XRP7704 Exar Corporation, XRP7704 Datasheet - Page 29

• Manufacturer Part Number: XRP7704
• Description: Quad-output Digital Pwm Buck Controller
• Manufacturer: Exar Corporation

REV 1.1.0
In general, the total input voltage ripple should be kept below 1.5% of VIN. The input voltage ripple also has two
major components: the voltage drop on the main capacitor
contribution to Input voltage ripple by each term can be calculated from:
Total input voltage ripple is the sum of the above:
Power MOSFETs Selection
Selecting MOSFETs with lower Rdson reduces conduction losses at the expense of increased switching losses. A
simplified expression for conduction losses is given by:
MOSFET’s junction temperature can be estimated from:
This assumes that the switching loss is the same as the conduction loss.
resistance from junction to ambient.
EXAR CONFIDENTIAL. PROPRIETARY. DO NOT DISTRIBUTE OR COPY.
Δ
Δ
V
V
ESR
P
Cin
T
Δ
cond
j
V
=
= 2
=
Tot
ESR
=
I
Quad-Output Digital PWM Buck Controller
P
=
out
I
cond
Δ
out
V
⋅
V
out
(
29
f
2
R
I
Cin
s
⋅
thja
C
out
(
V
R
Δ
in
+
in
dson
+
+
V
V
Δ
−
Cin
in
T
0
2
V
5 .
ambient
V
⋅
ESR
V
V
and the voltage drop due to ESR -
out
I
out
rip
in
)
)
R
thja
is the total MOSFET thermal
XRP7704
Δ
V
ESR
. The