MAX803L MAXIM [Maxim Integrated Products], MAX803L Datasheet - Page 5

• Manufacturer Part Number: MAX803L
• Description: 3-Pin Microprocessor Reset Circuits
• Manufacturer: MAXIM [Maxim Integrated Products]

_____________________Pin 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
below a preset threshold, keeping it asserted for at
least 140ms after V
old. The MAX803 uses an open-drain output, and the
MAX809/MAX810 have a push-pull output stage.
Connect a pull-up resistor on the MAX803’s RESET out-
put to any supply between 0 and 6V.
Figure 1. Maximum Transient Duration Without Causing a
Reset Pulse vs. Reset Comparator Overdrive
PIN
1
2
3
(MAX810)
(MAX803/
MAX809)
RESET
RESET
NAME
GND
V
400
320
240
160
CC
80
0
RESET COMPARATOR OVERDRIVE, V
1
MAX8_ _R/S/T/Z
T
A
= +25°C
_______________________________________________________________________________________
CC
Ground
RESET Output remains low while V
is below the reset threshold, and for at
least 140ms after V
reset threshold.
RESET Output remains high while V
is below the reset threshold, and for at
least 140ms after V
reset threshold.
Supply Voltage (+5V, +3.3V, +3.0V, or
+2.5V)
Detailed Description
has risen above the reset thresh-
10
MAX8_ _J/L/M
CC
3-Pin Microprocessor Reset Circuits
FUNCTION
supply voltage declines
100
TH
CC
CC
- V
CC
rises above the
rises above the
(mV)
1000
CC
CC
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
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
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
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
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
additional transient immunity.
When V
no longer sinks current—it becomes an open circuit.
Therefore, high-impedance CMOS logic inputs con-
nected to RESET can drift to undetermined voltages.
This presents no problem in most applications since
most µP and other circuitry is inoperative with V
below 1V. However, in applications where RESET must
be valid down to 0V, adding a pull-down resistor to
RESET causes any stray leakage currents to flow to
Figure 2. RESET Valid to V
CC
falls below 1V, the MAX809 RESET output
Negative-Going V
Applications Information
CC
Ensuring a Valid Reset Output
transients (glitches).
MAX809
GND
V
CC
CC
CC
RESET
= Ground Circuit
transient can have without
CC
Down to V
transient that goes
CC
R1
100k
CC
Transients
pin provides
CC
= 0
CC
CC
5
,