TPS65251 Datasheet, PDF (20/31 Pages) Texas Instruments – 4.5-V TO 18-V INPUT, HIGH CURRENT, SYNCHRONOUS STEP DOWN THREE BUCK SWITCHER WITH INTEGRATED FET

TPS65251
SLVSAA4B – JUNE 2010 – REVISED JANUARY 2011
BUCK 2 AND 3 LOSSES (W)
vs
OUTPUT CURRENT
V_IN = 12 V, f_SW = 500 kHz
V_O (From Top to Bottom) = 5 V , 3.3 V, 2.5 V, 1.8 V, 1.2 V
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BUCK 2 AND 3 LOSSES (W)
vs
OUTPUT CURRENT
V_IN = 12 V, f_SW = 1.1 MHz
V_O (From Top to Bottom) = 5 V , 3.3 V, 2.5 V, 1.8 V, 1.2 V
Figure 28.
Figure 29.
Low Power Mode Operation
By pulling the Low_p pin high all converters will operate in pulse-skipping mode, greatly reducing the overall
power consumption at light and no load conditions. Although each buck converter has a skip comparator that
makes sure regulation is not lost when a heavy load is applied and low power mode is enabled, system design
needs to make sure that the LP pin is pulled low for continuous loading in excess of 100 mA.
When low power is implemented, the peak inductor current used to charge the output capacitor is:
I_LIMIT = 0.25 · T_{SLEEP_CLK} · ^V¾ ^{IN -LVOUT}
(7)
Where T_{SLEEP_CLK} is half of the converter switching period, 2/f_SW.
The size of the additional ripple added to the output is:
( ) ^{DVOUT = ¾}C^{1 ·}
L_¾ · ₂I_LIMIT² _{· V¾ OUT · (}VV_{ININ - VOUT) -}
I_LOAD
f^¾ _{SLEEP_CLK}
(8)
And the peak output voltage during low power operation is:
V = V + _{OUT_PK}
OUT
D¾ V_2OUT
(9)
VOUT_PK
VOUT
Figure 30. Peak Output Voltage During Low Power Operation
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