.
For example, use a total of 1M = R1 + R2 + R3. For a
typical single-cell lithium ion battery, 3.6V is a good
“high threshold” because at 3.6V the battery is moder-
ately charged. Solving for R3:
VBAT (hi) = 1.245
1MΩ
R3
R3 = 344kΩ
.
GND
GND
Figure 3. Interfacing to µPs with Bidirectional Re
set I/O
Interfacing to µPs with Bidirectional Reset Pins
Since the RESET output on the G681L is open drain,
this device interfaces easily with µPs that have bidi-
rectional reset pins, such as the Motorola 68HC11.
Connecting the µP supervisor’s RESET output di-
rectly to the microcontroller’s (µC’s) RESET pin with
a single pull-up resistor allows either device to assert
reset (Figure 3).
Ver: 1.1
Jun 07, 2002
TEL: 886-3-5788833
http://www.gmt.com.tw
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