Datasheet

LVIN
EN
UVLO
PS
GND PGND
FB
VAUX
VOUT
TPS61200
VIN
VOUT
C1
C2
C3
L1
R1
R2
R3
R4
OUT
FB
V
R1 = R2 x - 1
V
æ ö
ç ÷
è ø
TPS61200
TPS61201
TPS61202
www.ti.com SLVS577D –MARCH 2007–REVISED MARCH 2013
APPLICATION INFORMATION
DESIGN PROCEDURE
The TPS6120x 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 0.7 V and 5.5 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 like solar cells or fuel cells with a typical output voltage between 0.3 V and 5.5 V can power
systems where the TPS6120x is used.
Programming the Output Voltage
Within the TPS6120X family, there are fixed and adjustable output voltage versions available. To properly
configure the fixed output voltage devices, the FB pin is used to sense the output voltage. This means that it
must be connected directly to VOUT. For the adjustable output voltage version, an external resistor divider is
used to adjust the output voltage. The resistor divider must be connected between VOUT, FB and GND. When
the output voltage is regulated properly, 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 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 at 1 μA or higher. It is
recommended to keep the value for this resistor in the range of 200 kΩ. The value of the resistor connected
between VOUT and FB, R1, depending on the needed output voltage (V
OUT
), can be calculated using
Equation 1:
(1)
As an example, for an output voltage of 3.3 V, a 1-MΩ resistor should be chosen for R
1
when a 180-kΩ is
selected for R
2
.
Figure 24. Typical Application Circuit for Adjustable Output Voltage Option
Programming the UVLO Threshold Voltage
The UVLO input can be used to shut down the main output if the supply voltage is getting too low. The internal
reference threshold is typically 250 mV. If the supply voltage should cause the shutdown when it is dropping
below 250 mV, V
IN
can be connected directly to the UVLO pin. If the shutdown should happen at higher voltages,
a resistor divider can be used. R3 and R4 in Figure 24 show an example of how to monitor the input voltage of
the circuit. The current through the resistive divider should be about 100 times greater than the current into the
UVLO pin. The typical current into the UVLO pin is 0.01 μA, and the voltage across R4 is equal to the UVLO
voltage threshold that is generated on-chip, which has a value of 250 mV. Therefore, the recommended value for
R4 is in the range of 250 kΩ. From this, the value of resistor R3, depending on the desired shutdown voltage
V
INMIN,
can be calculated using Equation 2.
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