sp784ct Exar Corporation, sp784ct Datasheet - Page 9

• Manufacturer Part Number: sp784ct
• Description: Programmable Charge Pump Corporation
• Manufacturer: Exar Corporation

SP782/SP784 DS/08
THEORY OF OPERATION
The SP782/784's charge pump design is based
on Sipex's original patented charge pump de-
sign (5,306,954) which uses a four–phase volt-
age shifting technique to attain symmetrical
10V power supplies. In addition, the SP782/
784 charge pump incorporates a "program-
mable" feature that produces an output of 10V
or 5V for V
and D1. The charge pump requires external
capacitors to store the charge. Figure 1 shows
the waveform found on the positive and nega-
tive side of capcitor C2. There is a free–running
oscillator that controls the four phases of the
voltage shifting. A description of each phase
follows.
Phase 1 ( 10V)
— V
the clock cycle, the positive side of capacitors
C
then switched to ground and the charge on C
is transferred to C
+5V, the voltage potential across capacitor C
is now 10V.
Phase 1 ( 5V)
— V
With the C
to +5V, C
charge on C
capacitor. Simultaneously the C
to ground and 5V charge on C
to the V
Phase 2 ( 10V)
— V
connects the negative terminal of C
storage capacitor and the positive terminal of
C
or the generated –5V to C
the positive side of capacitor C
+5V and the negative side is connected to
ground.
Phase 2 ( 5V)
— V
reconnected to V
capacitor. C
connected to C
now transferred to the V
1
2
to ground, and transfers the generated –l0V
and C
SS
SS
SS
SS
charge storage — During this phase of
& V
DD
transfer — Phase two of the clock
& V
2
l
+
1
are initially charged to +5V. C
storage capacitor.
is then switched to ground and the
and C
1
DD
SS
2
–
+
DD
is transferred to the V
3
and V
is switched to ground and C
charge storage and transfer —
. The 5V charge from Phase 1 is
2
2
charge storage — C
–
capacitors initially charged
. Since C
CC
DD
by two control pins, D0
to recharge the C
SS
3
. Simultaneously,
storage capacitor.
2
+
2
is connected to
1
+
2
is switched to
is transferred
–
is switched
2
SS
to the V
SP782/784 Programmable Charge Pump
storage
1
+
2
l
+
–
SS
1
is
is
is
–
2
1
9
V
or C
cycle begins again.
Phase 3
clock is identical to the first phase — the charge
transferred in C
terminal of C
side of capacitor C
voltage potential across C
output, C
potential on C
Phase 4
clock connects the negative terminal of C
ground and transfers the generated l0V or the
generated 5V across C
capacitor. Again, simultaneously with this, the
positive side of capacitor C
and the negative side is connected to ground,
and the cycle begins again.
Since both V
ated from V
V
approaches that generate V
a decrease in the magnitude of V
V
design.
Figure 2. Charge Pump Phase 1 for 10V.
Figure 3. Charge Pump Phase 1 for 5V.
— V
— V
SS
SS
+
due to the inherent inefficiencies in the
receives a continuous charge from either C
2
will be symmetrical. Older charge pump
. With the C1 capacitor charged to 5V, the
DD
DD
C
–5V
C
charge storage — The third phase of the
1
1
+
–
2
transfer — The fourth phase of the
+
–
V
+
V
CC
–5V
CC
CC
is connected to ground so that the
= +5V
1
= +5V
DD
, which is applied to the negative
2
in a no–load condition, V
1
is only +5V.
and V
produces –5V in the negative
C
C
2
2
2
+5V
+5V
+
–
. Since C
+
–
–5V
2
SS
© Copyright 2000 Sipex Corporation
to C
are separately gener-
2
1
–
is l0V. For the 5V
is switched to +5V
from V
4
+
+
C
–
–
C
, the V
C
2
C
4
4
3
+
3
–
–
+
+
–
is at +5V, the
V
V
V
V
DD
DD
SS
SS
compared to
+
Storage Capacitor
Storage Capacitor
Storage Capacitor
Storage Capacitor
DD
will show
storage
DD
2
and
to
1