LT1330
6
1330fb
PIN FUNCTIONS
V
CC
: 5V Input Supply Pin. This pin should be decoupled
with a 0.1μF ceramic capacitor close to the package pin.
Insuffi cient supply bypassing can result in low output drive
levels and erratic charge pump operation.
V
L
: 3V Logic Supply Pin for all RS232 Receivers. Like V
CC
,
the V
L
input should be decoupled with a 0.1μF ceramic
capacitor. This pin may also be connected to 5V.
GND: Ground Pin.
ON/OFF: TTL/CMOS Compatible Operating Mode Control.
A logic low puts the device in the low power shutdown
mode. All three drivers and four receivers (RX1, RX2,
RX3, and RX4) assume a high impedance output state
in shutdown. Only receiver RX5 remains active while the
transceiver is in shutdown. The transceiver consumes
only 60μA of supply current while in shutdown. A logic
high fully enables the transceiver.
DRIVER DISABLE: This pin provides an alternate control
for the charge pump and RS232 drivers. A logic high
on this pin shuts down the charge pump and places all
driver outputs in a high impedance state. All fi ve receivers
remain active under these conditions. Floating the driver
disable pin or driving it to a logic low level fully enables the
transceiver. A logic low on the ON/OFF pin supersedes the
state of the DRIVER DISABLE pin. Supply current drops
to 3mA when in driver disable mode.
V
+
: Positive Supply Output. V
+
≈ 2V
CC
– 1.5V. This pin
requires an external charge storage capacitor, C ≥ 1.0μF,
tied to ground or 5V. Larger value capacitors may be used
to reduce supply ripple. The ratio of the capacitors on V
+
and V
–
should be greater than 5 to 1.
V
–
: Negative Supply Output. V
–
≈ –(2V
CC
– 2.5V). This pin
requires an external charge storage capacitor, C ≥ 0.1μF.
See the Applications Information section for guidance in
choosing fi lter capacitors for V
+
and V
–
.
C1
+
, C1
–
, C2
+
, C2
–
: Commutating Capacitor Inputs
require two external capacitors, C ≥ 0.2μF: one from C1
+
to C1
–
, and another from C2
+
to C2
–
. The capacitor’s
effective series resistance should be less than 2Ω. For
C ≥ 1μF, low ESR tantalum capacitors work well, although
ceramic capacitors may be used with a minimal reduction
in charge pump compliance.
DRIVER IN: RS232 Driver Input Pins. These inputs are
TTL/CMOS compatible. Unused inputs should be connected
to V
CC
.
DRIVER 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 suffi cient for load conditions up to
2500pF. Outputs are in a high impedance state when in
shutdown mode, V
CC
= 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.
RX 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.
RX 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, including LOW-Q
RX OUT, are fully short-circuit protected to ground or V
CC
with the power on, off, or in shutdown mode.
LOW Q-CURRENT RX IN: Low Power Receiver Input.
This special receiver remains active when the part is in
shutdown mode, consuming typically 60μA. This receiver
has the same 5k input impedance and ±10kV ESD protection
characteristics as the other receivers.
LOW Q-CURRENT RX OUT: Low Power Receiver Output.
This pin produces the same TTL/CMOS output voltage
levels as receivers RX1, RX2, RX3, and RX4 with slightly
decreased speed and short-circuit current. Data rates to
120kbaud are supported by this receiver.
