L9700D データシートの表示（PDF） - STMicroelectronics

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L9700D

HEX PRECISION LIMITER

STMicroelectronics 

Figure 3 : Typical Application.

L9700

solete Product(s) The minimum value for CIN is determined by the ac-

b curacy required, the time taken to sample the input

O and the input impedance during that time, while the

- maximum value is determined by the required fre-

) quency response and the value of RS.

t(s Thus for a resistive input A/D connector where :

c TS = Sample time (Seconds)

du RD = Device input resistance (Ohms)

ro VIN = Input voltage (Volts)

P k = Required accuracy (%)

te Q1 = Charge on capacitor before sampling

le Q2 = Charge on capacitor after sampling

o ID = Device input current (Amps)

ObsThus :

k ⋅ Q1

Q1– Q2 = 100

but

Q1 = CIN VIN

and

Q1– Q2 = ID – TS

so that

and

so

k ⋅ CIN – VIN

ID TS =

100

ID ⋅ TS

CIN (min) = VIN ⋅ k Farad

100 ⋅ TS

CIN (min) = k ⋅ RD Farad

The calculation for a sample and hold type convertor

is even simpler :

k = Required accuracy (%)

CH = Hold capacitor (Farad)

100 ⋅ CH

CIN (min) = k

Farad

5/8

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