sp6669aek-l-tr Exar Corporation, sp6669aek-l-tr Datasheet - Page 8

• Manufacturer Part Number: sp6669aek-l-tr
• Description: 1.5mhz, 600ma Synchronous Step Down Converter
• Manufacturer: Exar Corporation

network must be connected in parallel to
the C
3- The input capacitor C
close as possible to the V
4- The SW and VFB nodes should be kept
as separate as possible to minize possible
effects
voltage swings of the SW node.
5- The ground plates of C
should be kept as close as possible.
Ouptut Voltage Ripple for V
V
When the input voltage V
output
transitions smoothly from the switching
PWM converter mode into a LDO mode.
The following diagram shows the output
voltage ripple versus the input voltage for
a 3.3V output setting and a 200mA
current load.
Rev D – 01/21/2008
OUT
OUT
for V
capacitor.
from
Fig.20: V
voltage
IN
decreasing close to V
the
OUT
V
Ripple Voltage
high
OUT
SP6669 1.5MHz 0.6A Sync. Step Down Converter © 2008 Exar Corporation
IN
,
IN
IN
must be kept as
frequency
pin.
is close to the
the
IN
IN
OUT
close to
and C
SP6669
and
OUT
8/10
Design Example
In a single Lithium-Ion battery powered
application, the V
4.2V. The desired output voltage is 1.8V.
The
calculated using the following equation
Subsituting
ΔI
A 2.2µH inductor can be choosen with this
application. An inductor of greater value
with
would provide better efficiency. The CIN
capacitor requires an RMS current rating
of at least I
most cases, a ceramic capacitor will
satisfy this requirement.
L
=240mA and f=1.5MHz gives
inductor
less
L
=
equivalent
THEORY OF OPERATION
f
LOAD(MAX)
Δ ⋅
1
L
V
value
I
=
IN
OUT
L
V
. 2
range is about 2.7V to
=1.8V,
OUT
/2 and low ESR. In
86
μ
⎛
⎜ ⎜
⎝
needed
series
1
H
−
V
V
OUT
IN
resistance
⎞
⎟ ⎟
⎠
V
can
IN
=4.2V,
be