ADP5043 Analog Devices, ADP5043 Datasheet - Page 25

• Manufacturer Part Number: ADP5043
• Description: Micro-PMU with 0.8 A Buck, 300 mA LDO, Supervisory, Watchdog, and Manual Reset
• Manufacturer: Analog Devices

Data Sheet
POWER DISSIPATION/THERMAL CONSIDERATIONS
The ADP5043 is a highly efficient micro PMU, and in most
cases the power dissipated in the device is not a concern.
However, if the device operates at high ambient temperatures
and with maximum loading conditions, the junction
temperature can reach the maximum allowable operating
limit (125°C).
When the junction temperature exceeds 150°C, the ADP5043
turns off all the regulators, allowing the device to cool down.
Once the die temperature falls below 135°C, the ADP5043
resumes normal operation.
This section provides guidelines to calculate the power dissi-
pated in the device and to make sure the ADP5043 operates
below the maximum allowable junction temperature.
The efficiency for each regulator on the ADP5043 is given by
where:
η is efficiency.
P
P
Power loss is given by
The power dissipation of the supervisory function is small and
can be neglected.
Power dissipation can be calculated in several ways. The most
intuitive and practical is to measure the power dissipated at
the input and all the outputs. The measurements should be
performed at the worst-case conditions (voltages, currents,
and temperature). The difference between input and output
power is dissipated in the device and the inductor. Use
Equation 4 to derive the power lost in the inductor, and from
this use Equation 3 to calculate the power dissipation in the
ADP5043 buck regulator.
A second method to estimate the power dissipation uses the
efficiency curves provided for the buck regulator, while the
power lost on the LDO is calculated using Equation 12. Once
the buck efficiency is known, use Equation 2b to derive the total
power lost in the buck regulator and inductor, use Equation 4
to derive the power lost in the inductor, and thus calculate the
power dissipation in the buck converter using Equation 3. Add
the power dissipated in the buck and in the LDO to find the
total dissipated power.
It should be noted that the buck efficiency curves are typical
values and may not be provided for all possible combinations
of V
necessary to include a safety margin when calculating the
power dissipated in the buck.
IN
OUT
is the input power.
IN
P
or
P
is the output power.
η
, V
LOSS
LOSS
=
OUT
P
= P
= P
P
OUT
IN
, and I
IN
OUT
×
− P
100%
(1-η)/η
OUT
OUT
. To account for these variations, it is
(2b)
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A third way to estimate the power dissipation is analytical and
involves modeling the losses in the buck circuit provided by
Equation 8 to Equation 11 and the losses in the LDO provided
by Equation 12.
Buck Regulator Power Dissipation
The power loss of the buck regulator is approximated by
where:
P
P
The inductor losses are external to the device and they don’t
have any effect on the die temperature.
The inductor losses are estimated (without core losses) by
where I
where r is the inductor ripple current.
f
L is inductance.
DCR
D is duty cycle.
The ADP5043 buck regulator power dissipation, P
includes the power switch conductive losses, the switch losses,
and the transition losses of each channel. There are other
sources of loss, but these are generally less significant at high
output load currents, where the thermal limit of the application
will be. Equation 8 shows the calculation made to estimate the
power dissipation in the buck regulator.
The power switch conductive losses are due to the output current,
I
switches that have internal resistance, R
amount of conductive power loss is found by:
For the ADP5043, at 125°C junction temperature and VIN =
3.6 V, R
approximately 0.16 Ω. At VIN = 2.3 V, these values change to
0.31 Ω and 0.21 Ω respectively, and at VIN = 5.5 V, the values
are 0.16 Ω and 0.14 Ω.
SW
OUT1
DBUCK
L
is the inductor power losses.
is switching frequency.
, flowing through the PMOSFET and the NMOSFET power
P
r ≈ V
D = V
P
P
L
P
I
LOSS
OUT1
is the inductor series resistance.
DBUCK
COND
L
is the power dissipation on the ADP5043 buck regulator.
OUT1(RMS)
DSON-P
≅
= P
OUT1
I
(
RMS
= [R
OUT1
OUT1
= P
DBUCK
is approximately 0.2 Ω, and R
)
× (1-D)/(I
/V
(
COND
DSON-P
=
is the RMS load current of the buck regulator.
RMS
IN1
I
OUT1
+ P
)
2
+ P
×
× D + R
L
DCR
×
SW
OUT1
+ P
1
+
L
× L × f
DSON-N
r
TRAN
/12
× (1 − D)] × I
SW
)
DSON-P
DSON-N
and R
OUT1
is
ADP5043
DBUCK
DSON-N
2
,
. The
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