LM3670 datasheet(12/17 Pages) NSC

Part #	LM3670

Description	Miniature Step-Down DC-DC Converter for Ultra Low Voltage Circuits

PDF	17 Pages

Scroll/Zoom	100%

Manufacturer	NSC [National Semiconductor (TI)]

Direct Link	http://www.national.com

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12 / 17 page

Operation Description (Continued)

Soft-Start

The LM3670 will have a soft-start circuit that limits in-rush

current during start-up. Typical currents and times are:

Current (mA)

Duration (µSec)

032

224

140

256

280

256

620

until soft start ends

Note 4: The first 32µS are to allow the bias currents to stabilize

LDO - Low Drop Out Operation

The LM3670 can operate at 100% duty cycle (no switching,

PMOS switch completely on) for low drop out support of the

output voltage. In this way the output voltage will be con-

trolled down to the lowest possible input voltage.

The minimum input voltage needed to support the output

voltage is

• I

LOAD

Load current

• R

DSON,

PFET

Drain to source resistance of PFET switch

in the triode region

• R

INDUCTOR Inductor resistance

20075803

FIGURE 5. Operation in PFM Mode and Transfer to PWM Mode

LM3670 Datasheet(PDF) 12 Page - National Semiconductor (TI)