参数资料
| 型号： | LTC1556CGN#TR |
| 厂商： | Linear Technology |
| 文件页数： | 10/12页 |
| 文件大小： | 0K |
| 描述： | IC LEVEL XLATOR/SIM PS 20SSOP |
| 标准包装： | 2,500 |
| 逻辑功能： | 电平移位器 |
| 位数： | 1 |
| 输入类型： | 电压 |
| 输出类型： | 电压 |
| 通道数： | 1 |
| 输出/通道数目： | 1 |
| 差分 - 输入:输出： | 无/无 |
| 传输延迟（最大）： | 18ns |
| 电源电压： | 1.8 V ~ 5.5 V |
| 工作温度： | 0°C ~ 70°C |
| 封装/外壳： | 20-SSOP（0.154"，3.90mm 宽） |
| 供应商设备封装： | 20-SSOP |
| 包装： | 带卷 (TR) |
7
LTC1555/LTC1556
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 VCC supply for the SIM and provide level
translators for communication between the SIM and the
controller.
VCC Voltage Regulator
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 VCC output. The wide VIN range
enables the parts to be powered directly from a battery (if
desired) rather than from a 3V DC/DC converter output.
When VIN is less than the desired VCC the parts operate as
switched capacitor voltage doublers. When VIN is greater
than VCC the parts operate as gated switch step-down
converters. In either case, voltage conversion requires
only one small flying capacitor and output capacitor.
The VCC output can be programmed to either 5V or 3V via
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 VCC output may also be connected directly to
VIN if desired. 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.
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 VIN to approximately 25mA
(COUT = 10F). Inrush current limiting is especially useful
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 DVCC.
APPLICATIONS INFORMATION
WU
U
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 10
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 COUTto22Forgreater
will reduce output voltage ripple—particularly with high VIN
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 VCC pin. Output voltage ripple is required for
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 (VIN < 8V) under maximum load is
75mV peak-to-peak with a low ESR, 10
F output capaci-
tor. For applications requiring VIN to exceed 8V, a 22F or
larger COUT capacitor is recommended to maintain maxi-
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 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 (< 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 VOUT with every clock cycle.
A 10
F ceramic capacitor on the VCC pin should produce
acceptable levels of output voltage ripple in nearly all
applications. However, there are several ways to further
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