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).

× T) where T is 64

times the period of the internal oscillator (approxi-

mately 25µs).

× T).

6) All card contacts become low impedance to GND;

up through an 11k

Ω resistor).

7) The internal oscillator returns to its lower frequency.

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-

ESR < 100m

Ω) should be connected to CGND and

placed near the DS8113’s VCC pin, and a 100nF or

220nF capacitor (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 VCC

• Removal of a card during a transaction

• Card voltage generator operating out of the speci-

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

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 DS8113 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.

Smart Card Interface

12

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