ICL7660 Datasheet, PDF (7/10 Pages) Intersil Corporation – CMOS Voltage Converters

ICL7660, ICL7660A
t₂
t₁
B
0
V
- (V+)
A
FIGURE 14. OUTPUT RIPPLE
C₁
+
10 F _-
1
8
2 _ICL7660 7
ICL7660A
3
“1”
6
4
5
V+
C₁
1
8
2 _ICL7660 7
ICL7660A
3
“n”
6
4
5
-
C_{2 +}
FIGURE 15. PARALLELING DEVICES
1
8
2 ICL7660 7
ICL7660A
3
“1”
6
4
5
V+
+
10 F _-
-
10 F
+
1
8
2 _ICL7660 7
ICL7660A
3
“n”
6
4
5_-
10 F
+
R_L
V_OUT = -nV+
FIGURE 16. CASCADING DEVICES FOR INCREASED OUTPUT VOLTAGE
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.
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
a value of -V+. The output impedance (R_O) is a function of
the ON resistance of the internal MOS switches (shown in
Figure 12), the switching frequency, the value of C₁ and C₂ ,
and the ESR (equivalent series resistance) of C1 and C2. A
good first order approximation for R_O is:
R_O 2(R_SW1 + R_SW3 + ESR_C1) +
2(R_SW2 + R_SW4 + ESR_C1) +
R_O
(f_PUMP =
2(R_SW1 + R_SW3 + ESR_C1) +
1
(f_PUMP) (C1) ^{+ ESRC2}
f_OSC
2
, R_SWX = MOSFET switch resistance)
Combining the four R_SWX terms as R_SW, we see that:
1
R_O
2 (R_SW) + _{(fPUMP) (C1)} + 4 (ESR_C1) + ESR_C2
RSW, the total switch resistance, is a function of supply
voltage and temperature (See the Output Source Resistance
graphs), typically 23 at 25^oC and 5V. Careful selection of
C₁ and C₂ will reduce the remaining terms, minimizing the
output impedance. High value capacitors will reduce the
1/(f_PUMP C₁) component, and low ESR capacitors will
lower the ESR term. Increasing the oscillator frequency will
reduce the 1/(f_PUMP C1) term, but may have the side
effect of a net increase in output impedance when C₁ > 10
F and there is no longer enough time to fully charge the
capacitors