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7V SERIES REGULATOR

SW

LM25007

VIN

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 / VIN

(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 VIN quiescent current in the shutdown mode is approximately 100µA internal to the

LM25007 plus the current in the RON resistor. See Figure 8.

Copyright © 2006–2013, Texas Instruments Incorporated

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Product Folder Links: LM25007