
GS7660
Vishay
formerly General Semiconductor
Document Number 74819
24-May-02
www.vishay.com
7
∑
P loss = Res.
P switch
Res.
P cap.
Res.+ P conversion
+
+
P outp.
Res.
I
L
2
f.
C1
f = f osc/2
P switch
Res.
+
= I
L
2
(
8 R
SW
+ 4 Esr
C1
+ Esr
C2
)
P cap.
Res.
P conversion =
1
2
1
2
f
C2
(
V ripple
2
–
2 Vout. V ripple
)]
C1
(
V
in
2
–
V
out
2
)
+
f = f osc/2
=
[
Voltage Doubling
Figure 11 shows two methods of voltage doubling. In Fig.
11a , R1 is added to ensure that doubling is not inhibited
by a non-destructive latch-up at start-up.This condition can
occur, since the ground pin (pin 3) is raised above the V
IN
pin ( pin 8) during start-up.
R1 increases output impedance and in higher current
applications where the voltage drop across R1 exceeds a two
diode drop, the doubling circuit of Fig 11b is recommended.
The voltage doubler of Fig. 11a is more accurate at low
load currents since the voltage drop across the diode is not
reflected at the output.
Figs. 11a and 11b
–
Voltage Doubler
1
2
3
4
8
7
6
5
8
7
6
5
10
μ
F
R1
200
V
IN
(1.5V to 6V)
1N914
C1
I
OUT
C2
10
μ
F
+
+
2V
IN
(3.0V to 12V)
500k
1
2
3
4
8
7
6
5
8
7
6
5
10
μ
F
10
μ
F
Required for
V+ < 3.0V
+
V
IN
(1.5V to 9.0V)
+
+
+
V
d
V
OUT
=
2V
IN
–2V
D
–
GS7660
GS7660
–
V
d
Oscillator Frequency Control
For normal operation, the Boost, and Oscillator Pins
should be left open. Connecting the Boost pin to the V
IN
supply will increase oscillator frequency by a factor of 5,
resulting in lower Output Impedance, less ripple, smaller
required capacitor values and moves the switching noise
out of the audio band. Lower oscillator frequency reduces
quiescent current.
The oscillator frequency can be further controlled by driving
the oscillator input from an external frequency source or
lowered , by connecting an external capacitor to the oscil-
lator input.
Efficiency, Output Impedance and Output Ripple
The power efficiency of a switched capacitor voltage con-
verter is dependent on the internal losses.
The total power loss is:
V ripple = I
L
(
+ 2 Esr
C2
)
1
2.
C2
.f
f = f osc/2
Vripple