LTC1955 Linear Technology, LTC1955 Datasheet - Page 7

• Manufacturer Part Number: LTC1955
• Description: Dual Smart Card Interface
• Manufacturer: Linear Technology

PI FU CTIO S
PRES A/PRES B: Card Socket. The PRES A/PRES B pins
are used to detect the presence of the smart cards. They
can be connected to either normally open or normally
closed detection switches on the smart card acceptor’s
sockets. The NC/NO pin should be set appropriately. These
pins have a pull-up current source on-chip so no external
components are required.
C4A/C8A: Card Socket. These pins connect to the C4 and
C8 pins of synchronous memory cards on smart card
socket A. The signal for these pins is unidirectional and can
only be sent to the card. Data for C4A and C8A is transmit-
ted via the DATA pin and may be selected in place of I/OA
via the serial port (see Table 4). When either C4A or C8A
is selected, it will follow the DATA pin. When it is dese-
lected, it will remain latched at its current state.
I/O A/I/O B: Card Socket. The I/O A/I/O B pins connect to
the I/O pins of the respective smart card sockets. When a
smart card is selected, its I/O pin connects to the DATA pin.
When a smart card is deselected, its I/O A/I/O B pin returns
to the idle state (H).
RST A/RST B: Card Socket. These pins should be con-
nected to the RST pins of the respective smart card
sockets. The RST A/RST B signals are derived from the R
pin. When a card is selected, its RST pin follows R
a card is deselected, the RST A/RST B pin for that channel
holds the current value on R
w w w . D a t a S h e e t 4 U . c o m
U
U
U
IN
.
IN
. When
IN
CLK A/CLK B: Card Socket. The CLK A/CLK B pins should
be connected to the CLK pins of the respective smart card
sockets. The CLK A/CLK B signals can be derived from
either the SYNC input or the ASYNC input depending on
which type of card is being accessed. The card type is
selected via the serial port (see Tables 1 and 3).
V
connected to the V
sockets. The activation of a V
the serial port (see Tables 1 and 2) and can be set to 0V,
1.8V, 3V or 5V. The voltage levels of the two card sockets
are controlled independently for maximum flexibility.
FAULT: Output. The FAULT pin can be used as an interrupt
to a microcontroller to indicate when a fault has occurred.
It is an open drain output, which is logically equivalent to
D4 + D5 + D12 + D13. (See Table 1)
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.
If external supply monitoring is not required, the UNDERV
pin should be connected to either SV
CCA
, V
CCB
: Card Socket. The V
CC
pins of the respective smart card
CCA
CCA
/V
CCB
/V
BATT
CCB
pin is controlled by
LTC1955
pins should be
or DV
CC
sn1955 1955fs
.
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