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參數(shù)資料
| 型號： | LTC1755 |
| 廠商： | Linear Technology Corporation |
| 英文描述： | 10-Bit D-Type Transparent Read-Back Latches 24-PDIP 0 to 70 |
| 中文描述： | 智能卡接口 |
| 文件頁數(shù)： | 8/12頁 |
| 文件大?。?/td> | 160K |
| 代理商： | LTC1755 |
8
LTC1755
APPLICATIO
S I
N
FOR
ATIO
U
10kV ESD Protection
All Smart Card pins (CLK, RST, I/O, AUX1, AUX2, V
CC
and
GND) can withstand over 10kV of human body model ESD
in situ. In order to ensure proper ESD protection, careful
board layout is required. The GND pin should be tied
directly to a ground plane. The V
CC
capacitor should be
located very close to the V
CC
pin and tied immediately to
the ground plane.
W
U
Capacitor Selection
The style and value of capacitors used with the LTC1755
determine several parameters such as output ripple volt-
age, charge pump strength, Smart Card switch debounce
time and V
CC
discharge rate.
Due to the switching nature of a capacitive charge pump,
low equivalent series resistance (ESR) capacitors are
recommended for the capacitors at V
IN
and V
CC
. When-
ever the flying capacitor is switched to the V
CC
charge
storage capacitor, considerable current flows. The prod-
uct of this high current and the ESR of the output capacitor
can generate substantial voltage spikes on the V
CC
output.
These spikes may cause problems with the Smart Card or
may interfere with the regulation loop of the LTC1755.
Therefore, ceramic or tantalum capacitors are recom-
mended rather than higher ESR aluminum capacitors.
Between ceramic and tantalum, ceramic capacitors gener-
ally have the lowest ESR. Some manufacturers have
developed low ESR tantalum capacitors but they can be
expensive and may still have higher ESR than ceramic
types. Thus, while they cannot be avoided, ESR spikes will
typically be lowest when using ceramic capacitors.
For ceramic capacitors there are several different materi-
als available to choose from. The choice of ceramic
material is generally based on factors such as available
capacitance, case size, voltage rating, electrical perfor-
mance and cost. For example, capacitors made of Y5V
material have high packing density, which provides high
capacitance for a given case size. However, Y5V capaci-
tors tend to lose considerable capacitance over the –40
°
C
to 85
°
C temperature range. X7R ceramic capacitors are
more stable over temperature but don’t provide the high
packing density. Therefore, large capacitance values are
generally not available in X7R ceramic.
The value and style of the flying capacitor are important
not only for the charge pump but also because they
provide the large debounce time for the Smart Card
detection channel. A 0.68
μ
F X7R capacitor is a good
choice for the flying capacitor because it provides fairly
constant capacitance over temperature and its value is not
prohibitively large.
The charge storage capacitor on the V
CC
pin determines
the ripple voltage magnitude and the discharge time of the
Smart Card voltage. To minimize ripple, generally, a large
value is needed. However, to meet the V
CC
discharge rate
specification, the value should not exceed 20
μ
F. A 10
μ
F
capacitor can be used but the ripple magnitude will be
higher leading to worse apparent DC load regulation.
Typically a 15
μ
F to 18
μ
F Y5V ceramic capacitor is the best
choice for the V
CC
charge storage capacitor. For best
performance, this capacitor should be connected as close
as possible to the V
CC
and GND pins. Note that most of the
electrostatic discharge (ESD) current on the six Smart
Card pins is absorbed by this capacitor.
The bypass capacitor at V
IN
is also important. Large dips
on the input supply due to ESR may cause problems with
the internal circuitry of the LTC1755. A good choice for the
input bypass capacitor is a 10
μ
F Y5V style ceramic
Dynamic Pull-Up Current Sources
The current sources on the bidirectional pins (DATA,
AUX2IN, AUX1IN, I/O, AUX2 and AUX1) are dynamically
activated to achieve a fast rise time with a relatively small
static current (Figure 1). Once a bidirectional pin is relin-
quished, a small start-up current begins to charge the
node. An edge rate detector determines if the pin is
released by comparing its slew rate with an internal
Figure 1. Dynamic Pull-Up Current Sources
–
+
δ
V
δ
t
I
START
1755 F01
V
REF
BIDIRECTIONAL PIN
V
CC
OR DV
CC
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LTC1755EGN | 功能描述:IC SMART CARD INTERFACE 24SSOP RoHS:否 類別:集成電路 (IC) >> 接口 - 專用 系列:- 特色產(chǎn)品:NXP - I2C Interface 標(biāo)準(zhǔn)包裝:1 系列:- 應(yīng)用:2 通道 I²C 多路復(fù)用器 接口:I²C，SM 總線 電源電壓:2.3 V ~ 5.5 V 封裝/外殼:16-TSSOP（0.173"，4.40mm 寬） 供應(yīng)商設(shè)備封裝:16-TSSOP 包裝:剪切帶 (CT) 安裝類型:表面貼裝 產(chǎn)品目錄頁面:825 (CN2011-ZH PDF) 其它名稱:568-1854-1 |
| LTC1755EGN#PBF | 功能描述:IC SMART CARD INTERFACE 24SSOP RoHS:是 類別:集成電路 (IC) >> 接口 - 專用 系列:- 特色產(chǎn)品:NXP - I2C Interface 標(biāo)準(zhǔn)包裝:1 系列:- 應(yīng)用:2 通道 I²C 多路復(fù)用器 接口:I²C，SM 總線 電源電壓:2.3 V ~ 5.5 V 封裝/外殼:16-TSSOP（0.173"，4.40mm 寬） 供應(yīng)商設(shè)備封裝:16-TSSOP 包裝:剪切帶 (CT) 安裝類型:表面貼裝 產(chǎn)品目錄頁面:825 (CN2011-ZH PDF) 其它名稱:568-1854-1 |
| LTC1755EGN#TR | 功能描述:IC SMART CARD INTERFACE 24SSOP RoHS:否 類別:集成電路 (IC) >> 接口 - 專用 系列:- 特色產(chǎn)品:NXP - I2C Interface 標(biāo)準(zhǔn)包裝:1 系列:- 應(yīng)用:2 通道 I²C 多路復(fù)用器 接口:I²C，SM 總線 電源電壓:2.3 V ~ 5.5 V 封裝/外殼:16-TSSOP（0.173"，4.40mm 寬） 供應(yīng)商設(shè)備封裝:16-TSSOP 包裝:剪切帶 (CT) 安裝類型:表面貼裝 產(chǎn)品目錄頁面:825 (CN2011-ZH PDF) 其它名稱:568-1854-1 |
| LTC1755EGN#TRPBF | 功能描述:IC SMART CARD INTERFACE 24SSOP RoHS:否 類別:集成電路 (IC) >> 接口 - 專用 系列:- 特色產(chǎn)品:NXP - I2C Interface 標(biāo)準(zhǔn)包裝:1 系列:- 應(yīng)用:2 通道 I²C 多路復(fù)用器 接口:I²C，SM 總線 電源電壓:2.3 V ~ 5.5 V 封裝/外殼:16-TSSOP（0.173"，4.40mm 寬） 供應(yīng)商設(shè)備封裝:16-TSSOP 包裝:剪切帶 (CT) 安裝類型:表面貼裝 產(chǎn)品目錄頁面:825 (CN2011-ZH PDF) 其它名稱:568-1854-1 |
| LTC1755EGNPBF | 制造商:Linear Technology 功能描述:Smart Card Interface LTC1755EGN |
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