AN1978 - APPLICATION NOTE

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obtain a higher current from the charge pump when pulsed load is applied on Vcc.

In the typical applications a 100nF filter capacitor is connected to the Vcc output, near the ST8004 pins

and another 100nF is connected, between C1 and C5, near the card slot as shown in Figure 7 and

Figure 9. In order to reduce the noise presence and avoid cross conduction effects the wire length

between ST8004 and the card should be as short as possible (a wire less than 5cm-long is suggested).

In this way the Vcc spikes are much lower than 350mVpp, even when an impulsive load up to 65mA is

applied, as specified in the NDS requirements.

Figure 7: Smart Card connection.

A typical Vcc output waveform, with an impulsive 65mA load applied (worst condition at f=55KHz;

D.C.=50%) is shown in Figure 8 where the measured ripple is lower than 240mVpp; the Vcc pin will be

able to handle fast current transient generated by the smart card and remain between 4.60V and 5.30V

for Class-A and between 2.7V and 3.3V for Class-B (including ripple).

15

16

19

18

17

14

13

10

11

12

CMDVCC

Vcc

RST

CLK

PRES

I/O

AUX2

AUX1

CGND

100nF

C1

C2

C3

C4

C5

C6

C7

C8

100nF

K1

K2

100K

Ω

C9

C10

J1

R1

CARD SLOT

CGND connections

between ST8004 and

Card should be short

and straight.

ST8004

C3 (CLK) wire

should be routed far

from the other card

contacts.