LTC1555LEGN-1.8#PBF Linear Technology, LTC1555LEGN-1.8#PBF Datasheet - Page 6

• Manufacturer Part Number: LTC1555LEGN-1.8#PBF
• Description: IC LEVEL TRANSLATOR 16-SSOP
• Manufacturer: Linear Technology

Specifications of LTC1555LEGN-1.8#PBF

• Logic Function: Level Shifter
• Number Of Bits: 1
• Input Type: Voltage
• Output Type: Voltage
• Number Of Channels: 1
• Number Of Outputs/channel: 1
• Differential - Input:output: No/No
• Propagation Delay (max): 18ns
• Voltage - Supply: 1.8 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 16-SSOP
• Supply Voltage: 1.8 V ~ 5.5 V
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Data Rate: -

LTC1555L
6
APPLICATIO S I FOR ATIO
The LTC1555L performs the two primary functions nec-
essary for low voltage controllers (e.g., GSM cellular
telephone controllers, smart card readers, etc.) to com-
municate with 5V SIMs or smart cards. The part produces
a regulated 3V or 5V V
provides level translators for communication between the
SIM and the controller.
V
The regulator section of the LTC1555L (refer to Block
Diagram) consists of a buck/boost charge pump DC/DC
converter. The charge pump can operate over a wide input
voltage range (2.6V to 6V) while maintaining a regulated
V
powered directly from a battery (if desired) rather than
from a DC/DC converter output. When V
selected V
capacitor voltage doubler. When V
the part operates as gated switch step-down converter. In
either case, voltage conversion requires only one small
flying capacitor and output capacitor.
The V
either 3V, 5V or direct connection to V
useful in applications where multiple voltage SIMs may be
used. When the charge pump is put into shutdown (M0,
M1 = 0), V
in proper system supply sequencing.
An internal soft-start feature helps to limit inrush currents
upon start-up or when coming out of shutdown mode.
Inrush current limiting is especially useful when powering
the LTC1555L from a DC/DC output since the unlimited
inrush current may approach 300mA and cause voltage
transients on the 3V supply. The part is fully short-circuit
and over temperature protected, and can survive an indefi-
nite short from V
Capacitor Selection
For best performance, it is recommended that low ESR
(< 0.5 ) capacitors be used for both C
noise and ripple. The C
either ceramic or tantalum and should be 1 F or greater
(ceramic capacitors will produce the smallest output ripple).
CC
CC
Voltage Regulator
output. The wide V
CC
output can be programmed via the M0-M1 pins to
CC
CC
is pulled to GND via an internal switch to aid
voltage, the part operates as a switched
CC
U
to GND.
IN
CC
IN
and C
U
supply for the SIM, and also
range enables the part to be
OUT
IN
W
capacitors should be
IN
is greater than V
IN
and C
. This flexibility is
IN
is less than the
OUT
U
to reduce
CC
,
If the input source impedance is very low (< 0.5 ), C
not be needed. Increasing the size of C
will reduce output voltage ripple—particularly with high V
voltages (4V or greater). A ceramic X5R or X7R type
capacitor is recommended for the flying capacitor C1 with
a value of 0.1 F or 0.22 F.
Output Ripple
Normal LTC1555L operation produces voltage ripple on
the V
to regulate. Low frequency ripple exists due to the hyster-
esis in the sense comparator and propagation delays in the
charge pump enable/disable circuits. High frequency ripple
is also present mainly from the ESR (equivalent series
resistance) in the output capacitor. Typical output ripple
(V
with a low ESR, 2.2 F output capacitor. (V
The magnitude of the ripple voltage depends on several
factors. High input voltages increase the output ripple
since more charge is delivered to C
A large C1 flying capacitor (> 0.22 F) also increases ripple
in step-up mode for the same reason. Large output current
load and/or a small output capacitor (< 1 F) results in
higher ripple due to higher output voltage dV/dt. High ESR
capacitors (ESR > 0.5 ) on the output pin cause high
frequency voltage spikes on V
A 2.2 F ceramic capacitor on the V
acceptable levels of output voltage ripple in nearly all
applications. Also, in order to keep noise down to a
minimum all capacitors should be placed close to
LTC1555L.
Level Translators
All SIMs and smart cards contain a clock input, a reset
input, and a bidirectional data input/output. The LTC1555L
provides level translators to allow controllers to
communicate with the SIM. (See Figure 1a and 1b). The
CLK and RST inputs to the SIM are level shifted from the
controller supply rails (DV
rails (V
provided two different ways. The first method is to use the
DATA pin as a bidirectional level translator. This configu-
ration is only allowed if the controller data output pin is
IN
< 4V) under maximum load is 75mV peak-to-peak
CC
CC
pin. Output voltage ripple is required for the parts
and GND). The data input to the SIM may be
CC
and GND) to the SIM supply
OUT
OUT
with every clock cycle.
CC
OUT
pin should produce
per charging cycle.
to 2.2 F or greater
CC
= 5V)
IN
may
IN