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參數(shù)資料
| 型號： | LTC1555LEGN#TRPBF |
| 廠商： | Linear Technology |
| 文件頁數(shù)： | 6/8頁 |
| 文件大?。?/td> | 0K |
| 描述： | IC LEVEL TRANSLATOR 16-SSOP |
| 標(biāo)準(zhǔn)包裝： | 2,500 |
| 邏輯功能： | 電平移位器 |
| 位數(shù)： | 1 |
| 輸入類型： | 電壓 |
| 輸出類型： | 電壓 |
| 通道數(shù)： | 1 |
| 輸出/通道數(shù)目： | 1 |
| 差分 - 輸入:輸出： | 無/無 |
| 傳輸延遲（最大）： | 18ns |
| 電源電壓： | 1.8 V ~ 5.5 V |
| 工作溫度： | -40°C ~ 85°C |
| 封裝/外殼： | 16-SSOP（0.154"，3.90mm 寬） |
| 供應(yīng)商設(shè)備封裝： | 16-SSOP |
| 包裝： | 帶卷 (TR) |
LTC1555L
6
APPLICATIO S I FOR ATIO
WU
U
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 VCC supply for the SIM, and also
provides level translators for communication between the
SIM and the controller.
VCC Voltage Regulator
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
VCC output. The wide VIN range enables the part to be
powered directly from a battery (if desired) rather than
from a DC/DC converter output. When VIN is less than the
selected VCC voltage, the part operates as a switched
capacitor voltage doubler. When VIN is greater than VCC,
the part operates as gated switch step-down converter. In
either case, voltage conversion requires only one small
flying capacitor and output capacitor.
The VCC output can be programmed via the M0-M1 pins to
either 3V, 5V or direct connection to VIN. This flexibility is
useful in applications where multiple voltage SIMs may be
used. When the charge pump is put into shutdown (M0,
M1 = 0), VCC is pulled to GND via an internal switch to aid
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 VCC to GND.
Capacitor Selection
For best performance, it is recommended that low ESR
(< 0.5
)capacitorsbeusedforbothCINandCOUTtoreduce
noise and ripple. The CIN and COUT capacitors should be
either ceramic or tantalum and should be 1
F or greater
(ceramic capacitors will produce the smallest output ripple).
If the input source impedance is very low (< 0.5
),CINmay
not be needed. Increasing the size of COUTto2.2Forgreater
will reduce output voltage ripple—particularly with high VIN
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 0.22F.
Output Ripple
Normal LTC1555L operation produces voltage ripple on
the VCC pin. Output voltage ripple is required for the parts
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
(VIN < 4V) under maximum load is 75mV peak-to-peak
with a low ESR, 2.2
F output capacitor. (VCC = 5V)
The magnitude of the ripple voltage depends on several
factors. High input voltages increase the output ripple
since more charge is delivered to COUT per charging cycle.
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 VOUT with every clock cycle.
A 2.2
F ceramic capacitor on the VCC pin should produce
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 (DVCC and GND) to the SIM supply
rails (VCC and GND). The data input to the SIM may be
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
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