sp3508 Exar Corporation, sp3508 Datasheet - Page 25

• Manufacturer Part Number: sp3508
• Description: Rugged 3.3v, 20mbps, 8 Channel Multiprotocol Tranciever With Programmable Dce/dte And Terminination Resistors
• Manufacturer: Exar Corporation

Figure 46. Charge Pump - Phase 2.
Figure 47.Charge Pump - Phase 3.
Phase 4
-V
the generated 5.5V across C2 to C
the regulated voltage, the internal oscillator is disabled and simultaneously with this, the positive side of
capacitor C1 is switched to V
The charge pump cycle will continue as long as the operational conditions for the internal oscillator are
present. Since both V+ and V- are separately generated from V
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 250kHz. The external capacitors can be as low as 1µF with a 16V breakdown voltage
rating.
Date: 10/29/04
Phase 2
-V
and the positive terminal of C2 to ground, and transfers the negative generated voltage to C
generated voltage is regulated to -5.5V. Simultaneously, the positive side of the capacitor C1 is switched
to V
Phase 3
-V
C1 produces -V
Since C2+ is at V
DD
SS1
DD
CC
transfer -The fourth phase of the clock connects the negative terminal of C2 to ground, and transfers
charge storage -The third phase of the clock is identical to the first phase-the charge transferred in
transfer -Phase two of the clock connects the negative terminal of C2 to the V
and the negative side is connected to ground.
CC
CC
in the negative terminal of C1 which is applied to the negative side of the capacitor C2.
, the voltage potential across C2 is 2xV
CC
C
C
1
–3V
1
and the negative side is connected to ground, and the cycle begins again.
+
–
+
–
V
VDD
SP3508 Enhanced WAN Multi–Mode Serial Transceiver
V
CC
CC
, the V
= +3V
= +3V
DD
C
C
storage capacitor. This voltage is regulated to +5.5V. At
2
+3V
–3V
2
+
–
–6V
25
+
–
CC
.
+
–
C
CC
C
VSS1
VDD
+
C
C
–
; in a no-load condition V+ and V- will
+
–
VSS1
VDD
+
–
V
V
DD
SS1
V
V
DD
SS
Storage Capacitor
Storage Capacitor
Storage Capacitor
Storage Capacitor
© Copyright 2004 Sipex Corporation
SS1
storage capacitor
FEATURES
VSS1
. This