Buck

or

Boost

Boost

Buck

Region I

Region II

Region III

High PFM Threshold

~1.016*Vout

Low1 PFM Threshold

~1.008*Vout

PFM Mode at Light Load

PWM Mode at

Moderate to Heavy

Loads

Inductor

Current

Ramp up

Inductor

current ramp

down

until

I inductor=0

High PFM

Voltage

Threshold

reached,

go into

Low power

mode, both

switches are off

Low PFM

Threshold,

turn on

Current load

increases,

draws Vout

towards

Low2 PFM

Threshold

Low2 PFM Threshold,

switch back to PWMmode

Load current

increases

Low2 PFM Threshold

Vout

LM3668-Q1

www.ti.com

SNVSA84A – APRIL 2015 – REVISED MAY 2015

Device Functional Modes (continued)

Figure 9. PFM to PWM Mode Transition

In addition to the auto mode transition, the LM3668-Q1 operates in PFM Buck or PFM Boost based on the

following conditions. There is a small delta (approximately 500 mV) known as dv1 (approximately 200 mV) and

•

•

mode.

•

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