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参数资料
| 型号： | LTC1955IUH#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 4/22页 |
| 文件大小： | 0K |
| 描述： | IC SMART CARD INTERFACE DL 32QFN |
| 标准包装： | 2,500 |
| 控制器类型： | 智能卡接口 |
| 接口： | 4 线串行 |
| 电源电压： | 1.7 V ~ 5.5 V |
| 电流 - 电源： | 10µA |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 32-WFQFN 裸露焊盘 |
| 供应商设备封装： | 32-QFN 裸露焊盘（5x5） |
| 包装： | 带卷 (TR) |
LTC1955
12
1955fd
For more information www.linear.com/LTC1955
Smart Card Detection Circuits
The PRES A/PRES B pins are used to detect the presence
of a smart card. An automatic debounce circuit waits until
a smart card has been present for a continuous period
of typically 35ms. Once a valid card indication exists,
the status bit for that channel is updated and may be
polled by cycling data through the serial port. The DOUT
pin (equivalent to D15) of the serial port can be used to
indicate the presence of a card on channel A in real time
if LD is held low.
The PRES A/PRES B pins have built-in pull-up current
sources, so no external components are required for
switchdetection.Thepull-upcurrentsourcesaredesigned
to have a small current when the pin voltage is below ap-
proximately 1V, but somewhat higher current when the
pin voltage reaches 1V. This helps maintain low power
dissipation when a card is present and yet fast response
time to a card removal.
The PRES A/PRES B pins can be configured to respond
to either normally open or normally closed switches via
the NC/NO pin.
Activation/Deactivation
For maximum flexibility, the activation sequencing of the
smart card is left to the application programmer. Upon
activation, to comply with relevant smart card standards,
none of the smart card signal pins will be allowed to go
highbeforethesmartcardsupplyvoltage(VCCA/VCCB)has
reached its final value. Deactivation can be achieved either
manually or automatically. An electrical fault condition will
trigger the automatic deactivation.
Manual deactivation may be performed under software
control by setting the smart card pins to 0V in the desired
sequence via the control pins (SYNC, ASYNC, RIN, DATA
and the serial port). For most applications, this will be
cumbersome and the built-in deactivation will be used
instead.
Automatic Deactivation
The built-in deactivation sequence can be executed via the
serial port simply by setting the appropriate control bits
(D0 and D1 or D8 and D9) to 0. The deactivation sequence
is outlined below.
1. The RST A/RST B pin for that channel is immediately
brought low.
2. The deactivation of the CLK A/CLK B pins depends upon
which type of card is used:
If the smart card was set to asynchronous mode, then
the CLK A/CLK B pin will be latched low on its next
falling edge. If no falling edges occur within 5s (min),
then the CLK A/CLK B line is forced low.
Ifthesmartcardwassettosynchronousmode,thenthe
CLK A/CLK B pin is immediately latched at its current
value (either high or low) and then forced low after a
duration of 5s (min). During the 5s timeout period,
changes on SYNC will be ignored.
3. The I/O A/I/O B, C4A and C8A pins for that channel are
brought low.
4. The VCCA/VCCB pin is brought low.
If an error occurs on one smart card, operation of the
other card is unaffected.
Electrical Fault Detection
Several types of faults are detected by the LTC1955. They
include VCCA/VCCB undervoltage, VCCA/VCCB overcurrent,
CLK A/CLK B, RST A/RST B, C8A, C4A short-circuit, card
removalduringatransaction,failedanswertoreset(ATR),
supplyundervoltageorUNDERVandchipovertemperature.
To prevent false errors from plaguing the microcontroller,
the electrical faults are acted upon only after a 5s (min)
timeout period. Card removal during transaction faults
initiate the deactivation sequence immediately.
operaTion
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