DS8024
Smart Card Interface
14
Applications Information
Performance can be affected by the layout of the appli-
cation. For example, an additional cross-capacitance of
1pF between card reader contacts C2 (RST) and C3
(CLK) or C2 (RST) and C7 (I/O) can cause contact C2
to be polluted with high-frequency noise from C3 (or
C7). In this case, include a 100pF capacitor between
contacts C2 and CGND.
Application recommendations include the following:
• Ensure there is ample ground area around the
DS8024 and the connector; place the DS8024
very near to the connector; decouple the V
DD
and
V
DDA
lines separately. These lines are best posi-
tioned under the connector.
• The DS8024 and the host microcontroller must use
the same V
DD
supply. Pins CLKDIV1, CLKDIV2,
RSTIN, PRES, AUX1IN, I/OIN, AUX2IN, 5V/3V,
CMDVCC, and OFF are referenced to V
DD
; if pin
XTAL1 is to be driven by an external clock, also
reference this pin to V
DD
.
• Trace C3 (CLK) should be placed as far as possi-
ble from the other traces.
• The trace connecting CGND to C5 (GND) should
be straight (the two capacitors on C1 (V
CC
) should
be connected to this ground trace).
• Avoid ground loops among CGND, PGND, and
GND.
• Decouple V
DDA
and V
DD
separately; if the two
supplies are the same in the application, they
should be connected in a star on the main trace.
• Connect a 100nF capacitor (ESR < 100mΩ)
between V
CC
and CGND and place near the
DS8024’s V
CC
pin.
• Connect a 100nF or 220nF capacitor (220nF pre-
ferred, ESR < 100mΩ) between V
CC
and CGND
and place near the smart card socket’s C1 contact.
With all these layout precautions, noise should be kept
to an acceptable level and jitter on C3 (CLK) should be
less than 100ps.
Technical Support
For technical support, go to https://support.maxim-
ic.com/micro.
Selector Guide
Note: Contact the factory for availability of other variants and
package options.
+
Denotes a lead(Pb)-free/RoHS-compliant package.
/V denotes an automotive qualified part.
