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

70

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

LOAD

Load current

DSON,

PFET

Drain to source resistance of PFET switch

in the triode region

20075803

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

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