LTC1955EUH Linear Technology, LTC1955EUH Datasheet - Page 15

• Manufacturer Part Number: LTC1955EUH
• Description: IC INTERFACE DL SMART CARD 32QFN
• Manufacturer: Linear Technology

Specifications of LTC1955EUH

• Controller Type: Smart Card Interface
• Interface: 4-Wire Serial
• Voltage - Supply: 1.7 V ~ 5.5 V
• Current - Supply: 10µA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-QFN
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIONS INFORMATION
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 confi gured 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 confi guration and
direction of data fl ow. 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 confi gured 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.
μCONTROLLER
MOSI
MISO
SCK
I/O
Figure 4. Microcontroller Interface
D
D
SCLK
LD
IN
OUT
LTC1955
Daisychained Operation
For applications requiring more than two card sockets,
the serial port of the LTC1955 is designed to be easily
daisychained. The D
nected directly to the D
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 V
problems in multiple LTC1955 applications when driving
the DATA or I/O pins low.
CARD A
CARD B
OUT
1955 F04
IN
pin of one LTC1955 can be con-
pin of another LTC1955. Rather
LTC1955
15
1955fb
OL