TPS61130 Datasheet, PDF (15/28 Pages) Texas Instruments – SYNCHRONOUS SEPIC / FLYBACK CONVERTER WITH 1.1A SWITCH AND INTEGRATED LDO

www.ti.com
APPLICATION INFORMATION
TPS61130
TPS61131
TPS61132
SLVS431A – JUNE 2002 – REVISED AUGUST 2003
DESIGN PROCEDURE
The TPS6113x dc/dc converters are intended for systems powered by a dual up to 4 cell NiCd or NiMH battery
with a typical terminal voltage between 1.8 V and 6.0 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 up to four primary and secondary
alkaline battery cells can be the power source in systems where the TPS6113x is used.
Programming the Output Voltage
DC/DC Converter
The output voltage of the TPS61130 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:
ǒ Ǔ ǒ Ǔ R3 + R6
VO
VFB
*
1
+ 180 kW
VO
500 mV
*
1
(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.
ǒ Ǔ CparR3 + 20 pF
200 kW
R6
*
1
(2)
Power
Supply
C3
10 µF
L1–A
22 µH
R1
R2
C7
U1
10 µF
SWN
SWP
VBAT
VOUT
LBI
SKIPEN
FB
LDOIN
LDOOUT
LDOSENSE
EN
LDOEN
LBO
GND
PGOOD
PGND
TPS6113xPW
L1–B
22 µH
R3
C6
2.2 µF
V_CC1
C4 Boost Output
100 µF
R6
V_CC2
R5
C5
LDO Output
2.2 µF
R4
R7
R9
Control
Outputs
Figure 24. Typical Application Circuit for Adjustable Output Voltage Option
15