Datasheet

 
 
SLVS391B − OCTOBER 2001 − REVISED FEBRUARY 2002
10
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PRINCIPLES OF OPERATION
The TPS6050x devices use fractional conversion to achieve high efficiency over a wide input and output voltage
range. Depending on the input to output voltage ratio and output current, internal circuitry switches between an
LDO mode, a 2/3x mode, a 0.5x mode, and a 1/3x mode.
LDO conversion mode
In the LDO mode, the flying capacitors are no longer used for transferring energy. The switches 1, 2, 5, and 6
are closed and connect the input directly with the output. This mode is automatically selected if the input to output
voltage ratio does not allow the use of another conversion mode with higher efficiency. In LDO mode, the
regulation is done by switching off MOSFET 2 and 6 until the output current reaches the linear-skip current (150
mA typ). At a higher output current, the output voltage is regulated by controlling the resistance of the switch.
The minimum input to output voltage difference required for regulation is 1 V.
C1F C2F
SW1
SW2
SW3
SW4
SW9
SW5
SW6
SW7
SW8
++
+
VIN
OUT
C
o
Figure 22. LDO Conversion Mode
2/3x conversion mode
In the first cycle, the two flying capacitors are connected in parallel and are charged up in series with the output
capacitor. In the second cycle, the flying capacitors are connected in series. This mode provides higher
efficiency than the LDO mode because the current into VIN is only 2/3 of the output current. The mode is
automatically selected if the input voltage is higher than 3/2 of the selected output voltage.
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 23. 2/3x Conversion Mode