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    參數(shù)資料
    型號: AD8403ARU1-REEL
    廠商: Analog Devices Inc
    文件頁數(shù): 14/32頁
    文件大?。?/td> 0K
    描述: IC POT DIG QUAD 1K 8BIT 24TSSOP
    產(chǎn)品變化通告: Product Discontinuance 27/Oct/2011
    標(biāo)準(zhǔn)包裝: 2,500
    接片: 256
    電阻(歐姆): 1k
    電路數(shù): 4
    溫度系數(shù): 標(biāo)準(zhǔn)值 500 ppm/°C
    存儲器類型: 易失
    接口: 4 線 SPI(芯片選擇)
    電源電壓: 2.7 V ~ 5.5 V
    工作溫度: -40°C ~ 125°C
    安裝類型: 表面貼裝
    封裝/外殼: 24-TSSOP(0.173",4.40mm 寬)
    供應(yīng)商設(shè)備封裝: 24-TSSOP
    包裝: 帶卷 (TR)
    AD8400/AD8402/AD8403
    Rev. E | Page 21 of 32
    Like a mechanical potentiometer, RDAC is symmetrical. The
    resistance between the Wiper W and Terminal A also produces
    a digitally controlled complementary resistance, RWA. When
    these terminals are used, the B terminal can be tied to the wiper
    or left floating. RWA starts at the maximum and decreases as the
    data loaded into the RDAC latch increases. The general transfer
    equation for this RWA is
    ()
    W
    AB
    WA
    R
    D
    R
    +
    ×
    =
    256
    (3)
    where D is the data loaded into the 8-bit RDAC# latch, and RAB
    is the nominal end-to-end resistance.
    For example, when the B terminal is either open-circuited or
    tied to the Wiper W, the following RDAC latch codes result in
    the following RWA (for the 10 kΩ version):
    Table 11.
    D (Dec)
    RWA (
    )
    Output State
    255
    89
    Full-Scale
    128
    5,050
    Midscale (RS = 0 Condition)
    1
    10,011
    1 LSB
    0
    10,050
    Zero-Scale
    The typical distribution of RAB from channel to channel
    matches within ±1%. However, device-to-device matching
    is process lot dependent and has a ±20% variation. The tem-
    perature coefficient, or the change in RAB with temperature,
    is 500 ppm/°C.
    The wiper-to-end-terminal resistance temperature coefficient
    has the best performance over the 10% to 100% of adjustment
    range where the internal wiper contact switches do not con-
    tribute any significant temperature related errors. The graph in
    Figure 18 shows the performance of RWB tempco vs. code. Using
    the potentiometer with codes below 32 results in the larger
    temperature coefficients plotted.
    PROGRAMMING THE POTENTIOMETER DIVIDER
    Voltage Output Operation
    The digital potentiometer easily generates an output voltage
    proportional to the input voltage applied to a given terminal.
    For example, connecting the A terminal to 5 V and the B termi-
    nal to ground produces an output voltage at the wiper starting
    at 0 V up to 1 LSB less than 5 V. Each LSB is equal to the voltage
    applied across the A to B terminals divided by the 256-position
    resolution of the potentiometer divider. The general equation
    defining the output voltage with respect to ground for any given
    input voltage applied to the A to B terminals is
    B
    AB
    W
    V
    D
    V
    +
    ×
    =
    256
    (4)
    Operation of the digital potentiometer in the voltage divider
    mode results in more accurate operation over temperature.
    Here the output voltage is dependent on the ratio of the internal
    resistors, not the absolute value; therefore, the temperature drift
    improves to 15 ppm/°C.
    At the lower wiper position settings, the potentiometer divider
    temperature coefficient increases because the contribution of
    the CMOS switch wiper resistance becomes an appreciable
    portion of the total resistance from the B terminal to the
    Wiper W. See Figure 17 for a plot of potentiometer tempco
    performance vs. code setting.
    DIGITAL INTERFACING
    The AD8400/AD8402/AD8403 contain a standard SPI-
    compatible, 3-wire, serial input control interface. The three
    inputs are clock (CLK), chip select (CS), and serial data input
    (SDI). The positive-edge sensitive CLK input requires clean
    transitions to avoid clocking incorrect data into the serial input
    register. For the best result, use logic transitions faster than
    1 V/μs. Standard logic families work well. If mechanical switches
    are used for product evaluation, they should be debounced by
    a flip-flop or other suitable means. The block diagrams in
    , and
    show the internal digital
    circuitry in more detail. When
    CS is taken active low, the clock
    loads data into the 10-bit serial register on each positive clock
    edge (see
    ).
    RDAC
    LATCH
    NO. 1
    GND
    A1
    W1
    B1
    VDD
    AD8400
    CS
    CLK
    8
    D7
    D0
    EN
    ADDR
    DEC
    A1
    A0
    SDI
    DI
    D0
    D7
    10-BIT
    SER
    REG
    0
    10
    92
    -0
    45
    Figure 46. AD8400 Block Diagram
    RDAC
    LATCH
    NO. 1
    R
    AGND
    RS
    A1
    W1
    B1
    VDD
    AD8402
    CS
    CLK
    D7
    D0
    RDAC
    LATCH
    NO. 2
    R
    A4
    W4
    B4
    D7
    D0
    EN
    ADDR
    DEC
    A1
    A0
    SDI
    DI
    10-BIT
    SER
    REG
    D0
    SHDN
    DGND
    D7
    8
    01
    09
    2-
    04
    6
    Figure 47. AD8402 Block Diagram
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