Datasheet

TDA8025_1 © NXP B.V. 2009. All rights reserved.
Product data sheet Rev. 01 — 6 April 2009 11 of 38
NXP Semiconductors
TDA8025
IC card interface
(9)
(10)
If we target 1 % accuracy resistors (β = 0.01) and R
sum
= 100 kΩ; V
th(max)
= 1.33 V (see
Table 8 on page 23) and V
DD(INTF)actmin
= 2.64 V then
• R1
nom
= 50.88 kΩ
• R2
nom
= 49.12 kΩ
Deactivation always occurs when
(11)
where
• V
th(min)
is the minimum falling external threshold voltage
• V
DD(INTF)deactmax
is the maximum value of V
DD(INTF)
below which deactivation always
occurs
• α
max
(12)
With the resulting values for R1
nom
, R2
nom
and β; V
th(min)
= 1.17 V (see Table 8 on
page 23) then V
DD(INTF)deactmax
is 2.28 V.
8.3 Clock circuits
The clock signal (pin CLK) to the card is either generated by the clock signal input on pin
XTAL1 or from a crystal (f
xtal
≤ 26 MHz) connected between pins XTAL1 and XTAL2. The
voltage level applied to pin ENCLKIN defines which clock signal is used. When pin
ENCLKIN is HIGH, connect the external clock to pin XTAL1.
Driving pin ENCLKIN LOW causes the external crystal to generate frequency f
xtal
. Using
pins CLKDIV1 and CLKDIV2, the crystal frequency can be set to either f
xtal
,
1
⁄
2
f
xtal
,
1
⁄
4
f
xtal
or
1
⁄
8
f
xtal
.
The frequency change is synchronous and as such during transition, no pulse is shorter
than 45 % of the smallest period. In addition, only the first and last clock pulse around the
change have the correct width. When dynamically changing the frequency, the
modification is only effective after 10 periods of XTAL1.
R1
nom
R2
nom
---------------
1 β–()
1 β+()
-----------------
V
DD INTF()actmin
V
th max()
----------------------------------------
1–


⋅=
R2
nom
R
sum
1
R1
nom
R2
nom
---------------
+


------------------------------
R
sum
1
1 β–()
1 β+()
-----------------
V
DD INTF()actmin
V
th max()
----------------------------------------
1–


⋅+


--------------------------------------------------------------------------------------------
==
V
PORADJ
V
th min()
< V
DD INTF()deactmax
V
th min()
α
max
-------------------
=⇒
α
max
1
1
R1
nom
1 β–()⋅
R2
nom
1 β+()⋅
-------------------------------------
+
-----------------------------------------------
V
th min()
V
DD INTF()deactmax
----------------------------------------------
==