LTC1955EUH Linear Technology, LTC1955EUH Datasheet - Page 9

• 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

OPERATION
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
loaded fi rst and D0 last. At the same time, the command
bits are being shifted into the D
are being shifted out of the D
are presented to D
all bits have been clocked into the shift register, the com-
mand data is loaded into the command latch by bringing
LD low. At this time, the command latch is updated and
the LTC1955 will begin to act on the new command set.
When LD is low, the shift register is transparent to the
status data of the two smart card channels. The status
data is latched into the shift register on the rising edge of
LD. SCLK should be held in the high state when idle and
should only be clocked when LD is high. Likewise, LD
should only be brought high when SCLK is high. Figure 1
shows the operation of the serial port.
Multiple LTC1955s may be daisychained together by
connecting the D
another. Figure 6 shows an example of multiple LTC1955s
daisychained together.
The maximum clock rate for the serial port is 10MHz.
The serial port controls the following parameters of each
smart card socket:
• Selection/deselection of a smart card
• V
• Clock mode of each card (synchronous or asynchronous)
IN
CC
input is loaded on the rising edge of SCLK. D15 is
voltage level of each card (5V/3V/1.8V/0V)
OUT
OUT
SCLK
D
pin of one LTC1955 to the D
OUT
D
LD
IN
on the rising edge of SCLK. Once
t
LC
X
OUT
D15
t
DS
IN
output. The status bits
D15
input, the status bits
t
DH
D14
D14
Figure 1. Serial Port Timing Diagram
t
DD
D13
IN
pin of
D2
• Operating mode of asynchronous cards (clock stop
• Selection of the I/O, C4 or C8 pins for card socket A
The serial port provides the following status data:
• It indicates the presence or absence of the smart
• It indicates the readiness of the smart card V
• It indicates fault status. In the event of an electrical or
Table 1 illustrates the command inputs and status outputs
associated with each bit of the serial data word.
Three voltage options are available from the LTC1955: 5V,
3V and 1.8V. Bits D0, D1 (card B) and D8, D9 (card A)
determine which voltage is selected. Setting both control
bits of a channel to 0 deactivates that channel and sets
the smart card supply voltage to 0V. If both channels are
deactivated, the LTC1955 is in shutdown. Table 2 shows
the operation of the supply control bits.
The CLK A/CLK B pins to the smart cards can be pro-
grammed for various modes. Both synchronous and asyn-
chronous cards are supported. There are several options
available with asynchronous cards. Table 3 shows how
all clock options are obtained using bits D5–D7 (card B)
and D13–D15 (card A). The default state of the LTC1955
on power up is synchronous mode.
t
H
high, low, ÷1, ÷2, ÷4 or ÷8)
cards.
Communication with a smart card is disabled until its
power supply voltage has reached the fi nal value.
ATR fault, the fault is reported. For electrical faults, the
LTC1955 will automatically deactivate the smart card.
D1
D1
D0
t
L
D0
D15 FROM
INPUT
t
CL
X
t
LW
1955 F01
D15
LTC1955
CC
supplies.
1955fb
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