TPS61030 Datasheet, PDF (14/20 Pages) Texas Instruments – 96% EFFICIENT SYNCHRONOUS BOOST CONVERTER WITH 4A SWITCH

TPS61030
TPS61031, TPS61032
SLUS534D – SEPTEMBER 2002 – REVISED APRIL 2004
www.ti.com
APPLICATION INFORMATION (continued)
ǒ Ǔ ǒ Ǔ R1 + R2
VBAT
VLBI_*threshold
*
1
+ 390 kW
VBAT
500 mV
*
1
(3)
The output of the low battery supervisor is a simple open-drain output that goes active low if the dedicated
battery voltage drops below the programmed threshold voltage on LBI. The output requires a pullup resistor with
a recommended value of 1 MΩ. The maximum voltage which is used to pull up the LBO outputs should not
exceed the output voltage of the dc/dc converter. If not used, the LBO pin can be left floating or tied to GND.
Inductor Selection
A boost converter normally requires two main passive components for storing energy during the conversion. A
boost inductor and a storage capacitor at the output are required. To select the boost inductor, it is
recommended to keep the possible peak inductor current below the current limit threshold of the power switch in
the chosen configuration. For example, the current limit threshold of the TPS6103x's switch is 4500 mA at an
output voltage of 5 V. The highest peak current through the inductor and the switch depends on the output load,
the input (V_BAT), and the output voltage (V_OUT). Estimation of the maximum average inductor current can be done
using Equation 4:
IL + IOUT
VOUT
VBAT 0.8
(4)
For example, for an output current of 1000 mA at 5 V, at least 3500 mA of average current flows through the
inductor at a minimum input voltage of 1.8 V.
The second parameter for choosing the inductor is the desired current ripple in the inductor. Normally, it is
advisable to work with a ripple of less than 20% of the average inductor current. A smaller ripple reduces the
magnetic hysteresis losses in the inductor, as well as output voltage ripple and EMI. But in the same way,
regulation time at load changes rises. In addition, a larger inductor increases the total system costs. With those
parameters, it is possible to calculate the value for the inductor by using Equation 5:
ǒ Ǔ VBAT VOUT–VBAT
L + _{DIL ƒ VOUT}
(5)
Parameter f is the switching frequency and ∆I_L is the ripple current in the inductor, i.e., 10% × I_L. In this example,
the desired inductor has the value of 5.5 µH. In typical applications a 6.8 µH inductance is recommended. The
minimum possible inductance value is 2.2 µH. With the calculated inductance and current values, it is possible to
choose a suitable inductor. Care has to be taken that load transients and losses in the circuit can lead to higher
currents as estimated in equation 4. Also, the losses in the inductor caused by magnetic hysteresis losses and
copper losses are a major parameter for total circuit efficiency.
The following inductor series from different suppliers have been used with the TPS6103x converters:
VENDOR
Sumida
Wurth Electronik
EPCOS
List of Inductors
INDUCTOR SERIES
CDRH124
CDRH103R
CDRH104R
7447779___
744771___
B82464G
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