Over-Voltage Comparator

The over-voltage comparator is provided to protect the out-

put from overvoltage conditions due to sudden input line

voltage changes or output loading changes. The over-

voltage comparator monitors the FB pin versus an internal

2.875V reference (OV_REF). If the voltage at FB rises above

OV_REF the comparator immediately terminates the buck

switch on time pulse.

ON Time generator and Shutdown

The on time of the LM5007 is set inversely proportional to

the input voltage by an external resistor connected between

Ron and Vin. The Ron terminal is a low impedance input

biased at approximately 1.5V. Thus the current through the

resistor and into the Ron terminal is approximately propor-

tional to Vin and used internally to control the on timer. This

scheme of input voltage feed-forward hysteretic operation

achieves nearly constant operational frequency over varying

line and load conditions. The on time equation for the

LM5007 is :

Ton=1.42x10

The R

tion which disables the regulator and significantly decreases

quiescent power dissipation. By pulling the R

0.7V logic threshold activates the low power shutdown

mode. The V

approximately 100µA internal to the LM5007 plus the current

in the R

20078306

FIGURE 2. Self Biased Configuration

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