SPC56EL54X datasheet(122/165 Pages) STMICROELECTRONICS

122 / 165 page

Electrical characteristics

SPC56ELx, SPC564Lx

122/165

DocID15457 Rev 12

Figure 11. 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

can again be simplified considering only CS as an additional worst

condition. In reality, the transient is faster, but the A/D converter circuitry has been

designed to be robust also in the very worst case: the sampling time TS is always much

longer than the internal time constant:

Equation 6

The charge of CP1 and CP2 is redistributed also on CS, determining a new value of the

voltage VA1 on the capacitance according to Equation 7:

Equation 7



A second charge transfer involves also CF (that is typically bigger than the on-chip

capacitance) through the resistance RL: again considering the worst case in which CP2

VA1

VA2

VCS

Voltage Transient on CS

V <0.5 LSB





1 < (RSW + RAD) CS << TS



2 = RL (CS + CP1 + CP2)







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



















SPC56EL54x Scheda tecnica(PDF) 122 Page - STMicroelectronics

SPC56EL54x Scheda tecnica(HTML) 122 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

Scheda tecnica Scarica

Link URL