ADP1828LC-EVALZ Analog Devices Inc, ADP1828LC-EVALZ Datasheet - Page 20

• Manufacturer Part Number: ADP1828LC-EVALZ
• Description: BOARD EVALUATION ADP1828LC
• Manufacturer: Analog Devices Inc

Specifications of ADP1828LC-EVALZ

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 1.8V
• Current - Output: 5A
• Voltage - Input: 5.5 ~ 13.2V
• Regulator Topology: Buck
• Frequency - Switching: 600kHz
• Board Type: Fully Populated
• Utilized Ic / Part: ADP1828
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

ADP1828
During a load step transient on the output, the output capacitor
supplies the load until the control loop has a chance to ramp the
inductor current. This initial output voltage deviation, due to a
change in load, is dependent on the output capacitor charac-
teristics. Again, usually the capacitor ESR dominates this
response, and the ΔV
load step current value for ΔI
SELECTING THE MOSFETS
The choice of MOSFET directly affects the dc-to-dc converter
performance. The MOSFET must have low on resistance to
reduce I
In addition, the MOSFET must have low thermal resistance to
ensure that the power dissipated in the MOSFET does not result
in excessive MOSFET die temperature.
The high-side MOSFET carries the load current during on-time
and usually carries most of the transition losses of the converter.
Typically, the lower the MOSFET’s on resistance, the higher the
gate charge and vice versa. Therefore, it is important to choose a
high-side MOSFET that balances the two losses. The conduction
loss of the high-side MOSFET is determined by the equation
where:
P
R
The gate charging loss is approximated by the equation
where:
P
V
Q
f
The high-side MOSFET transition loss is approximated by the
equation
where:
P
t
t
The total power dissipation of the high-side MOSFET is the
sum of all the previous losses, or
where P
SW
R
F
C
G
T
DSON
PV
G
is the MOSFET rise time.
is the MOSFET fall time.
is the high-side MOSFET switching loss power.
is the conduction power loss.
is the gate charging loss power.
is the converter switching frequency.
is the MOSFET total gate charge.
is the gate driver supply voltage.
P
P ≅
P
P
is the MOSFET on resistance.
T
C
G
HS
2
HS
≅
=
R losses and low gate charge to reduce transition losses.
≅
(
V
V
is the total high-side MOSFET power loss.
I
P
PV
IN
LOAD
C
I
Q
+
LOAD
G
P
)
G
2
f
SW
R
+
(
t
DSON
2
OUT
P
R
T
+
in Equation 6 can be used with the
⎛
⎜
⎜
⎝
t
F
V
V
)
OUT
L
IN
f
.
SW
⎞
⎟
⎟
⎠
(10)
Rev. C | Page 20 of 36
(7)
(8)
(9)
The conduction losses may need an adjustment to account
for the MOSFET R
MOSFET R
MOSFET data sheet should list the thermal resistance of the
package, θ
coefficient of the R
Equation 10, calculate the MOSFET junction temperature rise
over the ambient temperature of interest:
Then, calculate the new R
curve and the R
to calculate the MOSFET R
where T
and its typical value is 0.004/°C.
Then the conduction losses can be recalculated and the proce-
dure iterated until the junction temperature calculations are
relatively consistent.
The synchronous rectifier, or low-side MOSFET, carries the
inductor current when the high-side MOSFET is off. The low-
side MOSFET tran
the calculation. For high input voltage and low output voltage,
the low-side MOSFET carries the current most of the time.
Therefore, to achieve high efficiency, it is critical to optimize
the low-side MOSFET for low on resistance. In cases where the
power loss exceeds the MOSFET rating or lower resistance is
required than is available in a single MOSFET, connect multiple
low-side MOSFETs in parallel. T
power loss is
where:
P
R
Check the gate charge losses of the synchronous rectifier using
Equation 8 to be sure it is reasonable. If multiple low-side
MOSFETs are used in parallel, then use the parallel combina-
tion of the on resistances for determining RDSON to solve this
equation.
LS
DSON
is the total low-side MOSFET power loss.
T
R
P
is the total on resistance of the low-side MOSFET(s).
J
DSON
LS
= T
C
≅
is the temperature coefficient of the MOSFET’s R
JA
@ T
A
(
DSON
, along with a normalized curve of the temperature
I
+ θ
LOAD
J
JA
= R
DSON
increases with increasing temperature. The
P
)
D
2
DSON
sition loss is small and can be neglected in
DSON
DSON
R
specification at 25°C. An alternate method
DSON
. For the power dissipation estimated in
variation with temperature. Note that
@ 25°C (1 + T
DSON
⎡
⎢
⎣
1
DSON
−
from the temperature coefficient
V
he equation for low-side MOSFET
V
at a second temperature, T
OUT
IN
⎤
⎥
⎦
C
(T
J
− 25°C))
J
DSON
, is
(11)
(12)
(13)
,