MP1529DR MPS [Monolithic Power Systems], MP1529DR Datasheet - Page 9

• Manufacturer Part Number: MP1529DR
• Description: Fixed Frequency Step-Up Converter LCD Backlight Plus Flash
• Manufacturer: MPS [Monolithic Power Systems]

Selecting the Inductor
The inductor is required to force the output
voltage higher while being driven by the lower
input voltage. Choose an inductor that does not
saturate at the SW current limit.
A good rule for determining the inductance is to
allow the peak-to-peak ripple current to be
approximately 30%-50% of the maximum input
current. The maximum input current usually
occurs in flash mode. Make sure that the peak
inductor current is below 75% of the typical
current limit to prevent loss of regulation due to
the current limit variation.
Calculate the required inductance value L using
the equations:
Where ∆I is the peak-to-peak inductor ripple
current and η is the efficiency at flash mode. A
4.7µH or 10µH inductor is recommended for
most cell phone applications.
Selecting the Diode
The output rectifier diode supplies current to the
inductor when the internal MOSFET is off. To
reduce losses due to diode forward voltage and
recovery time, use a Schottky diode.
Choose a diode whose maximum reverse
voltage rating is greater than the maximum
output voltage. For output voltage less than
20V, it is recommended to choose the
MBR0520 for most applications.
MP1529 Rev. 1.0
11/23/2005
I
TM
∆
IN
I
MP1529 – FIXED FREQUENCY STEP-UP CONVERTER LCD BACKLIGHT PLUS FLASH
(
L
=
MAX
=
(
30
)
V
V
=
%
IN
OUT
V
(V
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
−
OUT
50
OUT
×
V
f
SW
%
IN
×
-
I
)
LED
×
I
V
IN
×
η
IN
(
∆
MAX
_
)
I
FL
)
© 2005 MPS. All Rights Reserved.
www.MonolithicPower.com
Selecting the Compensation Capacitor
The compensation capacitor needs to be
determined so that the control loop is slow
enough to allow for stable and smooth mode
transition.
recommended for most cell phone applications.
Selecting the Soft-Start Capacitor
The soft-start capacitor sets both the soft-start
timer and the PWM timer. A 10nF to 22nF
capacitor
applications.
Layout Considerations
High frequency switching regulators require
very careful layout for stable operation and low
noise. All components must be placed as close
to the IC as possible. Keep the path between
the SW pin, output diode, output capacitor and
GND pin extremely short for minimal noise and
ringing. The input capacitor must be placed
close to the IN pin for best decoupling. All
current setting resistors must be kept close to
the corresponding ISET pin to prevent noise
injection for accurate LED current setting. The
ground return of the input and output capacitors
should be tied close to the GND pin. See the
MP1529 demo board layout for reference.
A
is
1µF
recommended
ceramic
capacitor
for
most
is
9