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PDF LTC1756 Data sheet ( Hoja de datos )
| Número de pieza | LTC1756 | |
| Descripción | Smart Card Interface | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LTC1756 (archivo pdf) en la parte inferior de esta página. Total 16 Páginas | ||
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FEATURES
s Fully ISO 7816-3 and EMV Compliant
(Including Auxiliary I/O Pins)
s Buck-Boost Charge Pump Generates 3V or 5V
s 2.7V to 6.0V Input Voltage Range (LTC1755)
s Very Low Operating Current: 60µA
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 3V ↔ 5V Signal Level Translators
s Shutdown Current: < 1µA
s Short-Circuit and Overtemperature Protected
s Alarm Output Indicates Fault Condition
s Multiple Devices May Be Paralleled for
Multicard Applications (LTC1755)
s Available in 16- and 24-Pin SSOP Packages
U
APPLICATIO S
s Handheld Payment Terminals
s Pay Telephones
s ATMs
s Key Chain Readers
s Smart Card Readers
LTC1755/LTC1756
Smart Card Interface
DESCRIPTIO
The LTC®1755/LTC1756 universal Smart Card interfaces
are fully compliant with ISO 7816-3 and EMV specifica-
tions. The parts provide the smallest and simplest inter-
face circuits between 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. Internal soft-start mitigates start-
up problems that may result when the input power is
provided by another regulator. Multiple devices may be
paralleled and connected to a single controller for multicard
applications.
Battery life is maximized by 60µA operating current and
1µA shutdown current. The narrow SSOP packages mini-
mize PCB area for compact portable systems.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
SMART CARD
PRESENT SWITCH
C3
10µF
GND VCC
AUX1
SMART CARD
AUX2
I/O
RST
CLK
3.3V
C2
10µF
1
PRES
5V/3V
2
PWR
CARD
3
CS
ALARM
4
NC/NO READY
5
GND DVCC
6 VIN LTC1755 C –
7
VCC
C+
8
AUX1 AUX1IN
9
AUX2 AUX2IN
10
I/O
DATA
11
RST
RIN
12
CLK
CIN
24
23
22
21
20
19
18
17
16
15
14
13
C1
0.68µF
µCONTROLLER
17556 TA01
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
Power Efficiency vs Input Voltage
100
IL = 35mA
TA = 25°C
75
VCC = 3V
50
VCC = 5V
25
0
34
5
VIN INPUT VOLTAGE (V)
6
17556 G01
CARD, READY, ALARM Pull-Up
Current vs Temperature
10
8
6
DVCC = 5.5V
4
2 DVCC = 3V DVCC = 2V
0
–50 –25 0
25 50
TEMPERATURE (°C)
75 100
17556 G04
Oscillator Frequency
vs Temperature
1100
1000
900
VIN = 3.3V
800
700
VIN = 5V
VIN = 2.7V
600
500
–50 –25 0
25 50
TEMPERATURE (°C)
75 100
17556 G07
Card Detection Debounce Period
vs Temperature
150
CFLY = 0.68µF
125
100 VIN = 6V
75 VIN = 3.3V
VIN = 2.7V
50
25
0
–50 –25 0
25 50
TEMPERATURE (°C)
75 100
17556 G02
PRES Pin Pull-Up Current vs DVCC
12
VPRES = 0V
TA = 25°C
10
8
6
4
2
0
2 34
5
DVCC INPUT VOLTAGE (V)
17556 G05
Oscillator Frequency
vs Input Voltage
1100
1000
900
800
TA = 85°C
TA = 25°C
700 TA = – 40°C
600
500
2.5
3.0 3.5 4.0 4.5 5.0 5.5
VIN INPUT VOLTAGE (V)
17556 G07
LTC1755/LTC1756
I/O, AUX1, AUX2 Short-Circuit
Current vs Temperature
3.6
VCC = 5V
VIN = 3V
3.5
3.4
3.3
–50 –25 0
25 50
TEMPERATURE (°C)
75 100
17556 G03
DVCC Input Current vs DVCC Voltage
35
VPRES = 0V
30
TA = –40°C
TA = 25°C
25
TA = 85°C
20
15
10
5
123
45
67
DVCC INPUT VOLTAGE (V)
17556 G02
VIN Supply Current
vs Temperature
70
VIN = 3.3V
ICC = 0
60
50
40
–50 –25 0
25 50
TEMPERATURE (°C)
75 100
17556 G09
5
5 Page 
LTC1755/LTC1756
APPLICATIO S I FOR ATIO
10kV ESD Protection
All Smart Card pins (CLK, RST, I/O, AUX1, AUX2, VCC 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 VCC capacitor should be
located very close to the VCC pin and tied immediately to
the ground plane.
Capacitor Selection
The style and value of capacitors used with the LTC1755/
LTC1756 determine several parameters such as output
ripple voltage, charge pump strength, Smart Card switch
debounce time and VCC discharge rate.
Due to the switching nature of a capacitive charge pump,
low equivalent series resistance (ESR) capacitors are
recommended for the capacitors at VIN and VCC. When-
ever the flying capacitor is switched to the VCC 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 VCC output.
These spikes may cause problems with the Smart Card or
may interfere with the regulation loop of the LTC1755/
LTC1756. Therefore, ceramic or tantalum capacitors are
recommended rather than higher ESR aluminum capaci-
tors. Between ceramic and tantalum, ceramic capacitors
generally 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°C
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 0.68µF 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 VCC 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 VCC discharge rate
specification, the value should not exceed 20µF. A 10µF
capacitor can be used but the ripple magnitude will be
higher leading to worse apparent DC load regulation.
Typically a 15µF to 18µF Y5V ceramic capacitor is the best
choice for the VCC charge storage capacitor. For best
performance, this capacitor should be connected as close
as possible to the VCC and GND pins. Note that most of the
electrostatic discharge (ESD) current on the Smart Card
pins is absorbed by this capacitor.
The bypass capacitor at VIN is also important. Large dips
on the input supply due to ESR may cause problems with
the internal circuitry of the LTC1755/LTC1756. A good
choice for the input bypass capacitor is a 10µF 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
VCC OR DVCC
ISTART
+ VREF
–
δV
δt 17556 F01
BIDIRECTIONAL PIN
Figure 1. Dynamic Pull-Up Current Sources
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC1756.PDF ] | |
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