Datasheet

 
 
SLVS391B − OCTOBER 2001 − REVISED FEBRUARY 2002
11
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PRINCIPLES OF OPERATION
0.5x conversion mode
This conversion mode is internally selected if the input to output voltage ratio is greater than two (e.g. 3.6 V to
1.5 V conversion). In the 0.5x mode, the flying capacitors and the switches always work in parallel, which
reduces the resistance of the circuit compared to the other modes. In the first cycle, the flying capacitors are
charged in series with the output capacitors. In the second cycle, the flying capacitors are connected in parallel
with the output capacitor, which discharges the flying capacitors.
C1F C2F
SW1
SW2
SW3
SW4
SW9
SW5
SW6
SW7
SW8
++
+
VIN
OUT
C
o
SW1
SW2
SW3
SW4
SW9
SW5
SW6
SW7
SW8
++
+
VIN
OU
T
C
o
C1F C2F
Phase 1: Charging of Flying Caps Phase 2: Discharging of Flying Caps
Figure 24. 0.5x Conversion Mode
1/3x conversion mode
This mode was implemented to provide high efficiency even with an input to output voltage ratio greater than
three (e.g. 5 V to 1.5 V conversion). In the first cycle, the two flying capacitors are charged in series with the
output capacitor. In the next step, the flying capacitors which are charged to VIN/3, are connected in parallel
to the output capacitor.
SW1
SW2
SW3
SW4
SW9
SW5
SW6
SW7
SW8
++
+
VIN
OUT
C
o
SW1
SW2
SW3
SW4
SW9
SW5
SW6
SW7
SW8
++
+
VIN
OU
T
C
o
C1F C2F C1F C2F
Phase 1: Charging of Flying Caps Phase 2: Discharging of Flying Caps
Figure 25. 1/3x Conversion Mode