Texas Instruments TPS61181(82/81A)-259 Evaluation Board TPS61181(82/81A)EVM-259 TPS61181AEVM-259 TPS61181AEVM-259 데이터 시트
제품 코드
TPS61181AEVM-259
I
dc
+
V
O
I
O
V
in
h
I
pp
+
1
L
ǒ
1
V
O
*
V
bat
)
1
V
bat
Ǔ
F
S
I
p
+
I
dc
)
I
pp
2
SLVSAN6A
–
FEBRUARY 2011
–
REVISED MARCH 2011
APPLICATION INFORMATION
INDUCTOR SELECTION
Because the selection of the inductor affects a power supply
’
s steady state operation, transient behavior and
loop stability, the inductor is the most important component in switching power regulator design. There are three
specifications most important to the performance of the inductor: inductor value, DC resistance and saturation
current. The TPS61181A ICs are designed to work with inductor values between 4.7
specifications most important to the performance of the inductor: inductor value, DC resistance and saturation
current. The TPS61181A ICs are designed to work with inductor values between 4.7
μ
H and 10
μ
H. A 4.7
μ
H
inductor may be available in a smaller or lower profile package, while 10
μ
H may produce higher efficiency due to
lower inductor ripple. If the boost output current is limited by the over-current protection of the IC, using a 10
μ
H
inductor can offer higher output current.
The internal loop compensation for the PWM control is optimized for the recommended component values,
including typical tolerances. Inductor values can have
including typical tolerances. Inductor values can have
±
20% tolerance with no current bias. When the inductor
current approaches saturation level, its inductance can decrease 20 to 35% from the zero current value
depending on how the inductor vendor defines saturation
depending on how the inductor vendor defines saturation
In a boost regulator, the inductor DC current can be calculated as
(2)
Where
V
O
= boost output voltage
Io = boost output current
V
V
in
= boost input voltage
η
= power conversion efficiency, use 90% for TPS61181A applications
The inductor current peak to peak ripple can be calculated as
(3)
Where
I
pp
= inductor peak to peak ripple
L = inductor value
F
F
s
= Switching frequency
V
bat
= boost input voltage
Therefore, the peak current seen by the inductor is
(4)
Select the inductor with saturation current at least 25% higher than the calculated peak current. To calculate the
worse case inductor peak current, use minimum input voltage, maximum output voltage and maximum load
current.
worse case inductor peak current, use minimum input voltage, maximum output voltage and maximum load
current.
Regulator efficiency is dependent on the resistance of its high current path, switching losses associated with the
PWM switch and power diode. Although the TPS61181A ICs have optimized the internal switch resistance, the
overall efficiency still relies on the DC resistance (DCR) of the inductor; lower DCR improves efficiency.
However, there is a trade off between DCR and inductor footprint. Furthermore, shielded inductors typically have
a higher DCR than unshielded ones.
PWM switch and power diode. Although the TPS61181A ICs have optimized the internal switch resistance, the
overall efficiency still relies on the DC resistance (DCR) of the inductor; lower DCR improves efficiency.
However, there is a trade off between DCR and inductor footprint. Furthermore, shielded inductors typically have
a higher DCR than unshielded ones.
lists recommended inductor models.
14
Copyright
©
2011, Texas Instruments Incorporated
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