Datasheet

R
1
+ R
2
ǒ
V
OUT
V
FB
* 1
Ǔ
L1
VIN
VINA
EN
PS/SYNC
GND
L2
VOUT
FB
PGND
L1
R1
R2
C2
C3
C1
V
IN
V
OUT
TPS6303X
( )
0.5
1 IN1 OUT
μs
L = V V × ×
A
-
0.5
2 OUT
μs
L = V × ×
A
TPS63030
TPS63031
www.ti.com SLVS696B –OCTOBER 2008–REVISED MARCH 2012
APPLICATION INFORMATION
DESIGN PROCEDURE
The TPS6303x dc/dc converters are intended for systems powered by one-cell Li-Ion or Li-Polymer battery with a
typical voltage between 2.3 V and 4.5 V. They can also be used in systems powered by a double or triple cell
Alkaline, NiCd, or NiMH battery with a typical terminal voltage between 1.8 V and 5.5 V . Additionally, any other
voltage source with a typical output voltage between 1.8 V and 5.5 V can power systems where the TPS6303x is
used.
PROGRAMMING THE OUTPUT VOLTAGE
Within the TPS6303X family there are fixed and adjustable output voltage versions available. To properly
configure the fixed output voltage devices, the FB pin is used to sense the output voltage. This means that it
must be connected directly to VOUT. At the adjustable output voltage versions, an external resistor divider is
used to adjust the output voltage. The resistor divider must be connected between VOUT, FB and GND. When
the output voltage is regulated properly, the typical value of the voltage at the FB pin is 500mV. The maximum
recommended value for the output voltage is 5.5V. The current through the resistive divider should be about 100
times greater than the current into the FB pin. The typical current into the FB pin is 0.01 μA, and the voltage
across the resistor between FB and GND, R
2
, is typically 500 mV. Based on those two values, the recommended
value for R
2
should be lower than 500kΩ, in order to set the divider current at 1μA or higher. It is recommended
to keep the value for this resistor in the range of 200kΩ. From that, the value of the resistor connected between
VOUT and FB, R
1
, depending on the needed output voltage (V
OUT
), can be calculated using Equation 1:
(1)
Figure 21. Typical Application Circuit for Adjustable Output Voltage Option
INDUCTOR SELECTION
To properly configure the TPS6303X devices, an inductor must be connected between pin L1 and pin L2. To
estimate the inductance value Equation 2 and Equation 3 can be used.
(2)
(3)
In Equation 2 the minimum inductance value, L
1
for step down mode operation is calculated. V
IN1
is the
maximum input voltage. In Equation 3 the minimum inductance, L
2
, for boost mode operation is calculated. The
recommended minimum inductor value is either L
1
or L
2
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.
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