Texas Instruments TPS61080/81-147 Evaluation Board TPS61080/81EVM-147 TPS61080EVM-147 TPS61080EVM-147 Datenbogen
Produktcode
TPS61080EVM-147
V
ripple_ESR
+
I
out
R
ESR
C
out
+
ǒ
V
out
*
V
in
Ǔ
I
out
V
out
Fs
V
ripple
I
L_DC
+
V
out
I
out
V
in
h
SLVS644D – FEBRUARY 2006 – REVISED APRIL 2013
The inductor's inductance value determines the inductor ripple current. It is generally recommended to set peak
to peak ripple current given by
to peak ripple current given by
to 30–40% of DC current. Also, the inductor value should not be
beyond the range in the recommended operating conditions table. It is a good compromise of power losses and
inductor size. Inductor DC current can be calculated as
inductor size. Inductor DC current can be calculated as
(12)
The internal loop compensation for PWM control is optimized for the external component shown in the typical
application circuit with consideration of component tolerance. 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 0A value depending on how the inductor vendor defines saturation current. Using an inductor with a
smaller inductance value forces discontinuous PWM in which inductor current ramps down to zero before the end
of each switching cycle. It reduces the boost converter’s maximum output current, causes large input voltage
ripple and reduces efficiency. An inductor with larger inductance reduces the gain and phase margin of the
feedback loop, possibly resulting in instability.
application circuit with consideration of component tolerance. 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 0A value depending on how the inductor vendor defines saturation current. Using an inductor with a
smaller inductance value forces discontinuous PWM in which inductor current ramps down to zero before the end
of each switching cycle. It reduces the boost converter’s maximum output current, causes large input voltage
ripple and reduces efficiency. An inductor with larger inductance reduces the gain and phase margin of the
feedback loop, possibly resulting in instability.
For these reasons, 10
μ
H inductors are recommended for TPS61080 and 4.7
μ
H inductors for TPS61081 for most
applications. However, 10
μ
H inductor is also suitable for 600kHz switching frequency.
Regulator efficiency is dependent on the resistance of its high current path and switching losses associated with
the PWM switch and power diode. Although the TPS61080/1 has optimized the internal switches, the overall
efficiency still relies on inductor’s DC resistance (DCR); Lower DCR improves efficiency. However, there is a
trade off between DCR and inductor size, and shielded inductors typically have higher DCR than unshielded
ones.
the PWM switch and power diode. Although the TPS61080/1 has optimized the internal switches, the overall
efficiency still relies on inductor’s DC resistance (DCR); Lower DCR improves efficiency. However, there is a
trade off between DCR and inductor size, and shielded inductors typically have higher DCR than unshielded
ones.
list recommended inductor models.
Table 3. Recommended Inductor for TPS61080/1
TPS61080
L
DCR MAX
SATURATION CURRENT
Size
VENDOR
(
μ
H)
(m
Ω
)
(A)
(L×W×H mm)
VLCF4018T
10
188
0.74
4.0 × 4.0 × 1.8
TDK
CDRH4D16NP
10
118
0.96
4.0 × 4.0 × 1.8
Sumida
LQH43CN100K
10
240
0.65
4.5 × 3.6 × 2.6
Murata
TPS61081
L
DCR MAX
SATURATION CURRENT
Size
VENDOR
(
μ
H)
(m
Ω
)
(A)
(L×W×H mm)
VLCF5020T
4.7
122
1.74
5.0 × 5.0 × 2.0
TDK
VLCF5014A
6.8
190
1.4
5.0 × 5.0 × 1.4
TDK
CDRH4D14/HP
4.7
140
1.4
4.8 × 4.8 × 1.5
Sumida
CDRH4D22/HP
10
144
1.5
5.0 × 5.0 × 2.4
Sumida
INPUT AND OUTPUT CAPACITOR SELECTION
The output capacitor is mainly selected to meet output ripple and loop stability requirements. This ripple voltage
is related to the capacitor’s capacitance and its equivalent series resistance (ESR). Assuming a capacitor with
zero ESR, the minimum capacitance needed for a given ripple can be calculated by
is related to the capacitor’s capacitance and its equivalent series resistance (ESR). Assuming a capacitor with
zero ESR, the minimum capacitance needed for a given ripple can be calculated by
(13)
V
ripple
= Peak to peak output ripple.
For VIN = 3.6V, V
OUT
= 20V, and Fs = 1.2MHz, 0.1% ripple (20mV) would require 1.0
μ
capacitor, however, the
minimum recommended output capacitor for control loop stability is 4.7
μ
F. The output capacitor value must be
less than 30µF to ensure the startup current charges the output capacitor to the input voltage in less than 1.7ms.
For this value, ceramic capacitors are a good choice for its size, cost and availability.
For this value, ceramic capacitors are a good choice for its size, cost and availability.
The additional output ripple component caused by ESR is calculated using:
(14)
Due to its low ESR, V
ripple_ESR
can be neglected for ceramic capacitors, but must be considered if tantalum or
electrolytic capacitors are used.
Copyright © 2006–2013, Texas Instruments Incorporated
15
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