+10V
a) C
2+
GND
GND
b) C
2–
–10V
Figure 6. Charge Pump Waveforms
be symmetrical. Older charge pump approaches
that generate V
–
from V
+
will show a decrease in
the magnitude of V
–
compared to V
+
due to the
inherent inefficiencies in the design.
The clock rate for the charge pump typically
operates at 15kHz. The external capacitors can
be as low as 0.1µF with a 16V breakdown
voltage rating.
V
CC
= +5V
Shutdown (SD) and Enable (EN) for the
SP310E and SP312E
Both the
SP310E
and
SP312E
have a shutdown/
standby mode to conserve power in battery-pow-
ered systems. To activate the shutdown mode,
which stops the operation of the charge pump, a
logic “0” is applied to the appropriate control line.
For the
SP310E,
this control line is ON/OFF (pin
18). Activating the shutdown mode also puts the
+5V
C
1
+
–
C
4
+
–
+
C
2
+
–
–
V
DD
Storage Capacitor
V
SS
Storage Capacitor
–5V
–5V
C
3
Figure 7. Charge Pump — Phase 3
V
CC
= +5V
+10V
C
1
+
–
C
4
+
–
+
C
2
+
–
–
V
DD
Storage Capacitor
V
SS
Storage Capacitor
C
3
Figure 8. Charge Pump — Phase 4
Date: 7/19/04
SP202E Series High Performance RS232 Transceivers
© Copyright 2004 Sipex Corporation
7
SIPEX [ SIPEX CORPORATION ]
