LTC1755 LINER [Linear Technology], LTC1755 Datasheet - Page 9

• Manufacturer Part Number: LTC1755
• Description: Smart Card Interface
• Manufacturer: LINER [Linear Technology]

APPLICATIONS
reference value. If a valid transition is detected, a large
pull-up current enhances the edge rate on the node. The
higher slew rate corroborates the decision to charge the
node thereby effecting a dynamic form of hysteresis. Once
the node has reached the power supply voltage the internal
comparator requires several hundred nanoseconds to
reset. Pulling down on the pin before the reset delay
expires will result in a momentary contention and a higher
current flow. Therefore, the comparator delay sets the
upper limit on the maximum data rate of the bidirectional
channels to about 500kHz.
Synchronous Card Applications
For multicard synchronous applications the LTC1755 has
separate control pins for the CLK and I/O lines. The PWR
pin enables the charge pump as well as the CLK and RST
channels while the CS pin enables only the bidirectional
channels. In multicard applications the CS pin can be used
to disable communication to one card while leaving its
clock line running. With this option the same I/O pin can
be used for multiple cards. For simpler applications the CS
and PWR pins can be connected together to enable or
disable the entire chip.
Low Power Operation
The LTC1755 is inherently a low power device. When there
is no Smart Card present the supply current is less than
10 A. If DV
Smart Card is present the LTC1755 operates with a quies-
cent current of only 60 A, thus the majority of power is
consumed by charge pump losses and the card itself. If the
card can be made to consume less power during idle times
a significant power savings will be achieved. Whenever
possible Clock Stop Mode should be used (or alternatively
a very low “idling” clock speed). Furthermore, in the Active
state, the bidirectional pins should all be relinquished
whenever possible since there is some static current flow
when a bidirectional pin is pulled down.
Overtemperature Fault Protection
An overtemperature circuit disables the chip and activates
the ALARM pin if the IC’s junction temperature exceeds
150 C.
CC
is 0V the current drops below 1 A. When a
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INFORMATION
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Self-Start Mode
By connecting the CARD pin to the CS and PWR pins the
LTC1755 can be made to start up automatically when a
Smart Card is detected (Figure 2). In this mode, the READY
pin becomes an interrupt signal indicating to the micro-
controller that a Smart Card is present and that V
charge pump voltage, is at its final value. The Smart Card
remains powered as long as it is detected by the PRES pin.
When the Smart Card is removed the LTC1755 will auto-
matically be deactivated by the fault detection circuitry.
Deactivation Sequence
For maximum flexibility the Smart Card can be deactivated
either manually or automatically. In manual mode the
deactivation is controlled by explicitly manipulating the
LTC1755 input and control pins (DATA, AUX1IN, AUX2IN,
RIN and CIN followed by PWR and CS). In automatic mode
the PWR pin is used to perform the built-in deactivation
sequence. Once PWR is brought high the built-in
deactivation sequence occurs as follows:
In the event of a fault, the LTC1755 automatically
implements the built-in deactivation sequence.
AUX2
AUX1
RST
CLK
V
I/O
CC
I/O = DATA
RST = R
CLK = C
Figure 3. Deactivation Sequence
DEACTIVATION DIRECTIVE
Figure 2. Self-Start Mode
IN
IN
CARD
PWR
CS
1755 F02
LTC1755
1755 F03
CC
, the
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