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PDF AX6905 Data sheet ( Hoja de datos )
| Número de pieza | AX6905 | |
| Descripción | 3-Pin Microprocessor Reset Circuits | |
| Fabricantes | AXElite | |
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AX6905/6
3-Pin Microprocessor Reset Circuits
GENERAL DESCRIPTION
The AX6905/6 is used for microprocessor (μP) supervisory circuits to monitor the
power supplies in µP and digital systems. They provide excellent circuit reliability and low
cost by eliminating external components and adjustments when used with +5V, +3.3V, +3.0V,
+2.5V powered circuits.
These circuits perform a single function: they assert a reset signal whenever the VCC
supply voltage declines below a preset threshold, keeping it asserted for at least 200ms after
VCC has risen above the reset threshold. Reset thresholds suitable for operation with a
variety of supply voltages are available. The AX6905/6 has push pull outputs. The AX6905
have an active low RESET output, while the AX6906 has an active high RESET output.
The reset comparator is designed to ignore fast transients on VCC, and the outputs are
guaranteed to be in the correct logic state for VCC down to 1.0V. Low supply current makes
the AX6905/6 ideal for use in portable equipment. The AX6905/6 is available in a 3-pin
SOT-23 and SC70 package.
FEATURES
- Precision Monitoring of +2.5,+3V, +3.3V, and +5V Power-Supply Voltages
- Fully Specified Over Temperature
- Available in Three Output Configurations
- Push-PullRESET Low Output(AX6905)
- Push-Pull RESET High Output(AX6906)
- 200ms (Typ.)min Power-On Reset Pulse Width
- 25µA Supply Current
- Guaranteed Reset Valid to VCC = +1.0V
- Power Supply Transient Immunity
- No External Components
- Available in the 3-Pin Pb-Free SOT-23 and SC70 Package
1/10
Axelite Confidential Materials, do not copy or distribute without written consent.
Rev.1.2 Jul.30, 2010
1 page  
AX6905/6
FUNCTION DESCRIPTIONS
A microprocessor’s (μP’s) reset input starts the μP in a known state. The AX6905/6
asserts reset to prevent code-execution errors during power-up, power-down, or brownout
conditions. They assert a reset signal whenever the VCC supply voltage declines below a
preset threshold, keeping it asserted for at least 200ms after VCC has risen above the reset
threshold. The AX6905/6 has a push-pull output stage.
APPLICATION INFORMATION
Negative-Going VCC Transients
In addition to issuing a reset to the μP during power-up, power-down, and brownout
conditions, the AX6905/6 is relatively immune to short-duration negative-going VCC
transients (glitches).
The AX6905/6 does not generate a reset pulse. The graph was generated using a
negative going pulse applied to VCC, 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 VCC 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 VCC transient
that goes 50mV below the reset threshold A 0.1µF bypass capacitor mounted as close as
possible to the VCC pin provides additional transient immunity.
Ensuring a Valid Reset Output Down to VCC = 0
RESET Is guaranteed to be a logic low for VCC > 1.0V. Once VCC exceeds the reset
threshold, an internal timer keeps RESET low for the reset timeout period; after this interval,
RESET goes high. If a brownout condition occurs (VCC dips below the reset threshold),
RESET goes low. Any time VCC goes below the reset threshold, the internal timer resets
to zero, and RESET goes low. The internal timer starts after VCC returns above the reset
threshold, and RESET remains low for the reset timeout period.
When VCC falls below 1.0V, the AX6905 RESET output no longer sinks current—it becomes
an open circuit. Therefore, high-impedance CMOS logic inputs connected to RESET can drift
to undetermined voltages.
This presents no problem in most applications since most µP and other circuitry is
inoperative with VCC below 1.0V. 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 ground, holding RESET low. R1’s value is not critical; 100k is large enough not to load
RESET and small enough to pull RESET to ground. For the AX6906 if RESET is
required to remain valid for VCC < 1.0V.
5/10
Axelite Confidential Materials, do not copy or distribute without written consent.
Rev.1.2 Jul.30, 2010
5 Page | ||
| Páginas | Total 10 Páginas | |
| PDF Descargar | [ Datasheet AX6905.PDF ] | |
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