Datasheet

LM2660
www.ti.com SNVS135D –SEPTEMBER 1999–REVISED MAY 2013
Circuit Description
The LM2660 contains four large CMOS switches which are switched in a sequence to invert the input supply
voltage. Energy transfer and storage are provided by external capacitors. Figure 16 illustrates the voltage
conversion scheme. When S
1
and S
3
are closed, C
1
charges to the supply voltage V+. During this time interval
switches S
2
and S
4
are open. In the second time interval, S
1
and S
3
are open and S
2
and S
4
are closed, C
1
is
charging C
2
. After a number of cycles, the voltage across C
2
will be pumped to V+. Since the anode of C
2
is
connected to ground, the output at the cathode of C
2
equals −(V+) assuming no load on C
2
, no loss in the
switches, and no ESR in the capacitors. In reality, the charge transfer efficiency depends on the switching
frequency, the on-resistance of the switches, and the ESR of the capacitors.
Figure 16. Voltage Inverting Principle
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