SP3224E Datasheet, PDF (13/23 Pages) Sipex Corporation – 3.0V to 5.5V RS-232 Transceivers with Auto On-Line® Plus

are widely used for power-supply decou-
pling) are ideal for use on the charge pump.
The charge pumps are designed to be able
to function properly with a wide range of
capacitor styles and values. If polarized ca-
pacitors are used the positive and negative
terminals should be connected as shown
on the Typical Operating Circuit.
Capacitance values may be increased if
operating at higher Vcc or to provide great-
er stability as the capacitors age.
+
V
CC
Phases 1 and 3: Store/Double.
-
Double charge from C1 onto C2.
C2 is now charged to -2xVcc
C
+
1
C
+
2
e-
e-
+
V+
C
3
V- ₊
C
4
THEORY OF OPERATION
The SP3224E-SP3227E devices have the
advanced Auto On-Line^® Plus feature
RS-232 signals use both positive and neg-
ative voltages of greater than ±5V magni-
tude.Receivers have nominal 5kΩ imped-
ance to ground. Even when idle, drivers
will maintain output signal voltage creating
a continuous current flow. In low power,
battery operated devices this constant cur-
rent drain can decrease battery life
significantly.
+
V
CC
- _{Phase 2 – Vss transfer from C2 to C4.}
Meanwhile C1 is charged to Vcc
C
+
1
e-
+
C
+
V+
C
3
2
e-
e-
+
C
4
Vss
Patented 5,306,954
C
+
1
e-
+
V
CC
-
Phase 4 VDD transfer from C2 to C3.
Meanwhile C1 is charged to Vcc
V
DD
e+
e+
+
C
+
2
V+
C
3
V- +
C
4
Charge Pump Phases
Minimum Recommended Charge Pump Capacitor Values
Input Voltage Vcc
Charge Pump Capacitor Value for SP32XX
3.0V to 3.6V
C1-C4=0.1µF
4.5V to 5.5V
3.0V to 5.5V
C1=0.047µF, C2-C4=0.33µF
C1-C4=0.22µF
Charge Pump Capacitor Values
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com
13
SP3224E,3225E,3226E,3227E_101_081711