MAX6833(2002) 데이터 시트보기 (PDF) - Maxim Integrated
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MAX6833 Datasheet PDF : 11 Pages
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Ultra-Low-Voltage SC70 Voltage Detectors
and µP Reset Circuits
at RESET-IN allows for relatively large-value resistors to
be used, which reduce power consumption. For exam-
ple, for a 0.6V monitored trip level, if R2 = 200kΩ, then
R1 = 70.3kΩ. Note that the minimum VCC of 1.1V is
required to guarantee the RESET-IN threshold accura-
cy (see Electrical Characteristics table).
Applications Information
Negative-Going VCC Transients
In addition to issuing a reset to the µP during power-up,
power-down, and brownout conditions, the MAX6832–
MAX6840 are relatively immune to short-duration nega-
tive-going VCC transients (glitches).
Figure 2 shows typical transient duration vs. reset com-
parator overdrive, for which the MAX6832–MAX6840 do
not generate a reset pulse. The graph was generated
using a negative-going pulse applied to VCC, starting
0.1V above the actual reset threshold and ending
below it by the magnitude indicated (reset comparator
overdrive). The graph indicates the maximum pulse
width a negative-going VCC transient can have without
causing a reset pulse. As the magnitude of the tran-
sient increases (goes farther below the reset threshold),
the maximum allowable pulse width decreases. A 0.1µF
bypass capacitor mounted as close as possible to the
VCC pin provides additional transient immunity.
Ensuring a Valid Reset Output
Down to VCC = 0
When VCC falls below 0.55V, the MAX6832/MAX6835/
MAX6838 push-pull RESET output no longer sinks cur-
rent—it becomes an open circuit. Therefore, high-
impedance CMOS logic inputs connected to RESET
MAXIMUM TRANSIENT DURATION
vs. OVERDRIVE
900
800
700
600
500
RESET OCCURS
ABOVE THIS
400
LINE
300
200
100
0
1
10
100
OVERDRIVE VTH - VCC (mV)
Figure 2. Maximum Transient Duration Without Causing a
Reset Pulse vs. Reset Comparator Overdrive
can drift to undetermined voltages. This presents no
problem in most applications since most µP and other
circuitry are inoperative with VCC lower than 0.55V.
However, in applications where RESET must be valid
down to 0, adding a pulldown resistor to RESET causes
any stray leakage currents to flow to ground, holding
RESET low (Figure 3). R3’s value is not critical; 100kΩ
is large enough not to load RESET and small enough to
pull RESET to ground.
A 100kΩ pullup resistor to VCC is also recommended
for the MAX6833/MAX6836/MAX6839 if RESET is
required to remain valid for VCC < 0.85V.
VCC
MAX6832
MAX6835 RESET
MAX6838
GND
R3
100kΩ
Figure 3. RESET Valid to VCC = Ground Circuit
Interfacing to µPs with Bidirectional
Reset Pins
Since the RESET output on the MAX6834/MAX6837/
MAX6840 is open-drain, these devices interface easily
with µPs that have bidirectional reset pins. Connecting
the µP supervisor’s RESET output directly to the µP’s
RESET pin with a single pullup resistor allows either
device to assert a reset (Figure 4).
VCC
VCC
MAX6834
MAX6837
MAX6840 RESET
VCC
BIDIRECTIONAL
µP
RESET
INPUT
GND
GND
Figure 4. Interfacing to µPs with Bidirectional Reset I/O
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