LTC1955 Linear Technology, LTC1955 Datasheet
LTC1955
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LTC1955 Summary of contents
Page 1
... The card voltages can be independently set to 1.8V 5V. Both card interfaces include a card detection channel with automatic debounce circuitry. To reduce wiring costs, the LTC1955 interfaces to a microcontroller via a simple 4-wire serial interface. Multiple devices may be connected in daisy-chain fashion so that the number of wires to the card socket board is independent of the number of sock- ets ...
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... A CCA CCB CCA CCB No Cards Present CPO V = 3.075V 120mA, (Note 3) BATT CPO CCA CCB I = 0mA, 10% to 90% CCA/B Short-Circuit Duration .................... Indefinite ORDER PART NUMBER LTC1955EUH UH PART MARKING 1955 = 3.3V unless otherwise noted. CC MIN TYP MAX 2.7 5.5 250 400 350 500 0.75 1.75 1.7 5 0.5 1.5 5.7 8 ...
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... DATA DVCC Loaded with 50pF, 10 DATA Sink Current = – 500 0V) I/OA/B Source Current = I/OA/B CCA/B Loaded with 50pF, 10% to 90% Sink Current = – 200 A Source Current = 200 3.3V UNDERV LTC1955 = 3.3V unless otherwise noted. CC MIN TYP MAX UNITS 4.65 5.0 5.35 2.75 3.0 3.25 1.65 1.8 1.95 0.8 1.5 – 9 – 5 – ...
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... Sink Current = – 200 5.5V FAULT CONDITIONS C = 15pF LOAD Note 4: The LTC1955E is guaranteed to meet performance specifications from Specifications over the – operating ambient temperature range are assured by design, characterization and correlation with statistical process controls. . See Figure 6. I/O X Short-Circuit Current vs Temperature 6.0 ...
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... 0.5 0 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 V SUPPLY VOLTAGE (V) BATT 1955 G08 Deactivation Sequence RST A 5V/DIV CLK A 5V/DIV I/O A 5V/DIV V CCA 5V/DIV 10 s/DIV 1955 G11.eps LTC1955 Bidirectional Channel (I/O A, I/O B) Low Output Level vs Temperature 0. DATA V = 1.8V CCX I = –1mA OL 0. 2.7V BATT CCX 0. CCX 0.10 0.08 0.06 –40 – ...
Page 6
... DATA pin provides the bidirectional communication path to both smart cards. One, both or neither of the cards may be selected to communicate via the DATA pin. If several LTC1955s are connected in parallel, the DATA pin can be made high impedance by selecting neither card. The C4A and C8A synchronous card pins can be selected to con- nect to the DATA pin via the serial port (see Table 4) ...
Page 7
... UNDERV: Input. The UNDERV pin provides security by supplying a precision undervoltage threshold for external supply monitoring. An external resistive voltage divider programs the desired undervoltage threshold. Once UNDERV falls below 1.23V, the LTC1955 automatically begins the deactivation sequence on any channel that is active When ...
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... LTC1955 W BLOCK DIAGRA www.DataSheet4U.com V 17 CCB 20 I/O B SMART 18 CLK B CARD SOCKET B 19 RST B 21 PRES B 29 DATA SMART 31 ASYNC CARD 32 SYNC COMMUNICATIONS SERIAL PORT 28 D OUT COMMAND/STATUS 26 SCLK DATA CHARGE PUMP + – PGND CHARGE ...
Page 9
... Serial Port The microcontroller compatible serial port provides all of the command and control inputs for the LTC1955 as well as the status of the two smart cards. Data on the D is loaded on the rising edge of SCLK. D15 is loaded first and D0 last. At the same time the command bits are being ...
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... Options should be set to $0000 since this is the shutdown com- mand for the LTC1955. However, consider the example where some operation is already being performed on channel A. If, for example, the previous command was $BE00 (V ...
Page 11
... BIDIRECTIONAL PIN Figure 3. Dynamic Pull-Up Current Sources Clock Channels As described in the section Serial Port, the LTC1955 supports both synchronous and asynchronous smart cards. On start-up, or when bits D13-D15 for card A and bits D5-D7 for card B are set to 0s, the clock channel is in synchronous mode. The remaining modes are used for asynchronous cards ...
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... LTC1955 U OPERATIO www.DataSheet4U.com Smart Card Detection Circuits The PRES A/PRES B pins are used to detect the presence of a smart card. An automatic debounce circuit waits until a smart card has been present for a continuous period of typically 35ms. Once a valid card indication exists, the status bit for that channel is updated and may be polled by cycling data through the serial port ...
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... U OPERATIO www.DataSheet4U.com Electrical Fault Detection Several types of faults are detected by the LTC1955. They include V /V undervoltage, V CCA CCB CLK A/CLK B, RST A/RST B, C8A, C4A short circuit, card removal during a transaction, failed answer to reset (ATR), supply undervoltage or UNDERV and chip overtemperature. To prevent false errors from plaguing the microcontroller, the electrical faults are acted upon only after (min) timeout period ...
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... Capacitor Selection Warning: A polarized capacitor such as tantalum or alumi- num should never be used for the flying capacitor since its voltage can reverse upon start up of the LTC1955. Low ESR ceramic capacitors should always be used for the flying capacitor. A total of six capacitors are required to operate the LTC1955 ...
Page 15
... The static current can be brought back to the level of a single LTC1955 by setting bit D3 on all but one of the LTC1955s to 1 (see Table 1). Bit D3 disables the pull-up current source on the DATA pin. This will help prevent V problems in multiple LTC1955 applications when driving the DATA or I/O pins low ...
Page 16
... To reduce the maximum junction temperature, a good thermal connection to the PC board is recom- mended. Zero Shutdown Current Although the LTC1955 is designed to have very low shutdown current, it can still draw over a microampere on supply at 2.7V or greater during this period. BATT supply to ...
Page 17
... BATT able to the smart cards is limited by the charge pump. Figure 6 shows how the LTC1955 can be modeled as a Thevenin equivalent circuit to determine the amount of current available given the effective input voltage, 2V and the effective open-loop output resistance, R ...
Page 18
... GND UNDERV 24 FAULT OUT 26 SCLK DATA SYNC 31 ASYNC Figure 7. Multiple LTC1955s Daisy Chained Together PRES B PRES A SMART CARD VENDOR CARD LTC1955 15 CPO 4 PRES B PRES A SMART CARD VENDOR CARD LTC1955 15 CPO 4 ...
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... F08 U UH Package 32-Lead Plastic QFN (5mm 5mm) (Reference LTC DWG # 05-08-1693) 0.57 0.05 PACKAGE OUTLINE 0.23 0.05 0.50 BSC 0.75 0.05 5.00 0.10 (4 SIDES) 0.00 – 0.05 3.45 0.10 (4-SIDES) 0.200 REF LTC1955 100 C7 100 20pF C3 100 20pF C2 20pF 0.1 F Figure 9. Additional Components for Improved Compliance Testing BOTTOM VIEW—EXPOSED PAD ...
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... 10M 8.000MHz 27pF 27pF Battery Powered RS232 to Dual Smart Card Interface www.linear.com + 180k 262k 0.1 F 4.7 F Li-ION UNDERV V CC BATT 24 FAULT LTC1955EUH 3 C8A 4 C4A 5 I RST CLK A OUT 8 26 SCLK V CCA 0 PRES A ...