ICL7660S Intersil Corporation, ICL7660S Datasheet - Page 5

• Manufacturer Part Number: ICL7660S
• Description: Super Voltage Converter
• Manufacturer: Intersil Corporation

Typical Performance Curves
NOTE:
Detailed Description
The ICL7660S contains all the necessary circuitry to
complete a negative voltage converter, with the exception of
2 external capacitors which may be inexpensive 10 F
polarized electrolytic types. The mode of operation of the
device may be best understood by considering Figure 13,
which shows an idealized negative voltage converter.
Capacitor C
when switches S
and S
half cycle of operation, switches S
S
that the voltage on C
and no load on C
situation more closely than existing non-mechanical circuits.
NOTE: For large values of C
should be increased to 100 F.
In the ICL7660S, the 4 switches of Figure 13 are MOS power
switches; S
N-Channel devices. The main difficulty with this approach is
that in integrating the switches, the substrates of S
10 F
7. These curves include in the supply current that current fed directly into the load R
1
C
1
and S
supply current goes directly to the positive side of the load, and the other half, through the ICL7660S, to the negative side of the load. Ideally,
V
+
OUT
-
4
V+
are open during this half cycle.) During the second
3
open, thereby shifting capacitor C
2V
1
1
FIGURE 12. ICL7660S TEST CIRCUIT
is a P-Channel devices and S
is charged to a voltage, V+, for the half cycle
IN
1
2
3
4
, I
1
2
S
. The ICL7660S approaches this ideal
and S
ICL7660S
FIGURE 11. OUTPUT SOURCE RESISTANCE AS A FUNCTION OF OSCILLATOR FREQUENCY
2
2I
is exactly V+, assuming ideal switches
L
, so V
3
OSC
are closed. (Note: Switches S
3-40
IN
(>1000pF) the values of C
8
7
6
5
x I
S
2
and S
V
10 F
OUT
C
2
4
(Test Circuit Figure 12) (Continued)
400
300
200
100
x I
2
are closed, with
, S
0
+
-
L
1
100
.
to C
3
I
R
and S
L
I
L
S
V+ = 5V
T
I = 10mA
3
2
A
and S
such
V+
1
= 25
and C
4
(+5V)
-
OSCILLATOR FREQUENCY (Hz)
V
are
o
2
OUT
C
10 F
C
1
ICL7660S
4
2
= C
1k
2
C
100 F
=
1
= C
2
=
must always remain reverse biased with respect to their
sources, but not so much as to degrade their “ON”
resistances. In addition, at circuit start up, and under output
short circuit conditions (V
be sensed and the substrate bias adjusted accordingly.
Failure to accomplish this would result in high power losses
and probable device latchup.
This problem is eliminated in the ICL7660S by a logic network
which senses the output voltage (V
level translators, and switches the substrates of S
the correct level to maintain necessary reverse bias.
The voltage regulator portion of the ICL7660S is an integral
part of the anti-latchup circuitry, however its inherent voltage
drop can degrade operation at low voltages. Therefore, to
improve low voltage operation “LV” pin should be connected
to GND, disabling the regulator. For supply voltages greater
than 3.5V the LV terminal must be left open to insure latchup
proof operation, and prevent device damage.
Theoretical Power Efficiency
Considerations
In theory a voltage converter can approach 100% efficiency
if certain conditions are met:
1. The drive circuitry consumes minimal power.
2. The output switches have extremely low ON resistance
3. The impedance of the pump and reservoir capacitors are
and virtually no offset.
negligible at the pump frequency.
10k
C
1 F
L
1
from the V+ (See Figure 12). Thus, approximately half the
= C
2
=
100k
OUT
= V+), the output voltage must
OUT
) together with the
3
and S
4
to