LTC2935 查看數據表（PDF） - Linear Technology
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LTC2935 Datasheet PDF : 12 Pages
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LTC2935
APPLICATIONS INFORMATION
Selecting Output Logic Style
The LTC2935 status outputs are available in two op-
tions: open-drain (LTC2935-1/LTC2935-3) or active
pull-up (LTC2935-2/LTC2935-4). The open-drain options
(LTC2935-1/LTC2935-3) allow the outputs to be pulled up
to a user defined voltage with a resistor. The open-drain
pull-up voltage may be greater than VCC (5.5V maximum),
which is not always possible with inferior battery supervi-
sors, due to internal clamps. When the status outputs are
low, power is dissipated in the pull-up resistors. Recom-
mended resistor values lie in the range between 10k and
470k. Figure 1 demonstrates typical LTC2935-1/LTC2935-3
RST output behavior.
The active pull-up options (LTC2935-2/LTC2935-4) elimi-
nate the need for external pull-up resistors on the status
outputs. Integrated pull-up devices pull the outputs up to
VCC. Actively pulled up outputs may not be driven above
VCC.
Some applications require the RST and/or PFO outputs to
be valid with VCC down to ground. Active pull-up handles
this requirement with the addition of an external resistor
from the output to ground. The resistor provides a path
for leakage currents, preventing the output from floating to
undetermined voltages when connected to high impedance
(such as CMOS logic inputs). The resistor value should
be small enough to provide effective pull-down without
excessively loading the pull-up circuitry. A 100k resistor
from output to ground is satisfactory for most applications.
When the status outputs are high, power is dissipated in
the pull-down resistors. Figure 2 demonstrates typical
LTC2935-2/LTC2935-4 RST output behavior.
Manual Reset Input
When VCC is above its reset threshold, and the manual
reset input (MR) is pulled low, the RST output is forced low.
RST remains low for 200ms after the manual reset input is
released and pulled high. The manual reset input is pulled
up internally through 900k to VCC. If external leakage cur-
rents have the ability to pull down the manual reset input
below its logic threshold, a lower value pull-up resistor,
placed between VCC and MR will fix the problem.
Input MR is often pulled down through a pushbutton
switch requiring human contact. If extended ESD toler-
ance is required, series resistance between the switch and
the input is recommended. For most applications, a 10k
resistor provides sufficient current limiting.
3.5
LTC2935-1
S2 = GND
3.0 S1 = S0 = VCC
2.5
2.0
1.5
1.0
0.5
0
0 0.5 1 1.5 2 2.5 3 3.5
VCC (V)
2935 F01
Figure 1. RST vs VCC with 10k Pull-Up
3.5
LTC2935-2
S2 = GND
3.0 S1 = S0 = VCC
2.5
2.0
1.5
1.0
0.5
0
0 0.5 1 1.5 2 2.5 3 3.5
VCC (V)
2935 F02
Figure 2. RST vs VCC
2935fa
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