LTC4557EUD Linear Technology, LTC4557EUD Datasheet - Page 7

• Manufacturer Part Number: LTC4557EUD
• Description: IC DUAL SIM/SMART CARD PS 16QFN
• Manufacturer: Linear Technology

Specifications of LTC4557EUD

• Function: Power Management, Signal Level Translation
• Rf Type: Cellular, 3G, GSM
• Secondary Attributes: SIM & Smart Card Interface
• Package / Case: 16-WFQFN Exposed Pad
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

OPERATIO
The LTC4557 features two independent smart card chan-
nels. Only one of these channels may operate at a time.
Each channel is able to output two voltage levels: 1.8V
and 3V. The channel selection and voltage selection are
controlled by the ENABLE, M0 and M1 pins as shown in
Table 1.
Table 1. Channel and Voltage Truth Table
Bidirectional Channels
The bidirectional channels are level shifted to the appropri-
ate V
transistor performs the level shifting. The gate of the
NMOS transistor is biased such that the transistor is
completely off when both sides have relinquished the
channel. If one side of the channel asserts a LOW, then the
transistor will convey the LOW 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 receiv-
ing side will be dependent upon the voltage at the transmit-
ting side plus the IR drop of the pass transistor.
ENABLE
1
1
1
1
0
CCA,B
voltages at the I/OA,B pins. An NMOS pass
M1
0
0
1
1
X
U
M0
0
1
0
1
X
SELECTED CARD/VOLTAGE
Card A/1.8V
Card A/3V
Card B/1.8V
Card B/3V
A and B Disabled
SUPPLY
LOCAL
Figure 1. Dynamic Pull-Up Current Source
I
START
BIDIRECTIONAL
PIN
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/OA,B pin will be disabled and set to LOW.
If both cards are deselected, a weak pull-up ensures that
the DATA pin is held HIGH.
Dynamic Pull-up Current Sources
The current sources on the bidirectional pins (DATA/
I/OA,B) are dynamically activated to achieve a fast rise
time with a relatively small static current. Once a bidirec-
tional 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.
Reset Channels
When a card is selected, the reset channel provides a level
shifted path from the RSTIN pin to the RSTA,B pin. When
a card is deselected its reset pin is pulled LOW.
dv
dt
+
–
4557 F01
V
REF
LTC4557
7
4557f