LTC1555CGN Linear Technology, LTC1555CGN Datasheet - Page 7

• Manufacturer Part Number: LTC1555CGN
• Description: IC LEVEL TRANSLATOR 16-SSOP
• Manufacturer: Linear Technology

Specifications of LTC1555CGN

• 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: 0°C ~ 70°C
• Package / Case: 16-SSOP
• Supply Voltage: 1.8 V ~ 5.5 V
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Data Rate: -

APPLICATIONS
The LTC1555/LTC1556 perform the two primary func-
tions necessary for 3V controllers (e.g., GSM cellular
telephone controllers, smart card readers, etc.) to com-
municate with 5V SIMs or smart cards. They produce a
regulated 5V V
translators for communication between the SIM and the
controller.
V
The regulator section of the LTC1555/LTC1556 (refer to
the Block Diagram) consists of a step-up/step-down charge
pump DC/DC converter. The charge pump can operate
over a wide input voltage range (2.7V to 10V) while
maintaining a regulated V
enables the parts to be powered directly from a battery (if
desired) rather than from a 3V DC/DC converter output.
When V
switched capacitor voltage doublers. When V
than V
converters. In either case, voltage conversion requires
only one small flying capacitor and output capacitor.
The V
the M0 and M1 mode pins. This feature is useful in
applications where either a 5V or 3V SIM may be used. The
charge pump V
V
(M0, M1 = 0), V
to aid in proper system supply sequencing.
The soft start feature limits inrush currents upon start-up
or coming out of shutdown mode. When the SS pin is tied
to GND, the soft start feature is enabled. This limits the ef-
fective inrush current out of V
(C
when powering the LTC1555/LTC1556 from a 3V DC/DC
output since the unlimited inrush current may approach
200mA and cause voltage transients on the 3V supply. How-
ever, in cases where fast turn-on time is desired, the soft
start feature may be overridden by tying the SS pin to DV
CC
IN
OUT
if desired. When the charge pump is put into shutdown
Voltage Regulator
CC
= 10 F). Inrush current limiting is especially useful
CC
IN
output can be programmed to either 5V or 3V via
is less than the desired V
the parts operate as gated switch step-down
CC
CC
CC
output may also be connected directly to
supply for the SIM and provide level
is pulled to GND via an internal switch
U
INFORMATION
U
CC
output. The wide V
IN
to approximately 25mA
CC
W
the parts operate as
IN
U
is greater
IN
range
CC
.
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 10 F or greater
(ceramic capacitors will produce the smallest output ripple).
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 (8V or greater). A ceramic capacitor is recom-
mended for the flying capacitor C1 with a value of 0.1 F or
0.22 F.
Output Ripple
Normal LTC1555/LTC1556 operation produces voltage
ripple on the V
the parts to regulate. Low frequency ripple exists due to
the hysteresis 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
75mV peak-to-peak with a low ESR, 10 F output capaci-
tor. For applications requiring V
larger C
mum ripple in the 75mV range.
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 (< 10 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 10 F ceramic capacitor on the V
acceptable levels of output voltage ripple in nearly all
applications. However, there are several ways to further
OUT
capacitor is recommended to maintain maxi-
CC
pin. Output voltage ripple is required for
IN
LTC1555/LTC1556
IN
and C
< 8V) under maximum load is
OUT
IN
OUT
to exceed 8V, a 22 F or
OUT
with every clock cycle.
CC
capacitors should be
OUT
IN
pin should produce
per charging cycle.
and C
to 22 F or greater
OUT
to reduce
IN
may
7
IN