LM3370 datasheet(14/23 Pages) NSC

Part #	LM3370

Description	Dual Synchronous Step-Down DC-DC Converter with Dynamic Voltage Scaling Function

PDF	23 Pages

Scroll/Zoom	100%

Manufacturer	NSC [National Semiconductor (TI)]

Direct Link	http://www.national.com

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14 / 23 page

Operation Description (Continued)

FORCED PWM MODE

The LM3370 auto mode can be bypassed by forcing the

device to operate in PWM mode, this can be implemented

through the I

2C compatible interface; see Output Table on

page 19.

SOFT-START

The LM3370 has a soft start circuit that limits in-rush current

during start up. Soft start is activated only if EN goes from

logic low to logic high after V

IN reaches 2.7V.

LDO - LOW DROP OUT OPERATION

The LM3370 can operate at 100% duty cycle (no switching,

PFET 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 mini-

mum input voltage needed to support the output voltage is

IN,MIN =ILOAD*(RDSON,PFET +RINDUCTOR)+VOUT

• I

LOAD

load current

• R

DSON/PFET drain to source resistance of PFET switch in

the triode region

• R

INDUCTOR

inductor resistance

20167303

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

LM3370 Datasheet(PDF) 14 Page - National Semiconductor (TI)