Datasheet

R3 + R4
ǒ
V
O
V
FB
* 1
Ǔ
+ 180 kW
ǒ
V
O
500 mV
* 1
Ǔ
C
parR3
+ 20 pF
ǒ
200 kW
R4
* 1
Ǔ
SW
C1Power
Supply
L1
R1
R2
VBAT
VOUT
FB
C2 C3
LBO
PGND
LBI
PS
EN
GND
TPS61020
V
CC
Boost Output
Control Output
R3
R4
R5
R1 + R2
ǒ
V
BAT
V
LBI*threshold
* 1
Ǔ
+ 390 kW
ǒ
V
BAT
500 mV
* 1
Ǔ
TPS61020, TPS61024, TPS61025
TPS61026, TPS61027, TPS61028
TPS61029
www.ti.com SLVS451F –SEPTEMBER 2003–REVISED APRIL 2012
APPLICATION INFORMATION
DESIGN PROCEDURE
The TPS6102x dc/dc converters are intended for systems powered by a single up to triple cell Alkaline, NiCd,
NiMH battery with a typical terminal voltage between 0.9 V and 6.5 V. They can also be used in systems
powered by one-cell Li-Ion or Li-Polymer with a typical voltage between 2.5 V and 4.2 V. Additionally, any other
voltage source with a typical output voltage between 0.9 V and 6.5 V can power systems where the TPS6102x is
used.
PROGRAMMING THE OUTPUT VOLTAGE
The output voltage of the TPS61020 dc/dc converter can be adjusted with an external resistor divider. The typical
value of the voltage at the FB pin is 500 mV. 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 R4 is typically 500 mV. Based on those two
values, the recommended value for R4 should be lower than 500 kΩ, in order to set the divider current at 1 µA or
higher. Because of internal compensation circuitry the value for this resistor should be in the range of 200 kΩ.
From that, the value of resistor R3, depending on the needed output voltage (V
O
), can be calculated using
Equation 1:
(1)
If as an example, an output voltage of 3.3 V is needed, a 1.0-MΩ resistor should be chosen for R3. If for any
reason the value for R4 is chosen significantly lower than 200 kΩ additional capacitance in parallel to R3 is
recommended, in case the device shows unstable regulation of the output voltage. The required capacitance
value can be easily calculated using Equation 2:
(2)
Figure 22. Typical Application Circuit for Adjustable Output Voltage Option
PROGRAMMING THE LBI/LBO THRESHOLD VOLTAGE
The current through the resistive divider should be about 100 times greater than the current into the LBI pin. The
typical current into the LBI pin is 0.01 µA, and the voltage across R2 is equal to the LBI voltage threshold that is
generated on-chip, which has a value of 500 mV. The recommended value for R2 is therefore in the range of 500
kΩ. From that, the value of resistor R1, depending on the desired minimum battery voltage V
BAT,
can be
calculated using Equation 3.
(3)
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