TDA8024AT datasheet(14/29 Pages) PHILIPS

14 / 29 page

2004 July 12

Philips Semiconductors

Product speciﬁcation

IC card interface

TDA8024

8.9

VCC generator

The VCC generator has a capacity to supply up to 80 mA

continuously at 5 V and 65 mA at 3 V.

An internal overload detector operates at approximately

120 mA. Current samples to the detector are internally

filtered, allowing spurious current pulses up to 200 mA

with a duration in the order of

µs to be drawn by the card

without causing deactivation. The average current must

stay below the specified maximum current value.

For reasons of VCC voltage accuracy, a 100 nF capacitor

with an ESR < 100 m

Ω should be tied to CGND near to

pin VCC, and a 100 or 220 nF capacitor (220 nF is the best

choice) with the same ESR should be tied to CGND near

card reader contact C1.

8.10

Fault detection

The following fault conditions are monitored:

• Short-circuit or high current on VCC

• Removal of a card during a transaction

• VDD dropping

• DC/DC converter operating out of the specified values

(VDDP too low or current from VUP too high)

• Overheating.

There are two different cases (see Fig.10):

• 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. A voltage drop on the VDD supply

is detected by the supply supervisor, this generates an

internal Power-on reset pulse but does not act upon

OFF. No short-circuit or overheating is detected

because the card is not powered-up.

• CMDVCC LOW within a card session. Output OFF

goes LOW when a fault condition is detected. As soon

as this occurs, an emergency deactivation is performed

automatically (see Fig.11). When the system controller

resets CMDVCC to HIGH it may sense the OFF level

again after completing the deactivation sequence. This

distinguishes between a hardware problem or a card

extraction (OFF goes HIGH again if a card is present).

Depending on the type of card-present switch within the

connector (normally-closed or normally-open) and on the

mechanical characteristics of the switch, bouncing may

occur on the PRES signals at card insertion or withdrawal.

There is a debounce feature in the device with an 8 ms

typical duration (see Fig.10). When a card is inserted,

output OFF goes HIGH only at the end of the debounce

time.

When the card is extracted, an automatic deactivation

sequence of the card is performed on the first true/false

transition on PRES or PRES and output OFF goes LOW.

handbook, full pagewidth

MDB059

OFF

CMDVCC

PRES

VCC

debounce

deactivation caused by

cards withdrawal

deactivation caused by

short-circuit

debounce

Fig.10 Behaviour of OFF, CMDVCC, PRES and VCC.

See

“Application note AN10141” for software decision algorithm on OFF signal.

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