LTC1755

Smart Card Interface

October 1999

FEATURES

DESCRIPTIO

Fully ISO 7816-3 and EMV Compliant
(Including Auxiliary I/O Pins)

Buck-Boost Charge Pump Generates 3V or 5V

2.7V to 6.0V Input Voltage Range

Very Low Operating Current: 60

> 10kV ESD on All Smart Card Pins

Dynamic Pull-Ups Deliver Fast Signal Rise Times

Soft Start Limits Inrush Current at Turn On

5V Signal Level Translators

Shutdown Current: < 1

Short-Circuit and Overtemperature Protected

Alarm Output Indicates Fault Condition

Multiple Devices May Be Paralleled for
Multicard Applications

Available in 24-Pin SSOP Package

The LTC

1755 universal Smart Card interface is fully

compliant with ISO 7816-3 and EMV specifications. It
provides the smallest and simplest interface circuit be-
tween a host microcontroller and general purpose Smart
Cards.

An internal charge pump DC/DC converter delivers regu-
lated 3V or 5V to the Smart Card, while on-chip level
shifters allow connection to a low voltage controller. All
Smart Card contacts are rated for 10kV ESD, eliminating
the need for external ESD protection devices.

Input voltage may range from 2.7V to 6.0V, allowing direct
connection to a battery. Automatic DC/DC converter soft
start mitigates start-up problems that may result when the
input power is provided by another regulator. Multiple
LTC1755 devices may be paralleled and connected to a
single controller for multicard applications.

Battery life is maximized by 60

A operating current and

A shutdown current. The 24-pin SSOP package mini-

mizes PCB area for compact portable systems.

TYPICAL APPLICATIO

, LTC and LT are registered trademarks of Linear Technology Corporation.

APPLICATIO

Handheld Payment Terminals

Pay Telephones

ATMs

Key Chain Readers

Smart Card Readers

LTC1755

PRES

PWR

NC/NO

GND

AUX1

AUX2

I/O

RST

CLK

C2
10

AUX1

AUX2

I/O

RST

CLK

C1
0.68

GND

SMART CARD

1755 TA01

SMART CARD

PRESENT SWITCH

CONTROLLER

3.3V

5V/3V

CARD

ALARM

READY

AUX1IN

AUX2IN

DATA

RIN

CIN

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

Final Electrical Specifications

LTC1755

ABSOLUTE

AXI

RATINGS

PACKAGE/ORDER I FOR ATIO

ORDER PART

NUMBER

LTC1755EGN

JMAX

= 125

= 150

C/W

TOP VIEW

GN PACKAGE

24-LEAD NARROW PLASTIC SSOP

PRES

PWR

NC/NO

GND

AUX1

AUX2

I/O

RST

CLK

5V/3V

CARD

ALARM

READY

AUX1IN

AUX2IN

DATA

RIN

CIN

Consult factory for Industrial and Military grade parts.

ELECTRICAL CHARACTERISTICS

The

denotes specifications which apply over the full specified

temperature range, otherwise specificatons are at T

= 25

C. V

= 2.7V to 6V, DV

= 2V to 5.5V, unless otherwise noted.

(Note 1)

to GND ............................................... 0.3V to 6.5V

, V

to GND .................................... 0.3V to 5.5V

Digital Inputs to GND ................ 0.3V to (DV

+ 0.3V)

CLK, RST, I/O, AUX1,

AUX2 to GND .............................. 0.3V to V

+ 0.3V

Short-Circuit Duration ............................... Indefinite

Operating Temperature Range (Note 2) .. 40

C to 85

Storage Temperature Range ................ 65

C to 150

Lead Temperature (Soldering, 10 sec)................. 300

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Power Supply

Operating Voltage

2.7

Operating Voltage

2.0

5.5

VIN

Operating Current

ACTIVE State, I

VCC

= 0

100

DVCC

Operating Current

ACTIVE State, DV

= 3V

VIN

Shutdown Current

IDLE State, DV

= 0V, V

3.6V

IDLE State, DV

= 0V, 3.6V < V

IDLE State, DV

= 5.5V, V

Output Voltage

5V/3V = DV

4.75

5.00

5.25

5V/3V = 0V

2.80

3.00

3.20

VCC

Output Current

5V/3V = 0V

6.0V

5V/3V = DV

6.0V

5V/3V = 0V

2.7V

6.0V

5V/3V = DV

2.7V

6.0V

Turn-On Time

OUT

= 10

2.7

Discharge Time to 0.4V

VCC

= 0mA, V

= 5V, C

OUT

= 10

100

250

Controller Inputs/Outputs DATA, AUX1IN, AUX2IN, DV

= 3V

High Input Voltage Threshold (V

)

0.6 0.5 ˇ DV

Low Input Voltage Threshold (V

)

0.5 ˇ DV

0.3

High Level Output Voltage (V

)

Source Current = 20

0.7 ˇ DV

Low Level Output Voltage (V

)

Sink Current = 500

A (Note 3)

0.3

Output Rise/Fall Time

Loaded with 30pF

0.5

Input Current (I

)

CS = DV

LTC1755

ELECTRICAL CHARACTERISTICS

The

denotes specifications which apply over the full specified

temperature range, otherwise specificatons are at T

= 25

C. V

= 2.7V to 6V, DV

= 2V to 5.5V, unless otherwise noted.

Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.

Note 2: The LTC1755 is guaranteed to meet performance specifications
from 0

C to 70

C. Specifications over the 40

C to 85

C operating

temperature range are assured by design, characterization and correlation
with statistical process controls.

Note 3: The DATA, AUX1IN, AUX2IN, AUX1, AUX2 and I/O pull-down
drivers must sink up to 250

A sourced by the internal current sources.

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

RIN, CIN, PWR, CS, 5V/3V, NC/NO

High Input Voltage Threshold (V

)

0.7 ˇ DV

0.5 ˇ DV

Low Input Voltage Threshold (V

)

0.5 ˇ DV

0.2 ˇ DV

Input Current (I

)

READY, ALARM, CARD

Pull-Up Current (I

)

250

Low Level Output Voltage (V

)

Sink Current = 20

0.3

Smart Card Inputs/Outputs I/O, AUX1, AUX2, V

= 3V or 5V

High Input Voltage Threshold (V

)

IH(MAX)

0.6 ˇ V

0.5 ˇ V

Low Input Voltage Threshold (V

)

IL(MAX)

= 1mA

0.5 ˇ V

0.8

High Level Output Voltage (V

)

Source Current = 20

0.8 ˇ V

DATA, AUX1IN, AUX2IN = DV

Low Level Output Voltage (V

)

Sink Current = 1mA

0.3

DATA, AUX1IN, AUX2IN = 0V (Note 3)

Rise/ Fall Time

Loaded with 30pF

0.5

Short-Circuit Current

Shorted to V

3.5

CLK

High Level Output Voltage (V

)

Source Current = 100

0.5

Low Level Output Voltage (V

)

Sink Current = 200

0.3

CLK Rise/Fall Time

CLK Loaded with 30pF

CLK Frequency

CLK Loaded with 30pF

MHz

RST

High Level Output Voltage (V

)

Source Current = 200

0.8 ˇ V

Low Level Output Voltage (V

)

Sink Current = 200

0.3

RST Rise/Fall Time

Loaded with 30pF

0.5

PRES

High Input Voltage Threshold (V

)

0.7 ˇ DV

0.5 ˇ DV

Low Input Voltage Threshold (V

)

0.5 ˇ DV

0.2 ˇ DV

PRES Pull-Up Current

0.5

PRES Debounce Time

Proportional to the 0.68

F Charge Pump Capacitor

LTC1755

CTIO

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).

sets the logic reference level for the PRES pin.

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

) has reached its final value and communication with

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.

sets the logic reference level for the CS pin.

NC/NO (Pin 4): (Input) This pin controls the activation
level of the PRES pin. When it is high (DV

) the PRES pin

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

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.

sets the logic reference level for the NC/NO pin.

GND (Pin 5): Ground Reference for the IC. This pin should
be connected to a low impedance ground plane. Bypass
capacitors for V

and V

should be in close proximity to

the GND pin.

(Pin 6): Supply Voltage for the Charge Pump. May be

between 2.7V and 6V. A 10

F low ESR ceramic bypass ca-

pacitor is required on this pin for optimum performance.

(Pin 7): Regulated Smart Card Supply Voltage. This

pin should be connected to the Smart Card V

contact.

The 5V/3V pin determines the V

output voltage.

The V

pin is protected against short circuits by compar-

ing the actual output voltage with an internal reference
voltage. If V

is below its correct level (for as little as 5

the LTC1755 switches to the Alarm state (see the State
Diagram). The V

pin requires a 10

F charge storage

capacitor to ground. For optimum performance a low ESR
ceramic capacitor should be used.

During the Idle and Alarm states the V

pin is rapidly

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

LTC1755

CTIO

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

by current limiting to 5mA maximum.

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 11): (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

is stable.

Short-circuit protection is provided on the RST pin by
comparing RST with R

. If these signals differ for several

microseconds then the LTC1755 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 12): (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

is stable.

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

. If these signals differ for several mi-

croseconds then the LTC1755 switches to the Alarm state.
This fault checking is only performed after the V

pin has

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 13): (Input) Clock Input Pin from the Microcon-
troller. During the Active state this signal appears on the
CLK pin after being level-shifted and buffered.

sets the logic reference level for the C

pin.

RIN

(Pin 14): (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.

sets the logic reference level for the R

pin.

DATA (Pin 15): (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 or when CS is high
(see the State Diagram). It does not become active until the
READY signal goes low indicating that V

is stable.

AUX2IN (Pin 16): (Input/Output) Microcontroller Side
Auxiliary I/O pin. This pin is used for bidirectional auxiliary
data transfer between the microcontroller and the Smart
Card. It has the same characteristics as the DATA pin.

AUX1IN (Pin 17): (Input/Output) Microcontroller Side
Auxiliary I/O Pin. This pin is used for bidirectional auxiliary
data transfer between the microcontroller and the Smart
Card. It has the same characteristics as the DATA pin.

, C

(Pins 18, 19): Charge Pump Flying Capacitor

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.

LTC1755

CTIO

(Pin 20): Supply Voltage for the Microcontroller Side

Digital Input and Input/Output Pins (Typically 3V). If the
charge pump input pin (V

) is powered from the same

source as the microcontroller, then DV

should be con-

nected directly to V

. In this case only one (10

F) input

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

pin may be

between 2V and 5.5V.

The DV

pin is monitored for adequate voltage. If 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

). When the LTC1755 is

placed in the Active state the soft start feature slowly
ramps the V

voltage. A low on the READY pin indicates

that V

has reached its final value.

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.

CLK or RST invalid and overtemperature faults are de-
tected only after V

has reached its final value (as

indicated by the READY pin). V

underrange and card

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

to 5V. A valid low sets V

to 3V. The 5V/3V pin

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 LTC1755 must first be returned to

the Idle state by bringing the PWR pin high.

sets the logic reference level for the 5V/3V pin.

LTC1755

APPLICATIO

S I

FOR

ATIO

10kV ESD Protection

All Smart Card pins (CLK, RST, I/O, AUX1, AUX2, V

and

GND) can withstand over 10kV of human body model ESD
in situ. In order to ensure proper ESD protection, careful
board layout is required. The GND pin should be tied
directly to a ground plane. The V

capacitor should be

located very close to the V

pin and tied immediately to

the ground plane.

Capacitor Selection

The style and value of capacitors used with the LTC1755
determine several parameters such as output ripple volt-
age, charge pump strength, Smart Card switch debounce
time and V

discharge rate.

Due to the switching nature of a capacitive charge pump,
low equivalent series resistance (ESR) capacitors are
recommended for the capacitors at V

and V

. When-

ever the flying capacitor is switched to the V

charge

storage capacitor, considerable current flows. The prod-
uct of this high current and the ESR of the output capacitor
can generate substantial voltage spikes on the V

output.

These spikes may cause problems with the Smart Card or
may interfere with the regulation loop of the LTC1755.
Therefore, ceramic or tantalum capacitors are recom-
mended rather than higher ESR aluminum capacitors.
Between ceramic and tantalum, ceramic capacitors gener-
ally have the lowest ESR. Some manufacturers have
developed low ESR tantalum capacitors but they can be
expensive and may still have higher ESR than ceramic
types. Thus, while they cannot be avoided, ESR spikes will
typically be lowest when using ceramic capacitors.

For ceramic capacitors there are several different materi-
als available to choose from. The choice of ceramic
material is generally based on factors such as available
capacitance, case size, voltage rating, electrical perfor-
mance and cost. For example, capacitors made of Y5V
material have high packing density, which provides high
capacitance for a given case size. However, Y5V capaci-
tors tend to lose considerable capacitance over the 40

to 85

C temperature range. X7R ceramic capacitors are

more stable over temperature but don't provide the high
packing density. Therefore, large capacitance values are
generally not available in X7R ceramic.

The value and style of the flying capacitor are important
not only for the charge pump but also because they
provide the large debounce time for the Smart Card
detection channel. A 0.68

F X7R capacitor is a good

choice for the flying capacitor because it provides fairly
constant capacitance over temperature and its value is not
prohibitively large.

The charge storage capacitor on the V

pin determines

the ripple voltage magnitude and the discharge time of the
Smart Card voltage. To minimize ripple, generally, a large
value is needed. However, to meet the V

discharge rate

specification, the value should not exceed 20

F. A 10

capacitor can be used but the ripple magnitude will be
higher leading to worse apparent DC load regulation.
Typically a 15

F to 18

F Y5V ceramic capacitor is the best

choice for the V

charge storage capacitor. For best

performance, this capacitor should be connected as close
as possible to the V

and GND pins. Note that most of the

electrostatic discharge (ESD) current on the six Smart
Card pins is absorbed by this capacitor.

The bypass capacitor at V

is also important. Large dips

on the input supply due to ESR may cause problems with
the internal circuitry of the LTC1755. A good choice for the
input bypass capacitor is a 10

F Y5V style ceramic

Dynamic Pull-Up Current Sources

The current sources on the bidirectional pins (DATA,
AUX2IN, AUX1IN, I/O, AUX2 and AUX1) are dynamically
activated to achieve a fast rise time with a relatively small
static current (Figure 1). Once a bidirectional pin is relin-
quished, a small start-up current begins to charge the
node. An edge rate detector determines if the pin is
released by comparing its slew rate with an internal

Figure 1. Dynamic Pull-Up Current Sources

START

1755 F01

REF

BIDIRECTIONAL PIN

OR DV

LTC1755

APPLICATIO

S I

FOR

ATIO

Self-Start Mode

By connecting the CARD pin to the CS and PWR pins the
LTC1755 can be made to start up automatically when a
Smart Card is detected (Figure 2). In this mode, the READY
pin becomes an interrupt signal indicating to the micro-
controller that a Smart Card is present and that V

, the

charge pump voltage, is at its final value. The Smart Card
remains powered as long as it is detected by the PRES pin.
When the Smart Card is removed the LTC1755 will auto-
matically be deactivated by the fault detection circuitry.

reference value. If a valid transition is detected, a large
pull-up current enhances the edge rate on the node. The
higher slew rate corroborates the decision to charge the
node thereby effecting a dynamic form of hysteresis. Once
the node has reached the power supply voltage the internal
comparator requires several hundred nanoseconds to
reset. Pulling down on the pin before the reset delay
expires will result in a momentary contention and a higher
current flow. Therefore, the comparator delay sets the
upper limit on the maximum data rate of the bidirectional
channels to about 500kHz.

Synchronous Card Applications

For multicard synchronous applications the LTC1755 has
separate control pins for the CLK and I/O lines. The PWR
pin enables the charge pump as well as the CLK and RST
channels while the CS pin enables only the bidirectional
channels. In multicard applications the CS pin can be used
to disable communication to one card while leaving its
clock line running. With this option the same I/O pin can
be used for multiple cards. For simpler applications the CS
and PWR pins can be connected together to enable or
disable the entire chip.

Low Power Operation

The LTC1755 is inherently a low power device. When there
is no Smart Card present the supply current is less than
10

A. If DV

is 0V the current drops below 1

A. When a

Smart Card is present the LTC1755 operates with a quies-
cent current of only 60

A, thus the majority of power is

consumed by charge pump losses and the card itself. If the
card can be made to consume less power during idle times
a significant power savings will be achieved. Whenever
possible Clock Stop Mode should be used (or alternatively
a very low "idling" clock speed). Furthermore, in the Active
state, the bidirectional pins should all be relinquished
whenever possible since there is some static current flow
when a bidirectional pin is pulled down.

Overtemperature Fault Protection

An overtemperature circuit disables the chip and activates
the ALARM pin if the IC's junction temperature exceeds
150

Figure 2. Self-Start Mode

CARD

PWR

1755 F02

Deactivation Sequence

For maximum flexibility the Smart Card can be deactivated
either manually or automatically. In manual mode the
deactivation is controlled by explicitly manipulating the
LTC1755 input and control pins (DATA, AUX1IN, AUX2IN,
RIN and CIN followed by PWR and CS). In automatic mode
the PWR pin is used to perform the built-in deactivation
sequence. Once PWR is brought high the built-in
deactivation sequence occurs as follows:

1755 F03

RST

CLK

I/O

AUX2
AUX1

RST = R

DEACTIVATION DIRECTIVE

CLK = C

I/O = DATA

Figure 3. Deactivation Sequence

In the event of a fault, the LTC1755 automatically
implements the built-in deactivation sequence.

LTC1755

APPLICATIO

S I

FOR

ATIO

Figure 4. LTC1755 State Diagram

DEACTIVATION

NO
FAULT

FAULT

1755 F04

POWER OFF

IDLE

DEACTIVATION

ALARM

ACTIVE

FAULT

TIMEOUT

PWR = DV

PWR = 0V

PRES

NC/NO

FAULT > 5

PRES

NC/NO

ALARM/DEACTIVATION

Same as Idle/Deactivation except:

ALARM = L

The only possible next state is Idle/Deactivation which is
achieved by disabling the LTC1755 via the PWR pin
(i.e., PWR = DV

The alarm indication can be cleared by rapidly cycling the
PWR pin. However, a new activation cycle will not begin
until V

is or has dropped below approximately 1V.

ACTIVE

= 3V or 5V (as determined by the 5V/3V pin)

RST = R

, CLK = C

I/O, AUX2, AUX1, DATA, AUX2IN, AUX1IN = Ready for
data (after READY becomes low)

CARD = PRES

NC/NO

ALARM = H

FAULT TIMEOUT

Same as Active except:

The duration of a fault is being measured. If the fault
duration exceeds 5

s then the Alarm/Deactivation state

follows. If the fault duration is less than 5

s, then the

device is returned to the Active state.

State Definitions

IDLE/DEACTIVATION

, RST, CLK, I/O AUX2, AUX1 = L

READY, ALARM, DATA, AUX2IN, AUX1IN = Z

CARD = PRES

NC/NO

Once the LTC1755 enters the Idle/Deactivation state the
deactivation sequence begins. The deactivation sequence
will continue until V

is discharged to approximately 1V.

An activation command (PWR = 0V) will only be acknowl-
edged once this occurs.

LTC1755

LINEAR TECHNOLOGY CORPORATION 1999

1755i LT/TP 1099 4K ˇ PRINTED IN USA

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900

FAX: (408) 434-0507

www.linear-tech.com

TYPICAL APPLICATIO

PART NUMBER

DESCRIPTION

COMMENTS

LTC1514/LTC1515

Micropower Step-Up/Step-Down Inductorless

Regulated Output Up to 50mA, V

from 2V to 10V, SO-8 Package

DC/DC Converters

LTC1516

Micropower Regulated 5V Charge Pump

5V/50mA Output from 2V to 5V Input, S0-8 Package

LTC1555/LTC1556

SIM Power Supply and Level Translator

Step-Up/Step-Down Charge Pump + SIM Level Translators, >10kV ESD

LTC1754-5

5V Charge Pump with Shutdown in SOT-23

from 2.7V to 5.5V, 50mA Output with V

LTC1986

3V/5V SIM Power Supply in SOT-23

from 2.6V to 4.4V, 3V/5V Output at 10mA

RELATED PARTS

C2
10

C1
0.68

LTC1755

PRES

PWR

NC/NO

GND

AUX1

AUX2

I/O

RST

CLK

5V/3V

CARD

ALARM

READY

AUX1IN

AUX2IN

DATA

C5
10

C4
0.68

SMART CARD

PRESENT SWITCH

SMART CARD

PRESENT SWITCH

LTC1755

PRES

PWR

NC/NO

GND

AUX1

AUX2

I/O

RST

CLK

5V/3V

CARD

ALARM

READY

AUX1IN

AUX2IN

DATA

CONTROLLER

1755 TA02

AUX1

AUX2

I/O

RST

CLK

GND

SMART CARD

AUX1

AUX2

I/O

RST

CLK

GND

SMART CARD

Paralleling Devices for Multicard Applications

Part Number LTC1755