AIC1571 Ver la hoja de datos (PDF) - Analog Intergrations

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AIC1571

5-bit DAC, Synchronous PWM Power Regulator with Dual Linear Controllers

Analog Intergrations 

PUPPER

=

IOUT 2

× RDS(ON) × D +

IOUT

×

VIN ×

2

tSW

×

f

PLOWER = IOUT 2 × RDS(ON) × (1− D)

The equations above do not model power loss

due to the reverse recovery of the lower

MOSFET’s body diode.

The RDS(ON) is different for the two previous

equations even if the type devices is used for

both. This is because the gate drive applied to

the upper MOSFET is different than the lower

MOSFET. Logic level MOSFETs should be

selected based on on-resistance considera-

tions, RDS(ON) should be chosen base on input

and output voltage, allowable power dissipation

and maximum required output current. Power

dissipation should be calculated based pri-

marily on required efficiency or allowable ther-

mal dissipation.

Rectifier Schottky diode is a clamp that prevent

the loss parasitic MOSFET body diode from

AIC1571

conducting during the dead time between the

turn off of the lower MOSFET and the turn on

of the upper MOSFET. The diode’s rated re-

verse breakdown voltage must be greater than

twice the maximum input voltage.

Linear Controller MOSFET Selection

The power dissipated in a linear regulator is :

PLINEAR = IOUT × (VIN2 − VOUT)

Select a package and heatsink that maintains

junction temperature below the maximum rat-

ing while operation at the highest expected

ambient temperature.

Linear Output Capacitor

The output capacitors for the linear controller

provide dynamic load current. The linear con-

troller uses dominant pole compensation inte-

grated in the error amplifier and is insensitive to

output capacitor selection. COUT2 and COUT3

should be selected for transient load regulation.

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