LTC1756 Linear Technology, LTC1756 Datasheet - Page 4

• Manufacturer Part Number: LTC1756
• Description: Smart Card Interface
• Manufacturer: Linear Technology

PIN
LTC1756
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 normally
open 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.
PWR (Pin 2): (Input) A low on the PWR pin places the
LTC1756 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 I/O channel is also
enabled only after READY goes low.
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.
GND (Pin 3): Ground Reference for the IC. This pin should
be connected to a low impedance ground plane. Bypass
capacitors for V
the GND pin.
V
A 10 F low ESR ceramic bypass capacitor 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 LTC1756 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.
I/O (Pin 6): (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
4
IN
CC
CC
U
(Pin 4): Supply Voltage. May be between 2.7V and 5.5V.
(Pin 5): Regulated Smart Card Supply Voltage. This
) has reached its final value and communication with
CC
FUNCTIONS
pin is protected against short circuits by compar-
U
CC
is below its correct level (for as little as 5 s)
IN
CC
and V
pin requires a 10 F charge storage
U
CC
should be in close proximity to
CC
output voltage.
CC
pin is rapidly
CC
contact.
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
due to the pull-up current source. The I/O pin becomes a
low impedance to ground during the Idle state. It does not
become active until READY goes low indicating that V
stable.
Once READY is low, the I/O pin is protected against short
circuits to V
The DATA-I/O channel is bidirectional for half-duplex
transmissions. Its idle state is H-H. Once an L is detected
on one side of the channel the direction of transmission is
established. Specifically, the side which received an L first
is now the input, and the opposite side is the output.
Transmission from the output side back to the input side
is inhibited, thereby preventing a latch condition. Once the
input side releases its L, both sides return to H, and the
channel is now ready for a new L to be transmitted in either
direction. If an L is forced externally on the output side, and
it persists until after the L on the input side is released, this
illegal input will not be transmitted to the input side
because the transmission direction will not have changed.
The direction of transmission can only be established from
the idle (H-H) state and is determined by the first receipt
of an L on either side.
RST (Pin 7): (Output) Level-Shifted Reset Output Pin. This
pin should be connected to the Smart Card RST contact.
The RST pin becomes a low impedance to ground during
the Idle state (see the State Diagram). The reset channel
does not become active until the READY signal goes low
indicating that V
Short-circuit protection is provided on the RST pin by
comparing RST with R
microseconds then the LTC1756 switches to the Alarm
state. This fault checking is only performed after the V
has reached its final value (as indicated by the READY pin).
CLK (Pin 8): (Output) Level-Shifted Clock Output Pin. This
pin should be connected to the Smart Card CLK contact.
The CLK pin becomes a low impedance to ground during
the Idle state (see the State Diagram). The clock channel
does not become active until the READY signal goes low
indicating that V
CC
by current limiting to 5mA maximum.
CC
CC
is stable.
is stable.
IN
. If these signals differ for several
CC
CC
pin
is