DS8024
Smart Card Interface
11
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 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 or 65mA at 3V. 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 DS8024 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 DS8024
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 con-
nector’s card-present switch (normally closed or
normally open) and the mechanical characteristics
of the switch, bouncing can occur on the PRES sig-
nals at card insertion or withdrawal.
The DS8024 has a debounce feature with an 8ms typi-
cal 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)
The DS8024 (like the TDA8024) does not support a low-
power stop mode. For applications requiring low-power
support, refer to the DS8113.
Smart Card Power Select
The DS8024 supports two smart card V
CC
voltages: 3V
and 5V. The power select is controlled by the 5V/3V
signal as shown in Table 3. V
CC
is 5V if 5V/3V is assert-
ed to a logic-high state, and V
CC
is 3V if 5V/3V is pulled
to a logic-low state.
Table 3. V
CC
Select and Operation Mode
