DS8024-RJX+ datasheet(11/15 Pages) MAXIM

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Smart Card Interface

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 (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, AUX1, and AUX2 are pulled low (t13 = t10 + T).

4) VCC starts to fall (t14 = t10 + 1.5

× T).

5) When VCC reaches its inactive state, the deactiva-

tion sequence is complete (at tDE).

6) All card contacts become low impedance to GND;

I/OIN, AUX1IN, and AUX2IN remain at VDD (pulled

up through an 11k

Ω resistor).

7) The internal oscillator returns to its lower frequency.

VCC Generator

The card voltage (VCC) 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 VCC voltage accuracy.

Fault Detection

The DS8024 integrates circuitry to monitor the following

fault conditions:

• Short-circuit or high current on VCC

• Card removal while the interface is activated

•VDD dropping below threshold

• Card voltage generator operating out of the speci-

fied values (VDDA 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 VDD 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 VCC voltages: 3V

and 5V. The power select is controlled by the 5V/3V

signal as shown in Table 3. VCC is 5V if 5V/3V is assert-

ed to a logic-high state, and VCC is 3V if 5V/3V is pulled

to a logic-low state.

Table 3. VCC Select and Operation Mode

5V/3V

CMDVCC

VCC

SELECT (V)

CARD INTERFACE

STATUS

Activated

Inactivated

Activated

Inactivated

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