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SP331 Datasheet, PDF (9/13 Pages) Sipex Corporation – Programmable RS-232/RS-485 Transceiver | |||
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VCC = +5V
+
C1 â
â5V
+5V
+
C2 â
â5V
C4
+ â VDD Storage Capacitor
â + VSS Storage Capacitor
C3
Figure 11. Charge Pump Phase 1.
VCC = +5V
C4
+
+
+ â VDD Storage Capacitor
C1 â
C2 â
â + VSS Storage Capacitor
â10V
C3
Figure 12. Charge Pump Phase 2.
VCC = +5V
+
C1 â
â5V
+5V
+
C2 â
â5V
C4
+ â VDD Storage Capacitor
â + VSS Storage Capacitor
C3
Figure 13. Charge Pump Phase 3.
VCC = +5V
+10V
C4
+
+
+ â VDD Storage Capacitor
C1 â
C2 â
â + VSS Storage Capacitor
C3
Figure 14. Charge Pump Phase 4.
to ground and transfers the generated l0V
across C2 to C4, the VDD storage capacitor.
Again, simultaneously with this, the positive
side of capacitor C1 is switched to +5V and
the negative side is connected to ground,
and the cycle begins again.
Since both V+ and Vâ are separately gen-
erated from VCC in a noâload condition, V+
and Vâ will be symmetrical. Older charge
pump approaches that generate Vâ from
V+ will show a decrease in the magnitude
of Vâ compared to V+ due to the inherent
inefficiencies in the design.
The clock rate for the charge pump typically
operates at 15kHz. The external capaci-
tors 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 Vâ pins. The value of the external sup-
ply voltages 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 sequence of :+l0V, then +5V,
followed by âl0V.
+10V
a) C2+
GND
GND
b) C2-
-10V
Figure 15. Charge Pump Waveforms
Exar Corporation 48720 Kato Road, Fremont CA, 94538 ⢠510-668-7017 ⢠www.exar.com
SP331_100_012610
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