TRIP

TRIP

TRIP

V

(mV)

R

(k ) I

( A)

=

W ´

m

(

)

f

IND ripple

IN

OUT

OUT

TRIP

TRIP

OCP

DS(on)

DS(on)

SW

IN

I

(V

V

) V

V

V

1

I

8 R

2

8 R

2 L

V

æ

ö

-

´

ç

÷

=

+

=

+

´

ç

÷

´

´

´

´

è

ø

TPS51218

www.ti.com

SLUS935B

– MAY 2009 – REVISED FEBRUARY 2012

POWER-GOOD

The TPS51218 has powergood output that indicates high when switcher output is within the target. The

powergood function is activated after soft-start has finished. If the output voltage becomes within +10%/

–5% of

the target value, internal comparators detect power-good state and the power-good signal becomes high after a

1-ms internal delay. If the output voltage goes outside of +15%/

–10% of the target value, the powergood signal

becomes low after a 2-

μs internal delay. The powergood output is an open-drain output and must be pulled up

externally.

CURRENT SENSE AND OVER CURRENT PROTECTION

TPS51218 has cycle-by-cycle overcurrent limiting control. The inductor current is monitored during the OFF state

and the controller keeps the OFF state during the inductor current is larger than the overcurrent trip level. To

provide both good accuracy and cost effective solution, the TPS51218 supports temperature compensated

internally.

(4)

The inductor current is monitored by the voltage between GND pad and SW pin so that the SW pin should be

that GND should be connected to the proper current sensing device, i.e. the source terminal of the low-side

MOSFET.

(5)

In an overcurrent condition, the current to the load exceeds the current to the output capacitor thus the output

voltage tends to fall down. Eventually, it crosses the undervoltage protection threshold and shuts down the

controller.

When the device is operating in the forced continuous conduction mode, the negative current limit (NCL) protects

the external FET from carrying too much current. The NCL detect threshold is set as the same absolute value as

positive OCL but negative polarity. Please be noted the threshold still represents the valley value of the inductor

current.

OVER/UNDER VOLTAGE PROTECTION

TPS51218 monitors a resistor divided feedback voltage to detect over and undervoltage. When the feedback

voltage becomes higher than 120% of the target voltage, the OVP comparator output goes high and the circuit

latches as the high-side MOSFET driver OFF and the low-side MOSFET driver 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 counting. After a 1-ms delay, TPS51218 latches OFF both

high-side and low-side MOSFETs drivers. This function is enabled after 1.2 ms following EN has become high.

UVLO PROTECTION

TPS51218 has V5IN undervoltage lockout protection (UVLO). When the V5IN voltage is lower than UVLO

threshold voltage, the switch mode power supply shuts off. This is non-latch protection.

THERMAL SHUTDOWN

TPS51218 monitors the die temperature. If the temperature exceeds the threshold value (typically 145

°C), the

TPS51218 is shut off. This is non-latch protection.

Copyright

© 2009–2012, Texas Instruments Incorporated

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