SPC56EC74L7 datasheet(84/118 Pages) STMICROELECTRONICS

84 / 118 page

Electrical Characteristics

SPC564Bxx - SPC56ECxx

84/118

Doc ID 17478 Rev 4

Figure 17. Input equivalent circuit (extended channels)

A second aspect involving the capacitance network shall be considered. Assuming the three

capacitances CF, CP1 and CP2 are initially charged at the source voltage VA (refer to the

equivalent circuit reported in Figure 16): A charge sharing phenomenon is installed when

the sampling phase is started (A/D switch close).

Figure 18. Transient behavior during sampling phase

In particular two different transient periods can be distinguished:

A first and quick charge transfer from the internal capacitance CP1 and CP2 to the

sampling capacitance CS occurs (CS is supposed initially completely discharged):

considering a worst case (since the time constant in reality would be faster) in which

CP2 is reported in parallel to CP1 (call CP = CP1 + CP2), the two capacitances CP and

CS are in series, and the time constant is

Equation 5

RSW1

CP3

VDD

Sampling

Source

Filter

Current Limiter

EXTERNAL CIRCUIT

INTERNAL CIRCUIT SCHEME

RS Source Impedance

RF Filter Resistance

CF Filter Capacitance

RL Current Limiter Resistance

RSW Channel Selection Switch Impedance (two contributions RSW1 and RSW2)

RADSampling Switch Impedance

CP Pin Capacitance (three contributions, CP1, CP2 and CP3)

CS Sampling Capacitance

CP1

RAD

Channel

Selection

CP2

Extended

RSW2

Switch

VA1

VA2

VCS

Voltage Transient on CS

ΔV < 0.5 LSB

τ1 < (RSW + RAD) CS << TS

τ2 = RL (CS + CP1 + CP2)

τ1 RSW RAD

()

CP CS

•

CP CS

----------------------

•

SPC56EC74L7 데이터시트(PDF) 84 Page - STMicroelectronics

SPC56EC74L7 데이터시트(HTML) 84 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

데이터시트 다운로드

링크 URL