TPS61010, TPS61011
TPS61012, TPS61013
TPS61014, TPS61015, TPS61016
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SLVS314C–SEPTEMBER 2000–REVISED OCTOBER 2003
DESIGN PROCEDURE (continued)
V
V
BAT
BAT
ǒ Ǔ+ 500 kW ǒ Ǔ
R1 + R2
–1
–1
V
500 mV
REF
(2)
For example, if the low-battery detection circuit should flag an error condition on the LBO output pin at a battery
voltage of 1 V, a resistor in the range of 500 kΩ should be chosen for R1. The output of the low battery
comparator is a simple open-drain output that goes active low if the battery voltage drops below the programmed
threshold voltage on LBI. The output requires a pullup resistor with a recommended value of 1 MΩ, and should
only be pulled up to the VO. 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 is required and a storage capacitor at the output. 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 TPS61010’s switch is 1100 mA at an output voltage
of 3.3 V. The highest peak current through the inductor and the switch depends on the output load, the input
(VBAT), and the output voltage (VO). Estimation of the maximum average inductor current can be done using
Equation 3.
V
O
0.8
I + I
L
OUT
V
BAT
(3)
For example, for an output current of 100 mA at 3.3 V, at least 515-mA of current flows through the inductor at a
minimum input voltage of 0.8 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 4.
ǒV
BAT Ǔ
V
* V
BAT
OUT
L +
DI ƒ V
L
OUT
(4)
Parameter 7 is the switching frequency and∆ IL is the ripple current in the inductor, i.e., 20% × IL.
In this example, the desired inductor has the value of 12 µH. With this calculated value and the calculated
currents, it is possible to choose a suitable inductor. Care must be taken that load transients and losses in the
circuit can lead to higher currents as estimated in equation 3. 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 were tested. All work with the TPS6101x converter within
their specified parameters:
Table 1. Recommended Inductors
VENDOR
RECOMMENDED INDUCTOR SERIES
Sumida CDR74B
Sumida
Sumida CDRH74
Sumida CDRH5D18
Sumida CDRH6D38
Coilcraft DO 1608C
Coilcraft DS 1608C
Coilcraft
Coilcraft DS 3316
Coilcraft DT D03308P
16
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