LTC1755 LINER [Linear Technology], LTC1755 Datasheet - Page 4

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

PIN
LTC1755
PRES (Pin 1): (Input) Connects to the Smart Card acceptor’s
PRESENT indicator switch to detect if a card is inserted.
This pin has a pull-up current source so that a grounded
switch can be detected with no external components. The
pull-up current source is nonlinear, delivering higher
current when the PRES pin is above 1V but very little
current below 1V. This helps resist false card indications
due to leakage current. The activation state of the PRES pin
can be set by the NC/NO pin so that both normally open
(NO) and normally closed (NC) switches are easily recog-
nized (see NC/NO pin description).
DV
PWR (Pin 2): (Input) A low on the PWR pin places the
LTC1755 in the ACTIVE state enabling the charge pump.
The READY pin indicates when the card supply voltage
(V
the Smart Card is possible. The reset and clock channels
are enabled after READY goes low. The three I/O channels
are also enabled only after READY goes low, however they
may be disabled separately via the CS pin.
The falling edge of PWR latches the state of the 5V/3V pin.
After PWR is low, changes on the 5V/3V pin are ignored.
CS (Pin 3): (Input) The CS pin enables the three bidirec-
tional I/O channels of the LTC1755. When the I/O channels
are disabled the Smart Card pins (I/O, AUX1, AUX2) are
forced to logic one and the controller pins (DATA, AUX2IN,
AUX1IN) are high impedance. CS can be brought low
along with PWR when the device is first enabled, however
communication with the Smart Card is inhibited until V
reaches its final value as indicated by a low on the READY
pin.
DV
NC/NO (Pin 4): (Input) This pin controls the activation
level of the PRES pin. When it is high (DV
is active high. When it is low (GND) the PRES pin is active
low. In either case the presence of a Smart Card is
indicated by a low on the CARD output. When a ground
side normally open (NO) switch is used the NC/NO pin
should be grounded. When a ground side normally closed
(NC) switch is used the NC/NO pin should be connected to
DV
4
CC
U
CC
CC
CC
) has reached its final value and communication with
.
sets the logic reference level for the PRES pin.
sets the logic reference level for the CS pin.
FUNCTIONS
U
U
CC
) the PRES pin
CC
Note: If a normally closed switch is used, a small current
(several microamperes) will flow through the switch when-
ever a Smart Card is not present. For ultralow power
consumption in shutdown, a normally open switch is
optimum.
DV
GND (Pin 5): Ground Reference for the IC. This pin should
be connected to a low impedance ground plane. Bypass
capacitors for V
the GND pin.
V
between 2.7V and 6V. A 10 F low ESR ceramic bypass ca-
pacitor is required on this pin for optimum performance.
V
pin should be connected to the Smart Card V
The 5V/3V pin determines the V
The V
ing the actual output voltage with an internal reference
voltage. If V
the LTC1755 switches to the Alarm state (see the State
Diagram). The V
capacitor to ground. For optimum performance a low ESR
ceramic capacitor should be used.
During the Idle and Alarm states the V
discharged to ground to comply with the deactivation
requirements of the EMV and ISO-7816 specifications.
AUX1 (Pin 8): (Input/Output) Smart Card Side Auxiliary
I/O Pin. This pin is used for auxiliary bidirectional data
transfer between the microcontroller and the Smart Card.
It has the same characteristics as the I/O pin.
AUX2 (Pin 9): (Input/Output) Smart Card Side Auxiliary
I/O Pin. This pin is used for auxiliary bidirectional data
transfer between the microcontroller and the Smart Card.
It has the same characteristics as the I/O pin.
I/O (Pin 10): (Input/Output) Smart Card Side Data I/O Pin.
This pin is used for bidirectional data transfer between the
microcontroller and the Smart Card. It should be connected
to the Smart Card I/O contact. The Smart Card I/O pin must
be able to sink up to 250 A when driving the I/O pin low
IN
CC
CC
(Pin 6): Supply Voltage for the Charge Pump. May be
(Pin 7): Regulated Smart Card Supply Voltage. This
CC
sets the logic reference level for the NC/NO pin.
pin is protected against short circuits by compar-
CC
is below its correct level (for as little as 5 s)
IN
CC
and V
pin requires a 10 F charge storage
CC
should be in close proximity to
CC
output voltage.
CC
pin is rapidly
CC
contact.