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  • 參數(shù)資料
    型號(hào): TC1271SERC
    廠商: Microchip Technology Inc.
    英文描述: 4-Pin レP Reset Monitors
    中文描述: 4引腳レP復(fù)位監(jiān)控器
    文件頁(yè)數(shù): 5/12頁(yè)
    文件大?。?/td> 467K
    代理商: TC1271SERC
    2002 Microchip Technology Inc.
    DS21381B-page 5
    TC1270/TC1271
    3.0
    APPLICATIONS INFORMATION
    3.1
    V
    CC
    Transient Rejection
    The TC1270/TC1271 provides accurate V
    CC
    monitor-
    ing and reset timing during power-up, power-down, and
    brownout/sag conditions, and rejects negative-going
    transients (glitches) on the power supply line. Figure
    3-1
    shows the
    maximum transient
    maximum negative excursion (overdrive) for glitch
    rejection. Any combination of duration and overdrive
    that lays
    under
    the curve will
    not
    generate a reset
    signal. Combinations above the curve are detected as
    a brownout or power-down. Transient immunity can be
    improved by adding a capacitor in close proximity to the
    V
    CC
    pin of the TC1270/TC1271.
    duration
    vs.
    FIGURE 3-1:
    MAXIMUM TRANSIENT
    DURATION VS.
    OVERDRIVE FOR GLITCH
    REJECTION AT 25°C
    3.2
    RESET Signal Integrity During
    Power-Down
    The TC1270 RESET output is valid to V
    CC
    = 1.0V.
    Below this voltage the output becomes an "open
    circuit" and does not sink current. This means CMOS
    logic
    inputs
    to
    the
    μ
    P
    undetermined
    voltage.
    Most
    completely
    shut
    down
    well
    However,
    in
    situations
    where
    maintained valid to V
    CC
    = 0V, a pull-down resistor must
    will
    be
    digital
    above
    RESET
    floating
    systems
    this
    at
    an
    are
    voltage.
    must
    be
    be connected from RESET to ground to discharge stray
    capacitances and hold the output low (Figure 3-2). This
    resistor value, though not critical, should be chosen
    such that it does not appreciably load RESET under
    normal operation (100k
    will be suitable for most
    applications). Similarly, a pull-up resistor to V
    CC
    is
    required for the TC1271 to ensure a valid high RESET
    for V
    CC
    below 1.1V.
    FIGURE 3-2:
    ENSURING RESET VALID
    TO V
    CC
    = 0V
    3.3
    Processors With Bidirectional
    I/O Pins
    Some
    μ
    P's (such as Motorola 68HC11) have bi-
    directional reset pins. Depending on the current drive
    capability of the processor pin, an indeterminate logic
    level may result if there is a logic conflict. This can be
    avoided by adding a 4.7 k
    resistor in series with the
    output of the TC1270/TC1271 (Figure 3-3). If there are
    other components in the system which require a reset
    signal, they should be buffered so as not to load the
    reset line. If the other components are required to
    follow the reset I/O of the
    μ
    P, the buffer should be
    connected as shown with the solid line.
    FIGURE 3-3:
    INTERFACING TO
    BIDIRECTIONAL
    RESET I/O
    RESET COMPARATOR OVERDRIVE,
    V
    TH
    - V
    CC
    (mV)
    400
    240
    160
    320
    80
    0
    1
    10
    100
    1000
    M
    μ
    s
    T
    A
    °
    C
    V
    TH
    Duration
    Overdrive
    V
    CC
    TC127LMJ
    TC127xR/S/T
    TC1270
    V
    CC
    V
    CC
    R1
    100k
    RESET
    GND
    TC1270
    V
    CC
    RESET
    GND
    RESET
    GND
    Buffered RESET
    To Other System
    Components
    Buffer
    μ
    P
    4.7k
    V
    CC
    V
    CC
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