LTC1324 データシートの表示（PDF） - Linear Technology
部品番号
コンポーネント説明
メーカー
LTC1324 Datasheet PDF : 8 Pages
| |||
U
W
SWITCHING WAVEFORMS
3V
RXEN
0V
5V
RXO, RXO, RXDO
VOL
VOH
RXO, RXO, RXDO
0V
1.5V
1.5V
f = 1MHz: tr ≤ 10ns: tf ≤ 10ns
tZL
tLZ
2.3V
OUTPUT NORMALLY LOW
tZH
tHZ
OUTPUT NORMALLY HIGH
2.3V
Figure 7. Receiver Enable and Disable
0.5V
0.5V
1324 F07
LTC1324
APPLICATIONS INFORMATION
Thermal Shutdown Protection
The LTC1324 includes a thermal shutdown circuit which
protects against prolonged shorts at the driver outputs. If
a driver output is shorted to another output, ground or to
the power supply, the current will be initially limited to a
maximum of 250mA. When the die temperature rises
above 150°C, the thermal shutdown circuit turns off the
driver outputs. When the die cools to about 130°C, the
outputs turn on. If the short still exists, the part will heat
again and the cycle will repeat. This oscillation occurs at
about 10Hz and prevents the part from being damaged by
excessive power dissipation. When the short is removed,
the part will return to normal operation.
Power Shutdown
The power shutdown feature of the LTC1324 is designed
for battery-powered systems. When SHDN is forced high,
the part enters shutdown mode. In shutdown, the supply
current typically drops from 1mA to 1µA and the driver and
receiver outputs are three-stated.
Supply Bypassing
The LTC1324 requires VCC be bypassed to prevent data
errors. A 1µF capacitor from VCC to ground is adequate.
EMI Filters and Slew Rate Control
Most LocalTalk applications need to use an electromag-
netic interference (EMI) filter consisting of a resistor-
capacitor T network between each driver, receiver and the
connector. Unfortunately, the resistors will attenuate the
driver’s output signal applied to the cable. Because the
LTC1324 uses a single 5V supply, the resistors’ values
should be reduced to 5.1Ω to ensure enough voltage
swing on the cable (Figure 8). Another way to get maxi-
mum swing and EMI immunity is to use a ferrite bead and
capacitor as the T network (Figure 9). For data rates below
250kbps, the LTC1324 features a low EMI mode which
limits the rise time of the drivers to 400ns. With a lower
rise time, the EMI network can be eliminated, allowing
more signal voltage to reach the cable. Figures 10 and 11
show the output signals of the driver with different slew
rates.
TXD+
TXD
TXD–
5.1Ω
5.1Ω
5.1Ω
100pF
5.1Ω
100pF
120Ω
1324 F08
Figure 8
FERRITE BEAD
FERRITE BEAD
100pF
1324 F09
Figure 9
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
7
Share Link: 