5

LTC4557

4557f

DATA (Pin 8): Input/Output. Microcontroller side data I/O

pin. The DATA pin provides the bidirectional communica-

tion path to both cards. Only one of the cards may be

selected to communicate via the DATA pin. The pin pos-

sesses a dynamically activated pull-up current source,

allowing the controller to use an open-drain output. The

current source maintains a HIGH state. This pin is held

HIGH by a weak pull-up when the ENABLE pin is LOW.

RSTIN (Pin 9): Input. The RSTIN pin supplies the reset

signal to the cards. It is level shifted and transmitted

directly to the RST pin of the selected card.

CLKIN (Pin 10): Input. The CLKIN pin supplies the clock

signal to the cards. It is level shifted and transmitted

directly to the CLK pin of the selected card.

M0/M1 (Pins 12, 11): Inputs. The M0 and M1 pins select

which set of SIM/smart card pins are active and at which

voltage level they operate. The truth table for these pins

follows:

M1

M0

SELECTED CARD/VOLTAGE

0

0

Card A/1.8V

0

1

Card A/3V

1

0

Card B/1.8V

1

1

Card B/3V

ENABLE (Pin 13): Input. The ENABLE pin shuts down the

chip when LOW.

EXPOSED PAD (Pin 17): Chip Ground. This ground pad

must be soldered directly to a PCB ground plane.

PI FU CTIO S

logic.

sections of the LTC4557.

by the M0, M1 and ENABLE inputs. They can be set to 0V,

be active at a time.

CLKA/CLKB (Pins 5, 16): Card Socket. The CLKA/CLKB

pins should be connected to the CLK pins of the respective

card sockets. The CLKA/CLKB signals are derived from the

CLKIN pin. They provide a level shifted CLKIN signal to the

selected card. The CLKA/CLKB pins are gated off until

RSTA/RSTB (Pins 6, 15): Card Socket. The RSTA/RSTB

pins should be connected to the RST pins of the respective

card sockets. The RSTA/RSTB signals are derived from

the RSTIN pin. When a card is selected, its RST pin follows

attain their correct values.

I/OA, I/OB (Pins 7, 14): Card Socket. The I/OA, I/OB pins

connect to the I/O pins of the respective card sockets.

When a card is selected, its I/O pin transmits/receives data

to/from the DATA pin. The I/OA, I/OB pins are gated off