MAX6315 MAXIM [Maxim Integrated Products], MAX6315 Datasheet - Page 4

• Manufacturer Part Number: MAX6315
• Description: Open-Drain SOT ?P Reset Circuit
• Manufacturer: MAXIM [Maxim Integrated Products]

A microprocessor’s (µP’s) reset input starts the µP in a
known state. The MAX6315 asserts reset to prevent
code-execution errors during power-up, power-down,
or brownout conditions. RESET is guaranteed to be a
logic low for V
Once V
timer keeps reset asserted for the reset timeout period
(t
condition occurs (monitored voltage dips below its pro-
grammed reset threshold), RESET goes low. Any time
V
resets to zero and RESET goes low. The internal timer
starts when V
RESET remains low for the reset timeout period.
The MAX6315’s RESET output structure is a simple
open-drain N-channel MOSFET switch. Connect a pull-
up resistor to any supply in the 0V to +6V range. Select
a resistor value large enough to register a logic low
when RESET is asserted (see Electrical Characteristics ),
and small enough to register a logic high while supply-
ing all input current and leakage paths connected to the
RESET line. A 10kΩ pull-up is sufficient in most applica-
tions.
Often, the pull-up connected to the MAX6315’s RESET
output will connect to the supply voltage monitored at
the IC’s V
open-drain output to level-shift from the monitored sup-
ply to reset circuitry powered by some other supply
(Figure 1). This is one useful feature of an open-drain
output. Keep in mind that as the MAX6315’s V
decreases below 1V, so does the IC’s ability to sink
current at RESET. Finally, with any pull-up, RESET will
be pulled high as V
where this occurs depends on the pull-up resistor value
and the voltage to which it connects (see Electrical
Characteristics ).
Many µP-based products require manual-reset capabil-
ity, allowing the operator, a test technician, or external
logic circuitry to initiate a reset. A logic low on MR
asserts reset. Reset remains asserted while MR is low,
and for the reset active timeout period after MR returns
high.
MR has an internal 63kΩ pull-up resistor, so it can be
left open if not used. Connect a normally open momen-
tary switch from MR to GND to create a manual reset
function; external debounce circuitry is not required.
Open-Drain SOT µP Reset Circuit
4
_______________Detailed Description
RP
CC
_______________________________________________________________________________________
); after this interval RESET goes high. If a brownout
dips below the reset threshold, the internal timer
CC
CC
exceeds the reset threshold, the internal
pin. However, some systems may use the
CC
CC
returns above the reset threshold, and
> 1V (see Electrical Characteristics ).
CC
decays toward 0V. The voltage
Manual-Reset Input
Reset Output
CC
If MR is driven from long cables or if the device is used
in a noisy environment, connecting a 0.1µF capacitor
from MR to ground provides additional noise immunity.
In addition to issuing a reset to the µP during power-up,
power-down, and brownout conditions, these devices
are relatively immune to short-duration negative-going
transients (glitches). The Typical Operating Character-
istics show the Maximum Transient Duration vs. Reset
Threshold Overdrive, for which reset pulses are not
generated. The graph was produced using negative-
going pulses, starting at V
the programmed reset threshold by the magnitude indi-
cated (reset threshold overdrive). The graph shows the
maximum pulse width that a negative-going V
sient may typically have without causing a reset pulse
to be issued. As the transient amplitude increases (i.e.,
goes farther below the reset threshold), the maximum
allowable pulse width decreases. A 0.1µF bypass
capacitor mounted close to V
transient immunity.
Figure 1. MAX6315 Open-Drain
with Multiple Supplies
__________Applications Information
MR
MAX6315
+3.3V
Negative-Going V
V
CC
GND
RESET
RST
10k
RESET Output Allows Use
CC
max and ending below
provides additional
CC
5V SYSTEM
+5.0V
Transients
CC
tran-