Datasheet

OUTA
OUTA OUTA
C OUTA
I
2.9 A
V I ESR 2.9 A 10 m 174 mV
4 f C 4 50 kHz 100 F
D
D = + D ´ = + ´ W =
´ ´ ´ ´ m
OUTA(Ripple)
OUTA(Ripple) OUTA(Ripple)
SW OUTA
I
1 A
V I ESR 1 A 10 m 13.1mV
8 f C 8 400 kHz 100 F
= + ´ = + ´ W =
´ ´ ´ ´ m
OUTA
OUTA
SW OUTA
2 I
2 2.9 A
C 72.5 F
f V 400 kHz 0.2 V
´ D
´
» = = m
´ D ´
SENSE
FLR
SW
R
15 m
L K 200 7.5 H
f 400 kHz
W
= ´ = ´ = m
SENSE
50 mV
R 17 m
3 A
= = W
TPS43330-Q1
TPS43332-Q1
www.ti.com SLVSA82E –MARCH 2011–REVISED APRIL 2013
Current-Sense Resistor R
SENSE
Based on the typical characteristics for the V
SENSE
limit with V
IN
versus duty cycle, the sense limit is
approximately 65 mV (at V
IN
= 12 V and duty cycle of 5 V / 12 V = 0.416). Allowing for tolerances and ripple
currents, choose a V
SENSE
maximum of 50 mV.
Select 15 mΩ.
Inductor Selection L
As explained in the description of the buck controllers, for optimal slope compensation and loop response,
choose the inductor such that:
K
FLR
= coil-selection constant = 200
Choose a standard value of 8.2 µH. For the buck converter, choose the inductor saturation currents and core to
sustain the maximum currents.
Inductor Ripple Current I
RIPPLE
At the nominal input voltage of 12 V, this inductor value causes a ripple current of 30% of I
OUT max
≈ 1 A.
Output Capacitor C
OUTA
Select an output capacitance C
OUTA
of 100 µF with low ESR in the range of 10 mΩ, giving ∆V
OUT(Ripple)
≈ 15 mV
and a ∆V drop of ≈ 180 mV during a load step, which does not trigger the power-good comparator and is within
the required limits.
Bandwidth of Buck Converter f
C
Use the following guidelines to set frequency poles, zeroes, and crossover values for the trade-off between
stability and transient response.
• Crossover frequency f
C
between f
SW
/ 6 and f
SW
/ 10. Assume f
C
= 50 kHz.
• Select the zero f
z
≈ f
C
/ 10
• Make the second pole f
P2
≈ f
SW
/ 2
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