AN2859 Datasheet, PDF (14/29 Pages) STMicroelectronics – Multiplexed diagnostics of AC switches using two STCC08

Resistance settings
3
Resistance settings
AN2859
Equation 13 shows how to select values for R₁ and R₃ resistances. I_{AVF_Max} is the
maximum current sunk by the STCC08 AVF pin and should be lower than 5 mA.
Equation 13
R₁
= R₃
=R
≥
2 · V_{CC_Max}
I_{AVF_Max}
Knowing the R₁ and R₃ resistor standard values, the tolerance of the resistors, the STCC08
AVF output electrical dispersion and the DC power supply characteristic, R₂ and R₄
resistances value should be chosen by using equations 14 , 15 , and 16 (see also
Appendix C).
Equation 14
⎧⇒
⎪
V_{1_Min} > V_{0_Max}
⎪
⎪
⎪
⎪
⎪
⎨
⎪⇒
⎪
⎪
⎪
⎪
⎜⎝⎛^R
R₄ >
+ R₂
⎟⎠⎞
⎡
· _⎢⎢V_{AVF_L_Max}
⎢⎣
·
⎜⎛
⎜⎜⎝
X_{R_Max}
X_{R_Min}
⎟⎞²
⎟⎟⎠
−
V_{AVF_L_Min}
⎤
⎥
⎥
⎥⎦
V_{CC_Min}
−
V_{AVF_L_Max}
·_{⎜⎜⎜⎝⎛}
X_{R_Max}
X_{R_Min}
⎟⎞²
⎟⎟⎠
⎪
⎩
Equation 15
⎧⇒ V_{2_Min} > V_{1_Max}
⎪
⎪
⎪
⎪
⎪
⎪
⎨
⎪⇒
⎪
⎪
⎪
⎪
R₄
<
R₂
⎡
· _⎢⎢V_{CC_Min}
⎢⎣
−
V_{AVF_L_Max}
⎜⎛
⎜⎜⎝
X_{R_Max}
X_{R_Min}
⎟⎞²
⎤
⎥
⎟⎟⎠
⎥
⎥⎦
⎡
− R · _⎢⎢V_{AVF_L_Max}
⎢⎣
· _{⎜⎜⎜⎝⎛}
X_{R_Max}
X_{R_Min}
V_{CC_Max}
· _{⎜⎜⎜⎝⎛}
X_{R_Max}
X_{R_Min}
⎟⎞²
⎟⎟⎠
−
V_{AVF_L_Min}
⎟⎞²
⎟⎟⎠
−
V_{AVF_L_Min}
⎤
⎥
⎥
⎥⎦
⎪
⎩
Equation 16
⎧⇒
⎪
V_{3_Min} > V_{2_Max}
⎪
⎪
⎪
⎪⎪
⎨
⎪⇒
⎪
⎪
⎪
⎪
R₄
R₂ ·
>
⎡
⎢⎢^VCC_Max
⎣
− V_{CC_Min}
·
X_{R_Min}
⎤
⎥
X_{R_Max}
⎥
⎦
−R
V_{CC_Min} · ^XR_Min − V_{AVF_L_Max}
X_{R_Max}
⎪⎩
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