6
For more information www.linear.com/LTC1955
Typical perForMance characTerisTics
Charge Pump and LDO Activation Deactivation Sequence Data – I/O Channel, C
L
= 50pF
pin FuncTions
SV
BATT
: Power. Supply voltage for analog sections of the
LTC1955.
PV
BATT
: Power. Supply voltage for the charge pump.
DV
CC
: 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).
R
IN
: Input. The R
IN
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
.
D
IN
: Input. Input for the serial port. Command data is
shifted into D
IN
synchronously with SCLK. D
IN
can be
connected directly to a microcontroller or the D
OUT
pin of
another LTC1955 for daisychained operation.
D
OUT
: Output. Output for the serial port. Smart card status
data is shifted out of D
OUT
synchronously with SCLK. D
OUT
can be connected directly to a microcontroller or the D
IN
pin of another LTC1955 for daisychained operation.
10µs/DIV
V
CCA
5V/DIV
I/O A
5V/DIV
CLK A
5V/DIV
RST A
5V/DIV
1955 G11
1ms/DIV
V
CCA
5V/DIV
V
CPO
5V/DIV
I/O A
5V/DIV
1955 G10
100ns/DIV
DATA
2V/DIV
I/O A
2V/DIV
1955 G12
