Datasheet

TDA8025_1 © NXP B.V. 2009. All rights reserved.
Product data sheet Rev. 01 — 6 April 2009 10 of 38
NXP Semiconductors
TDA8025
IC card interface
The voltage on PORADJ (V
PORADJ
) can be calculated as:
where:
• V
DD(INTF)
is the interface supply voltage
• ratio α
(2)
An activation can be triggered if
(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:
(4)
where
(5)
If ∆R1 is the maximum spread of R1 and ∆R2 is the maximum spread of R2 then:
(6)
(7)
(8)
where
• where β is the accuracy ratio of R1 and R2 (R1 and R2 are considered to be of the
same type).
Then
V
PORADJ
α= V
DD INTF()
×
α
1
1
R1
R2
-------
+
----------------
=
V
DD INTF()
α V
th max()
>× V
DD INTF()
V
th max()
α
--------------------
>⇒
V
DD INTF()actmin
V
th max()
α
min
--------------------
=
α
min
1
1
R1
max
R2
min
---------------
+
-------------------------
=
R1
max
R1
nom
∆R1+ R1
nom
1
∆R1
R1
nom
---------------
+


⋅==
R2
min
R2
nom
∆R2– R2
nom
1
∆R2
R2
nom
---------------
–


⋅==
α
min
1
1
R1
nom
1
∆R1
R1
nom
---------------
+


⋅
R2
nom
1
∆R2
R2
nom
---------------
–


⋅
---------------------------------------------------
+
------------------------------------------------------------
1
1
R1
nom
1 β+()⋅
R2
nom
1 β–()⋅
-------------------------------------
+
-----------------------------------------------
V
th max()
V
DD INTF()actmin
----------------------------------------
===