AIC1574 Ver la hoja de datos (PDF) - Analog Intergrations

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AIC1574

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

Analog Intergrations 

perature at high ambient temperature by calcu-

lating the temperature rise according to package

thermal resistance specifications.

PUPPER = IOUT2 × RDS(ON) × D + IOUT × VIN × tSW × f

2

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 se-

lected based on on-resistance considerations,

RDS(ON) should be chosen base on input and

output voltage, allowable power dissipation and

maximum required output current. Power dissi-

pation should be calculated based primarily on

required efficiency or allowable thermal dissipa-

tion.

Rectifier Schottky diode is a clamp that prevent

the loss parasitic MOSFET body diode from

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 reverse

AIC1574

breakdown voltage must be greater than twice

the maximum input voltage.

Linear Controller MOSFET Selection

The power dissipated in a linear regulator is :

PLINEAR = IOUT2 × (VIN2 − VOUT2 )

Select a package and heatsink that maintains

junction temperature below the maximum rating

while operation at the highest expected ambient

temperature.

Linear Output Capacitor

The output capacitors for the linear regulator and

linear controller provide dynamic load current.

The linear controller uses dominant pole com-

pensation integrated in the error amplifier and is

insensitive to output capacitor selection. COUT2,

COUT3 and COUT4 should be selected for tran-

sient load regulation.

PWM Feedback Analysis

∆VOSC

VDAC

VEA

ERROR AMP.

PWM COMP.

Compensation

Networks

VIN

Q1

LO

+

CO

Q2

RESR

VOUT

Modulation

Gain

18

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