LTC1955IUH - Linear Technology Corporation

LTC1955

1955fc

For more information www.linear.com/LTC1955

TYPICAL APPLICATION

DESCRIPTION

Dual Smart Card Interface

with Serial Control

The LT C

1955 provides all necessary supervisory and

power control functions for two smart cards, two S.A.M.

cards or a combination of S.A.M. and smart cards. It

provides a charge pump for battery-powered applications

as well as all necessary level shifting circuitry.

The card voltages can be independently set to 1.8V, 3V or

5V. Both card interfaces include a card detection channel

with automatic debounce circuitry. To reduce wiring costs,

the LTC1955 interfaces to a microcontroller via a simple

4-wire serial interface. Multiple devices may be connected

in daisychain fashion so that the number of wires to the

card socket board is independent of the number of sockets.

Status data is returned over the same interface.

Extensive security features ensure proper deactivation

sequencing in the event of a supply fault or a smart card

electrical fault. The smart card pins can withstand greater

than 10kV ESD in-situ with no additional components.

The LTC1955 is available in a low proﬁle (0.75mm) 5mm

× 5mm QFN package.

Deactivation Sequence

FEATURES

APPLICATIONS

n Compatible with ISO7816-3 and EMV Electrical

Speciﬁcations

n Power Management and Control for Two Smart Cards

n Control/Status Serial Port May Be Daisychained for

Multicard Applications

n Automatic Shutdown on Electrical Faults

n Buck/Boost Charge Pump Generates 5V, 3V or 1.8V

Outputs (Smart Card Classes A, B and C)

n Independent 5V/3V/1.8V Level Control for Both Cards

n Automatic Level Translation

n Supervisory Functions Prevent Smart Card Faults

n Low Operating Current: 250µA Typical

n Ultralow Shutdown Current

n >10kV ESD on Smart Card Pins

n Small 32-Lead 5mm × 5mm QFN Package

n Handheld Payment Terminals

n Pay Telephones

n ATM Machines

n POS Terminals

n Computer Keyboards

n Multiple S.A.M. Sockets

10µs/DIV

VCCA

5V/DIV

I/O A

5V/DIV

CLK A

5V/DIV

RST A

5V/DIV

1955 TA01a

4-WIRE

COMMAND

INTERFACE

4-WIRE

CARD

INTERFACE

SMART CARD

VENDOR CARD

C8A

C4A

I/O A

RST A

CLK A

VCCA

PRES B

2CARD

DETECT

151114

12,13

9, 10

I/O B

RST B

CLK B

VCCB

DVCC

VBATT

GND

FAULT

DIN

DOUT

SCLK

DATA

RIN

SYNC

ASYNC

NC/NO

PRES A

UNDERV

240k

LTC1955

1µF

4.7µF

1955 TA01b

1µF

4.7µF0.1µF

C+C–CPO

180k

INPUT

POWER

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

Protected by U.S. Patents, including 6356140, 6411531.

LTC1955

1955fc

For more information www.linear.com/LTC1955

PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS

VBATT, DVCC, CPO, FAULT,

UNDERV to GND ....................................... –0.3V to 6.0V

PRES A/PRES B, DATA, RIN, SYNC, ASYNC,

LD, DIN, SCLK to GND .................–0.3V to (DVCC + 0.3V)

I/O A ............................................ –0.3V to (VCCA + 0.3V)

I/O B ............................................ –0.3V to (VCCB + 0.3V)

IVCCA/IVCCB.............................................................80mA

VCCA/VCCB Short-Circuit Duration ..................... Indeﬁnite

Operating Temperature Range (Note 4).... –40°C to 85°C

Junction Temperature ........................................... 125°C

Storage Temperature Range ................... –65°C to 125°C

(Note 1)

SGND

31 30 29 28 27 26 25

9 10 11 12

TOP VIEW

UH PACKAGE

32-LEAD (5mm × 5mm) PLASTIC QFN

13 14 15 16

1DVCC

PRES A

C8A

C4A

I/O A

RST A

CLK A

VCCA

FAULT

UNDERV

NC/NO

PRES B

I/O B

RST B

CLK B

VCCB

SYNC

ASYNC

RIN

DATA

DOUT

DIN

SCLK

SGND

PGND

C–

SVBATT

PVBATT

C+

CPO

TJMAX = 125°C, θJA = 34°C/W

EXPOSED PAD (PIN 33) IS SGND, MUST BE SOLDERED TO PCB

ORDER INFORMATION

LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LTC1955EUH#PBF LTC1955EUH#TRPBF 1955 32-Lead (5mm × 5mm) Plastic QFN –40°C to 85°C

LTC1955IUH#PBF LTC1955IUH#TRPBF 1955 32-Lead (5mm × 5mm) Plastic QFN –40°C to 85°C

LEAD BASED FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LTC1955EUH LTC1955EUH#TR 1955 32-Lead (5mm × 5mm) Plastic QFN –40°C to 85°C

LTC1955IUH LTC1955IUH#TR 1955 32-Lead (5mm × 5mm) Plastic QFN –40°C to 85°C

Consult LTC Marketing for parts speciﬁed with wider operating temperature ranges. *The temperature grade is identiﬁed by a label on the shipping container.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/

For more information on tape and reel speciﬁcations, go to: http://www.linear.com/tapeandreel/

ELECTRICAL CHARACTERISTICS

PARAMETER CONDITIONS MIN TYP MAX UNITS

Input Power Supply

VBATT Operating Voltage l2.7 5.5 V

IPVBATT + ISVBATT Operating Current VCCA = 5V, VCCB = 0V, ICCA = 0µA

VCCA = VCCB = 5V, ICCA = ICCB = 0µA

250

350

400

500

µA

IPVBATT + ISVBATT Shutdown Current No Cards Present. VCPO = 0V l0.75 1.75 µA

DVCC Operating Voltage l1.7 5.5 V

The l denotes the speciﬁcations which apply over the full operating

temperature range, otherwise speciﬁcations are at TA = 25°C. VPVBATT = VSVBATT = 3.3V, DVCC = 3.3V, unless otherwise noted.

LTC1955

1955fc

For more information www.linear.com/LTC1955

ELECTRICAL CHARACTERISTICS

The l denotes the speciﬁcations which apply over the full operating

temperature range, otherwise speciﬁcations are at TA = 25°C. VPVBATT = VSVBATT = 3.3V, DVCC = 3.3V, unless otherwise noted.

PARAMETER CONDITIONS MIN TYP MAX UNITS

IDVCC Operating Current l10 25 µA

IDVCC Shutdown Current l0.5 1.5 µA

Charge Pump

ROLCP 5V Mode Open-Loop Output Resistance VBATT = 3.075V, ICPO = ICCA + ICCB = 120mA (Note 3) l5.7 8.5 Ω

CPO Turn-On Time ICCA/B = 0mA, 10% to 90% l0.6 1.5 ms

Smart Card Supplies VCCA, VCCB

VCCA/B Output Voltage 5V Mode, 0 < ICCA/B < 60mA

3V Mode, 0 < ICCA/B < 50mA

1.8V Mode, 0 < ICCA/B < 30mA

4.65

2.75

1.65

1.8

5.35

3.25

1.95

VCCA/B Turn-On Time ICCA/B = 0mA, 10% to 90% l0.8 1.5 ms

Undervoltage Detection Relative to Nominal Output l–9 –5 –2.5 %

Overcurrent Detection 5V Mode l65 100 135 mA

Smart Card Detection

Debounce Time ( PRES A/B to D15/D7) VNC/NO = 0V l20 35 60 ms

PRES A, PRES B Pull-Up Current VPRESA/B = 0 l1.25 2.5 µA

Deactivation Time ( RST to VCC = 0.4V) ICCA/B = 0mA, CVCCA/B = 1µF l20 250 µs

CLK A, CLK B

Low Level Output Voltage (VOL), (Note 2) Sink Current = –200µA l0.2 V

High Level Output Voltage (VOH), (Note 2) Source Current = 200µA lVCCA/B – 0.2 V

Rise/Fall Time (Note 2) Loaded with 50pF, 10% to 90% l16 ns

CLK A, CLK B Frequency (Note 2) l10 MHz

RST A, RST B, C4A, C8A

Low Level Output Voltage (VOL), (Note 2) Sink Current = –200µA l0.2 V

High Level Output Voltage (VOH), (Note 2) Source Current = 200µA lVCCA/B – 0.2 V

Rise/Fall Time (Note 2) Loaded with 50pF, 10% to 90% l100 ns

I/O A, I/O B

Low Level Output Voltage (VOL), (Note 2) Sink Current = –1mA (VDATA = 0V) l0.3 V

High Level Output Voltage (VOH), (Note 2) Source Current = 20µA (VDATA = VDVCC)l0.85 • VCCA/B V

Rise/Fall Time (Note 2) Loaded with 50pF, 10% to 90% l500 ns

Short-Circuit Current (Note 2) VDATA = 0V l5 10 mA

DATA

Low Level Output Voltage (VOL) Sink Current = –500µA (VI/OA/B = 0V) l0.3 V

High Level Output Voltage (VOH) Source Current = 20µA (VI/OA/B = VCCA/B)l0.8 • DVCC V

Rise/Fall Time Loaded with 50pF, 10% to 90% l500 ns

RIN, DIN, SCLK, LD, SYNC, ASYNC, NC/NO

Low Input Threshold (VIL)l0.15 • DVCC V

High Input Threshold (VIH)l0.85 • DVCC V

Input Current (IIH/IIL)l–1 1 µA

LTC1955

1955fc

For more information www.linear.com/LTC1955

ELECTRICAL CHARACTERISTICS

The l denotes the speciﬁcations which apply over the full operating

temperature range, otherwise speciﬁcations are at TA = 25°C. VPVBATT = VSVBATT = 3.3V, DVCC = 3.3V, unless otherwise noted.

PARAMETER CONDITIONS MIN TYP MAX UNITS

DOUT

Low Level Output Voltage (VOL) Sink Current = –200µA l0.3 V

High Level Output Voltage (VOH) Source Current = 200µA lDVCC – 0.3 V

UNDERV

Threshold l1.17 1.23 1.29 V

Leakage Current VUNDERV = 3.3V l50 nA

FAULT

Low Level Output Voltage (VOL) Sink Current = –200µA l0.005 0.3 V

Leakage Current VFAULT = 5.5V l1 µA

Note 1: Stresses beyond those listed under Absolute Maximum Ratings

may cause permanent damage to the device. Exposure to any Absolute

Maximum Rating condition for extended periods may affect device

reliability and lifetime.

Note 2: This speciﬁcation applies to all three smart card voltage classes:

1.8V, 3V and 5V.

Note 3: ROLCP @ (2VBATT – VCPO)/ICPO; VCPO will depend upon total load

(ICCA + ICCB) and minimum supply voltage VBATT. See Figure 5.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Serial Port Timing

tDS DIN Valid to SCLK Setup l8 ns

tDH DIN Valid to SCLK Hold l8 ns

tDD DOUT Output Delay CLOAD = 15pF l15 60 ns

tLSCLK Low Time l50 ns

tHSCLK High Time l50 ns

tCL SCLK to LD l50 ns

tLC LD to SCLK l0 ns

Note 4: The LTC1955E is guaranteed to meet performance speciﬁcations

from 0°C to 85°C. Speciﬁcations over the –40°C to 85°C operating

ambient temperature range are assured by design, characterization and

correlation with statistical process controls. The LTC1955I is guaranteed to

meet performance speciﬁcations over the full –40°C to 85°C temperature

range.

LTC1955

1955fc

For more information www.linear.com/LTC1955

TYPICAL PERFORMANCE CHARACTERISTICS

VCCX Overcurrent Shutdown

Threshold vs Temperature

Card Detection Debounce Time

vs VBATT Supply Voltage

Bidirectional Channel (I/O A, I/O B)

Low Output Level vs Temperature

VBATT Quiescent Current

[IBATT – 2 (ICCA + ICCB)]

vs Load Current

VBATT Shutdown Current

vs Supply Voltage

DVCC Shutdown Current

vs Supply Voltage

No Load Supply Current vs VBATT

I/O X Short-Circuit Current

vs Temperature

Charge Pump Open-Loop Output

Resistance vs Temperature

(2VIN – VCPO) / ILOAD(MAX)

SUPPLY VOLTAGE (V)

2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5

SUPPLY CURRENT (µA)

1955 G01

600

500

400

300

200

100

TA = 25°C

ICCA = ICCB = 0µA

VCCA = VCCB = 5V

VCCA = 1.8V, VCCB = 0V

TEMPERATURE (°C)

–40 –15 10 35 60 85

SHORT-CIRCUIT CURRENT (mA)

1955 G02

6.0

5.5

5.0

4.5

4.0

3.5

DVCC = VBATT = 5.5V

VCCX = 5V

TEMPERATURE (°C)

–40 –15 10 35 60 85

OUTPUT RESISTANCE (Ω)

1955 G03

7.0

6.5

6.0

5.5

5.0

4.5

VIN = 2.7V

VCPO = 4.9V

TEMPERATURE (°C)

–40 –15 10 35 60 85

LOAD CURRENT (mA)

1955 G04

180

160

140

120

100

VBATT = 3.3V

VCPO = 5.75V

VCCX = 1.8V

VCCX = 3V

VCCX = 5V

VBATT SUPPLY VOLTAGE (V)

2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5

DEBOUNCE TIME (ms)

1955 G05

TA = 85°C

TA = 25°C

TA = –40°C

TEMPERATURE (°C)

–40 –15 10 35 60 85

I/O A, I/O B LOW OUTPUT VOLTAGE (V)

1955 G06

0.16

0.14

0.12

0.10

0.08

0.06

VDATA = 0V

IOL = –1mA

VBATT = 2.7V VCCX = 1.8V

VCCX = 3V

VCCX = 5V

LOAD CURRENT (A)

BATT

QUIESCENT CURRENT (mA)

10µ 1m 10m

1955 G07

100µ 100m

VBATT = 3.1V

TA = 25°C

VBATT SUPPLY VOLTAGE (V)

2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5

SUPPLY CURRENT (µA)

1955 G08

3.0

2.5

2.0

1.5

1.0

0.5

TA = 85°C

TA = 25°C

TA = –40°C

VDVCC = VBATT

VDVCC SUPPLY VOLTAGE (V)

2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5

SUPPLY CURRENT (µA)

1955 G09

1.0

0.8

0.6

0.4

0.2

TA = 25°C, 85°C

TA = –40°C

VDVCC = VBATT

LTC1955

1955fc

For more information www.linear.com/LTC1955

TYPICAL PERFORMANCE CHARACTERISTICS

Charge Pump and LDO Activation Deactivation Sequence Data – I/O Channel, CL = 50pF

PIN FUNCTIONS

SVBATT: Power. Supply voltage for analog sections of the

LTC1955.

PVB ATT : Power. Supply voltage for the charge pump.

DVCC: Power. Reference voltage for the control logic.

SGND: Ground. Signal ground for analog sections of the

LTC1955. The Exposed Pad must be soldered to PCB

ground.

PGND: Ground. Power ground for the charge pump. This

pin should be connected directly to a low impedance

ground plane.

CPO: Charge Pump. CPO is the output of the charge pump.

When one or both of the smart cards requires power, the

charge pump will charge CPO to either 3.7V or 5.35V

depending on what smart card voltages are required. A

low impedance 4.7µF X5R or X7R ceramic capacitor is

required on CPO.

C+, C–: Charge Pump. Charge pump ﬂying capacitor pins.

A 1µF X5R or X7R ceramic capacitor should be connected

from C+ to C–.

DATA: Input/Output. Microcontroller side data I/O pin. The

DATA pin provides the bidirectional communication path

to both smart cards. One, both or neither of the cards may

be selected to communicate via the DATA pin. If several

LTC1955s are connected in parallel, the DATA pin can be

made high impedance by selecting neither card. The C4A

and C8A synchronous card pins can be selected to connect

to the DATA pin via the serial port (see Table 4).

RIN: Input. The RIN pin supplies the RST signal to both

smart cards. It is level shifted and transmitted directly

to the RST pin of a selected card socket. When a card is

deselected, the RST A/RST B pin for that channel is latched

at its current state.

SYNC: Input. The SYNC pin provides the clock input for

synchronous smart cards. When a synchronous card

is selected, its CLK pin follows SYNC directly. When a

synchronous card is deselected, the CLK A/CLK B pin for

that channel is latched at its current state.

ASYNC: Input. The ASYNC pin provides the clock input

for asynchronous cards and should be connected to a free

running clock. The clock signal to the smart card can be

a ÷1, ÷2, ÷4 or ÷8 version of the signal on ASYNC. Asyn-

chronous cards can also be placed in clock stop mode

with the clock stopped either high or low.

DIN: Input. Input for the serial port. Command data is

shifted into DIN synchronously with SCLK. DIN can be

connected directly to a microcontroller or the DOUT pin of

another LTC1955 for daisychained operation.

DOUT: Output. Output for the serial port. Smart card status

data is shifted out of DOUT synchronously with SCLK. DOUT

can be connected directly to a microcontroller or the DIN

pin of another LTC1955 for daisychained operation.

10µs/DIV

VCCA

5V/DIV

I/O A

5V/DIV

CLK A

5V/DIV

RST A

5V/DIV

1955 G11

1ms/DIV

VCCA

5V/DIV

VCPO

5V/DIV

I/O A

5V/DIV

1955 G10 100ns/DIV

DATA

2V/DIV

I/O A

2V/DIV

1955 G12

LTC1955

1955fc

For more information www.linear.com/LTC1955

PIN FUNCTIONS

SCLK: Input. The SCLK pin clocks the serial port. Each

new data bit is received on the rising edge of SCLK. SCLK

should be left high during idle times and should not be

clocked when LD is low.

LD: Input. The falling edge of this pin loads the current

state of the shift register into the command register.

Command changes to both smart card channels will be

updated on the falling edge of LD. The rising edge of LD

latches status information from the smart card channels

into the shift register for the next read/write cycle.

NC/NO: Input. This pin controls the activation level of the

PRES A/PRES B pins. When it is high (DVCC), the PRES

pins are active high. When it is low (GND), the PRES pins

are active low. When a ground side N.O. switch is used,

the NC/NO pin should be grounded. When a ground side

N.C. switch is used, the NC/NO pin should be connected

to DVCC.

Note: If an N.C. switch is used, a small current (several

microamperes) will ﬂow through the switch whenever a

smart card is not present. For ultralow power consumption

in shutdown, an N.O. switch is optimum.

PRES A/PRES B: Card Socket. The PRES A/PRES B pins

are used to detect the presence of the smart cards. They

can be connected to either normally open or normally

closed detection switches on the smart card acceptor’s

sockets. The NC/NO pin should be set appropriately. These

pins have a pull-up current source on-chip so no external

components are required.

C4A/C8A: Card Socket. These pins connect to the C4

and C8 pins of synchronous memory cards on smart

card socket A. The signal for these pins is unidirectional

and can only be sent to the card. Data for C4A and C8A

is transmitted via the DATA pin and may be selected

in place of I/OA via the serial port (see Table 4). When

either C4A or C8A is selected, it will follow the DATA

pin. When it is deselected, it will remain latched at its

current state.

I/O A/I/O B: Card Socket. The I/O A/I/O B pins connect to

the I/O pins of the respective smart card sockets. When

a smart card is selected, its I/O pin connects to the DATA

pin. When a smart card is deselected, its I/O A/I/O B pin

returns to the idle state (H).

RST A/RST B: Card Socket. These pins should be connected

to the RST pins of the respective smart card sockets. The

RST A/RST B signals are derived from the RIN pin. When

a card is selected, its RST pin follows RIN. When a card

is deselected, the RST A/RST B pin for that channel holds

the current value on RIN.

CLK A/CLK B: Card Socket. The CLK A/CLK B pins should

be connected to the CLK pins of the respective smart card

sockets. The CLK A/CLK B signals can be derived from

either the SYNC input or the ASYNC input depending on

which type of card is being accessed. The card type is

selected via the serial port (see Tables 1 and 3).

VCCA, VCCB: Card Socket. The VCCA/VCCB pins should be

connected to the VCC pins of the respective smart card

sockets. The activation of a VCCA/VCCB pin is controlled by

the serial port (see Tables 1 and 2) and can be set to 0V,

1.8V, 3V or 5V. The voltage levels of the two card sockets

are controlled independently for maximum ﬂexibility.

FAULT: Output. The FAULT pin can be used as an interrupt

to a microcontroller to indicate when a fault has occurred.

It is an open-drain output, which is logically equivalent to

D4 + D5 + D12 + D13. (See Table 1)

UNDERV: Input. The UNDERV pin provides security by

supplying a precision undervoltage threshold for ex-

ternal supply monitoring. An external resistive voltage

divider programs the desired undervoltage threshold.

Once UNDERV falls below 1.23V, the LTC1955 automati-

cally begins the deactivation sequence on any channel

that is active.

If external supply monitoring is not required, the UNDERV

pin should be connected to either SVBATT or DVCC.

LTC1955

1955fc

For more information www.linear.com/LTC1955

BLOCK DIAGRAM

C4A

C8A

I/O A

RST A

VCCB

CLK A

VCCA

SVBATT

DVCC

PGND

CHARGE PUMP

FAULT

NC/NO

UNDERV

1.23V

SGND

PRES A

1955 BD

SMART

CARD

SOCKET B SMART

CARD

SOCKET A

DIGITAL

SUPPLY

SMART

CARD

COMMUNICATIONS

SERIAL PORT

COMMAND/STATUS

DATA

C+C–CPO

–

RESET

CONTROL

LOGIC

STATUS DATA

COMMAND LATCH

SHIFT REGISTER

–

LDO A

CLK B

RST B

I/O B

PRES B

DIN

DOUT

SCLK

LDO B

CLOCK

CONTROL

LOGIC

CHARGE

PUMP

DATA

ASYNC

SYNC

RIN

14 11 10 12

PVBATT

13 15

LTC1955

1955fc

For more information www.linear.com/LTC1955

OPERATION

Serial Port

The microcontroller compatible serial port provides all

of the command and control inputs for the LTC1955, as

well as the status of the two smart cards. Data on the DIN

input is loaded on the rising edge of SCLK. D15 is loaded

ﬁrst and D0 last. At the same time, the command bits are

being shifted into the DIN input, the status bits are being

shifted out of the DOUT output. The status bits are presented

to DOUT on the rising edge of SCLK. Once all bits have

been clocked into the shift register, the command data is

loaded into the command latch by bringing LD low. At this

time, the command latch is updated and the LTC1955 will

begin to act on the new command set. The status data

is latched into the shift register on the rising edge of LD.

SCLK should be low when LD is brought low and should

be high when LD is brought high. This requires a 9th clock

cycle per transaction. Figure 1 shows the recommended

operation of the serial port.

Multiple LTC1955s may be daisychained together by

connecting the DOUT pin of one LTC1955 to the DIN pin of

another. Figure 6 shows an example of multiple LTC1955s

daisychained together.

The maximum clock rate for the serial port is 10MHz.

The serial port controls the following parameters of each

smart card socket:

• Selection/deselection of a smart card

• VCC voltage level of each card (5V/3V/1.8V/0V)

• Clock mode of each card (synchronous or asynchronous)

• Operating mode of asynchronous cards (clock stop

high, low, ÷1, ÷2, ÷4 or ÷8)

• Selection of the I/O, C4 or C8 pins for card socket A

The serial port provides the following status data:

• It indicates the presence or absence of the smart

cards.

• It indicates the readiness of the smart card VCC supplies.

Communication with a smart card is disabled until its

power supply voltage has reached the ﬁnal value.

• It indicates fault status. In the event of an electrical or

ATR fault, the fault is reported. For electrical faults, the

LTC1955 will automatically deactivate the smart card.

Table 1 illustrates the command inputs and status outputs

associated with each bit of the serial data word.

Three voltage options are available from the LTC1955: 5V,

3V and 1.8V. Bits D0, D1 (card B) and D8, D9 (card A)

determine which voltage is selected. Setting both control

bits of a channel to 0 deactivates that channel and sets

the smart card supply voltage to 0V. If both channels are

deactivated, the LTC1955 is in shutdown. Table 2 shows

the operation of the supply control bits.

The CLK A/CLK B pins to the smart cards can be pro-

grammed for various modes. Both synchronous and asyn-

chronous cards are supported. There are several options

available with asynchronous cards. Table 3 shows how

all clock options are obtained using bits D5–D7 (card B)

and D13–D15 (card A). The default state of the LTC1955

on power up is synchronous mode.

DIN

SCLK

XD0D15X D1

DOUT D15 FROM

INPUT

1955 F01

D14 D13D15 D1

tLC tDH tDD

tDS tHtLtCL

D14 D2

Figure 1. Serial Port Timing Diagram

LTC1955

1955fc

For more information www.linear.com/LTC1955

To receive status data from the serial port, a read/write op-

eration must be performed. When polling for the presence

of a smart card on both channels, the input word should

be set to $0000 since this is the shutdown command for

the LTC1955. However

, consider the example where some

operation is already being performed on channel A. If, for

example, the previous command was $BE00 (VCCA set to

3V, card selected, I/O A connected to DATA and CLK A set

to ASYNC÷2), then the commands for this channel must

be rewritten to the serial port each time. To poll for the

presence of a card on channel B, or even the VCCA ready

status, then $BE00 should be rewritten on each new read/

write cycle. Once a card is detected on channel B, the

commands for channel B can be changed but the $BExx

should continue to be rewritten for channel A.

Bidirectional Channels

The bidirectional channels are level shifted to the appropri-

ate VCCA/B voltages at the I/O A/I/O B pins.

An NMOS pass transistor performs the level shifting. The

gate of the NMOS transistor is biased such that the transis-

tor is completely off when both sides have relinquished

the channel. If one side of the channel asserts an L, then

the transistor will convey the L to the other side. Note that

current passes from the receiving side of the channel to the

transmitting side. The low output voltage of the receiving

side will be dependent upon the voltage at the transmitting

side plus the I • R drop of the pass transistor.

When a card socket is selected, it becomes a candidate

to drive data on the DATA pin, and likewise, receive data

from the DATA pin. When a card socket is deselected, the

voltage on its I/O A/I/O B pin will return to the idle state

(H), and the DATA side of that channel will become high

impedance. If both cards are deselected, the DATA pin

will be high impedance.

Both cards may be deselected at the same time to allow

communication with a second LTC1955.

Card channel A includes provision for unidirectional

communication with the C4 and C8 pins of the smart

card. The C4, C8 and I/O pins of card A are individually

multiplexed to the DATA pin using bits D11 and D12, as

shown in Table 4.

OPERATION

Table 1. Serial Port Comand

STATUS OUTPUT BIT COMMAND INPUT

CARD B 0 D0 VCCB Options

(See Table 2)

0 D1

0 D2 Card B Select/Deselect

0 D3 Data Pull-Up Defeat

Card B Electrical Fault D4 Reserved (Always Set to “0”)

Card B ATR Fault D5 Card B Clock Options

(See Table 3)

Card B VCC Ready D6

Card B Present D7

CARD A 0 D8 VCCA Options

(See Table 2)

0 D9

0 D10 Card A Select/Deselect

0 D11 Card A Communications

Options (See Table 4)

Card A Electrical Fault D12

Card A ATR Fault D13 Card A Clock Options

(See Table 3)

Card A VCC Ready D14

Card A Present D15

Table 2. VCC and Shutdown Options

STATUS (CARD A)

STATUS (CARD B)

0 0 VCC = 0V (Shutdown)

0 1 VCC = 1.8V

1 0 VCC = 3V

1 1 VCC = 5V

Table 3. Clock Options

D15

D14

D13

CLOCK MODE (CARD B)

CLOCK MODE (CARD A)

0 0 0 Synchronous Mode

0 0 1 Unused

0 1 0 Asynchronous Stop Low

0 1 1 Asynchronous Stop High

1 0 0 Asynchronous ÷1

1 0 1 Asynchronous ÷2

1 1 0 Asynchronous ÷4

1 1 1 Asynchronous ÷8

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Table 4. Card A Communications Options

D12 D11 CARD A COMMUNICATION MODE

0 0 Nothing Selected

0 1 C4A Connected to DATA Pin

1 0 C8A Connected to DATA Pin

1 1 I/O A Connected to DATA Pin

Note that if a reset is initiated with both cards selected,

then both may give an answer to reset and collide on the

DATA line. No damage will occur but data could be lost

or corrupted.

Dynamic Pull-Up Current Sources

The current sources on the bidirectional pins (DATA, I/O

A/I/O B) are dynamically activated to achieve a fast rise time

with a relatively small static current.* Once a bidirectional

pin is relinquished, 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

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 affecting a dynamic form of hysteresis.

Clock Channels

As described in the section Serial Port, the LTC1955 sup-

ports both synchronous and asynchronous smart cards.

On start-up, or when bits D13-D15 for card A and bits

D5-D7 for card B are set to 0s, the clock channel is in

synchronous mode. The remaining modes are used for

asynchronous cards.

In synchronous mode, the CLK A/CLK B pins follow the

SYNC pin for a channel that is selected. If a channel is

deselected (via the serial port), the CLK A/CLK B line for

that channel is latched at its current value.

In asynchronous mode, the CLK A/CLK B pins follow either

the ASYNC pin (÷1 mode) or a divided version of this pin.

The CLK A/CLK B pins can also be stopped high or low.

The available divider ratios include ÷2, ÷4 and ÷8. When

switching between divider ratios, the internal selection

circuitry ensures that no spikes or glitches appear on the

CLK A/CLK B pins. Consequently, it may take up to 8 clock

pulses for the clock frequency change command to take

affect. Synchronization circuitry ensures that no glitches

occur when entering or exiting one of the stop modes.

For example, when entering stop low mode, the selection

circuitry waits for the next falling edge of the respective

CLK A/CLK B signal to make the change. Likewise, if stop

high is selected, it will occur on the next rising edge.

Deselection of an asynchronous card does not affect its

CLK A/CLK B pin. Its clock can be started, stopped or its

divider ratio changed at any time.

To clean up the duty cycle of the incoming clock in asyn-

chronous applications, any of the clock divider modes ÷2,

÷4 or ÷8 will yield a very nearly 50% duty cycle.

Additional synchronization circuitry prevents glitches from

occurring when switching between synchronous mode and

asynchronous mode. Because of this circuitry, two edges

(a falling edge followed by a rising edge) are necessary

at the CLK pin to switch modes from asynchronous to

synchronous. For example, if clock stop mode is engaged,

the clock channel will not change modes until clock stop

mode is disengaged.

Any combination of cards, synchronous or asynchronous,

can be used as both channels can be set to any of the

clock modes or divider ratios independently.

Both SYNC and ASYNC inputs are independently level

shifted to the appropriate voltage for the CLK A/CLK B

pins (5V, 3V, 1.8V).

Reset Channels

When a card is selected, the reset channels provide a level

shifted path from the RIN pin to the RST A/RST B pins.

When a card is deselected, its RST A/RST B pin is latched

at the current value of RIN.

–

VREF

LOCAL

SUPPLY

BIDIRECTIONAL

PIN 1955 F02

ISTART

Figure 2. Dynamic Pull-Up Current Sources

OPERATION

* U.S. Patent No. 6,356,140

LTC1955

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For more information www.linear.com/LTC1955

Smart Card Detection Circuits

The PRES A/PRES B pins are used to detect the presence

of a smart card. An automatic debounce circuit waits until

a smart card has been present for a continuous period

of typically 35ms. Once a valid card indication exists,

the status bit for that channel is updated and may be

polled by cycling data through the serial port. The DOUT

pin (equivalent to D15) of the serial port can be used to

indicate the presence of a card on channel A in real time

if LD is held low.

The PRES A/PRES B pins have built-in pull-up current

sources, so no external components are required for

switch detection. The pull-up current sources are designed

to have a small current when the pin voltage is below ap-

proximately 1V, but somewhat higher current when the

pin voltage reaches 1V. This helps maintain low power

dissipation when a card is present and yet fast response

time to a card removal.

The PRES A/PRES B pins can be conﬁgured to respond

to either normally open or normally closed switches via

the NC/NO pin.

Activation/Deactivation

For maximum ﬂexibility, the activation sequencing of the

smart card is left to the application programmer. Upon

activation, to comply with relevant smart card standards,

none of the smart card signal pins will be allowed to go

high before the smart card supply voltage (VCCA/VCCB) has

reached its ﬁnal value. Deactivation can be achieved either

manually or automatically. An electrical fault condition will

trigger the automatic deactivation.

Manual deactivation may be performed under software

control by setting the smart card pins to 0V in the desired

sequence via the control pins (SYNC, ASYNC, RIN, DATA

and the serial port). For most applications, this will be

cumbersome and the built-in deactivation will be used

instead.

Automatic Deactivation

The built-in deactivation sequence can be executed via the

serial port simply by setting the appropriate control bits

(D0 and D1 or D8 and D9) to 0. The deactivation sequence

is outlined below.

1. The RST A/RST B pin for that channel is immediately

brought low.

2. The deactivation of the CLK A/CLK B pins depends upon

which type of card is used:

If the smart card was set to asynchronous mode, then

the CLK A/CLK B pin will be latched low on its next

falling edge. If no falling edges occur within 5µs (min),

then the CLK A/CLK B line is forced low.

If the smart card was set to synchronous mode, then the

CLK A/CLK B pin is immediately latched at its current

value (either high or low) and then forced low after a

duration of 5µs (min). During the 5µs timeout period,

changes on SYNC will be ignored.

3. The I/O A/I/O B, C4A and C8A pins for that channel are

brought low.

4. The VCCA/VCCB pin is brought low.

If an error occurs on one smart card, operation of the

other card is unaffected.

Electrical Fault Detection

Several types of faults are detected by the LTC1955. They

include VCCA/VCCB undervoltage, VCCA/VCCB overcurrent,

CLK A/CLK B, RST A/RST B, C8A, C4A short-circuit, card

removal during a transaction, failed answer to reset (ATR),

supply undervoltage or UNDERV and chip overtemperature.

To prevent false errors from plaguing the microcontroller,

the electrical faults are acted upon only after a 5µs (min)

timeout period. Card removal during transaction faults

initiate the deactivation sequence immediately.

OPERATION

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VCCA/VCCB undervoltage faults are determined by compar-

ing the actual output voltage with the internal reference

voltage. If the output is more than ~5% below its set point

for the entire timeout period, the fault is reported and the

deactivation sequence is initiated.

VCCA/VCCB overcurrent faults are detected by comparing

the output current of the LDOs with an internal reference

level. If the current of an LDO is more than 100mA (typ)

for the entire timeout period, the fault is reported and the

deactivation sequence is initiated.

CLK A/CLK B and RST A/RST B faults are detected by

comparing the outputs of these pins with their expected

signals. If the signal on a pin is incorrect for the entire

timeout period, the fault is reported and the deactivation

sequence is initiated.

The clock channels are a special case. Since they can have

a free running clock, the error indication is accumulated

over a longer period of time without being cleared. Even

though the clock may be running, an error will still be

detected.

An overtemperature fault is detected by sensing the junction

temperature of the IC. If the junction temperature exceeds

approximately 150°C for the entire timeout period, the

fault is reported by setting both fault bits (D4 and D12)

and the deactivation sequence is initiated.

A card removal fault is determined as soon as the PRES A/

PRES B pin is high (for NC/NO = 0). Once this occurs,

the fault is reported and the deactivation sequence is

initiated.

If no card is present, and the application software attempts

to power-up a card socket, an automatic fault will result

on that channel.

Short-circuits on the I/O A/I/O B lines will not be detected

by the fault detection hardware; however, a short-circuit

from these lines to their respective VCCA/VCCB pins will

be compliant with the maximum current limits set by ap-

plicable standards (<15mA).

An electrical fault can be cleared on either channel by

setting the voltage of that channel to 0V. Set D0 and D1

to OO to clear channel B and set D8 and D9 to 00 to clear

channel A. It is not necessary to set all four bits to zeros.

Answer to Reset (ATR) Fault Detection

Answer to reset faults are detected by an internal counter

that is started once the RST A/B line goes high. If the DATA

pin remains high for 40,000 clock cycles, the ATR fault bit

for a given channel is set in the serial port’s status register

(see Table 1) and the FAULT pin is brought low.

An ATR fault cannot occur if the clock mode of a chan-

nel is set to synchronous. ATR faults will only occur for

asynchronous smart cards.

ATR faults are cleared by bringing the RST A/B pin low

for the faulted channel. This will also clear the FAULT pin

to the Hi-Z state (assuming no other errors are causing

FAULT to be low).

An ATR fault will not automatically deactivate a card

channel. It is the application programmer’s responsibility

to check the status register for ATR faults and deacti-

vate the smart card channel in accordance with smart

card standards. Generally, the application has 50ms

(EMV 2.1.3.1, 2.1.3.2) from the 40,000th clock pulse to

deactivate the card. Once the LTC1955 receives the de-

activation command, it will shut down a card channel in

less than 250µs.

Using the FAULT Pin

The FAULT pin can be used as an interrupt to a microcon-

troller. It is an open-drain output and generally requires

a pull-up resistor. The FAULT pin will go low when either

an electrical fault, or an answer to reset fault, occurs on

either channel. Thus, there are four possible faults that

can cause it to indicate a problem. The serial port’s status

curred and on which channel. The FAULT pin is logically

equivalent to D4 + D5 + D12 + D13 (see Table 1).

OPERATION

LTC1955

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For more information www.linear.com/LTC1955

10kV ESD Protection

All smart card pins (CLK A/CLK B, RST A/RST B, I/O A/I/O B,

C4A, C8A and VCCA/VCCB) can withstand over 10kV of

human body model ESD in-situ. In order to ensure proper

ESD protection, careful board layout is required. The

PGND and SGND pins should be tied directly to a ground

plane. The VCCA/VCCB capacitors should be located very

close to the VCCA/VCCB pins and tied immediately to the

ground plane.

Capacitor Selection

Warning: A polarized capacitor such as tantalum or alumi-

num should never be used for the ﬂying capacitor since

its voltage can reverse upon start-up of the LTC1955.

Low ESR ceramic capacitors should always be used for

the ﬂying capacitor.

A total of six capacitors are required to operate the LTC1955.

An input bypass capacitor is required at PVBATT, SVBATT

and DVCC. Output bypass capacitors are required on each

of the smart card VCCA/VCCB pins. A charge pump ﬂying

capacitor is required from C+ to C– and a charge storage

capacitor is required on the charge pump out pin CPO.

To prevent excessive noise spikes due to charge pump

operation, low ESR (equivalent series resistance) multi-

layer ceramic capacitors are strongly recommended.

There are several types of ceramic capacitors available, each

having considerably different characteristics. For example,

X7R/X5R ceramic capacitors have excellent voltage and

temperature stability but relatively low packing density.

Y5V ceramic capacitors have apparently higher packing

density but poor performance over their rated voltage or

temperature ranges. Under certain voltage and temperature

conditions, Y5V and X7R/X5R ceramic capacitors can be

compared directly by case size rather than speciﬁed value

for a desired minimum capacitance.

Placement of the capacitors is critical for correct operation

of the LTC1955. Because the charge pump generates large

current steps, all of the capacitors should be placed as close

to the LTC1955 as possible. The low impedance nature of

multilayer ceramic chip capacitors will minimize voltage

spikes but only if the power path is kept very short (i.e.,

minimum inductance). The PVBATT/SVBATT nodes should

APPLICATIONS INFORMATION

be especially well bypassed. The capacitor for this node

should be directly adjacent to the QFN package. The CPO

and ﬂying capacitors should be very close as well. The

LTC1955 can tolerate more distance between the LDO

capacitors and the VCCA/B pins.

Figure 3 shows an example of a tight printed circuit

board using single-layer copper. For best performance, a

multilayer board can be used and should employ a solid

ground plane on at least one layer.

The following capacitors are recommended for use with

the LTC1955.

TYPE VALUE CASE SIZE MURATA P/N

CIN

CPO

X5R 4.7µF 0805 GRM40-034 X5R 475K 6.3

CF LY

VCCA/B

X5R 1µF 0603 GRM39 X5R 105K 6.3

CDVCC X5R 0.1µF 0402 GRM36 X5R 104K 10

Figure 3. Optimum Single-Layer PCB Layout

VCCA

GND VBATT VCCB 1955 F03

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Interfacing to a Microcontroller

The serial port of the LTC1955 can be connected directly

to a 68HC11 style microcontroller’s serial port. The mcro-

controller should be conﬁgured as the master device and

its clock’s idle state should be set to high (MSTR = 1,

CPOL = 1 and CPHA = 0 for the MC68HC11 family).

Figure 4 shows the recommended conﬁguration and

direction of data ﬂow. Note that an additional I/O line

is necessary for LD to load the data once it has shifted

around the loop. Command data is latched into the com-

mand register on the falling edge of the LD signal. The

LTC1955 will begin to act on new command data as soon

as LD goes low. Any general purpose microcontroller I/O

line can be conﬁgured to control the LD pin.

The status of the LTC1955 is returned over the serial

port. Status data is latched into the shift register on the

rising edge of the LD pin. Whenever the system is wait-

ing for status data from the LTC1955, its LD pin should

be held low.

Daisychained Operation

For applications requiring more than two card sockets,

the serial port of the L

TC1955 is designed to be easily

daisychained. The DOUT pin of one LTC1955 can be con-

nected directly to the DIN pin of another LTC1955. Rather

than sending two 8-bit bytes before asserting LD, the

microcontroller should send two 8-bit bytes per device. LD

should only be asserted after all devices have been updated.

Figure 6 shows three LTC1955s cascaded in daisychain

fashion. In this case, the microcontroller would write six

8-bit bytes before asserting the LD pin. Alternatively, if

two serial ports are available on the microcontroller, then

two LTC1955s can be controlled independently.

If the DATA lines of two or more LTC1955s are connected

together, the static pull-up current will be the sum of the

devices. The static current can be brought back to the level

of a single LTC1955 by setting bit D3 on all but one of the

LTC1955s to 1 (see Table 1). Bit D3 disables the pull-up

current source on the DATA pin. This will help prevent VOL

problems in multiple LTC1955 applications when driving

the DATA or I/O pins low.

CARD A

CARD B

1955 F04

DIN

DOUT

SCLK

LTC1955

MOSI

MISO

SCK

I/O

µCONTROLLER

Figure 4. Microcontroller Interface

APPLICATIONS INFORMATION

LTC1955

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For more information www.linear.com/LTC1955

Using S.A.M. Cards

For applications using one or more installed S.A.M.

cards, the PRES A/PRES B pins for those sockets must

be grounded before operation of the card can occur

(assuming NC/NO is grounded). The PRES A/PRES B

pull-up current is designed for very low consumption,

but ultralow current can be achieved in shutdown by us-

ing a microcontroller output to pull down on the PRES

A/PRES B pins only when communication is necessary.

The fault detection circuitry will not allow a card socket

to be operated unless a card is detected.

Asynchronous Channel A Card Detection

Since the shift register is transparent when LD is held

low, DOUT is the same as D15. Recall from Table 1 that

D15 indicates the status of the card detection channel for

channel A. Thus, it is not necessary to perform an entire

read/write operation to determine the card detection

status of channel A. With LD low, DOUT can be used to

generate a real time card detection interrupt. This could be

useful for one S.A.M. card, one smart card application.

Inter Card Communication

Communication is possible directly from one card socket

to the other when both cards are selected at the same

time. This can be achieved by the following sequence of

actions.

1. Start with both cards off and deselected

2. Activate the supply of the slave card

3. Select the slave card only

4. Initiate a reset on the slave card

5. Deselect the slave card

6. Activate the supply of the master card

7. Select the master card only

8. Initiate a reset on the master card

9. Select both cards

Using the UNDERV Pin

The UNDERV pin can be used to add protection against a

supply undervoltage fault. By using two external program-

ming resistors, the undervoltage detection can be set to an

arbitrary level (Figure 7). To ensure that the smart cards

are properly shut down, there must be sufﬁcient energy

available in the input bypass capacitor to run one or both

smart cards until the deactivation cycle begins. It can take

approximately 30µs from the detection of a fault until the

deactivation sequence begins. It is desirable to maintain

the VBATT supply at 2.7V or greater during this period.

Consider the following (worst-case) example:

1. The UNDERV pin is programmed to trip below 3.1V.

2. It is possible to have both cards activated at 5V and

drawing 60mA.

Since the output voltage is programmed to 5V, the charge

pump will be acting as a voltage doubler. With two cards

drawing 60mA each, the input current will be 2 • (60mA

+ 60mA), or about 240mA. Allowing the VBATT supply to

droop from 3.1V to 2.7V during the 30µs timeout period,

the input capacitance would need to be at least:

240mA / [(3.1V – 2.7V) / 30µs] or 18µF.

Thermal Management

To minimize power dissipation, the LTC1955 will actively

decide whether to step up or down depending on the

required output voltages and available input voltage.

However, for optimum efﬁciency, the LTC1955 should be

powered from a 3.3V supply.

If the input voltage is above 3.6V, and both cards are

drawing maximum current, there can be substantial power

dissipation in the LTC1955. If the junction temperature in-

creases above approximately 150°C, the thermal shutdown

circuitry will automatically deactivate both channels. To

reduce the maximum junction temperature, a good thermal

connection to the PC board is recommended.

Zero Shutdown Current

Although the LTC1955 is designed to have very low shut-

down current, it can still draw over a microampere on both

APPLICATIONS INFORMATION

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For more information www.linear.com/LTC1955

DVCC and VBATT when in shutdown. For applications that

require virtually zero shutdown current, the DVCC pin can

be grounded. This will reduce the VBATT current to well

under a single microampere. Internal logic ensures that

the LTC1955 is in shutdown when DVCC is grounded. Note,

however, that all of the logic signals that are referenced

to DVCC (DIN, SCLK, LD, DATA, RIN, SYNC, ASYNC and

NC/NO) will have to be at 0V as well, to prevent ESD diodes

to DVCC from being forward-biased.

Operation at Higher Supplies

If a 5.5V to 6V supply voltage is available, it is possible

to achieve some power savings by bypassing the charge

pump. The higher supply can be connected directly to the

CPO pin. As long as the voltage on CPO is higher than that

at which it ordinarily regulates (5.35V or 3.7V depending

on voltage selections), the charge pump’s oscillator will

not run. This conﬁguration can give considerable power

savings since the charge pump is not being used.

A voltage source is still needed on both DVCC and SVBATT/

PVBATT in this conﬁguration. Recall that DVCC sets the

logic reference level for all the control and smart card

communication pins. The voltage on SVBATT/PVBATT can

be any convenient level that meets the parameters in the

Electrical Characteristics table.

The 5.5V to 6V supply can be left permanently connected

to CPO, but there will be approximately 5µA of current ﬂow

into CPO when the LTC1955 is in shutdown.

Charge Pump Strength

Under low VBATT conditions, the amount of current available

to the smart cards is limited by the charge pump.

Figure 5 shows how the LTC1955 can be modeled as a

Thevenin equivalent circuit to determine the amount of

current available given the effective input voltage, 2VBATT

and the effective open-loop output resistance, ROLCP.

From Figure 5, the available current is given by:

ICCA +ICCB ≤

BATT

– V

CPO

OLCP

ROLCP is dependent on a number of factors including the

switching term, 1/(fOSC • CF LY ), internal switch resistances

and the nonoverlap period of the switching circuit. How-

ever, for a given ROLCP, the minimum CPO voltage can be

determined from the following expression:

VCPO ≥ 2VBATT – (ICCA + ICCB)ROLCP

The LDOs have been designed to meet all applicable smart

card standards for VCC with VCPO as low as 5.13V. Given

this information, trade-offs can be made by the user with

regard to total consumption (ICCA + ICCB) and minimum

supply voltage.

–LDO A2VBATT

1955 F05

CPOROLCP

VCCA LDO B VCCB

Figure 5. Equivalent Open-Loop Circuit

Changing the Smart Card Supply Voltage

Although the LTC1955 control system will allow the smart

card voltage to be changed from one value to the next

without an interim power-down, this is not recommended.

When changing from a higher voltage to a lower voltage

there will generally not be a problem; however, changing

from a lower voltage to a higher voltage will result in both

an undervoltage condition and an overcurrent condition

on that channel. The likely result is that the channel will

automatically deactivate. Applicable smart card standards

specify that the smart card supply be powered to zero

before applying a new voltage.

Compliance Testing

Inductance due to long leads on type approval equipment

can cause ringing and overshoot that leads to testing

problems. Small amounts of capacitance and damp-

ing resistors can be included in the application without

compromising the normal electrical performance of the

TC1955 or smart card system. Generally, a 100Ω resis-

tor and a 20pF capacitor will accomplish this, as shown

in Figure 8.

APPLICATIONS INFORMATION

LTC1955

1955fc

For more information www.linear.com/LTC1955

Figure 6. Multiple LTC1955s Daisychained Together

APPLICATIONS INFORMATION

4-WIRE

COMMAND

INTERFACE

4-WIRE

CARD

INTERFACE

SMART CARD

VENDOR CARD

LTC1955

4.7µF

1µF

DIN

DOUT

SCLK

DATA

RIN

SYNC

ASYNC

CPO

INPUT

POWER

FAULT

VBATT

GND

DVCC

UNDERV

FAULT

PRES APRES BC+

C–

SMART CARD

VENDOR CARD

LTC1955

4.7µF

DIN

DOUT

SCLK

DATA

RIN

SYNC

ASYNC

CPO

VBATT

GND

DVCC

UNDERV

FAULT

VENDOR CARD

1955 F07

LTC1955

4.7µF

DIN

DOUT

SCLK

DATA

RIN

SYNC

ASYNC

CPO

VBATT

GND

DVCC

UNDERV

FAULT

4.7µF

12, 13

9, 10

12, 13

9, 10

12, 13

9, 10

21 2

11 14

1µF

PRES APRES BC+

C–

21 211 14

1µF

PRES A

PRES BC+

C–

21 211 14

LTC1955

1955fc

For more information www.linear.com/LTC1955

APPLICATIONS INFORMATION

Figure 7. Setting the Undervoltage Trip Point

Figure 8. Additional Components for

Improved Compliance Testing

LTC1955

1955 F08

MAIN SUPPLY

VTRIP = 1.23V (1 + R1/R2)

UNDERV

SMART

CARD

SOCKET

I/O X

CLK X

RST X

VCCX

C1 C5

LTC1955

100Ω

1µF 0.1µF

20pF

1955 F09

20pF

LTC1955

1955fc

For more information www.linear.com/LTC1955

PACKAGE DESCRIPTION

Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.

5.00 ±0.10

(4 SIDES)

NOTE:

1. DRAWING PROPOSED TO BE A JEDEC PACKAGE OUTLINE

M0-220 VARIATION WHHD-(X) (TO BE APPROVED)

2. DRAWING NOT TO SCALE

3. ALL DIMENSIONS ARE IN MILLIMETERS

4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE

MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.20mm ON ANY SIDE

5. EXPOSED PAD SHALL BE SOLDER PLATED

6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION

ON THE TOP AND BOTTOM OF PACKAGE

PIN 1

TOP MARK

(NOTE 6)

0.40 ±0.10

BOTTOM VIEW—EXPOSED PAD

3.50 REF

(4-SIDES)

3.45 ±0.10

0.75 ±0.05 R = 0.115

TYP

0.25 ±0.05

(UH32) QFN 0406 REV D

0.50 BSC

0.200 REF

0.00 – 0.05

0.70 ±0.05

3.50 REF

(4 SIDES)

4.10 ±0.05

5.50 ±0.05

0.25 ±0.05

PACKAGE OUTLINE

0.50 BSC

RECOMMENDED SOLDER PAD LAYOUT

APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED

PIN 1 NOTCH R = 0.30 TYP

OR 0.35 × 45° CHAMFER

R = 0.05

TYP

3.45 ±0.05

UH Package

32-Lead Plastic QFN (5mm × 5mm)

(Reference LTC DWG # 05-08-1693 Rev D)

LTC1955

1955fc

For more information www.linear.com/LTC1955

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 representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

REVISION HISTORY

REV DATE DESCRIPTION PAGE NUMBER

C 11/13 Remove tLW spec from Serial Port Timing

Revised Serial Port Timing section and diagram

(Revision history begins at Rev C)

LTC1955

1955fc

For more information www.linear.com/LTC1955

 LINEAR TECHNOLOGY CORPORATION 2002

LT 1113 REV C • PRINTED IN USA

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LTC1955

RELATED PARTS

TYPICAL APPLICATION

PART NUMBER DESCRIPTION COMMENTS

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VOUT = 3V/5V, VIN = 2.7V to 10V, SSOP-16/-20 Package

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VOUT = 1.8V/3V/5V, VIN = 2.6V to 6V, SSOP-16 Package

LTC4555 SIM Power Supply and Level Translator VOUT = 1.8V/3V, VIN = 3V to 6V, 3mm × 3mm QFN Package

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CARD A

CARD B

LTC1955EUH

1µF

DIN

DVCC

VCC UNDERV VBATT

ASYNC

DOUT

SYNC

SCLK

RIN

DATA

I/O B

RST B

CLK B

VCCB

I/O A

C4A

C8A

RST A

CLK A

VCCA

CPOV–GND NC/NOC–

11 14 15

C+

FAULT

1955 TA02

2314 12, 13

PRES B

PRES A 2

9, 10 22

4.7µF

28 15

0.1µF

V+

0.1µF

1µF

0.1µF

0.1µF C5

GND

DB9

0.1µF

XIRQ

19 37

0.1µF 180k

Li-ION

4.7µF

262k +

RST

136

VCC18

4 5

VCC3

VCCA

GND

LTC1728ES5-1.8

DREN

RXEN

MOD B

VDD VRH

22 26 2718 20

XTALEXTALVRL VSS

GND MODA

47k

RST

47k

RESET

FAULT

(MOSI) PD3

IRQ

(2MHz) E

(MISO) PD2

DR1IN

RX1OUT

3DR1OUT

RX1IN

PD1 (TXD)

PD0 (RXD)

PB1

(SCK) PD4

PB0

(SS) PD5

(IC3) PA0 28

PC0

0.1µF 3C2–

2C2+

0.1µF 6C1–

5C1+

0.1µF

C3–

C3+

10M

8.000MHz

27pF27pF

MC68L11E9PB2LTC1348CG

Battery-Powered RS232 to Dual Smart Card Interface