1
LTC1756
Smart Card Interface
February 2000
FEATURES
DESCRIPTIO
N
U
s
Fully ISO 7816-3 and EMV Compliant
s
Buck-Boost Charge Pump Generates 3V or 5V
s
2.7V to 5.5V Input Voltage Range
s
3V
5V Signal Level Translator
s
> 10kV ESD on All Smart Card Pins
s
Dynamic Pull-Ups Deliver Fast Signal Rise Times
s
Soft Start Limits Inrush Current at Turn On
s
Very Low Operating Current: 75
A
s
Shutdown Current: < 2.5
A
s
Short-Circuit and Overtemperature Protected
s
Available in 16-Pin SSOP Package
The LTC
1756 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 an on-chip level
shifter allows a 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 5.5V, 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.
Battery life is maximized by 75
A operating current and
2
A shutdown current. The 16-pin SSOP package mini-
mizes PCB area for compact portable systems.
TYPICAL APPLICATIO
N
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, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO
N
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s
Handheld Payment Terminals
s
Pay Telephones
s
ATMs
s
Key Chain Readers
s
Smart Card Readers
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
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
LTC1756
PRES
PWR
GND
V
IN
V
CC
I/O
RST
CLK
C2
10
F
N.O.
C3
10
F
V
CC
I/O
RST
CLK
C1
0.68
F
GND
SMART CARD
1756 TA01
SMART CARD
PRESENT SWITCH
CONTROLLER
3.3V
5V/3V
CARD
READY
C
C
+
DATA
RIN
CIN
2
LTC1756
ABSOLUTE
M
AXI
M
U
M
RATINGS
W
W
W
U
W
U
U
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
LTC1756EGN
T
JMAX
= 125
C,
JA
= 135
C/W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full specified
temperature range, otherwise specificatons are at T
A
= 25
C. V
IN
= 2.7V to 5.5V, unless otherwise noted.
(Note 1)
V
IN
to GND ............................................... 0.3V to 6.0V
V
CC
to GND .............................................. 0.3V to 5.5V
Digital Inputs to GND ..................... 0.3V to V
IN
+ 0.3V
CLK, RST, I/O to GND ..................... 0.3V to V
CC
+ 0.3V
V
CC
Short-Circuit Duration ............................... Indefinite
Operating Temperature Range (Note 2) .. 40
C to 85
C
Storage Temperature Range ................ 65
C to 150
C
Lead Temperature (Soldering, 10 sec)................. 300
C
GN PACKAGE
16-LEAD NARROW PLASTIC SSOP
1
2
3
4
5
6
7
8
TOP VIEW
16
15
14
13
12
11
10
9
PRES
PWR
GND
V
IN
V
CC
I/O
RST
CLK
5V/3V
CARD
READY
C
C
+
DATA
RIN
CIN
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Power Supply
V
IN
Operating Voltage
q
2.7
5.5
V
I
VIN
Operating Current
ACTIVE State, I
VCC
= 0
q
75
150
A
I
VIN
Shutdown Current
IDLE State, V
IN
3.6V
q
2.5
A
IDLE State, 3.6V
V
IN
5.5V
q
10
A
V
CC
Output Voltage
5V/3V = V
IN
q
4.75
5.00
5.25
V
5V/3V = 0V
q
2.80
3.00
3.20
V
I
VCC
Output Current
5V/3V = 0V
3V
V
IN
5.5V
q
55
mA
5V/3V = V
IN
3V
V
IN
5.5V
q
65
mA
5V/3V = 0V
2.7V
V
IN
5.5V
q
55
mA
5V/3V = V
IN
2.7V
V
IN
5.5V
q
40
mA
V
CC
Turn-On Time
C
OUT
= 10
F,
PWR to
READY
q
2.7
12
ms
V
CC
Discharge Time to 0.4V
I
VCC
= 0mA, V
CC
= 5V, C
OUT
= 10
F
q
100
250
s
Controller Input/Output DATA
High Input Voltage Threshold (V
IH
)
q
V
IN
0.6
0.5 V
IN
V
Low Input Voltage Threshold (V
IL
)
q
0.5 V
IN
0.3
V
High Level Output Voltage (V
OH
)
Source Current = 20
A
q
0.7 V
IN
V
Low Level Output Voltage (V
OL
)
Sink Current = 500
A (Note 3)
q
0.3
V
Output Rise/Fall Time
Loaded with 30pF, 10% to 90%
q
0.5
s
Input Current (I
IH
/I
IL
)
PWR = V
IN
q
1
1
A
3
LTC1756
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full specified
temperature range, otherwise specificatons are at T
A
= 25
C. V
IN
= 2.7V 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 LTC1756 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 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, 5V/3V
High Input Voltage Threshold (V
IH
)
q
0.7 V
IN
0.5 V
IN
V
Low Input Voltage Threshold (V
IL
)
q
0.5 V
IN
0.2 V
IN
V
Input Current (I
IH
/I
IL
)
q
1
1
A
READY, CARD
Pull-Up Current (I
OH
)
q
250
nA
Low Level Output Voltage (V
OL
)
Sink Current = 20
A
q
0.3
V
Smart Card Input/Output I/O, V
CC
= 3V or 5V
High Input Voltage Threshold (V
IH
)
I
IH(MAX)
=
20
A
q
0.6 V
CC
0.5 V
CC
V
Low Input Voltage Threshold (V
IL
)
I
IL(MAX)
= 1mA
q
0.5 V
CC
0.8
V
High Level Output Voltage (V
OH
)
Source Current = 20
A, DATA = V
IN
q
0.8 V
CC
V
Low Level Output Voltage (V
OL
)
Sink Current = 1mA, DATA = 0V (Note 3)
q
0.3
V
Rise/ Fall Time
Loaded with 30pF, 10% to 90%
q
0.5
s
Short-Circuit Current
Shorted to V
CC
q
3.5
5
mA
CLK
High Level Output Voltage (V
OH
)
Source Current = 100
A
q
V
CC
0.5
V
Low Level Output Voltage (V
OL
)
Sink Current = 200
A
q
0.3
V
CLK Rise/Fall Time
CLK Loaded with 30pF
q
16
ns
CLK Frequency
CLK Loaded with 30pF
q
5
MHz
RST
High Level Output Voltage (V
OH
)
Source Current = 200
A
q
0.8 V
CC
V
Low Level Output Voltage (V
OL
)
Sink Current = 200
A
q
0.3
V
RST Rise/Fall Time
Loaded with 30pF
q
0.5
s
PRES
High Input Voltage Threshold (V
IH
)
q
0.7 V
IN
0.5 V
IN
V
Low Input Voltage Threshold (V
IL
)
q
0.5 V
IN
0.2 V
IN
V
PRES Pull-Up Current
V
PRES
= 0V
q
0.5
1
A
PRES Debounce Time
Proportional to the 0.68
F Charge Pump Capacitor
q
40
80
ms
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LTC1756
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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
CC
) 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 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
IN
and V
CC
should be in close proximity to
the GND pin.
V
IN
(Pin 4): Supply Voltage. May be between 2.7V and 5.5V.
A 10
F low ESR ceramic bypass capacitor is required on
this pin for optimum performance.
V
CC
(Pin 5): Regulated Smart Card Supply Voltage. This
pin should be connected to the Smart Card V
CC
contact.
The 5V/3V pin determines the V
CC
output voltage.
The V
CC
pin is protected against short circuits by compar-
ing the actual output voltage with an internal reference
voltage. If V
CC
is below its correct level (for as little as 5
s)
the LTC1756 switches to the Alarm state (see the State
Diagram). The V
CC
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
CC
pin is rapidly
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
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
CC
is
stable.
Once READY is low, the I/O pin is protected against short
circuits to V
CC
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 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
CC
is stable.
Short-circuit protection is provided on the RST pin by
comparing RST with R
IN
. If these signals differ for several
microseconds then the LTC1756 switches to the Alarm
state. This fault checking is only performed after the V
CC
pin
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
is stable.
5
LTC1756
PI
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Short-circuit protection is provided on the CLK pin by com-
paring CLK with C
IN
. If these signals differ for several mi-
croseconds then the LTC1756 switches to the Alarm state.
This fault checking is only performed after the V
CC
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 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
CC
is stable.
C
+
, C
(Pins 12, 13): 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.
READY (Pin 14): (Output) Readiness Indicator of the
Smart Card Supply Voltage (V
CC
). When the LTC1756 is
placed in the Active state the soft start feature slowly
ramps the V
CC
voltage. A low on the READY pin indicates
that V
CC
has reached its final value.
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
mode. The LTC1756 detects faults such as V
CC
underrange
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
CC
has reached its final value. V
CC
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
CC
, the
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
CC
,
such as a direct short circuit from V
CC
to GND, the
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
CC
)
of the DC/DC converter during the Active state. A valid high
sets V
CC
to 5V. A valid low sets V
CC
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
CC
the LTC1756 must first be returned to
the Idle state by bringing the PWR pin high.
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