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    參數(shù)資料
    

    


    


    
型號(hào)：
LM3812MX-1.0

    

    
廠商：
NATIONAL SEMICONDUCTOR CORP

    

    
元件分類：
電源管理

    

    
英文描述：
Precision Current Gauge IC with Ultra Low Loss Sense Element and PWM Output

    

    
中文描述：
2-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO8

    

    
封裝：
0.150 INCH, PLASTIC, SOP-8

    

    
文件頁(yè)數(shù)：
11/14頁(yè)

    

    
文件大小：
258K

    

    
代理商：
LM3812MX-1.0


    

    

    

	
    
    
    

    
    
	
    PWM Output and Current
    Accuracy
    Offset
    The PWM output is quantized to 1024 levels. Therefore, the
    duty cycle can change only in increments of 1/1024.
    There is a one-half (0.5) quantization cycle delay in the out-
    put of the PWM circuitry. That is to say that instead of a duty
    cycle of N/1024, the duty cycle actually is (N+
    1
    2
    )/1024.
    The quantization error can be corrected for if a more precise
    result is desired. To correct for this error, simply subtract
    1/2048 from the measured duty cycle.
    The extra half cycle delay will show up as a DC offset of
    1
    2
    bit if it is not corrected for. This is approximately 1.1 mA for 1
    Amp parts, and 11 mA for 7 Amp parts.
    Jitter
    In addition to quantization, the duty cycle will contain some
    jitter. The jitter is quite small (for example, the standard de-
    viation of jitter is only 0.1% for the LM3812/13-1.0). Statisti-
    cally the jitter can cause an error in a current sample. Be-
    cause the jitter is a random variable, the mean and standard
    deviation are used. The mean, or average value, of the jitter
    is zero. The standard deviation (0.1%) can be used to define
    the peak error caused from jitter.
    The “crest factor” has often been used to define the maxi-
    mum error caused by jitter. The crest factor defines a limit
    within which 99.7% of the samples fall. The crest factor is de-
    fined as
     ±
    0.3% error in the duty cycle.
    Since the jitter is a random variable, averaging multiple out-
    puts will reduce the effective jitter. Obeying statistical laws,
    the jitter is reduced by the square root of the number of read-
    ings that are averaged. For example, if four readings of the
    duty cycle are averaged, the resulting jitter (and crest factor)
    are reduced by a factor of two.
    Jitter and Noise
    Jitter in the PWM output appears as noise in the current
    measurement. The Electrical Characteristics show noise
    measured in current RMS (root mean square).Arbitrarily one
    could specify PWM jitter, as opposed to noise. In either case
    the effect results in a random error in an individual current
    measurement.
    Noise, just like jitter, can be reduced by averaging many
    readings. The RMS value of the noise corresponds to one
    standard deviation. The “crest factor” can be calculated in
    terms of current, and is equal to
     ±
    3 sigma (RMS value of the
    noise).
    Noise will also be reduced by averaging multiple readings,
    and follows the statistical laws of a random variable.
    Accuracy of 7A Versions
    The graph of Figure 7shows two possible responses to a 7A
    current step. The flat response shows basically a 7A level
    with some noise. This is what is possible with a good thick
    trace and a good thermal connection to the IC on the sense
    pins.
    The second trace that asymptotically approaches a higher
    value shows what can happen under extremely poor thermal
    conditions. Here a very small wire connects the IC to the cur-
    rent source. The very small wire does not allow heat in the
    sense resistor to dissipate. Hence, as the sense resistor
    heats up, a temperature difference between the sense ele-
    ment and the die gets larger, and an error develops. Eventu-
    ally the temperature difference reaches steady state, which
    accounts for the under-damped exponential response.
    Accuracy versus Noise
    The graph shown in Figure 8 illustrates the typical response
    of
     ±
    1 Ampere current gauges. In this graph, the horizontal
    axis indicates time, and the vertical axis indicates measured
    current (the PWM duty cycle has been converted to current).
    The graph was generated for an actual current of 500 mA.
    The difference between successive readings manifests itself
    as jitter in the PWM output or noise in the current measure-
    ment (when duty cycle of the PWM output is converted to
    current).
    The accuracy of the measurement depends on the noise in
    the current waveform. The accuracy can be improved by av-
    eraging several outputs. Although there is variation in suc-
    cessive readings, a very accurate measurement can be ob-
    tained by averaging the readings. For example, on
    averaging the readings shown in this example, the average
    current measurement is 502.3 mA (Figure 8). This value is
    very close to the actual value of 500 mA. Moreover, the ac-
    curacy depends on the number of readings that are
    averaged.
    DS100122-23
    FIGURE 7. Transient Response to 7 Amp Step Current
    DS100122-26
    FIGURE 8. Typical Response of LM3812-1.0/LM3813-1.0
    www.national.com
    11
    
    
    
    
    
    


    


    

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    相關(guān)代理商/技術(shù)參數(shù)
    		

    參數(shù)描述
    		

    
    

    
LM3812MX-7.0
功能描述:IC CURRENT GAUGE 4% 8SOIC RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)流/電流管理 系列:- 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS
	Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:50 系列:- 功能:電流開(kāi)關(guān) 檢測(cè)方法:- 精確度:±10% 輸入電壓:1.7 V ~ 5.5 V 電流 - 輸出:600mA 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:10-UFQFN 供應(yīng)商設(shè)備封裝:10-UTQFN（1.4x1.8） 包裝:管件

    

    
LM3812PM-1.0
 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Current-Sense Gauge

    

    
LM3812PM-7.0
 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Current-Sense Gauge

    

    
LM3813
 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Precision Current Gauge IC with Ultra Low Loss Sense Element and PWM Output

    

    
LM3813EVAL
功能描述:EVALUATION BOARD FOR LM3813 RoHS:是 類別:編程器，開(kāi)發(fā)系統(tǒng) >> 評(píng)估演示板和套件 系列:- 標(biāo)準(zhǔn)包裝:1 系列:PCI Express® (PCIe) 主要目的:接口，收發(fā)器，PCI Express 嵌入式:- 已用 IC / 零件:DS80PCI800 主要屬性:- 次要屬性:- 已供物品:板

    

    
    
    
    
	
    	
    
    
     
     
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