Philips Semiconductors
Product specification
IC card interface
8.9
V
CC
generator
TDA8024
There are two different cases (see Fig.10):
•
CMDVCC HIGH outside a card session.
Output OFF
is LOW if a card is not in the card reader, and HIGH if a
card is in the reader. A voltage drop on the V
DD
supply
is detected by the supply supervisor, this generates an
internal Power-on reset pulse but does not act upon
OFF. No short-circuit or overheating is detected
because the card is not powered-up.
•
CMDVCC LOW within a card session.
Output OFF
goes LOW when a fault condition is detected. As soon
as this occurs, an emergency deactivation is performed
automatically (see Fig.11). When the system controller
resets CMDVCC to HIGH it may sense the OFF level
again after completing the deactivation sequence. This
distinguishes between a hardware problem or a card
extraction (OFF goes HIGH again if a card is present).
Depending on the type of card-present switch within the
connector (normally-closed or normally-open) and on the
mechanical characteristics of the switch, bouncing may
occur on the PRES signals at card insertion or withdrawal.
There is a debounce feature in the device with an 8 ms
typical duration (see Fig.10). When a card is inserted,
output OFF goes HIGH only at the end of the debounce
time.
When the card is extracted, an automatic deactivation
sequence of the card is performed on the first true/false
transition on PRES or PRES and output OFF goes LOW.
The V
CC
generator has a capacity to supply up to 80 mA
continuously at 5 V and 65 mA at 3 V.
An internal overload detector operates at approximately
120 mA. Current samples to the detector are internally
filtered, allowing spurious current pulses up to 200 mA
with a duration in the order of
µs
to be drawn by the card
without causing deactivation. The average current must
stay below the specified maximum current value.
For reasons of V
CC
voltage accuracy, a 100 nF capacitor
with an ESR < 100 mΩ should be tied to CGND near to
pin V
CC
, and a 100 or 220 nF capacitor (220 nF is the best
choice) with the same ESR should be tied to CGND near
card reader contact C1.
8.10
Fault detection
The following fault conditions are monitored:
•
Short-circuit or high current on V
CC
•
Removal of a card during a transaction
•
V
DD
dropping
•
DC/DC converter operating out of the specified values
(V
DDP
too low or current from V
UP
too high)
•
Overheating.
handbook, full pagewidth
PRES
OFF
CMDVCC
debounce
VCC
deactivation caused by
cards withdrawal
deactivation caused by
short-circuit
debounce
MDB059
See
“Application note AN10141”
for software decision algorithm on OFF signal.
Fig.10 Behaviour of OFF, CMDVCC, PRES and V
CC
.
2004 July 12
14
PHILIPS [ NXP SEMICONDUCTORS ]
