LT1180A Просмотр технического описания (PDF) - Linear Technology
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LT1180A Datasheet PDF : 12 Pages
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LT1180A/LT1181A
PI FU CTIO S
TR1 IN, TR2 IN: RS232 Driver Input Pins. These inputs are
TTL/CMOS compatible. Inputs should not be allowed to
float. Tie unused inputs to VCC.
TR1 OUT, TR2 OUT: Driver Outputs at RS232 Voltage
Levels. Driver output swing meets RS232 levels for loads
up to 3k. Slew rates are controlled for lightly loaded lines.
Output current capability is sufficient for load conditions
up to 2500pF. Outputs are in a high impedance state when
in shutdown mode, VCC = 0V, or when the driver disable
pin is active. Outputs are fully short-circuit protected from
V – + 30V to V + – 30V. Applying higher voltages will not
damage the device if the overdrive is moderately current
limited. Short circuits on one output can load the power
supply generator and may disrupt the signal levels of the
other outputs. The driver outputs are protected against
ESD to ±10kV for human body model discharges.
REC1 IN, REC2 IN: Receiver Inputs. These pins accept
RS232 level signals (±30V) into a protected 5k terminating
resistor. The receiver inputs are protected against ESD to
±10kV for human body model discharges. Each receiver
provides 0.4V of hysteresis for noise immunity. Open
receiver inputs assume a logic low state.
REC1 OUT, REC2 OUT: Receiver outputs with TTL/CMOS
Voltage Levels. Outputs are in a high impedance state
when in shutdown mode to allow data line sharing. Outputs
are fully short-circuit protected to ground or VCC with the
power on, off or in the shutdown mode.
C1+, C1–, C2 +, C2 –: Commutating Capacitor Inputs.
These pins require two external capacitors C ≥ 0.1µF: one
from C1+ to C1– and another from C2+ to C2 –. C1 should
be deleted if a separate 12V supply is available and con-
nected to pin C1+. Similarly, C2 should be deleted if a
separate – 12V supply is connected to pin V –.
U
ESD PROTECTIO
The RS232 line inputs of the LT1180A/LT1181A have on-
chip protection from ESD transients up to ±10kV. The
protection structures act to divert the static discharge
safely to system ground. In order for the ESD protection to
function effectively, the power supply and ground pins of
the circuit must be connected to ground through low
impedances. The power supply decoupling capacitors and
charge pump storage capacitors provide this low imped-
ance in normal application of the circuit. The only con-
straint is that low ESR capacitors must be used for
bypassing and charge storage. ESD testing must be done
with pins VCC, VL, V+, V –, and GND shorted to ground or
connected with low ESR capacitors.
ESD Test Circuit
+
0.1µF
+
0.1µF
0.1µF
1
NC
2 C1+
+ 3 V+
LT1180A
18
ON/OFF
5V VCC 17
16
GND
4 C1–
DR1 OUT 15
5 C2+
RX1 IN 14
0.1µF
6 C2–
+ 7 V–
RX1 OUT 13
DR1 IN 12
RS232
LINE PINS
PROTECTED
TO ±10kV
8 DR2 OUT
9 RX2 IN
DR2 IN 11
RX2 OUT 10
+
0.1µF
RS232
LINE PINS
PROTECTED
TO ±10kV
LT1180A • ESD TC
11801afb
6
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