DS8023
Smart Card Interface
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Deactivation Sequence
When the host microcontroller is done communicating
with the smart card, it sets the CMDVCC line high to
execute an automatic deactivation sequence and
returns the card interface to the inactive mode.
The following sequence of events occurs during a
deactivation sequence (Figure 5):
1) RST goes low (t
10
).
2) CLK is held low (t
12
= t
10
+ 0.5 × T), where T is 64
times the period of the internal oscillator (approxi-
mately 25µs).
3) I/O, AUX1, and AUX2 are pulled low (t
13
= t
10
+ T).
4) V
CC
starts to fall (t
14
= t
10
+ 1.5 × T).
5) When V
CC
reaches its inactive state, the deactiva-
tion sequence is complete (at t
DE
).
6) All card contacts become low impedance to GND;
I/OIN, AUX1IN, and AUX2IN remain at V
DD
(pulled
up through an internal 11kΩ resistor).
7) The internal oscillator returns to its lower frequency.
V
CC
Generator
The card voltage (V
CC
) generator can supply up to
80mA continuously at 5V, 65mA at 3V, or 30mA at 1.8V.
An internal overload detector triggers at approximately
120mA. Current samples to the detector are filtered.
This allows spurious current pulses (with a duration of a
few µs) up to 200mA to be drawn without causing
deactivation. The average current must stay below the
specified maximum current value.
See the
Applications Information
section for recommen-
dations to help maintain V
CC
voltage accuracy.
Fault Detection
The DS8023 integrates circuitry to monitor the following
fault conditions:
• Short circuit or high current on V
CC
• Card removal while the interface is activated
•V
DD
dropping below threshold
• Card voltage generator operating out of the speci-
fied values (V
DDA
too low or current consumption
too high)
• Overheating
There are two different cases for how the DS8023
reacts to fault detection (Figure 6):
• Outside a Card Session (CMDVCC High). Output
OFF is low if a card is not in the card reader and
high if a card is in the reader. The V
DD
supply is
monitored—a decrease in input voltage generates
an internal power-on reset pulse but does not
affect the OFF signal. Short-circuit and tempera-
ture detection are disabled because the card is
not powered up.
• Within a Card Session (CMDVCC Low). Output
OFF goes low when a fault condition is detected,
and an emergency deactivation is performed auto-
matically (Figure 7). When the system controller
resets CMDVCC to high, it may sense the OFF
level again after completing the deactivation
sequence. This distinguishes between a card
extraction and a hardware problem (OFF goes high
again if a card is present).
Depending on the connector’s card-present switch
(normally closed or normally open) and the mechanical
characteristics of the switch, bouncing can occur on
the PRES signals at card insertion or withdrawal. The
DS8023 has a debounce feature with an 8ms typical
duration (Figure 6). When a card is inserted, output
OFF goes high after the debounce time delay. When
the card is extracted, an automatic deactivation
sequence of the card is performed on the first true/false
transition on PRES and output OFF goes low.
Stop Mode (Low-Power Mode)
A low-power state, stop mode, can be entered by forc-
ing the CMDVCC, 5V/3V, and 1_8V input pins to a
logic-high state. Stop mode can only be entered when
the smart card interface is inactive. In stop mode all
internal analog circuits are disabled. The OFF pin fol-
lows the status of the PRES pin. To exit stop mode,
change the state of one or more of the three control
pins to a logic-low. An internal 220µs (typ) power-up
delay and the 8ms PRES debounce delay are in effect
and OFF is asserted to allow the internal circuitry to sta-
bilize. This prevents smart card access from occurring
after leaving the stop mode. Figure 8 shows the control
sequence for entering and exiting stop mode. Note that
an in-progress deactivation sequence always finishes
before the DS8023 enters low-power stop mode.
