Datasheet

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APPLICATION INFORMATION
DESIGN PROCEDURE
Programming the Output Voltage
R3  R6 

V
O
V
FB
–1

 180 k 

V
O
500 mV
–1

(1)
C
parR3
 20 pF 

200 k
R6
 1

(2)
SWN
C3
10 µF
Power
Supply
L1
10 µH
R1
R2
VBAT
VOUT
FB
R3
R6
LDOIN
R5
R4
LDOSENSE
LDOOUT
R7 R9
C6
2.2 µF
C4
100 µF
U1
LBO
PGOOD
PGND
LBI
SKIPEN
EN
LDOEN
GND
TPS6112xPW
V
CC1
Boost Output
V
CC2
LDO Output
Control
Outputs
SWP
C5
2.2 µF
TPS61120
TPS61122, TPS61121
SLVS427C – JUNE 2002 – REVISED APRIL 2004
The TPS6112x dc/dc converters are intended for systems powered by a dual or triple cell NiCd or NiMH battery
with a typical terminal voltage between 1.8 V and 5.5 V. They can also be used in systems powered by one-cell
Li-Ion with a typical stack voltage between 2.5 V and 4.2 V. Additionally, two or three primary and secondary
alkaline battery cells can be the power source in systems where the TPS6112x is used.
DC/DC Converter
The output voltage of the TPS61120 dc/dc converter section can be adjusted with an external resistor divider.
The typical value of the voltage on the FB pin is 500 mV. The maximum allowed 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 R6 is typically 500 mV. Based on those
two values, the recommended value for R6 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 :
If as an example, an output voltage of 3.3 V is needed, a 1-MΩ resistor should be chosen for R3. If for any
reason the value for R6 is chosen significantly lower than 200 kΩ additional capacitance in parallel to R3 is
recommended. The required capacitance value can be easily calculated using Equation 2 .
Figure 24. Typical Application Circuit for Adjustable Output Voltage Option
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