Current Protection

(

)

(

)

(

)

(

)

TRIP

TRIP

TRIP

R

k

I

A

V

mV

24 mV

9

W ´

m

=

-

(3)

( )

( )

(

)

f

IN

OUT

OUT

TRIP

RIPPLE

TRIP

OCP

IN

DS on

DS on

V

V

V

V

I

V

1

I

R

2

R

2 L

V

-

´

=

+

=

+

´

´ ´

(4)

Overvoltage and Undervoltage Protection

TPS51123

TPS51123 has cycle-by-cycle over current 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 over current trip level.

In order to provide both good accuracy and cost effective solution, TPS51123 supports temperature

internally.

Note that when TRIPx voltage is under a certain thershould (typically 0.4V), the switcher channel concerned is

shut down. The inductor current is monitored by the voltage between GND pin and LLx pin so that LLx pin should

be connected to the drain terminal of the bottom MOSFET properly. Itrip has 4500 ppm/°C temperature slope to

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

MOSFET.

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

voltage tends to fall down. Eventually, it ends up with crossing the under voltage protection threshold and

shutdown both channels.

TPS51123 monitors a resistor divided feedback voltage to detect over and under voltage. When the feedback

voltage becomes higher than 115% of the target voltage, the OVP comparator output goes high and the circuit

latches as the top MOSFET driver OFF and the bottom MOSFET driver ON.

Also, TPS51123 monitors VOx voltage directly and if it becomes greater than 5.75 V the TPS51123 turns off the

top MOSFET driver.

When the feedback voltage becomes lower than 60% of the target voltage, the UVP comparator output goes

high and an internal UVP delay counter begins counting. After 32

µs, TPS51123 latches OFF both top and

bottom MOSFETs drivers, and shut off both drivers of another channel. This function is enabled after 2 ms

following ENC has become high.

22

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