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參數(shù)資料
| 型號(hào)： | LTC1955 |
| 廠商： | Linear Technology Corporation |
| 英文描述： | Dual Smart Card Interface with Serial Control |
| 中文描述： | 雙智能卡接口，具有串行控制 |
| 文件頁數(shù)： | 17/20頁 |
| 文件大小： | 259K |
| 代理商： | LTC1955 |
LTC1955
17
sn1955 1955fs
both DV
CC
and V
BATT
when in shutdown. For applications
that require virtually zero shutdown current, the DV
CC
pin
can be grounded. This will reduce the V
BATT
current to well
under a single microampere. Internal logic ensures that
the LTC1955 is in shutdown when DV
CC
is grounded.
Note, however, that all of the logic signals that are refer-
enced to DV
CC
(D
IN
, SCLK, LD, DATA, R
IN
, SYNC, ASYNC
and NC/NO) will have to be at 0V as well to prevent ESD
diodes to DV
CC
from being forward biased.
Operation at Higher Supplies
If a 5.5V to 6V supply voltage is available, it is possible to
achieve some power savings by bypassing the charge
pump. The higher supply can be connected directly to the
CPO pin. As long as the voltage on CPO is higher than that
at which it ordinarily regulates (5.35V or 3.7V depending
on voltage selections) the charge pump’s oscillator will
not run. This configuration can give considerable power
savings since the charge pump is not being used.
A voltage source is still needed on both DV
CC
and SV
BATT
/
PV
BATT
in this configuration. Recall that DV
CC
sets the
logic reference level for all the control and smart card
communication pins. The voltage on SV
BATT
/PV
BATT
can
be any convenient level that meets the parameters in the
Electrical Characteristics table.
The 5.5V to 6V supply can be left permanently connected
to CPO but there will be approximately 5
μ
A of current flow
into CPO when the LTC1955 is in shutdown.
Charge Pump Strength
Under low V
BATT
conditions, the amount of current avail-
able to the smart cards is limited by the charge pump.
Figure 6 shows how the LTC1955 can be modeled as a
Thevenin equivalent circuit to determine the amount of
current available given the effective input voltage, 2V
BATT
and the effective open-loop output resistance, R
OLCP
.
From Figure 6, the available current is given by:
I
I
V
V
R
CCA
CCB
BATT
CPO
OLCP
+
≤
2
–
APPLICATIU
W
U
U
R
OLCP
is dependent on a number of factors including the
switching term, 1/(f
OSC
C
FLY
), internal switch resis-
tances and the nonoverlap period of the switching circuit.
However, for a given R
OLCP
, the minimum CPO voltage can
be determined from the following expression:
V
V
I
I
R
)
CPO
BATT
CCA
CCB
OLCP
≥
+
2
– (
The LDOs have been designed to meet all applicable smart
card standards for V
CC
with V
CPO
as low as 5.13V. Given
this information, trade-offs can be made by the user with
regard to total consumption (I
CCA
+ I
CCB
) and minimum
supply voltage.
+
LDO A
2V
BATT
1955 F06
CPO
R
OLCP
V
CCA
LDO B
V
CCB
Changing the Smart Card Supply Voltage
Although the LTC1955 control system will allow the smart
card voltage to be changed from one value to the next
without an interim power down, this is not recommended.
When changing from a higher voltage to a lower voltage
there will generally not be a problem; however, changing
from a lower voltage to a higher voltage will result in both
an undervoltage condition and an overcurrent condition
on that channel. The likely result is that the channel will
automatically deactivate. Applicable smart card standards
specify that the smart card supply be powered to zero
before applying a new voltage.
Compliance Testing
Inductance due to long leads on type approval equipment
can cause ringing and overshoot that leads to testing
problems. Small amounts of capacitance and damping
resistors can be included in the application without com-
promising the normal electrical performance of the
LTC1955 or smart card system. Generally a 100
resistor
and a 20pF capacitor will accomplish this as shown in
Figure 9.
Figure 6. Equivalent Open-Loop Circuit
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| LTC1955EUH | 功能描述:IC INTERFACE DL SMART CARD 32QFN RoHS:否 類別:集成電路 (IC) >> 接口 - 控制器 系列:- 標(biāo)準(zhǔn)包裝:2,450 系列:- 控制器類型:SPI 總線至 I²C 總線橋接 接口:I²C，串行，SPI 電源電壓:2.4 V ~ 3.6 V 電流 - 電源:11mA 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:24-VFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:24-HVQFN（4x4） 包裝:托盤 配用:568-3511-ND - DEMO BOARD SPI TO I2C 其它名稱:935286452157SC18IS600IBSSC18IS600IBS-ND |
| LTC1955EUH#PBF | 功能描述:IC INTERFACE DL SMART CARD 32QFN RoHS:是 類別:集成電路 (IC) >> 接口 - 控制器 系列:- 標(biāo)準(zhǔn)包裝:2,450 系列:- 控制器類型:SPI 總線至 I²C 總線橋接 接口:I²C，串行，SPI 電源電壓:2.4 V ~ 3.6 V 電流 - 電源:11mA 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:24-VFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:24-HVQFN（4x4） 包裝:托盤 配用:568-3511-ND - DEMO BOARD SPI TO I2C 其它名稱:935286452157SC18IS600IBSSC18IS600IBS-ND |
| LTC1955EUH#TR | 功能描述:IC SMART CARD INTERFC DUAL 32QFN RoHS:否 類別:集成電路 (IC) >> 接口 - 控制器 系列:- 標(biāo)準(zhǔn)包裝:2,450 系列:- 控制器類型:SPI 總線至 I²C 總線橋接 接口:I²C，串行，SPI 電源電壓:2.4 V ~ 3.6 V 電流 - 電源:11mA 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:24-VFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:24-HVQFN（4x4） 包裝:托盤 配用:568-3511-ND - DEMO BOARD SPI TO I2C 其它名稱:935286452157SC18IS600IBSSC18IS600IBS-ND |
| LTC1955EUH#TRPBF | 功能描述:IC INTERFACE DL SMART CARD 32QFN RoHS:是 類別:集成電路 (IC) >> 接口 - 控制器 系列:- 標(biāo)準(zhǔn)包裝:2,450 系列:- 控制器類型:SPI 總線至 I²C 總線橋接 接口:I²C，串行，SPI 電源電壓:2.4 V ~ 3.6 V 電流 - 電源:11mA 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:24-VFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:24-HVQFN（4x4） 包裝:托盤 配用:568-3511-ND - DEMO BOARD SPI TO I2C 其它名稱:935286452157SC18IS600IBSSC18IS600IBS-ND |
| LTC1955IUH#PBF | 功能描述:IC SMART CARD INTERFACE DL 32QFN RoHS:是 類別:集成電路 (IC) >> 接口 - 控制器 系列:- 標(biāo)準(zhǔn)包裝:2,450 系列:- 控制器類型:SPI 總線至 I²C 總線橋接 接口:I²C，串行，SPI 電源電壓:2.4 V ~ 3.6 V 電流 - 電源:11mA 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:24-VFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:24-HVQFN（4x4） 包裝:托盤 配用:568-3511-ND - DEMO BOARD SPI TO I2C 其它名稱:935286452157SC18IS600IBSSC18IS600IBS-ND |
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