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參數(shù)資料
| 型號： | MC145406SD |
| 廠商： | MOTOROLA INC |
| 元件分類： | 通用總線功能 |
| 英文描述： | UltraLow-Supply Current/Supply-Voltage Supervisory Circuits 6-SOT-23 -40 to 85 |
| 中文描述： | LINE TRANSCEIVER, PDSO16 |
| 封裝： | SSOP-16 |
| 文件頁數(shù)： | 5/12頁 |
| 文件大?。?/td> | 155K |
| 代理商： | MC145406SD |
MC145406
5
MOTOROLA
APPLICATIONS INFORMATION
The MC145406 has been designed to meet the electrical
specifications of standards EIA 232–E and CCITT V.28.
EIA 232–E defines the electrical and physical interface be-
tween Data Communication Equipment (DCE) and Data
Terminal Equipment (DTE). A DCE is connected to a DTE
using a cable that typically carries up to 25 leads. These
leads, referred to as interchange circuits, allow the transfer
of timing, data, control, and test signals. Electrically this
transfer requires level shifting between the TTL/CMOS log-
ic levels of the computer or modem and the high voltage lev-
els of EIA 232–E, which can range from
±
3 to
±
25 V. The
MC145406 provides the necessary level shifting as well as
meeting other aspects of the EIA 232–E specification.
DRIVERS
As defined by the specification, an EIA 232–E driver pres-
ents a voltage of between
±
5 to
±
15 V into a load of be-
tween 3 to 7 k
. A logic 1 at the driver input results in a
voltage of between –
5 to – 15 V. A logic 0 results in a voltage
between + 5 to + 15V. When operating VDD and VSS at
±
7 to
±
12 V, the MC145406 meets this requirement. When operat-
ing at
±
5 V, the MC145406 drivers produce less than
±
5 V at the output (when terminated), which does not meet
EIA 232–E specification. However, the output voltages when
using a
±
5 V power supply are high enough (around
±
4 V) to permit proper reception by an EIA 232–E receiver,
and can be used in applications where strict compliance to
EIA 232–E is not required.
Another requirement of the MC145406 drivers is that
they withstand a short to another driver in the EIA 232–E
cable. The worst–case condition that is permitted by
EIA 232–E is a
±
15 V source that is current limited to 500
mA. The MC145406 drivers can withstand this condition
momentarily. In most short circuit conditions the source
driver will have a series 300
output impedance needed
to satisfy the EIA 232–E driver requirements. This will re-
duce the short circuit current to under 40 mA which is an
acceptable level for the MC145406 to withstand.
Unlike some other drivers, the MC145406 drivers feature
an internally–limited output slew–rate that does not exceed
30 V per
μ
s.
RECEIVERS
The job of an EIA 232–E receiver is to level–shift voltages
in the range of – 25 to + 25 V down to TTL/CMOS logic lev-
els (0 to + 5 V). A voltage of between – 3 and – 25 V on Rx1
is defined as a mark and produces a logic 1 at DO1. A volt-
age between + 3 and + 25 V is a space and produces a logic
zero. While receiving these signals, the Rx inputs must pres-
ent a resistance between 3 and 7 k
. Nominally, the input re-
sistance of the Rx1–Rx3 inputs is 5.4 k
.
The input threshold of the Rx1–Rx3 inputs is typically
biased at 1.8 V above ground (GND) with typically 800 mV of
hysteresis included to improve noise immunity. The 1.8 V
bias forces the appropriate DO pin to a logic 1 when its Rx
input is open or grounded as called for in the EIA 232–E
specification. Notice that TTL logic levels can be applied to
the Rx inputs in lieu of normal EIA 232–E signal levels. This
might be helpful in situations where access to the modem or
computer through the EIA 232–E connector is necessary
with TTL devices. However, it is important not to connect the
EIA 232–E outputs (Tx1–Tx3) to TTL inputs since TTL oper-
ates off + 5 V only, and may be damaged by the high output
voltage of the MC145406.
The DO outputs are to be connected to a TTL or CMOS
input (such as an input to a modem chip). These outputs
will swing from VCC to ground, allowing the designer to op-
erate the DO and DI pins from digital power supply. The Tx
and Rx sections are independently powered by VDD and
VSS so that one may run logic at + 5 V and the EIA 232–E
signals at
±
12 V.
POWER SUPPLY CONSIDERATIONS
Figure 4 shows a technique to guard against excessive
device current.
The diode D1 prevents excessive current from flowing
through an internal diode from the VCC pin to the VDD pin
when VDD < VCC by approximately 0.6 V. This high current
condition can exist for a short period of time during power
up/down. Additionally, if the + 12 V supply is switched off
while the + 5 V is on and the off supply is a low impedance
to ground, the diode D1 will prevent current flow through
the internal diode.
The diode D2 is used as a voltage clamp, to prevent VSS
from drifting positive to VCC, in the event that power is re-
moved from VSS (Pin 12). If VSS power is removed, and the
impedance from the VSS pin to ground is greater than
approximately 3 k
, this pin will be pulled to VCC by internal
circuitry causing excessive current in the VCC pin.
If by design, neither of the above conditions are allowed
to exist, then the diodes D1 and D2 are not required.
ESD PROTECTION
ESD protection on IC devices that have their pins accessi-
ble to the outside world is essential. High static voltages ap-
plied to the pins when someone touches them either directly
or indirectly can cause damage to gate oxides and transistor
junctions by coupling a portion of the energy from the I/O pin
to the power supply buses of the IC. This coupling will usually
occur through the internal ESD protection diodes. The key to
protecting the IC is to shunt as much of the energy to ground
as possible before it enters the IC. Figure 4 shows a tech-
nique which will clamp the ESD voltage at approximately
±
15 V using the MMVZ15VDLT1. Any residual voltage which
appears on the supply pins is shunted to ground through the
capacitors C1–C3. This scheme has provided protection to
the interface part up to
±
10 kV, using the human body model
test.
相關PDF資料 |
PDF描述 |
|---|---|
| MC145407 | 5 Volt Only Driver/ Receiver(5V 驅(qū)動器/接收器) |
| MC145407DW | UltraLow-Supply Current/Supply-Voltage Supervisory Circuits 6-SOT-23 -40 to 85 |
| MC145407P | UltraLow-Supply Current/Supply-Voltage Supervisory Circuits 6-SOT-23 -40 to 85 |
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| MC145407DW | 制造商:Motorola Inc 功能描述: 制造商:Motorola Inc 功能描述:Line Transceiver, 3-Driver, 3-Receiver, 20 Pin, Plastic, SOP |
| MC145407DWR2 | 制造商:Motorola Inc 功能描述:Line Transceiver, 3-Driver, 3-Receiver, 20 Pin, Plastic, SOP |
| MC145408DWR2 | 制造商:Freescale Semiconductor 功能描述:CMOS DRIVER/RECEIVER, 5 X 5 |
| MC145412P | 制造商:Motorola Inc 功能描述: |
| MC14541BCP | 功能描述:計時器和支持產(chǎn)品 LOG CMOS OSILATR TIMER RoHS:否 制造商:Micrel 類型:Standard 封裝 / 箱體:SOT-23 內(nèi)部定時器數(shù)量:1 電源電壓-最大:18 V 電源電壓-最小:2.7 V 最大功率耗散: 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 封裝:Reel |
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