TLV61220
SLVSB53 –MAY 2012
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APPLICATION INFORMATION
DESIGN PROCEDURE
The TLV61220 is intended for systems powered by a single cell battery to up to three Alkaline, NiCd or NiMH
cells with a typical terminal 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 TLV61220.
Adjustable output voltage version
An external resistor divider is used to adjust the output voltage. The resistor divider needs to be connected
between VOUT, FB and GND as shown in Figure 16. When the output voltage is regulated properly, the typical
voltage value at the FB pin is 500 mV for the adjustable devices. The maximum recommended value for the
output voltage is 5.5 V. 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, R2, is typically 500 mV. Based on those two values, the recommended value for R2
should be lower than 500 kΩ, in order to set the divider current to 1 μA or higher. The value of the resistor
connected between VOUT and FB, R1, depending on the needed output voltage (VOUT), can be calculated using
Equation 1:
æ
ç
è
ö
÷
ø
V
OUT
R
= R
x
2
- 1
1
V
FB
(1)
As an example, if an output voltage of 3.3 V is needed, a 1-MΩ resistor is calculated for R1 when for R2 a 180-kΩ
has been selected.
TLV61220
L1 4.7:H
SW
VOUT
V
OUT
3.3V/20mA
R1
1MS
VBAT
EN
FB
C2
V
10:F
R2
IN
1V to 3V
180kS
C1
10:F
GND
Figure 16. Typical Application Circuit for Adjustable Output Voltage Option
Inductor Selection
To make sure that the TLV61220 can operate, a suitable inductor must be connected between pin VBAT and pin
SW. 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 2.
V ´(VOUT - V )
´
1
IN
IN
L =
f ´ 200 mA
VOUT
(2)
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 3 gives the peak current estimate.
V
´ IOUT
ì
ï
í
OUT
+ 100 mA; continous current operation
discontinuous current operation
0.8´ V
IL,MAX
=
IN
ï
200 mA;
î
(3)
12
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