t6309a TM Technology Inc., t6309a Datasheet - Page 10

• Manufacturer Part Number: t6309a
• Description: Micropower Step-up Dc/dc Converter
• Manufacturer: TM Technology Inc.

tm
used.
Resistance) ceramic capacitor with value of
1uF to 4.7uF would be suitable.
The output capacitor is used to sustain the
output voltage when the internal MOSFET is
switched on and smoothing the ripple voltage.
The larger the output ripple, the larger the line
regulation, which means the LED current
changes if the input voltage changes. Low
ESR capacitor should be used to reduce
output ripple voltage. Use a 4.7uF to 10uF
ceramic output capacitor with about 50mOhm
to 150mOhm ESR to provide stable switching
and good line regulation.
Schottky Diode Selection
DC-DC converters. The most important
parameters which affect the efficiency are the
forward voltage drop, V
recovery time. The forward voltage drop
creates a loss just by having a voltage across
the device while a current flowing through it.
The reverse recovery time generates a loss
when the diode is reverse biased, and the
current appears to actually flow backwards
through the diode due to the minority carriers
being swept from the P-N junction. A
Schottky
characteristics is recommended:
Small forward voltage, VF = 0.3 V
Small reverse leakage current Fast reverse
recovery time/switching speed Rated current
larger than peak inductor current Reverse
TM Technology Inc. reserves the right
to change products or specifications without notice.
The diode is the largest source of loss in
Small
CH
TE
diode
ESR ( Equivalent Series
with
F
, and the reverse
the
following
P. 10
voltage larger than output voltage.
Layout Considerations
High switching frequencies make PC board
layout a very important part of design. Good
design minimizes excessive EMI on the
feedback paths and voltage gradients in the
ground plane, both of which can result in
instability or regulation errors.
Connect the inductor, input filter capacitor,
and output filter capacitor as close to the
device as possible, and keep their traces short,
direct, and wide to reduce power loss so as to
improve efficiency. Connect their ground pins
at a single common node in a star ground
configuration, or at a full ground plane.
The output capacitor should be placed close
to the output terminals to obtain better
smoothing effect on the output ripple.
In addition, the ground connection for the
sense resistor Rs should be tied directly to the
GND pin and not shared with any other
component. This ensures a clean, noise-free
connection.
Publication Date: MAY. 2007
T6309A
Revision: A