TPS61050_15 Datasheet, PDF (30/49 Pages) Texas Instruments – High-Power White LED Driver 2-MHz Synchronous Boost Converter

TPS61050, TPS61052
SLUS525A – MARCH 2007 – REVISED SEPTEMBER 2015
www.ti.com
8.2.1.2 Detailed Design Procedure
8.2.1.2.1 Inductor Selecton
A boost converter requires two main passive components for storing energy during the conversion. A boost
inductor and a storage capacitor at the output are required. The TPS6105x device integrates a current limit
protection circuitry. The peak current of the NMOS switch is sensed to limit the maximum current flowing through
the switch and the inductor. The typical peak current limit (1000 mA / 1500 mA / 2000 mA) is user selectable
through the I²C interface.
To optimize solution size the TPS6105x device has been designed to operate with inductance values from a
minimum of 1.3 μH to a maximum of 2.9 μH. In typical high-current white LED applications, TI recommends an
inductance of 2.2 μH.
To select the boost inductor, TI recommends keeping the possible peak inductor current below the current limit
threshold of the power switch in the chosen configuration. The highest peak current through the inductor and the
power switch depends on the output load, the input and output voltages. Estimation of the maximum average
inductor current and the maximum inductor peak current can be done using Equation 1 and Equation 2:
I_L
» I_OUT
=
V_OUT
h ´ V_IN
(1)
I_L
(PEAK) =
V_IN ´ D
2´f ´L
+
I_OUT
(1- D)´
h
with
D
=
V_OUT - V_IN
V_OUT
(2)
with:
f = switching frequency (2 MHz)
L = inductance value (2.2 μH)
η = estimated efficiency (85%)
For example, for an output current of 500 mA at 5 V, the TPS6105x device must be set for a 1000 mA current
limit operation together with an inductor supporting this peak current.
The losses in the inductor caused by magnetic hysteresis losses and copper losses are a major parameter for
total circuit efficiency.
MANUFACTURER
TDK
TAIYO YUDEN
TDK
COILCRAFT
MURATA
TOKO
Table 4. List of Inductors
SERIES
VLF3010AT
NR3010
VLF3014AT
LPS3015
LQH3NP
FDSE0312
DIMENSIONS
2.6 mm × 2.8 mm × 1 mm maximum height
3 mm × 3 mm × 1 mm maximum height
2.6 mm × 2.8 mm × 1.4 mm maximum height
3 mm × 3 mm × 1.5 mm maximum height
3 mm × 3 mm × 1.5 mm maximum height
3 mm × 3 mm × 1.2 mm maximum height
ILIM SETTINGS
1000 mA (typical)
1500 mA (typical)
2000 mA (typical)
8.2.1.2.2 Capacitor Selection
8.2.1.2.2.1 Input Capacitor
For good input voltage filtering low ESR ceramic capacitors are recommended. A 10-μF input capacitor is
recommended to improve transient behavior of the regulator and EMI behavior of the total power supply circuit.
The input capacitor should be placed as close as possible to the input pin of the converter.
8.2.1.2.2.2 Output Capacitor
The primary parameter necessary to define the output capacitor is the maximum allowed output voltage ripple of
the converter. This ripple is determined by two parameters of the capacitor, the capacitance and the ESR. It is
possible to calculate the minimum capacitance needed for the defined ripple, supposing that the ESR is zero, by
using Equation 3:
C_min
»
I_OUT ´ (V_OUT - V_IN )
f ´ DV ´ V_OUT
(3)
30
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