ST8004CD View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'ST8004CD' PDF : 19 Pages View PDF
ST8004
• VCC falls to zero → (t14 = t11 +½3T); the deactivation sequence is completed when VCC reaches its
inactive state
• VUP falls to zero → (t15 = t11 +5T) and all card contacts become low-impedance to GND;
• I/OUC, AUX1UC and AUX2UC remain pulled up to VDD via a 10 kΩ resistor.
FAULT DETECTION
The following fault conditions are monitored by the circuit:
Short-circuit or high current on VCC
Removing card during transaction
VDD dropping
Overheating.
There are two different cases (Fig. 5)
1. CMDVCC HIGH: (outside a card session) then, OFF is LOW if the card is not in the reader, and HIGH
if the card is in the reader. A supply voltage drop on VDD is detected by the supply supervisor, which
generates an internal power-on reset pulse, but does not act upon OFF. The card is not powered-up, so
no short-circuit or overheating is detected.
2. CMDVCC LOW: (within a card session) then, OFF falls LOW if the card is extracted, or if a short-circuit
has occurred on VCC, or if the temperature on the IC has become too high. As soon as the fault is
detected, an emergency deactivation is automatically performed (see Fig.6). When the system controller
sets CMDVCC back to HIGH, it may sense OFF again in order to distinguish between a hardware problem
or a card extraction. If a supply voltage drop on VDD is detected while the card is activated, then an
emergency deactivation will be performed and OFF goes LOW.
When OFF level falls low, the system controller must wait not less than 160µs before setting high again
the CMDVCC command.
Depending on the type of card presence switch within the connector (normally closed or normal open),
and on the mechanical characteristics of the switch, a bouncing may occur on presence signals at card
insertion or withdrawal. There is no debounce feature in the device, so the software has to take it into
account; however, the detection of card take off during active phase, which initiates an automatic
deactivation sequence is done on the first True/False transition on PRES or PRES, and is memorized until
the system controller sets CMDVCC High. So, the software may take some time waiting for presence
switches to be stabilized without causing any delay on the necessary fast and normalized deactivation
sequence.
14/19
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