5

LTC1756

Short-circuit protection is provided on the CLK pin by com-

croseconds then the LTC1756 switches to the Alarm state.

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

µA 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

Terminals. Optimum values for the flying capacitor range

from 0.68

µF to 1µF. Best performance is achieved with a

low ESR X7R ceramic capacitor.

READY (Pin 14): (Output) Readiness Indicator of the

placed in the Active state the soft start feature slowly

The READY pin is configured as an open-drain pull-down

with a weak pull-up current source.

The READY pin also indicates if the LTC1756 is in Alarm

for at least 5

µs, overtemperature shutdown, CLK or RST

invalid output levels and card removal during Active

state. CLK or RST invalid and overtemperature faults are

underrange and card removal during Active faults are

detected at any time during the Active period (i.e., once

PWR = 0V).

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.

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

µs of card removal.

of the DC/DC converter during the Active state. A valid high

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 Idle state by bringing the PWR pin high.