ICL7662_06 Datasheet, PDF (10/10 Pages) Intersil Corporation – CMOS Voltage Converter

ICL7662
+
C₁ -
V+
1
8
2
ICL7662
7
D₁
3
6
4
5
-+
D₂
C₂
V_OUT =
- (nV_IN - V_FDX)
-
+ ^C3
V_OUT = (2V+) -
(V_FD1) - (V_FD2)
+
- ^C4
FIGURE 23. COMBINED NEGATIVE CONVERTER
AND POSITIVE DOUBLER
Combined Negative Voltage Conversion and Posi-
tive Supply Doubling
Figure 23 combines the functions shown in Figure 16 and
Figure 22 to provide negative voltage conversion and
positive voltage doubling simultaneously. This approach
would be, for example, suitable for generating +9V and -5V
from an existing +5V supply. In this instance capacitors C₁
and C₃ perform the pump and reservoir functions
respectively for the generation of the negative voltage, while
capacitors C₂ and C₄ are pump and reservoir respectively
for the doubled positive voltage. There is a penalty in this
configuration which combines both functions, however, in
that the source impedances of the generated supplies will be
somewhat higher due to the finite impedance of the common
charge pump driver at pin 2 of the device.
Voltage Splitting
The bidirectional characteristics can also be used to split a
higher supply in half, as shown in Figure 24. The combined
load will be evenly shared between the two sides and, a high
value resistor to the LV pin ensures start-up. Because the
switches share the load in parallel, the output impedance is
much lower than in the standard circuits, and higher currents
can be drawn from the device. By using this circuit, and then
the circuit of Figure 19, +30V can be converted (via +15V,
and -15V) to a nominal -30V, although with rather high series
output resistance (~250Ω).
Regulated Negative Voltage Supply
In some cases, the output impedance of the ICL7662 can be a
problem, particularly if the load current varies substantially. The
circuit of Figure 25 can be used to overcome this by controlling
the input voltage, via an ICL7611 low-power CMOS op amp, in
such a way as to maintain a nearly constant output voltage.
Direct feedback is inadvisable, since the ICL7662s output does
not respond instantaneously to a change in input, but only after
the switching delay. The circuit shown supplies enough delay to
accommodate the ICL7662, while maintaining adequate
feedback. An increase in pump and storage capacitors is
desirable, and the values shown provides an output impedance
of less than 5Ω to a load of 10mA.
Other Applications
Further information on the operation and use of the ICL7662
may be found in AN051 “Principles and Applications of the
ICL7660 CMOS Voltage Converter”.
+
R_L1
50µF
-
1
V+
8
V_OUT
=V+ ^-
2
V-
+
50µF
-
2
ICL7662
7
3
6
R_L2
4
5
+
50µF
-
V-
FIGURE 24. SPLITTING A SUPPLY IN HALF
+8V
56K
50K
100K
50K
+8V
-
ICL7611
+
ICL8069
+
100µF
-
100Ω
-
10µF
+
1
8
2 _ICL7662
7
3
6
4
5
V_OUT
800K
250K
VOLTAGE
ADJUST
-
+ ^100µF
FIGURE 25. REGULATING THE OUTPUT VOLTAGE
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