LTC1955EUH Linear Technology, LTC1955EUH Datasheet - Page 10

• Manufacturer Part Number: LTC1955EUH
• Description: IC INTERFACE DL SMART CARD 32QFN
• Manufacturer: Linear Technology

Specifications of LTC1955EUH

• Controller Type: Smart Card Interface
• Interface: 4-Wire Serial
• Voltage - Supply: 1.7 V ~ 5.5 V
• Current - Supply: 10µA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-QFN
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

LTC1955
OPERATION
Table 1. Serial Port Comand
CARD B
CARD A
Table 2. V
Table 3. Clock Options
10
D15
D9
D1
D7
0
0
1
1
0
0
0
0
1
1
1
1
D14
STATUS OUTPUT
0
0
0
0
Card B Electrical Fault
Card B ATR Fault
Card B V
Card B Present
0
0
0
0
Card A Electrical Fault
Card A ATR Fault
Card A V
Card A Present
D8
D0
D6
CC
0
0
1
1
0
0
1
1
0
1
0
1
and Shutdown Options
STATUS (CARD A)
STATUS (CARD B)
V
V
V
V
CC
CC
CC
CC
CC
CC
D13
D5
0
1
0
1
0
1
0
1
Ready
Ready
= 0V (Shutdown)
= 1.8V
= 3V
= 5V
CLOCK MODE (CARD B)
CLOCK MODE (CARD A)
Synchronous Mode
Unused
Asynchronous Stop Low
Asynchronous Stop High
Asynchronous ÷1
Asynchronous ÷2
Asynchronous ÷4
Asynchronous ÷8
D10 Card A Select/Deselect
D11 Card A Communications
D12
D13 Card A Clock Options
D14
D15
BIT
D0
D1
D2
D3
D4
D5
D6
D7
D8
D9
V
(See Table 2)
Card B Select/Deselect
Data Pull-Up Defeat
Reserved (Always Set to “0”)
Card B Clock Options
(See Table 3)
V
(See Table 2)
Options (See Table 4)
(See Table 3)
COMMAND INPUT
CCB
CCA
Options
Options
To receive status data from the serial port, a read/write op-
eration must be performed. When polling for the presence
of a smart card on both channels, the input word should
be set to $0000 since this is the shutdown command 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
3V, card selected, I/O A connected to DATA and CLK A set
to ASYNC÷2), then the commands for this channel must
be rewritten to the serial port each time. To poll for the
presence of a card on channel B, or even the V
status, then $BE00 should be rewritten on each new
read/write cycle. Once a card is detected on channel B, the
commands for channel B can be changed but the $BExx
should continue to be rewritten for channel A.
Bidirectional Channels
The bidirectional channels are level shifted to the appropri-
ate V
An NMOS pass transistor performs the level shifting. The
gate of the NMOS transistor is biased such that the transis-
tor is completely off when both sides have relinquished
the channel. If one side of the channel asserts an L, then
the transistor will convey the L to the other side. Note that
current passes from the receiving side of the channel to the
transmitting side. The low output voltage of the receiving
side will be dependent upon the voltage at the transmitting
side plus the I • R drop of the pass transistor.
When a card socket is selected, it becomes a candidate
to drive data on the DATA pin, and likewise, receive data
from the DATA pin. When a card socket is deselected, the
voltage on its I/O A/I/O B pin will return to the idle state
(H), and the DATA side of that channel will become high
impedance. If both cards are deselected, the DATA pin
will be high impedance.
Both cards may be deselected at the same time to allow
communication with a second LTC1955.
Card channel A includes provision for unidirectional
communication with the C4 and C8 pins of the smart
card. The C4, C8 and I/O pins of card A are individually
multiplexed to the DATA pin using bits D11 and D12, as
shown in Table 4.
CCA/B
voltages at the I/O A/I/O B pins.
CCA
CCA
set to
ready
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