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參數資料
| 型號： | TLC1225INW |
| 廠商： | TEXAS INSTRUMENTS INC |
| 元件分類： | ADC |
| 英文描述： | 1-CH 12-BIT SUCCESSIVE APPROXIMATION ADC, PARALLEL ACCESS, PDIP28 |
| 封裝： | PLASTIC, DIP-28 |
| 文件頁數： | 3/15頁 |
| 文件大小： | 230K |
| 代理商： | TLC1225INW |
TLC1225I, TLC1225M
SELF-CALIBRATING 12-BIT-PLUS-SIGN
ANALOG-TO-DIGITAL CONVERTERS
SLAS029B – AUGUST 1990 – REVISED DECEMBER 1993
11
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
analog inputs
differential inputs provide common-mode rejection
The differential inputs reduce common-mode noise. Common-mode noise is noise common to both IN + and
IN – inputs, such as 60-Hz noise. There is no time interval between the sampling of the IN + and IN –, so these
inputs are truly differential. No conversion errors result from a time interval between the sampling of the IN + and
IN – inputs.
input bypass capacitors
Input bypass capacitors can be used for noise filtering; however, the charge on these bypass capacitors is
depleted during the input sampling sequence when the internal sampling capacitors are charged. The charging
of the bypass capacitors through the differential source resistances must keep pace with the charge depletion
of the bypass capacitors during the input sampling sequence. Higher source resistances reduce the amount
of charging current for the bypass capacitors. Also fast, successive conversion has the greatest charge
depletion effect on the bypass capacitors. The above phenomenon becomes more significant as source
resistances and the conversion rate (i.e., higher clock frequency and conversion initiation rate) increase.
In addition, if the above phenomenon prevents the bypass capacitors from fully charging between conversions,
voltage drops across the source resistances result due to the ongoing bypass capacitor charging currents. The
voltage drops cause a conversion error. Also, the voltage drops increase with higher | VI+ – VI– | values, higher
source resistances, and lower charge on the bypass capacitors (i.e., faster conversion rate).
For low-source-resistance applications (Rsource < 100 ), a 0.001-F bypass capacitor at the inputs prevents
pickup due to the series lead inductance of a long wire. A 100-
resistor can be placed between the capacitor
and the output of an operational amplifier to isolate the capacitor from the operational amplifier.
input leads
The input leads should be kept as short as possible since the coupling of noise and digital clock signals to the
the inputs can cause errors.
power supply considerations
Noise spikes on the VCC lines can cause conversion error. Low-inductance tantalum capacitors (> 1 F) with
short leads should be used to bypass ANLG VCC and DGTL VCC. A separate regulator for the TLC1225 and other
analog circuitry greatly reduces digital noise on the supply line. A ferrite bead or equivalent inductance can be
used between the analog and digital ground planes if the digital ground noise is excessive.
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