Texas Instruments TPS61166-446 Evaluation Board TPS61166EVM-446 TPS61166EVM-446 TPS61166EVM-446 Datenbogen
Produktcode
TPS61166EVM-446
L
L_peak
L_DC
L_DC
I
I
= I
+
2
Vout
Iout
I
=
Vin
D
´
´ h
(4)
INPUT AND OUTPUT CAPACITOR SELECTION
out
out
ripple
D
I
C
=
Fs
V
´
´
(5)
LAYOUT CONSIDERATIONS
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..........................................................................................................................................................................................
SLVS991 – SEPTEMBER 2009
Where
I
L_DC
= Inductor average current
η
= Estimated converter efficiency
The inductor value should not be outside the 2.2
µ
H to 10
µ
H range listed in the recommended operating
conditions table, otherwise internal slope compensation and loop compensation are ineffective.
lists the
recommended inductors for the TPS61166.
Table 1. Recommended Inductors for the TPS61166
L
DCR MAX
SATURATION
PART NUMBER
SIZE (L×W×H mm)
VENDOR
(
µ
H)
(m
Ω)
CURRENT (A)
#A915_Y-4R7M
4.7
45
1.5
5.2x5.2x3.0
Toko
#A915_Y-100M
10
90
1.09
5.2x5.2x3.0
Toko
VLS4012-4R7M
4.7
132
1.1
4.0x4.0x1.2
TDK
VLS4012-100M
10
240
0.82
4.0x4.0x1.2
TDK
CDRH3D23/HP
4.7
95.5
1.6
4.0x4.0x2.5
Sumida
LPS4012-472ML
4.7
175
1.6
4.0x4.0x1.2
Coilcraft
The output capacitor is mainly selected to meet the requirements for output ripple and loop stability. This ripple
voltage is related to the capacitor’s capacitance and its equivalent series resistance (ESR). Assuming a ceramic
capacitor with zero ESR, the minimum capacitance needed for a given ripple can be calculated by
voltage is related to the capacitor’s capacitance and its equivalent series resistance (ESR). Assuming a ceramic
capacitor with zero ESR, the minimum capacitance needed for a given ripple can be calculated by
:
where, V
ripple
= peak to peak output ripple. The ESR impact on the output ripple must be considered if tantalum
or electrolytic capacitors are used.
Care must be taken when evaluating a ceramic capacitor’s derating under dc bias, aging, and ac signal. For
example, larger form factor capacitors (in 1206 size) have their self resonant frequencies in the range of the
switching frequency. So the effective capacitance is significantly lower. The dc bias can also significantly reduce
capacitance. A ceramic capacitor can loose as much as 50% of its capacitance at its rated voltage. Therefore,
always leave margin on the voltage rating to ensure adequate capacitance at the required output voltage.
example, larger form factor capacitors (in 1206 size) have their self resonant frequencies in the range of the
switching frequency. So the effective capacitance is significantly lower. The dc bias can also significantly reduce
capacitance. A ceramic capacitor can loose as much as 50% of its capacitance at its rated voltage. Therefore,
always leave margin on the voltage rating to ensure adequate capacitance at the required output voltage.
At least a 4.7-
µ
F input capacitor is recommended. The output requires a capacitor in the range of 1
µ
F to 10
µ
F.
The output capacitor affects the loop stability of the boost regulator. If the output capacitor is below the range,
the boost regulator can potentially become unstable.
the boost regulator can potentially become unstable.
The popular vendors for high value ceramic capacitors are:
•
TDK (
•
Murata (
)
As for all switching power supplies, especially those running at high switching frequency and high currents,
layout is an important design step. If layout is not carefully performed, the regulator could suffer from instability
as well as noise problems. To maximize efficiency, switch rise and fall times are very fast. To prevent radiation of
layout is an important design step. If layout is not carefully performed, the regulator could suffer from instability
as well as noise problems. To maximize efficiency, switch rise and fall times are very fast. To prevent radiation of
Copyright © 2009, Texas Instruments Incorporated
13
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