LTC3406ABES5(RevA) データシートの表示（PDF） - Linear Technology

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LTC3406ABES5
(Rev.:RevA)

1.5MHz, 600mA Synchronous Step-Down Regulator in ThinSOT

Linear Technology 

LTC3406AB

OPERATION (Refer to Functional Diagram)

Dropout Operation

As the input supply voltage decreases to a value approach-

ing the output voltage, the duty cycle increases toward the

maximum on-time. Further reduction of the supply voltage

forces the main switch to remain on for more than one cycle

until it reaches 100% duty cycle. The output voltage will

then be determined by the input voltage minus the voltage

drop across the P-channel MOSFET and the inductor.

An important detail to remember is that at low input supply

voltages, the RDS(ON) of the P-channel switch increases

(see Typical Performance Characteristics). Therefore,

the user should calculate the power dissipation when the

LTC3406AB is used at 100% duty cycle with low input

voltage (See Thermal Considerations in the Applications

Information section).

Slope Compensation and Inductor Peak Current

Slope compensation provides stability in constant fre-

quency architectures by preventing subharmonic oscilla-

tions at high duty cycles. It is accomplished internally by

adding a compensating ramp to the inductor current signal

at duty cycles in excess of 40%. Normally, this results in

a reduction of maximum inductor peak current for duty

cycles >40%. However, the LTC3406AB uses a patented

scheme that counteracts this compensating ramp, which

allows the maximum inductor peak current to remain

unaffected throughout all duty cycles.

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