LM25575MHX datasheet(19/30 Pages) TI

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BST

VCC

GND

LM25575

COUT

OUT

BST

VCC

GND

LM25575

VOUT

COUT

LM25575, LM25575-Q1

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SNVS479G – JANUARY 2007 – REVISED APRIL 2013

BIAS POWER DISSIPATION REDUCTION

Buck regulators operating with high input voltage can dissipate an appreciable amount of power for the bias of

the IC. The VCC regulator must step-down the input voltage VIN to a nominal VCC level of 7V. The large voltage

drop across the VCC regulator translates into a large power dissipation within the Vcc regulator. There are several

techniques that can significantly reduce this bias regulator power dissipation. Figure 12 and Figure 13 depict two

methods to bias the IC from the output voltage. In each case the internal Vcc regulator is used to initially bias the

VCC pin. After the output voltage is established, the VCC pin potential is raised above the nominal 7V regulation

level, which effectively disables the internal VCC regulator. The voltage applied to the VCC pin should never

exceed 14V. The VCC voltage should never be larger than the VIN voltage.

Figure 12. VCC Bias from VOUT for 8V < VOUT < 14V

Figure 13. VCC Bias with Additional Winding on the Output Inductor

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LM25575MHX Datasheet(PDF) 19 Page - Texas Instruments