DS8313 Datasheet, PDF (12/18 Pages) Maxim Integrated Products – Smart Card Interface

Smart Card Interface
Deactivation Sequence
When a session is completed, the host microcontroller
sets the CMDVCC line high to execute an automatic
deactivation sequence and returns the card interface to
the inactive mode (Figure 5).
1) RST goes low (t₁₀).
2) CLK is held low (t₁₂ = t₁₀ + 0.5 × T) where T is 64
times the period of the internal oscillator (approxi-
mately 25µs).
3) I/O pin is pulled low (t₁₃ = t₁₀ + T).
4) V_CC starts to fall (t₁₄ = t₁₀ + 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 remains at V_DD (pulled up through an 11kΩ
resistor).
7) The internal oscillator returns to its lower frequency.
V_CC Generator
The V_CC generator has a capacity to supply up to
80mA continuously at 5V, 65mA at 3V, and 30mA at
1.8V. An internal overload detector triggers at approxi-
mately 120mA. Current samples to the detector are fil-
tered. 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. To main-
tain V_CC voltage accuracy, a 100nF capacitor (with an
ESR < 100mΩ) should be connected to CGND and
placed near the V_CC pin, and a 100nF or 220nF capaci-
tor (220nF is the best choice) with the same ESR should
be connected to CGND and placed near the smart
card reader’s C1 contact.
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
• 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 (Figure 6):
• 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. 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 is disabled because the card is not
powered up.
• CMDVCC Low Within a Card Session. 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 DS8313/DS8314 have a debounce feature with an
8ms typical duration (Figure 6). When a card is insert-
ed, output OFF goes high after the debounce time
delay. When the card is extracted, an automatic deacti-
vation sequence of the card is performed on the first
true/false transition on PRES and output OFF goes low.
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