ADP3050ARZ-3.3-RL View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
ADP3050ARZ-3.3-RL Datasheet PDF : 20 Pages
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ADP3050
VIN (MIN ) =
VOUT + VSAT
0.85
(12)
THERMAL CONSIDERATIONS
Several factors contribute to IC power dissipation: ac and dc
switch losses, boost current, and quiescent current. The following
formulas are used to calculate these losses to determine the power
dissipation of the IC. These formulas assume continuous mode
operation, but they provide a reasonable estimate for disconti-
nuous mode systems (do not use these formulas to calculate
efficiency at light loads).
Switch loss
( ) PSW
= IOUT
×VSAT
×
VOUT
VIN
+
t OV
× IOUT
×VIN ×
f SW
(13)
Boost current loss
PBOOST
=
I OUT
βSW
× VOUT 2
VIN
(14)
Quiescent current loss
( ) ( ) PQ = VIN × IQ + VOUT × I BIAS
(15)
where:
VSAT is ~0.6 V at IOUT = 800 mA (taken from Figure 15).
fSW is the switch frequency (200 kHz).
tOV is the switch current/voltage overlap time (~50 ns).
βSW is the current gain of the NPN power switch (~50).
IQ is the quiescent current drawn from VIN (~1 mA).
IBIAS is the quiescent current drawn from VOUT (~4 mA).
For example, a 5 V to 3.3 V system with IOUT = 800 mA
Data Sheet
PSW
= 0.8×0.6×
3.3
5.0
+
( ) 50×10−9 ×0.8×5.0×200×103 = 357 mW
PBOOST
= 0.8 × 3.32
50 5.0
= 35 mW
( ) ( ) PQ = 5×10−3 + 3.3× 4×10−3 =18 mW
For a total IC power dissipation of
PTOTAL = PSW + PBOOST + PQ = 410 mW
(16)
The ADP3050 is offered in a thermally enhanced (not Pb-free)
8-lead SOIC package with a thermal resistance, θJA, of 60.6°C/W,
and in a standard Pb-free 8-lead SOIC package with θJA of
87.5°C/W.
The maximum die temperature, TJ, is calculated using the
thermal resistance and the maximum ambient temperature
TJ =TA + θ JA × PTOTAL
(17)
For the previous example (5 V to 3.3 V at 800 mA system, Pb-
free 8-lead SOIC package using good layout techniques) with a
worst-case ambient temperature of 70°C
TJ = 70°C + 87.5°C/W × 0.41 = 105.9°C
The maximum operating junction (die) temperature is 125°C,
therefore this system operates within the safe limits of the
ADP3050. Check the die temperature at minimum and
maximum supply voltages to ensure proper operation under all
conditions. Although the PCB and its copper traces provide
sufficient heat sinking, it is important to follow the layout
suggestions in the Board Layout Guidelines section. For any
design that combines high output current with high duty cycle
and/or high input voltage, the junction temperature must be
calculated to ensure normal operation. Always use the
equations in this section to estimate the power dissipation.
Rev. C | Page 16 of 20
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