AIC1570 Datasheet, PDF (16/18 Pages) Analog Intergrations Corporation – 5-bit DAC, Synchronous PWM Power Regulator with LDO and Linear Controller

AIC1570
and switching loss. The gate charge losses are
proportional to the switching frequency and are
dissipated by the AIC1570. However, the gate
charge increases the switching interval, t_SW which
increase the upper MOSFET switching losses.
Ensure that both MOSFETs are within their
maximum junction temperature at high ambient
temperature by calculating the temperature rise
according to package thermal resistance
specifications.
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 R_DS(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 considerations,
R_DS(ON) should be chosen base on input and
output voltage, allowable power dissipation and
maximum required output current. Power
dissipation should be calculated based primarily
on required efficiency or allowable thermal
dissipation.
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
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
compensation integrated in the error amplifier
and is insensitive to output capacitor selection.
C_OUT3 should be selected for transient load
regulation. The output capacitor for the linear
regulator provides loop stability.
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