t6309a TM Technology Inc., t6309a Datasheet - Page 9

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

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4. Using a Logic Signal
The LED current can be controlled in discrete
steps with a logic signal as shown in the
figure below. When the NMOS is off, R1 set
the minimum current. When the NMOS is on,
R2 sets the LED current increment value.
Start-Up and Inrush Current
The T6309A has no internal soft start circuit
included to achieve minimum start-up delay.
All inductive step-up converters have higher
inrush current during start-up. The inrush
current for T6309A is about 200mA. If soft-
start is required, a recommended external
circuit is shown in the below figure.
TM Technology Inc. reserves the right
to change products or specifications without notice.
Logic
Signal
T6309A
GND
CH
FB
TE
R2
D1
D2
T6309A
4.7K
FB
2.2nF
1K
R
1
R
S
P. 9
Output Voltage Selection
Referring to Fig. 4, select an output voltage
for
connecting FB to a resistive divider between
the output and GND. The V
V
Higher R1,R2 values reduce quiescent current,
but give bad noise immunity. To keep stable
feedback loop operation and better noise
immunity, select (R1+R2) value less than
1MOhm.
Inductor Selection
The T6309A is designed to work well with a
10uH inductor in most applications. Low
inductance values supply higher output
current, but also increase the ripple and
reduce efficiency. Higher inductor values
reduce ripple and improve efficiency, but also
limit output current. Choose a low DC-
resistance inductor, usually less than 1 Ohm
to minimize loss. It is necessary to choose an
inductor with saturation current greater than
the peak current that the inductor will
encounter in the application. Saturation
occurs when the inductor’s magnetic flux
density reaches the maximum level the core
can support and inductance falls. Inductor
with 600mA rating or greater would be
suitable for the T6309A.
Capacitor Selection
The input capacitor stabilizes the input
voltage and minimizes the peak current ripple
from the source. The value of the capacitor
depends on the impedance of the input source
OUT
= (1+R1/R2) x 1.19V
T6309A-B
Publication Date: MAY. 2007
(1.19V
OUT
reference)
can be set as:
T6309A
Revision: A
by