ICL7660S Intersil Corporation, ICL7660S Datasheet - Page 6

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

The ICL7660S approaches these conditions for negative
voltage conversion if large values of C
ENERGY IS LOST ONLY IN THE TRANSFER OF CHARGE
BETWEEN CAPACITORS IF A CHANGE IN VOLTAGE
OCCURS. The energy lost is defined by:
E =
where V
and transfer cycles. If the impedances of C
relatively high at the pump frequency (refer to Figure 13)
compared to the value of R
difference in the voltages V
desirable to make C
voltage ripple, but also to employ a correspondingly large
value for C
operation.
Do’s and Don’ts
V
1. Do not exceed maximum supply voltages.
2. Do not connect LV terminal to GND for supply voltage
3. Do not short circuit the output to V
4. When using polarized capacitors, the + terminal of C
5. If the voltage supply driving the ICL7660S has a large
6. User should insure that the output (pin 5) does not go
IN
FIGURE 13. IDEALIZED NEGATIVE VOLTAGE CONVERTER
8
greater than 3.5V.
voltages above 5.5V for extended periods, however, tran-
sient conditions including start-up are okay.
must be connected to pin 2 of the ICL7660S and the +
terminal of C
source impedance (25 - 30 ), then a 2.2 F capacitor
from pin 8 to ground may be required to limit rate of rise
of input voltage to less than 2V/ s.
more positive than GND (pin 3). Device latch up will occur
under these conditions.
A 1N914 or similar diode placed in parallel with C
prevent the device from latching up under these condi-
tions. (Anode pin 5, Cathode pin 3).
1
/
2
3
C
1
1
and V
(V
1
1
in order to achieve maximum efficiency of
2
S
S
- V
3
1
2
2
7
are the voltages on C
2
must be connected to GND.
2
2
)
as large as possible to eliminate output
2
4
3-41
L
1
, there will be substantial
and V
C
1
S
S
4
2
2
. Therefore it is not only
+
1
1
and C
supply for supply
during the pump
1
and C
2
are used.
C
2
V
2
OUT
are
2
3
5
will
=
1
-
V
ICL7660S
IN
Typical Applications
Simple Negative Voltage Converter
The majority of applications will undoubtedly utilize the
ICL7660S for generation of negative supply voltages. Figure
14 shows typical connections to provide a negative supply
where a positive supply of +1.5V to +12V is available. Keep
in mind that pin 6 (LV) is tied to the supply negative (GND)
for supply voltage below 3.5V.
The output characteristics of the circuit in Figure 14 can be
approximated by an ideal voltage source in series with a
resistance as shown in Figure 14B. The voltage source has
a value of -(V+). The output impedance (R
the ON resistance of the internal MOS switches (shown in
Figure 13), the switching frequency, the value of C
and the ESR (equivalent series resistance) of C
good first order approximation for R
Combining the four R
R
voltage and temperature (See the Output Source Resistance
graphs), typically 23 at 25
and C
impedance. High value capacitors will reduce the 1/(f
C
term. Increasing the oscillator frequency will reduce the
1/(f
increase in output impedance when C
10 F
R
+
(f
R
FIGURE 14. SIMPLE NEGATIVE CONVERTER AND ITS
f
SW
1
PUMP
O
O
PUMP
) component, and low ESR capacitors will lower the ESR
PUMP
+
-
C
1
, the total switch resistance, is a function of supply
2(R
2 x R
1
2
=
will reduce the remaining terms, minimizing the output
x
SW1
x C
1
2
3
4
SW
f
OSC
+ ESR
1
+ R
2
+
OUTPUT EQUIVALENT
) term, but may have the side effect of a net
ICL7660S
SW3
f
PUMP
C2
C
14A.
1
, R
+ ESR
1
SWX
SWX
x
10 F
8
7
6
5
C1
terms as R
o
C and 5V. Careful selection of C
= MOSFET switch resistance)
) + 2(R
+
-
+ 4 x ESR
V+
V
SW2
OUT
O
1
SW
is:
> 10 F and is not long
=
+ R
C1
-
, we see that:
V+
SW
O
+ ESR
) is a function of
4 + ESR
V+
1
C2
+
and C
-
1
R
14B.
PUMP
and C
C1
O
)
2
V
. A
OUT
2
x
1
,