TPS54240_14 Datasheet, PDF (16/54 Pages) Texas Instruments – 3.5V to 42V STEP DOWN SWIFT™ DC/DC CONVERTER WITH ECO-MODE™

TPS54240
SLVSAA6A – APRIL 2010 – REVISED DECEMBER 2012
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DETAILED DESCRIPTION (continued)
Overload Recovery Circuit
The TPS54240 has an overload recovery (OLR) circuit. The OLR circuit will slow start the output from the
overload voltage to the nominal regulation voltage once the fault condition is removed. The OLR circuit will
discharge the SS/TR pin to a voltage slightly greater than the VSENSE pin voltage using an internal pull down of
382μA when the error amplifier is changed to a high voltage from a fault condition. When the fault condition is
removed, the output will slow start from the fault voltage to nominal output voltage.
Sequencing
Many of the common power supply sequencing methods can be implemented using the SS/TR, EN and PWRGD
pins. The sequential method can be implemented using an open drain output of a power on reset pin of another
device. The sequential method is illustrated in Figure 30 using two TPS54240 devices. The power good is
coupled to the EN pin on the TPS54240 which will enable the second power supply once the primary supply
reaches regulation. If needed, a 1nF ceramic capacitor on the EN pin of the second power supply will provide a
1ms start up delay. Figure 31 shows the results of Figure 30.
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PWRGD
EN
SS /TR
TPS54240
EN
SS /TR
PWRGD
EN1
PWRGD1
VOUT1
VOUT2
Figure 30. Schematic for Sequential Start-Up
Sequence
Figure 31. Sequential Startup using EN and
PWRGD
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