LTC1756 Linear Technology, LTC1756 Datasheet - Page 5

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

Short-circuit protection is provided on the CLK pin by com-
paring CLK with C
croseconds then the LTC1756 switches to the Alarm state.
This fault checking is only performed after the V
reached its final value (as indicated by the READY pin).
The clock channel is optimized for signal integrity in order
to meet the stringent duty cycle requirements of the EMV
specification. Therefore, to reduce power in low power
applications, clock stop mode is recommended when data
is not being exchanged.
CIN (Pin 9): (Input) Clock Input Pin from the Microcontrol-
ler. During the Active state this signal appears on the CLK
pin after being level-shifted and buffered.
RIN (Pin 10): (Input) Reset Input Pin from the Microcon-
troller. During the Active state this signal appears on the
RST pin after being level-shifted and buffered.
DATA (Pin 11): (Input/Output) Microcontroller Side Data
I/O Pin. This pin is used for bidirectional data transfer
between the microcontroller and the Smart Card. The
microcontroller data pin must be open drain and must be
able to sink up to 250 A when driving the DATA pin low
due to the pull-up current source. The DATA pin becomes
high impedance during the Idle state (see the State Dia-
gram). It does not become active until the READY signal
goes low indicating that V
C
Terminals. Optimum values for the flying capacitor range
from 0.68 F to 1 F. Best performance is achieved with a
low ESR X7R ceramic capacitor.
READY (Pin 14): (Output) Readiness Indicator of the
Smart Card Supply Voltage (V
placed in the Active state the soft start feature slowly
ramps the V
that V
The READY pin is configured as an open-drain pull-down
with a weak pull-up current source.
PIN
+
, C
U
CC
–
FUNCTIONS
(Pins 12, 13): Charge Pump Flying Capacitor
has reached its final value.
U
CC
voltage. A low on the READY pin indicates
IN
. If these signals differ for several mi-
U
CC
is stable.
CC
). When the LTC1756 is
CC
pin has
The READY pin also indicates if the LTC1756 is in Alarm
mode. The LTC1756 detects faults such as V
for at least 5 s, overtemperature shutdown, CLK or RST
invalid output levels and card removal during Active
state. CLK or RST invalid and overtemperature faults are
detected only after V
underrange and card removal during Active faults are
detected at any time during the Active period (i.e., once
PWR = 0V).
If the LTC1756 has been activated normally and V
card voltage, has reached its final value then READY will
go low indicating normal operation. If, following this, a
fault occurs and the LTC1756 enters the Alarm state, the
READY pin will return high.
In the event that a fault precedes the activation of V
such as a direct short circuit from V
LTC1756 will attempt to operate until the fault is detected
and then automatically shut down and enter the Alarm
state. In this case the READY pin will never go low after the
command to start the smart card is given (i.e., PWR = 0V).
If the LTC1756 enters the Alarm state it can only be
cleared by returning the PWR pin high.
CARD (Pin 15): (Output) Level-Shifted and Debounced
PRES Signal from the Smart Card Acceptor Switch. When
a valid card indication appears, this pin communicates the
presence of the Smart Card to the microcontroller. The
CARD pin has an open-drain active pull-down with a weak
pull-up current source. The debounce circuit ensures that
a card has been present for a continuous period of at least
40ms before asserting CARD low. The CARD pin returns
high within 50 s of card removal.
5V/3V (Pin 16): (Input) Controls the output voltage (V
of the DC/DC converter during the Active state. A valid high
sets V
is latched on the falling edge of the PWR pin. When PWR
is low, changes on the 5V/3V pin are ignored. To change
the voltage on V
the Idle state by bringing the PWR pin high.
CC
to 5V. A valid low sets V
CC
the LTC1756 must first be returned to
CC
has reached its final value. V
CC
to 3V. The 5V/3V pin
CC
LTC1756
CC
to GND, the
underrange
CC
, the
5
CC
CC
CC
)
,