TPS63000
TPS63001
TPS63002
www.ti.com
SLVS520–MARCH 2006
APPLICATION INFORMATION (continued)
ǒV
OUTǓ
V
) V
OUT
V
IN1
f 0.3 A
L ń
1
IN1
(3)
(4)
ǒV
IN2Ǔ
V
) V
in2
V
OUT
f 0.3 A
L ń
2
OUT
In both equations f is the nominal switching frequency. In Equation 3 the minimum inductance value, L1 for step
down mode operation is calculated. VIN1 is the maximum input voltage. In Equation 4 the minimum inductance,
L2, for boost mode operation is calculated. VIN2 is the minimum input voltage. The recommended minimum
inductor value is either L1 or L2 whichever is higher. As an example, a suitable inductor, for generating 3.3V from
a Li-Ion battery with a battery voltage range from 2.5V up to 4.2V, is 2.2 µH. The recommended inductor value
range is between 1.5 µH and 4.7 µH. In general this means that at high voltage conversion rates higher inductor
values offer better performance.
With the choosen inductance value the peak current for the inductor in steady state operation can be calculated.
Equation 5 shows how to calculate the peak current I1 in step down mode operation and Equation 6 shows how
to calculate the peak current I2 in boost mode operation.
OUTǓVIN1
V
ń V
I
OUT
OUT
0.8
I ǒ
)
1
2 V
f L
IN1
(5)
ǓV
V
ń V
V
I
IN2
OUT
IN2
OUT
0.8 V
OUT
I ǒ
)
2
2 V
f L
IN2
OUT
(6)
The critical current value for selecting the right inductor is the higher value of I1 and I2. It also needs to be
considered that load transients and error conditions may cause higher inductor currents. It also needs to be
taken into account when selecting an appropriate inductor. The following inductor series from different suppliers
have been used with the TPS6300x converters:
Table 1. List of Inductors
VENDOR
Coiltronics
MuRata
INDUCTOR SERIES
Tajo Yuden
VLF4012
VLF3215
TDK
Capacitor Selection
Input Capacitor
At least a 4.7 µF input capacitor is recommended to improve transient behavior of the regulator and EMI
behavior of the total power supply circuit. A ceramic capacitor placed as close as possible to the VIN and PGND
pins of the IC, is recommended.
Output Capacitor
For the output capacitor it is as well recommended to use small ceramic capacitors placed as close as possible
to the VOUT and PGND pins of the IC. If, for any reason, the application requires to use a large capacitors which
needs longer connections to the IC, using a smaller ceramic capacitor in parallel to the large one is
recommended. This small capacitor should be as close as possible to the VOUT and PGND pins of the IC.
To get an estimate of the recommended minimum output capacitance Equation 7 can be used.
9
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