sp331 Exar Corporation, sp331 Datasheet - Page 9

• Manufacturer Part Number: sp331
• Description: Programmable Dual Rs-232/rs-485 Transceiver
• Manufacturer: Exar Corporation

Figure 11. Charge Pump Phase 1.
Figure 12. Charge Pump Phase 2.
Figure 14. Charge Pump Phase 4.
Date: 03-04-05
Figure 13. Charge Pump Phase 3.
Figure 15. Charge Pump Waveforms
C
C
C
1
C
1
1
–5V
+
–
1
+
–
+
–
V
–5V
+
–
V
V
CC
V
CC
CC
CC
= +5V
= +5V
= +5V
= +5V
C
C
C
C
2
2
2
2
+10V
–10V
+5V
–5V
+
+
–
–
+
–
+5V
–5V
+
–
a) C
b) C
2
2
+
-
GND
GND
+
+
–
–
+
–
+
–
C
C
+10V
C
C
C
-10V
C
C
C
4
4
4
4
3
+
+
3
3
–
3
–
+
+
–
–
V
V
V
V
V
V
Programmable Dual RS-232/RS-485 Transceiver
V
V
DD
SS
DD
SS
DD
SS
DD
SS
Storage Capacitor
Storage Capacitor
Storage Capacitor
Storage Capacitor
Storage Capacitor
Storage Capacitor
Storage Capacitor
Storage Capacitor
9
simultaneously with this, the positive side of
capacitor C
side is connected to ground, and the cycle begins
again.
Since both V+ and V
from V
be symmetrical. Older charge pump approaches
that generate V
in the magnitude of V
the inherent inefficiencies in the design.
The clock rate for the charge pump typically
operates at 15kHz. The external capacitors must
be 0.1µF with a 16V breakdown rating.
External Power Supplies
For applications that do not require +5V only,
external supplies can be applied at the V+ and
V
ages must be no greater than ±l0V. The current
drain for the ±10V supplies is used for RS-232.
For the RS-232 driver the current requirement
will be 3.5mA per driver. The external power
supplies should provide a power supply se-
quence of :+l0V, then +5V, followed by –l0V.
–
pins. The value of the external supply volt-
CC
in a no–load condition, V+ and V
1
is switched to +5V and the negative
–
from V+ will show a decrease
–
–
are separately generated
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compared to V+ due to
–
will