TDA8025 Datasheet, PDF (10/38 Pages) NXP Semiconductors – IC card interface

NXP Semiconductors
TDA8025
IC card interface
The voltage on PORADJ (V_PORADJ) can be calculated as: V _PORADJ = α × V _DD(INTF)
where:
• V_DD(INTF) is the interface supply voltage
• ratio α
α = ₁-----₊--¹----_RR--------₁₂---
(2)
An activation can be triggered if
V _DD(INTF) × α > V _th(max) ⇒ V _DD(INTF) > ^V-----^t-^h---_α⁽--^m----^a--^x--⁾
(3)
where
• V_th(max) is the maximum rising external threshold voltage
The resistance spread of R1 between a minimum value R1_min and a maximum value
R1_max induces a spread of the ratio α. This is also true for R2. Based on this:
V _{DD(INTF)actmin} = ^V-----^t_α-^h---_m⁽--^m--_i-_n-^a--^x--⁾
(4)
where
α_min = -₁----₊------_R-_R--¹_-----1-_2-----m-_m------a-i---_n--x
(5)
If ∆R1 is the maximum spread of R1 and ∆R2 is the maximum spread of R2 then:
R1_max
=
R1_nom + ∆R1
=
R
1_n
om
⋅


1
+
-_R--^∆--₁--^R-_n--_o-¹--_m--_
(6)
R2_min
=
R2_nom – ∆R2
=
R
2_no
m
⋅


1
–
-_R--^∆--₂--^R-_n--_o-²--_m--_
(7)
α_min
=
1^-----+^{------RR--------12------nn-----o}-_o^----m-_m---------^{⋅⋅----1-------1}-₁^--------+-_–----------_R^-R---------_∆∆------₂^--1--------_RR----_nn---------_o-^o--₂₁--------_mm----------_-^{---}
=
1^-----+^{------RR--------12------n-}_n----^o-_o^-----m1_m---------^⋅-_â‹-----^(-₍----¹¹---------^+-_–--------_β-^β-------₎₎-
=
-----------^V----^t--^h--⁽--^m----^a--^x---⁾---------
V _{DD(INTF)actmin}
(8)
where
• where β is the accuracy ratio of R1 and R2 (R1 and R2 are considered to be of the
same type).
Then
TDA8025_1
Product data sheet
Rev. 01 — 6 April 2009
© NXP B.V. 2009. All rights reserved.
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