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TDA8025 Datasheet(PDF) 11 Page - NXP Semiconductors |
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TDA8025 Datasheet(HTML) 11 Page - NXP Semiconductors |
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11 / 38 page  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; Vth(max) = 1.33 V (see Table 8 on page 23) and VDD(INTF)actmin = 2.64 V then • R1nom = 50.88 kΩ • R2nom = 49.12 kΩ Deactivation always occurs when (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 • α max (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 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 fxtal. Using pins CLKDIV1 and CLKDIV2, the crystal frequency can be set to either fxtal, 1⁄2 fxtal, 1⁄4 fxtal or 1 ⁄ 8 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 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 ---------------------------------------------- == |
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