SP3244ECY-L Exar Corporation, SP3244ECY-L Datasheet - Page 12

• Manufacturer Part Number: SP3244ECY-L
• Description: IC TXRX RS232 28TSSOP
• Manufacturer: Exar Corporation
• Type: Transceiverr

Specifications of SP3244ECY-L

• Package / Case: 28-TSSOP (0.173", 4.40mm Width)
• Number Of Drivers/receivers: 3/5
• Protocol: RS232
• Voltage - Supply: 3 V ~ 5.5 V
• Mounting Type: Surface Mount
• Maximum Operating Temperature: + 70 C
• Minimum Operating Temperature: 0 C
• Function: Transceiver
• Mounting Style: SMD/SMT
• Supply Current: 1 uA
• Supply Voltage (max): + 6 V
• Supply Voltage (min): - 0.3 V
• Logic Type: RS-232 Transceivers
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant
• Other names: 1016-1129

Phase 2
VSS transfer and invert: Phase two connects
the negative terminal of C2 to the VSS stor-
age capacitor and the positive terminal of C2 to
ground. This transfers the doubled and inverted
(V–) voltage onto C3. Meanwhile, capacitor
C1 charged from VCC to prepare it for its next
phase.
Phase 3
identical to the first phase. The positive ter-
minals of capacitors C and C2 are charged
from V
connected to ground. C+ is then connected
to ground and the stored charge from C– is
superimposed onto C2–. Since C2+ is still
connected to V
capacitor C2 is now 2 x V
Phase 4
V
negative terminal of C2 to ground and the posi-
tive terminal of C2 to the V
This transfers the doubled (V+) voltage onto C4.
Meanwhile, capacitor C1 charged from V
prepare it for its next phase.
The Exar charge pump generates V+ and
V– independently from V
condition V+ and V- will be symmetrical. Older
charge pump approaches generate V+ and then
use part of that stored charge to generate V-.
Because of inherent losses the magnitude of V-
will be smaller than V+ on these older designs.
Under lightly loaded conditions the intelligent
pump oscillator maximizes efficiency by running
only as needed to maintain V+ and V–. Since
interface transceivers often spend much of their
time at idle this power-efficient innovation can
greatly reduce total power consumption. This
improvement is made possible by the indepen-
dent phase sequence of the Exar charge-pump
design.
The clock rate for the charge pump typically op-
erates at greater than 70kHz allowing the pump
to run efficiently with small 0.1μF capacitors.
Efficient operation depends on rapidly charging
and discharging C and C2, therefore capacitors
should be mounted close to the IC and have low
ESR (equivalent series resistance). Inexpensive
V
dd
dd
transfer: The fourth phase connects the
charge store and double: Phase three is
cc
with their negative terminals initially
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 50-668-707 • www.exar.com
cc
the voltage potential across
cc
cc
dd
. Hence in a no–load
.
storage capacitor.
cc
to
2
surface mount ceramic capacitors (such as are
widely used for power-supply decoupling) are
ideal for use on the charge pump. The charge
pumps are designed to be able to function prop-
erly with a wide range of capacitor styles and val-
ues. If polarized capacitors are used the positive
and negative terminals should be connected as
shown on the Typical Operating Circuit.
Capacitance values may be increased if operat-
ing at higher V
the capacitors age.
Auto On-Line
The SP3244E/3245E devices have the advanced
Auto On-Line
turning off the charge pumps and driver outputs
when the transceiver inputs are idle for more
than 30 seconds.
RS-232 signals use both positive and negative
voltages of greater than ±5V magnitude. Receiv-
ers have nominal 5kΩ impedance to ground.
Even when idle, drivers will maintain output
signal voltage creating a continuous current
flow. In low power, battery operated devices this
constant current drain can decrease battery life
significantly.
Auto On-Line
to emulate the behavior of devices with our
earlier Auto On-line
Plus puts the device into a low power mode
when driver or receiver inputs are idle and
re-awakes upon detecting signal transitions.
Auto On-Line
mode when receiver inputs are left floating and
re-awakes when receivers are driven greater
than ±2.7V magnitude by incoming RS-232
signal.
Reciever 5kΩ Current path to
®
®
®
®
cc
puts the device into a low power
Plus feature that saves power by
Plus devices may be configured
Plus Circuitry
or to provide greater stability as
®
feature. Auto On-Line
SP3244E_SP3245E_00_2509
Receiver
DESCRIPTION
5k Ω
®