MAX6345MUT-T View Datasheet(PDF) - Maxim Integrated
Part Name
Description
Manufacturer
MAX6345MUT-T Datasheet PDF : 8 Pages
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6-Pin µP Reset Circuit with
Power-Fail Comparator
+3.3V
VCC
+5.0V
10kΩ
RESET
MAX6343
VCC
µP
RESET
GND
Figure 3. Open-Drain RESET Output Allows Use with Multiple
Supplies
VCC
VCC MAX6342
MAX6345
GND
RESET
100kΩ
160
140
120
100
80
MAX634_L/M
60
40
20
MAX634_T/S/R/Z
0
1
10
100
1000
RESET COMPARATOR OVERDRIVE, VTH - VCC (mV)
Figure 4. Maximum Transient Duration Magnitude Rejection
VCC
100kΩ
VCC
RESET
GND MAX6344
MAX6345
Figure 5. Ensuring RESET Valid to VCC = 0 on Active-Low
Push-Pull Outputs
Power-Fail Comparator
The power-fail comparator is useful for various purpos-
es because the power-fail output (PFO) is independent
of the reset output. The inverting input is internally con-
nected to a +1.25V reference.
To build an early-warning circuit for power failure, con-
nect the PFI pin to a voltage divider (see the Typical
Oper-ating Circuit). Choose the voltage-divider ratio so
that the voltage at PFI falls below +1.25V just before the
+5V regulator drops out. Use PFO to interrupt the µP to
prepare for an orderly shutdown.
Applications Information
Negative-Going VCC Transients
The MAX6342–MAX6345 supervisors are immune to
short-duration, negative-going VCC transients (glitches)
that usually do not require the entire system to shut down.
Figure 4 shows typical transient duration vs. reset com-
parator overdrive, for which the MAX6342–MAX6345 do
not generate a reset pulse. The graph was generated
using a negative-going pulse applied to VCC, starting
Figure 6. Ensuring RESET Valid to VCC = 0 on Active-High
Push-Pull Outputs
0.5V above the actual reset threshold and ending below
it by the magnitude indicated (reset comparator over-
drive). The graph indicates the maximum pulse width a
negative-going VCC transient can have without causing
a reset pulse. As the magnitude of the transient increas-
es (goes further below the reset threshold), the maxi-
mum allowable pulse width decreases.
Typically, a VCC transient that goes 100mV below the
reset threshold and lasts 12µs or less will not cause a
reset pulse. A 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
The MAX6342–MAX6345 are guaranteed to operate
properly down to VCC = +1V. In applications that require
valid reset levels down to VCC = 0, a pulldown resistor to
active-low outputs (MAX6342/MAX6345) and a pullup
resistor to active-high outputs (MAX6344/MAX6345)
ensure that the reset line is valid when the reset output is
no longer sinking or sourcing current (Figures 5 and 6).
6 _______________________________________________________________________________________
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