MAX6394US480D3/V+T Maxim Integrated, MAX6394US480D3/V+T Datasheet - Page 4

• Manufacturer Part Number: MAX6394US480D3/V+T
• Description: Supervisory Circuits High-Accuracy uP Reset Circuit
• Manufacturer: Maxim Integrated
• Series: MAX6394r

Specifications of MAX6394US480D3/V+T

• Rohs: yes

A microprocessor’s (µP’s) reset input starts the µP in a
known state. The MAX6394 asserts a reset signal to
prevent code-execution errors during power-up, power-
down, or brownout conditions. RESET is guaranteed to
be a logic-low for V
Characteristics table). Once V
threshold, the internal timer keeps RESET asserted for
the reset timeout period (t
goes high. If a brownout condition occurs (monitored
voltage dips below its programmed reset threshold),
RESET goes low. Any time V
threshold, the internal timer resets to zero and RESET
goes low. The internal timer starts when V
above the reset threshold, and RESET remains low for
the reset timeout period.
The MAX6394’s RESET output structure is a simple
open-drain n-channel MOSFET switch. Connect a pullup
resistor to any supply in the 0 to +6V range. Select a
resistor value large enough to register a logic-low when
RESET is asserted (see the Electrical Characteristics
table), and small enough to register a logic-high while
supplying all input current and leakage paths connect-
ed to the RESET line. A 10kΩ pullup is sufficient in most
applications.
Often, the pullup connected to the MAX6394’s RESET
output connects to the supply voltage monitored at the
IC’s VCC pin. However, some systems may use the
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 MAX6394’s V
decreases below 1V, so does the IC’s ability to sink
current at RESET. Finally, with any pullup, RESET is
pulled high as V
where this occurs depends on the pullup resistor value
and the voltage to which it connects (see the Electrical
Characteristics table).
Many µP-based products require manual-reset capa-
bility, allowing the operator, a test technician, or exter-
nal 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 pullup resistor, so it can be
left open if not used. Connect a normally open momen-
High-Accuracy µP Reset Circuit
4
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
CC
decays toward 0V. The voltage
Detailed Description
CC
RP
> 1V (see the Electrical
); after this interval RESET
CC
Manual-Reset Input
CC
dips below the reset
exceeds the reset
Reset Output
CC
returns
CC
tary switch from MR to GND to create a manual reset
function; external debounce circuitry is not required.
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 VRST max and ending below
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 VCC provides additional
transient immunity.
TRANSISTOR COUNT: 519
Figure 1. MAX6394 Open-Drain RESET Output Allows Use with
Multiple Supplies
MR
MAX6394
+3.3V
Negative-Going V
VCC
Applications Information
GND
RESET
10kΩ
Chip Information
CC
5V SYSTEM
+5.0V
Transients
CC
tran-