+

+

+

7V SERIES REGULATOR

SW

LM25007

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

(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

Copyright © 2006–2013, Texas Instruments Incorporated

Submit Documentation Feedback

9

Product Folder Links: LM25007