Datasheet

BAT min
RHP
INmax
V
f 32 kHz
2 I L
= =
p ´ ´
SENSE
0.2 V
R 25 m
7.85 A
= = W
RIPPLE
PEAK INmax
I
3.1 A
I I 6.3 A + 7.85 A
2 2
= + = =
BAT ON
BAT
INripplemax INripplemax SW
V t
V
5 V
L 4.9 H
I I 2 f 2.52 A 2 200 kHz
´
= = = = m
´ ´ ´ ´
BAT
31.3 W
I (at V = 5 V) 6.3 A
INmax
5 V
= =
OUT
INmax
P
25 W
P 31.3 W
Efficiency 0.8
= = =
TPS43330-Q1
TPS43332-Q1
www.ti.com SLVSA82E –MARCH 2011–REVISED APRIL 2013
Boost Maximum Input Current I
IN_MAX
The maximum input current flows at the minimum input voltage and maximum load. The efficiency for V
BAT
= 5 V
at 2.5 A is 80%, based on the typical characteristics plot.
Hence,
Boost Inductor Selection, L
Allow input ripple current of 40% of I
IN max
at V
BAT
= 5 V.
Choose a lower value of 4 µH in order to ensure a high RHP-zero frequency while making a compromise that
expects a high current ripple. This inductor selection also makes the boost converter operate in discontinuous
conduction mode, where it is easier to compensate.
The inductor saturation current must be higher than the peak inductor current and some percentage higher than
the maximum current-limit value set by the external resistive sensing element.
Determine the saturation rating at the minimum input voltage, maximum output current, and maximum core
temperature for the application.
Inductor Ripple Current, I
RIPPLE
Based on an inductor value of 4 µH, the ripple current is approximately 3.1 A.
Peak Current in Low-Side FET, I
PEAK
Based on this peak current value, calculate the external current-sense resistor R
SENSE
.
Select 20 mΩ, allowing for tolerance.
The filter component values R
IFLT
and C
IFLT
for current sense are 1.5 kΩ and 1 nF, respectively, which allows for
good noise immunity.
Right Half-Plane Zero RHP Frequency, f
RHP
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