ADP2442-EVALZ Analog Devices, ADP2442-EVALZ Datasheet - Page 31

• Manufacturer Part Number: ADP2442-EVALZ
• Description: Power Management IC Development Tools Eval board
• Manufacturer: Analog Devices
• Type: DC/DC Converters, Regulators & Controllersr
• Series: ADP2442r

Specifications of ADP2442-EVALZ

• Rohs: yes
• Tool Is For Evaluation Of: ADP2442
• Factory Pack Quantity: 1

Data Sheet
POWER DISSIPATION AND THERMAL CONSIDERATIONS
POWER DISSIPATION
The efficiency of a dc-to-dc regulator is
where:
P
P
The power loss of a dc-to-dc regulator is
There are four main sources of power loss in a dc-to-dc regulator
•
•
•
•
Inductor Losses
Inductor conduction losses are caused by the flow of current
through the inductor DCR (internal resistance). The inductor
power loss (excluding core loss) is
Power Switch Conduction Losses
Power switch conduction losses are caused by the output current,
I
that have internal resistance, R
can be approximated as follows:
P
Switching Losses
Switching losses are associated with the current drawn by the
driver to turn the power devices on and off at the switching
frequency. Each time a power device gate is turned on and off,
the driver transfers a charge (∆Q) from the input supply to the
gate and then from the gate to ground.
The amount of switching loss can by calculated as follows:
where:
Q
side devices and is approximately 18 nC.
f
SW
OUT
IN
OUT
COND
G_TOTAL
is the switching frequency.
is the input power.
, flowing through the N-channel MOSFET power switches
P
Inductor losses
Power switch conduction losses
Switching losses
Transition losses
P
P
is the output power.
Efficiency
= [R
LOSS
L
SW
= I
is the total gate charge of both the high-side and low-
= Q
= P
OUT
DS(ON) – HIGH SIDE
G_TOTAL
IN
2
× DCR
=
− P
P
P
OUT
OUT
× V
IN
L
×
IN
× D + R
100
× f
SW
%
DS(ON)
DS(ON) – LOW SIDE
. The amount of power loss
× (1 – D)] × I
OUT
(26)
(27)
(29)
Rev. 0 | Page 31 of 36
2
(28)
Transition Losses
Transition losses occur because the N-channel MOSFET power
switch cannot turn on or off instantaneously. During a switch
node transition, the power switch provides all of the inductor
current, and the source-to-drain voltage of the power switch is
half the input, resulting in power loss. Transition losses increase
as the load current and input voltage increase; these losses
occur twice for each switching cycle.
The transition losses can be calculated as follows:
where t
node and are each approximately 10 ns for a 24 V input.
THERMAL CONSIDERATIONS
The power dissipated by the regulator increases the die junction
temperature, T
where the temperature rise, T
dissipation, P
The proportionality coefficient is defined as the thermal
resistance from the junction temperature of the die to the
ambient temperature, as follows:
where θ
equals 40°C/W for the JEDEC board (see Table 3).
When designing an application for a particular ambient tempera-
ture range, calculate the expected
due to the conduction, switching, and transition losses using
Equation 28, Equation 29, and Equation 30, and then estimate
the temperature rise using Equation 31 and Equation 32. Improved
thermal performance can be achieved by good board layout.
For example, on the
EVALZ), the measured θ
the ADP2442-EVALZ evaluation board is shown in Figure 68
and Figure 69.
T
T
P
J
R
TRANS
= T
ON
= θ
JA
is the junction-to-ambient thermal resistance and
and t
A
JA
=
+ T
+ P
D
V
, in the package.
J
OFF
, above the ambient temperature, T
2
IN
R
D
are the rise time and fall time of the switch
×
ADP2442
I
OUT
JA
×
is <30°C/W. Thermal performance of
(
t
ON
R
evaluation board (ADP2442-
, is proportional to the power
+
ADP2442
t
OFF
)
f
SW
power dissipation (P
ADP2442
A
, as follows:
(30)
(31)
(32)
D
)