TPS54226

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SLVSA14A – OCTOBER 2009 – REVISED OCTOBER 2009

Power Good

The power good function is activated after soft start has finished. The power good function becomes active after

1.7 times soft-start time. When the output voltage is within -10% of the target value, internal comparators detect

power good state and the power good signal becomes high. The power good output, PG, is an open drain

output. If the feedback voltage goes under 15% of the target value, the power good signal becomes low after a

10

μs internal delay.

Output Discharge Control

TPS54226 discharges the output when EN is low, or the controller is turned off by the protection functions (OVP,

UVP, UVLO and thermal shutdown). The output is discharged by an internal 50-

Ω MOSFET which is connected

from VO to PGND. The internal low-side MOSFET is not turned on during the output discharge operation to

avoid the possibility of causing negative voltage at the output.

Current Protection

Output current is limited by cycle-by-cycle overcurrent limiting control. The inductor current is monitored during

the OFF state and the controller keeps the OFF state when the inductor current is larger than the over current

trip level. To provide both good accuracy and cost effective solution, the device supports temperature

The inductor current is monitored by the voltage between PGND pin and SW1/SW2 pin. In an overcurrent

condition, the current to the load exceeds the current to the output capacitor; thus, the output voltage tends to fall

off. Eventually, it will end up with crossing the undervoltage protection threshold and shutdown.

Over/Under Voltage Protection

The TPS54226 detects over and undervoltage conditions by monitoring the feedback voltage (VFB). This

function is enabled after approximately 1.7 times the soft-start time.When the feedback voltage becomes higher

than 120% of the target voltage, the OVP comparator output goes high and the circuit latches the high-side

MOSFET driver turns off and the low-side MOSFET turns on. When the feedback voltage becomes lower than

70% of the target voltage, the UVP comparator output goes high and an internal UVP delay counter begins. After

250

μs, the device latches off both internal top and bottom MOSFET.

UVLO Protection

than UVLO threshold voltage, the TPS54226 is shut off. This is protection is non-latching.

Thermal Shutdown

Thermal protection is self-activating. If the junction temperature exceeds the threshold value (typically 150°C),

the TPS54226 shuts off. This protection is non-latching.

Copyright © 2009, Texas Instruments Incorporated

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Product Folder Link(s): TPS54226