lt8415 Linear Technology Corporation, lt8415 Datasheet - Page 8

• Manufacturer Part Number: lt8415
• Description: Ultralow Power Boost Converter With Dual Half-bridge Switches
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
LT8415
Inductor Selection
Several inductors that work well with the LT8415 are listed
in Table 1. The tables are not complete, and 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, as many different
sizes and shapes are available.
Inductors with a value of 47μH or higher are recommended
for most LT8415 designs. Inductors with low core losses
and small DCR (copper wire resistance) are good choices
for LT8415 applications. For full output power, the induc-
tor should have a saturation current rating higher than
the peak inductor current. The peak inductor current can
be calculated as:
where the worst case I
value in Henrys and V
circuit.
Table 1. Recommended Inductors for LT8415
PART
LQH2MCN680K02
LQH32CN101K53
DO2010-683ML
DO2010-104ML
LPS3015-104ML
LPS3015-154ML
Capacitor Selection
The small size and low ESR of ceramic capacitors make
them suitable for most LT8415 applications. X5R and
X7R types are recommended because they retain their
capacitance over wider voltage and temperature ranges
than other types such as Y5V or Z5U. A 2.2μF or higher
input capacitor and a 0.1μF to 1μF output capacitor are
suffi cient for most applications. Always use a capacitor
with a suffi cient voltage rating. Many ceramic capacitors
rated at 0.1μF to 1μF have greatly reduced capacitance
when bias voltages are applied. Be sure to check actual
capacitance at the desired output voltage. Generally a 0603
or 0805 size capacitor will be adequate. A 0.1μF to 1μF
8
I
PK
= I
LIMIT
+
(μH)
68
100
68
100
100
150
L
V
IN
• 150 •10
DCR
(μH)
IN
6.6
3.5
8.8
15.7
3.4
6.1
LIMIT
is the input voltage to the boost
L
2.0 × 1.6 × 0.9
3.2 × 2.5 × 2.0
2.0 × 2.0 × 1.0
2.0 × 2.0 × 1.0
3.0 × 3.0 × 1.4
3.0 × 3.0 × 1.4
is 30mA. L is the inductance
(mm)
− 6
SIZE
mA
VENDOR
Murata
www.murata.com
Coilcraft
www.coilcraft.com
capacitor placed on the CAP node is recommended to fi lter
the inductor current while a 0.1μF to 1μF capacitor placed
on the V
and stability. To make the V
putting a capacitor on the V
not required. A 47nF to 220nF 0402 capacitor will be suf-
fi cient. See also Soft-Start section for more information
about a capacitor across V
capacitor manufacturers. Consult the manufacturers for
more detailed information and for their entire selection
of related parts.
Table 2. Recommended Ceramic Capacitor Manufacturers
MANUFACTURER
Taiyo Yuden
Murata
AVX
Kemet
TDK
Setting Output Voltage
The output voltage is set by the FBP pin voltage, and V
is equal to 31.85 • V
shown in Figure 1. Since the V
reference (~1.235V), the FBP voltage can be easily set by
a resistor divider from the V
resistance of this resistor divider should be kept larger than
200KΩ to prevent loading down the V
can also be biased directly by an external reference. For
over voltage protection, the output voltage is limited to
40V. Therefore, if V
voltage will stay at 40V.
OUT
50
40
30
20
10
0
Figure 1. FBP to V
node will give excellent transient response
0
PHONE
[phone]
[phone]
[phone]
[phone]
[phone]
FBP
0.5
FBP
FBP VOLTAGE (V)
is higher than 1.235V, the output
REF
when the output is regulated,
REF
REF
REF
1
. Table 2 shows a list of several
OUT
pin less sensitive to noise,
pin is recommended, but
pin to ground. The series
Transfer Curve
REF
1.5
pin provides a good
WEBSITE
www.t-yuden.com
www.murata.com
www.avxcorp.com
www.kemet.com
www.tdk.com
REF
8415 F01
pin. The FBP pin
2
OUT
8415f