lt8410 Linear Technology Corporation, lt8410 Datasheet - Page 9

• Manufacturer Part Number: lt8410
• Description: Lt8410/lt8410-1-ultralow Power Boost Converter With Output Disconnect
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
or 0805 size capacitor will be adequate. A 0.1μF to 1μF
capacitor placed on the CAP node is recommended to filter
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
required. A 47nF to 220nF 0402 capacitor will be sufficient.
Table 2 shows a list of several 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. V
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
overvoltage protection, the output voltage is limited to
40V. Therefore, if V
voltage will stay at 40V.
OUT
Figure 1. FBP to V
node will give excellent transient response
50
40
30
20
10
0
0
[phone]
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FBP
FBP
PHONE
0.5
when the output is regulated, as
is higher than 1.235V, the output
FBP VOLTAGE (V)
REF
REF
REF
OUT
pin is recommended, but not
1
pin less sensitive to noise,
Transfer Curve
www.t-yuden.com
www.murata.com
www.avxcorp.com
www.kemet.com
www.tdk.com
pin to ground. The series
REF
pin provides a good
1.5
REF
WEB SITE
pin. The FBP pin
8410-1 F01
2
OUT
is
Connecting the Load to the CAP Node
The efficiency of the converter can be improved by con-
necting the load to the CAP pin instead of the V
The power loss in the PMOS disconnect circuit is then
made negligible. No quiescent current will be consumed
in the internal feedback resistor divider string during
shutdown since the PMOS transistor will be open and the
internal feedback resistor divider is connected at the V
pin. The disadvantage of this method is that the CAP node
cannot go to ground during shutdown, but will be limited
to around a diode drop below V
part should only sink current. Never force external power
supplies onto the CAP or V
Maximum Output Load Current
The maximum output current of a particular LT8410 series
circuit is a function of several circuit variables. The following
method can be helpful in predicting the maximum load
current for a given circuit:
Step 1. Calculate the peak inductor current:
where I
respectively. L is the inductance value in henrys and V
is the input voltage to the boost circuit.
Step 2. Calculate the inductor ripple current:
where V
ripple current is less than the peak current, then the circuit
will only operate in discontinuous conduction mode. The
inductor value should be increased so that I
An application circuit can be designed to operate only in
discontinuous mode, but the output current capability
will be reduced.
Step 3. Calculate the average input current:
I
I
I
IN(AVG)
PK
RIPPLE
= I
LIMIT
OUT
LIMIT
=
= I
is the desired output voltage. If the inductor
is 25mA and 8mA for LT8410 and LT8410-1
(
PK
V
+
OUT
–
V
IN
+ 1 – V
I
RIPPLE
• 150 • 10
2
LT8410/LT8410-1
L
IN
L
mA
OUT
)
• 200 • 10
CC
pins.
– 6
. Loads connected to the
mA
– 6
mA
RIPPLE
OUT
< I
pin.
84101fb
9
OUT
PK
IN
.