Datasheet

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7V SERIES REGULATOR
SW
LM25007
V
IN
BST
VCC
SELF-BIAS
DIODE
0.01 PF
0.1 PF
10V
10k
30k
LM25007
www.ti.com SNVS401C –JANUARY 2006–REVISED FEBRUARY 2013
Figure 7. Self Biased Configuration
Over-Voltage Comparator
The over-voltage comparator is provided to protect the output 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. If the voltage at FB rises above 2.875V the comparator immediately terminates the
buck switch on-time pulse.
ON Time generator and Shutdown
The on-time of the LM25007 is set inversely proportional to the input voltage by an external resistor connected
between RON/SD and VIN. The RON/SD terminal is a low impedance input biased at approximately 1.5V. The
current through the resistor and into the RON/SD pin is approximately proportional 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 LM25007 is :
Ton = 1.42 x 10
-10
x R
ON
/ V
IN
(4)
The RON/SD pin of the LM25007 also provides a shutdown function which disables the regulator and
significantly decreases quiescent power dissipation. By pulling the pin below 0.7V activates the low power
shutdown mode. The V
IN
quiescent current in the shutdown mode is approximately 100µA internal to the
LM25007 plus the current in the R
ON
resistor. See Figure 8.
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