LT1937 LINER [Linear Technology], LT1937 Datasheet - Page 14

• Manufacturer Part Number: LT1937
• Description: 20mA LED Driver and OLED Driver with Integrated Schottky in 3mm x 2mm DFN
• Manufacturer: LINER [Linear Technology]

LT3498
Inductor Selection
Several recommended inductors that work well with the
OLED driver of the LT3498 are listed in Table 5, although
there are many other manufacturers and devices that can
be used. Consult each manufacturer for more detailed
information and for their entire selection of related parts.
Many different sizes and shapes are available. Use the
equations and recommendations in the next few sections
to fi nd the correct inductance value for your design.
Table 5: Recommended Inductors
PART
LQH32CN100K53
LQH2MCN100K02
LQH32CN150K53
LQH2MCN150K02
SD3110-100
SD3110-150
Inductor Selection—Boost Regulator
The formula below calculates the appropriate inductor
value to be used for the low noise boost regulator of
the LT3498 (or at least provides a good starting point).
This value provides a good tradeoff in inductor size and
system performance. Pick a standard inductor close to
this value. A larger value can be used to slightly increase
the available output current, but limit it to around twice
the value calculated below, as too large of an inductance
will decrease the output voltage ripple without providing
much additional output current. A smaller value can be
used (especially for systems with output voltages greater
than 12V) to give a smaller physical size. Inductance can
be calculated as:
where V
the minimum input voltage. Generally, a 10µH or 15µH
inductor is a good choice.
APPLICATIONS INFORMATION—OLED DRIVER
14
L
(
V
OUT2
OUT
2
is the desired output voltage and V
V
(µH)
10
10
15
15
10
15
IN MIN
L
(
0.505
0.764
MAX
DCR
0.58
)
(Ω)
0.3
1.2
1.6
0 5
.
CURRENT
V
RATING
(mA)
) • .
450
225
300
200
470
380
0 66
VENDOR
Murata
www.murata.com
Cooper
www.cooperet.com
(
H
)
IN(MIN)
is
Capacitor Selection
The small size and low ESR of ceramic capacitors makes
them suitable for most OLED Driver applications. X5R and
X7R types are recommended because they retain their ca-
pacitance over wider voltage and temperature ranges than
other types such as Y5V or Z5U. A 4.7µF input capacitor
and a 10µF output capacitor are suffi cient for most appli-
cations for the OLED Driver. Always use a capacitor with
a suffi cient voltage rating. Many capacitors rated at 10µF,
particularly 0805 or 0603 case sizes, have greatly reduced
capacitance when bias voltages are applied. Be sure to check
actual capacitance at the desired output voltage. Generally
a 1206 size capacitor will be adequate. A 0.47µF capaci-
tor placed on the CAP node is recommended to fi lter the
inductor current while the larger 10µF placed on the V
node will give excellent transient response and stability.
Table 6 shows a list of several capacitor manufacturers.
Consult the manufacturers for more detailed information
and for their entire selection of related parts.
Table 6. Recommended Ceramic Capacitor Manufacturers
MANUFACTURER
Taiyo Yuden
AVX
Murata
Kemet
Setting Output Voltage and the Auxiliary
Reference Input
The OLED driver of the LT3498 is equipped with both an
internal 1.215V reference and an auxiliary reference input.
This allows the user to select between using the built-in
reference, and supplying an external reference voltage.
The voltage at the CTRL2 pin can be adjusted while the
chip is operating to alter the output voltage of the LT3498
for purposes such as display dimming or contrast adjust-
ment. To use the internal 1.215V reference, the CTRL2 pin
must be held higher than 1.5V. When the CTRL2 pin is
held between 0V and 1.5V the OLED driver will regulate
the output such that the FB2 pin voltage is nearly equal to
the CTRL2 pin voltage. At CTRL2 voltages close to 1.215V,
PHONE
408-573-4150
843-448-9411
814-237-1431
408-986-0424
URL
www.t-yuden.com
www.avxcorp.com
www.murata.com
www.kemet.com
OUT
3498f