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| ST8024CDR |
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 STMICROELECTRONICS
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22 page 
Functional description ST8024 22/31 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 100 nF capacitor with the same ESR should be tied to CGND near card reader contact C1. 5.10 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 Figure 8): –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 Figure 9). 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 Figure 8). 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. Figure 8. Behavior of OFF, CMDVCC, PRES and VCC |
