3-Pin Microprocessor Reset Circuits
Selector Guide
PART/SUFFIX
MAX803L
MAX803M
MAX803T
MAX803S
MAX803R
MAX803Z
MAX809L
MAX809M
MAX809J
MAX809T
MAX809S
MAX809R
MAX809Z
MAX810L
MAX810M
MAX810T
MAX810S
MAX810R
MAX810Z
RESET THRESHOLD (V)
4.63
4.38
3.08
2.93
2.63
2.32
4.63
4.38
4.00
3.08
2.93
2.63
2.32
4.63
4.38
3.08
2.93
2.63
2.32
OUTPUT TYPE
OPEN-DRAIN
RESET
OPEN-DRAIN
RESET
OPEN-DRAIN
RESET
OPEN-DRAIN
RESET
OPEN-DRAIN
RESET
OPEN-DRAIN
RESET
PUSH-PULL
RESET
PUSH-PULL
RESET
PUSH-PULL
RESET
PUSH-PULL
RESET
PUSH-PULL
RESET
PUSH-PULL
RESET
PUSH-PULL
RESET
PUSH-PULL RESET
PUSH-PULL RESET
PUSH-PULL RESET
PUSH-PULL RESET
PUSH-PULL RESET
PUSH-PULL RESET
TOP MARK
SOT
⎯
⎯
⎯
⎯
⎯
⎯
AAAA
ABAA
CWAA
ACAA
ADAA
AFAA
⎯
AGAA
AHAA
AJAA
AKAA
ALAA
⎯
SC70
AAZ
ABA
ABB
ABC
ABD
ABE
AAN
AAO
⎯
AAP
AAQ
AAR
AAS
AAT
AAU
AAV
AAX
AAW
AAY
MAX803L/M/R/S/T/Z, MAX809J/L/M/R/S/T/Z, MAX810L/M/R/S/T/Z
Detailed Description
A microprocessor’s (µP’s) reset input starts the µP in a
known state. The MAX803/MAX809/MAX810 assert
reset to prevent code-execution errors during power-
up, power-down, or brownout conditions. They assert a
reset signal whenever the V
CC
supply voltage declines
below a preset threshold, keeping it asserted for at
least 140ms after V
CC
has risen above the reset thresh-
old. The MAX803 uses an open-drain output, and the
MAX809/MAX810 have a push-pull output stage.
Connect a pullup resistor on the MAX803’s
RESET
out-
put to any supply between 0 and 6V.
Applications Information
Negative-Going V
CC
Transients
In addition to issuing a reset to the µP during power-up,
power-down, and brownout conditions, the MAX803/
MAX809/MAX810 are relatively immune to short-duration
negative-going V
CC
transients (glitches).
Figure 1 shows typical transient duration vs. reset com-
parator overdrive, for which the MAX803/MAX809/
MAX810 do
not
generate a reset pulse. The graph was
generated using a negative-going pulse applied to V
CC
,
starting 0.5V above the actual reset threshold and end-
ing below it by the magnitude indicated (reset compara-
tor overdrive). The graph indicates the maximum pulse
width a negative-going V
CC
transient can have without
causing a reset pulse. As the magnitude of the transient
increases (goes farther below the reset threshold), the
maximum allowable pulse width decreases. Typically, for
the MAX8__L and MAX8__M, a V
CC
transient that goes
100mV below the reset threshold and lasts 20µs or less
will not cause a reset pulse. A 0.1µF bypass capacitor
mounted as close as possible to the V
CC
pin provides
additional transient immunity.
Pin Description
PIN
1
NAME
GND
RESET
(MAX803/
MAX809)
2
RESET
(MAX810)
Ground
RESET
Output remains low while V
CC
is below the reset threshold, and for at
least 140ms after V
CC
rises above the
reset threshold.
RESET Output remains high while V
CC
is below the reset threshold, and for at
least 140ms after V
CC
rises above the
reset threshold.
Supply Voltage (+5V, +3.3V, +3.0V, or
+2.5V)
FUNCTION
3
V
CC
When V
CC
falls below 1V, the MAX809
RESET
output
no longer sinks current—it becomes an open circuit.
5
Ensuring a Valid Reset Output
Down to V
CC
= 0V
_______________________________________________________________________________________
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
