5
LT1537
CCHARA TERIST
ICS
UW
AT
Y
P
I
CA
LPER
F
O
R
C
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Shutdown to Driver Output
Driver Output Waveforms
LT1537 • TPC12
10
5
0
–10
–5
DRIVER OUTPUT
R
L
= 3k
C
L
= 2500pF
INPUT
DRIVER OUTPUT
R
L
= 3k
LT1537 • TPC13
DRIVER
OUTPUT HIGH
R
L
= 3k
ON/OFF PIN
DRIVER
OUTPUT LOW
R
L
= 3k
PI FU CTIO S
U
UU
V
CC
: 5V Input Supply Pin. Supply current drops to zero in
the shutdown mode. 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.
GND: Ground Pin.
ON/OFF: TTL/CMOS Compatible Operating Mode Control.
A logic LOW puts the device in the shutdown mode which
reduces input supply current to zero and places all of the
drivers and receivers in high impedance state. 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 drivers
in a high impedance state. 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 1.5mA when in
DRIVER DISABLE mode.
V
+
: Positive Supply Output (RS232 Drivers). V
+
≈ 2V
CC
–
1.5V. This pin requires an external charge storage capaci-
tor C ≥ 0.1µF, tied to ground or V
CC
. Larger value capaci-
tors may be used to reduce supply ripple. With multiple
transceivers, the V
+
and V
–
pins may be paralleled into
common capacitors. For large numbers of transceivers,
increasing the size of the shared common storage capaci-
tors is recommended to reduce ripple.
V
–
: Negative Supply Output (RS232 Drivers). V
–
≈
–(2V
CC
– 2.5V). This pin requires an external charge
storage capacitor C ≥ 0.1µF. V
–
is short-circuit proof for
30 seconds.
C1
+
, C1
–
, C2
+
, C2
–
: Commutating Capacitor Inputs. These
pins require two external capacitors C ≥ 0.2µF: one from
C1
+
to C1
–
and another from C2
+
to C2
–
. To maintain
charge pump efficiency, the capacitor’s effective series
resistance should be less than 2Ω. Low ESR ceramic
capacitors work well in this application.
DRIVER IN: RS232 Driver Input Pins. These inputs are
TTL/CMOS compatible. Inputs should not be allowed to
float. Tie unused inputs 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 sufficient 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
–
+ 25V to V
+
– 25V. 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 ±5kV for human body model discharges.
