LTC1755 LINER [Linear Technology], LTC1755 Datasheet - Page 6

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

PIN
LTC1755
DV
Digital Input and Input/Output Pins (Typically 3V). If the
charge pump input pin (V
source as the microcontroller, then DV
nected directly to V
bypass capacitor is needed for the LTC1755. If the DV
pin is powered separately then it should be bypassed
separately with a 0.1 F capacitor. The DV
between 2V and 5.5V.
The DV
drops below approximately 1.5V the LTC1755 automati-
cally enters the Idle state.
READY (Pin 21): (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. This permits wired-
OR connections of multiple LTC1755s to a single micro-
controller.
ALARM (Pin 22): (Output) A low on this pin indicates that
a fault has occurred and that the LTC1755 is in the Alarm
state (see the State Diagram). Possible faults include V
underrange for at least 5 s, overtemperature shutdown,
CLK or RST invalid output levels, and card removal during
the Active state.
6
U
CC
(Pin 20): Supply Voltage for the Microcontroller Side
CC
FUNCTIONS
CC
has reached its final value.
pin is monitored for adequate voltage. If DV
U
CC
voltage. A low on the READY pin indicates
IN
U
. In this case only one (10 F) input
IN
) is powered from the same
CC
). When the LTC1755 is
CC
should be con-
CC
pin may be
CC
CC
CC
CLK or RST invalid and overtemperature faults are de-
tected only after V
indicated by the READY pin). V
removal during Active faults are detected at any time
during the Active period (i.e., once PWR = 0V).
The ALARM pin is configured as an open-drain pull-down
with a weak pull-up current source. This permits wired-
OR connections of multiple LTC1755s to a single micro-
controller.
CARD (Pin 23): (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 for logic-OR connections. 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. The PRES pin, in conjunction with the NC/NO pin,
determines if a card is present.
5V/3V (Pin 24): (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.
DV
CC
sets the logic reference level for the 5V/3V pin.
CC
to 5V. A valid low sets V
CC
the LTC1755 must first be returned to
CC
has reached its final value (as
CC
CC
underrange and card
to 3V. The 5V/3V pin
CC
)