ap1702bw Diodes, Inc., ap1702bw Datasheet - Page 4

• Manufacturer Part Number: ap1702bw
• Description: 3-pin Microprocessor Reset Circuits
• Manufacturer: Diodes, Inc.

Typical Application Circuit
Function Description
known state. The AP1701/2/3/4 assert reset to prevent
code-execution errors during power-up, power-down, or
brownout conditions. They assert a reset signal whenever the V
supply voltage declines below a preset threshold, keeping it
asserted for at least 240ms after V
threshold. The AP1701/2/3/4 have a push-pull output stage.
Applications Information
Negative-Going V
power-down, and brownout conditions, the AP1701/2/3/4 are
relatively immune to short-duration negative-going V
(glitches).
graph was generated using a negative going pulse applied to V
starting 0.5V above the actual reset threshold and ending below it
by the magnitude indicated (reset comparator overdrive). The
graph indicates the maximum pulse width a negative going V
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, a V
threshold and lasts 100µs or less will not cause a reset pulse. A
0.1µF bypass capacitor mounted as close as possible to the V
pin provides additional transient immunity.
Ensuring a Valid Reset Output
Down to V
Once V
AP1701/2/3/4 Rev. 2
RESET
RESET
RESET
A microprocessor’s (µP’s) reset input starts the µP in a
In addition to issuing a reset to the µP during power-up,
The AP1701/2/3/4 do not generate a reset pulse. The
RESET
CC
exceeds the reset threshold, an internal timer keeps
CC
low for the reset timeout period; after this interval,
goes high. If a brownout condition occurs (V
CC
= 0
transient that goes 100mV below the reset
is guaranteed to be a logic low for V
CC
Transients
0.1uF
Cin
CC
has risen above the reset
V
CC
AP170X
GND
V
CC
NOT RECOMMENDED FOR NEW
CC
(RESET)
www.diodes.com
DESIGN, USE (APX809/810)
RESET
CC
transients
> 1V.
CC
dips
4 of 10
CC
CC
CC
CC
3-PIN MICROPROCESSOR RESET CIRCUITS
,
below the reset threshold),
goes below the reset threshold, the internal timer resets to zero,
and
returns above the reset threshold, and
for the reset timeout period.
output no longer sinks current—it becomes an open circuit.
Therefore, high-impedance CMOS logic inputs connected to
This presents no problem in most applications since most µP and
other circuitry is inoperative with V
applications where
pull down resistor to
currents to flow to ground, holding
not critical; 100k are large enough not to load
small enough to pull
RESET
Benefits of Highly Accurate Reset Threshold
between 5% and 10% below the value of nominal supply voltages.
This ensures a reset will not occur within 5% of the nominal
supply, but will occur when the supply is 10% below nominal.
When using ICs rated at only the nominal supply ±5%, this leaves
a zone of uncertainty where the supply is between 5% and 10%
low, and where the reset may or may not be asserted.
RESET
Most µP supervisor ICs has reset threshold voltages
RESET
When V
Microprocessor
RESET
INPUT
is required to remain valid for V
can drift to undetermined voltages.
CC
falls below 1V, the AP1701/3
V
goes low. The internal timer starts after V
GND
CC
RESET
RESET
RESET
RESET
must be valid down to 0V, adding a
AP1701/2/3/4
causes any stray leakage
to ground. For the AP1702/4 if
CC
RESET
below 1V. However, in
goes low. Any time V
RESET
CC
©
< 1V.
JANUARY 2007
Diodes Incorporated
RESET
low. R1’s value is
RESET
remains low
and
CC
CC