Datasheet
´
´
´
IN OUT IN
OUT
V (V - V )
1
L =
f 200 mA V
L
L
1
VIN
VOUT
FB
C
2
EN
GND
TPS6122x
fixedoutputvoltage
V
OUT
V
IN
C
1
TPS61220, TPS61221, TPS61222
www.ti.com
SLVS776A –JANUARY 2009–REVISED APRIL 2014
10 Applications and Implementation
10.1 Application Information
The TPS6122x family devices provide a power-supply solution for products powered by either a single-cell, two-
cell, or three-cell alkaline, NiCd or NiMH, or one-cell Li-Ion or Li-polymer battery. Use the following design
procedure to select component values for the TPS61220 device and the TPS61222 device. Alternatively, use the
SwitcherPro™ tool. This section presents a simplified discussion of the design process.
10.2 Typical Applications
10.2.1 Specific Application, Fixed Output Voltage Supply
Figure 24. Typical Application Circuit For Fixed Output Voltage Option
10.2.1.1 Design Requirements
• Single 5 V output at up to 60 mA
• Power source, two AA alkaline cells
• Greater than 90% conversion efficiency
10.2.1.2 Detailed Design Procedure
10.2.1.2.1 Device Choice
The TPS61222 DC/DC converter is intended for systems powered by anything from a single cell through up to
three Alkaline, NiCd or NiMH cells with a total typical pin voltage between 0.7 V and 5.5 V. They can also be
used in systems powered by one-cell Li-Ion or Li-Polymer batteries with a typical voltage between 2.5 V and 4.2
V. Additionally, any other voltage source with a typical output voltage between 0.7 V and 5.5 V can be used with
the TPS61222.
10.2.1.2.2 Programming The Output Voltage
In the fixed-voltage version used for this example, the output voltage is set by an internal resistor divider. The FB
pin is used to sense the output voltage. To configure the device properly, connect the FB pin directly to VOUT as
shown in Figure 24.
10.2.1.2.3 Inductor Selection
To make sure that the device can operate, a suitable inductor must be connected between pin VIN and pin L.
Inductor values of 4.7 μH show good performance over the whole input and output voltage range.
Choosing other inductance values affects the switching frequency f proportional to 1/L as shown in Equation 1.
(1)
Choosing inductor values higher than 4.7 μH can improve efficiency due to reduced switching frequency and
therefore with reduced switching losses. Using inductor values below 2.2 μH is not recommended.
Having selected an inductance value, the peak current for the inductor in steady-state operation can be
calculated. Equation 2 gives the peak-current estimate.
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