ICL7660, ICL7660A
The voltage regulator portion of the ICL7660 and ICL7660A is
ENERGY IS LOST ONLY IN THE TRANSFER OF
CHARGE BETWEEN CAPACITORS IF A CHANGE IN
VOLTAGE OCCURS. The energy lost is defined by:
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 the “LV” pin should be
connected to GROUND, 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.
1
2
2
E = / C (V - V )
2
2
1
1
where V and V are the voltages on C during the pump and
1
2
1
1
transfer cycles. If the impedances of C and C are relatively
2
high at the pump frequency (refer to Figure 12) compared to
the value of R , there will be a substantial difference in the
8
S
2
S
1
2
L
V
IN
voltages V and V . Therefore it is not only desirable to make
1
2
C
C as large as possible to eliminate output voltage ripple, but
1
2
3
3
5
also to employ a correspondingly large value for C in order to
1
achieve maximum efficiency of operation.
C
2
S
S
4
3
Do’s And Don’ts
1. Do not exceed maximum supply voltages.
V
= -V
IN
OUT
2. Do not connect LV terminal to GROUND for supply
7
voltages greater than 3.5V.
FIGURE 12. IDEALIZED NEGATIVE VOLTAGE CONVERTER
3. Do not short circuit the output to V+ supply for supply
voltages above 5.5V for extended periods, however,
transient conditions including start-up are okay.
Theoretical Power Efficiency
Cons iderations
4. When using polarized capacitors, the + terminal of C
1
must be connected to pin 2 of the ICL7660 and ICL7660A
In theory a voltage converter can approach 100% efficiency
if certain conditions are met.
and the + terminal of C must be connected to GROUND.
2
5. If the voltage supply driving the ICL7660 and ICL7660A
has a large source impedance (25Ω - 30Ω), then a 2.2µF
capacitor from pin 8 to ground may be required to limit
rate of rise of input voltage to less than 2V/µs.
1. The driver circuitry consumes minimal power.
2. The output switches have extremely low ON resistance
and virtually no offset.
6. User should insure that the output (pin 5) does not go
more positive than GND (pin 3). Device latch up will occur
under these conditions. A 1N914 or similar diode placed
3. The impedances of the pump and reservoir capacitors
are negligible at the pump frequency.
The ICL7660 and ICL7660A approach these conditions for
negative voltage conversion if large values of C and C
in parallel with C will prevent the device from latching up
2
under these conditions. (Anode pin 5, Cathode pin 3).
1
2
are used.
V+
1
2
3
4
8
7
6
5
R
O
V
OUT
ICL7660
ICL7660A
+
10µF
-
-
V+
+
V
= -V+
OUT
-
10µF
+
FIGURE 13A. CONFIGURATION
FIGURE 13B. THEVENIN EQUIVALENT
FIGURE 13. SIMPLE NEGATIVE CONVERTER
FN3072.7
7
October 10, 2005
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