ICL7660, ICL7660A
t
t
1
2
B
0
V
A
-(V+)
FIGURE 14. OUTPUT RIPPLE
V+
1
2
3
4
8
7
6
ICL7660
ICL7660A
“1”
1
2
8
7
6
5
C
1
R
L
ICL7660
5
ICL7660A
“n”
C
3
4
1
-
+
C
2
FIGURE 15. PARALLELING DEVICES
V+
1
8
ICL7660
2
3
4
7
6
5
1
2
3
4
8
ICL7660A
“1”
+
10µF
-
7
6
5
ICL7660
ICL7660A
“n”
+
10µF
-
V
= -nV+
OUT
-
10µF
-
+
10µF
+
FIGURE 16. CASCADING DEVICES FOR INCREASED OUTPUT VOLTAGE
2(R
R ≅
O
+ R
SW3
+ ESR ) +
C1
Typical Applications
Simple Negative Voltage Converter
The majority of applications will undoubtedly utilize the ICL7660
and ICL7660A for generation of negative supply voltages.
Figure 13 shows typical connections to provide a negative
supply negative (GND) for supply voltages below 3.5V.
SW1
1
+ ESR
C2
(f
) (C1)
PUMP
f
OSC
(f
=
, R = MOSFET switch resistance)
SWX
PUMP
2
Combining the four R
terms as R , we see that:
SW
SWX
1
R
≅
2 (R ) +
+ 4 (ESR ) + ESR
C1 C2
SW
O
(f
) (C1)
PUMP
The output characteristics of the circuit in Figure 13A can be
approximated by an ideal voltage source in series with a
resistance as shown in Figure 13B. The voltage source has
RSW, the total switch resistance, is a function of supply
voltage and temperature (See the Output Source Resistance
a value of -V+. The output impedance (R ) is a function of
O
graphs), typically 23Ω at 25°C and 5V. Careful selection of
the ON resistance of the internal MOS switches (shown in
C and C will reduce the remaining terms, minimizing the
1
2
Figure 12), the switching frequency, the value of C and C ,
1
2
output impedance. High value capacitors will reduce the
1/(f • C ) component, and low ESR capacitors will
and the ESR (equivalent series resistance) of C1 and C2. A
good first order approximation for R is:
PUMP
1
O
lower the ESR term. Increasing the oscillator frequency will
reduce the 1/(f
• C1) term, but may have the side effect
2(R
2(R
+ R
+ R
+ ESR ) +
C1
+ ESR ) +
R
≅
PUMP
SW1
SW2
SW3
SW4
O
of a net increase in output impedance when C > 10µF and
1
C1
there is no longer enough time to fully charge the capacitors
FN3072.7
8
October 10, 2005
INTERSIL [ Intersil ]
