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TDA8025 Datasheet, PDF (11/38 Pages) NXP Semiconductors – IC card interface | |||
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NXP Semiconductors
TDA8025
IC card interface
-R----1---n--o---m--
R2nom
=
(-(--11----+-â----ββ----))
â

ï£
V-----D----D---(--I--N---T---F---)--a---c--t--m---i--n
V th(max)
â
1
(9)
R2nom = ï£ï£«---1-----+--R----RR--s----u--21---m---nn-----oo-----mm------- = ï£ï£«---1-----+-----(-(----11---------+-â--------β-β-------))----â
---ï£ï£«---V-------R--D-----s---D--u--V--(-m---I--t--N--h-----(T---m--F------a-)----ax-----)c----t----m-------i---n----â-----1-------
(10)
If we target 1 % accuracy resistors (β = 0.01) and Rsum = 100 kâ¦; Vth(max) = 1.33 V (see
Table 8 on page 23) and VDD(INTF)actmin = 2.64 V then
⢠R1nom = 50.88 kâ¦
⢠R2nom = 49.12 kâ¦
Deactivation always occurs when
V PORADJ < V th(min) â V DD(INTF)deactmax = V----α-t-h--m-(--m-a--xi--n---)
(11)
where
⢠Vth(min) is the minimum falling external threshold voltage
⢠VDD(INTF)deactmax is the maximum value of VDD(INTF) below which deactivation always
occurs
⢠αmax
αmax = 1-----+------RR--------21------nn-----o-o----m-1m---------â
â
------((-----11---------+â---------β-β-------))- = V-----D----D---(--VI--N--t-T-h--F(--m-)--d-i-n-e--)a---c--t--m---a---x
(12)
With the resulting values for R1nom, R2nom and β; Vth(min) = 1.17 V (see Table 8 on
page 23) then VDD(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 (fxtal ⤠26 MHz) connected between pins XTAL1 and XTAL2. The
voltage level applied to pin ENCLKIN deï¬nes 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 fxtal. Using
pins CLKDIV1 and CLKDIV2, the crystal frequency can be set to either fxtal, 1â2 fxtal, 1â4 fxtal
or 1â8 fxtal.
The frequency change is synchronous and as such during transition, no pulse is shorter
than 45 % of the smallest period. In addition, only the ï¬rst and last clock pulse around the
change have the correct width. When dynamically changing the frequency, the
modiï¬cation is only effective after 10 periods of XTAL1.
TDA8025_1
Product data sheet
Rev. 01 â 6 April 2009
© NXP B.V. 2009. All rights reserved.
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