NCN8024
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13
POWER−DOWN
When the communication session is completed the
NCN8024 runs a deactivation sequence by setting High
CMDVCC. The below power down sequence is executed:
• CRD_RST is forced to Low
• CRD_CLK is set Low 12 ms after CRD_RST.
• CRD_IO, CRD_AUX1 and CRD_AUX2 are pulled Low
• Finally CRD_V
CC
supply can be shut−off.
Figure 6. Deactivation Sequence
CRD_RST
CRD_IO
CRD_CLK
CMDVCC
CRD_VCC
t
deact
FAULT DETECTION
In order to protect both the interface and the external smart
card, the NCN8024 provides security features to prevent
failures or damages as depicted here after.
• Card extraction detection
• V
DD
under voltage detection
• Short−circuit or overload on CRD_V
CC
• Card pin current limitation: in the case of a short circuit
to ground. No feedback is provided to the external MPU.
• DC/DC operation: the internal circuit continuously
senses the CRD_V
CC
voltage (in the case of either over
or under voltage situation).
• DC/DC operation: under−voltage detection on V
DDP
or
overload on VUP
• Overheating
Figure 7. Fault Detection and Interrupt Management
Debounce Debounce
Powerdown Caused by
Short−Circuit
Powerdown Resulting of
Card Extraction
INT
CRD_VCC
CRD_PRES
CMDVCC
Interrupt Pin Management:
A card session is opened by toggling CMDVCC High to
Low.
Before a card session, CMDVCC is supposed to be in a
High position. INT is Low if no card is present in the card
connector (Normally open or normally closed type). INT is
High if a card is present. If a card is inserted (INT = High)
and if V
DD
drops below the UVLO threshold then INT pin
drops Low immediately. It turns back High when V
DD
increases again over the UVLO limit (including hysteresis),
a card being still present.
During a card session, CMDVCC is Low and INT pin
goes Low when a fault is detected. In that case a deactivation
is immediately and automatically performed (see Figure 6).
When the microcontroller resets CMDVCC to High it can
sense the INT level again after having got completed the
deactivation.
As illustrated by Figure 7 the device has a debounce timer
of 8 ms typical duration. When a card is inserted, output INT
goes High only at the end of the debounce time. When the
card is removed a deactivation sequence is automatically
and immediately performed and INT goes Low.
