Datasheet

( )
sμ2.0
IV
VVV
L
OUT
2
OUT
INOUT
2
IN
MIN
××
×
-×
=
OUT
I
V200
3R =
L
C
1
L
1
VIN
VOUT
FB
C
2
EN
GND
TPS61260
V
OUT
V
IN
R
1
R
2
RI
R
3
÷
÷
ø
ö
ç
ç
è
æ
-×= 1
V
V
2R1R
FB
OUT
TPS61260, TPS61261
SLVSA99A –MAY 2011–REVISED FEBRUARY 2013 www.ti.com
APPLICATION INFORMATION
PROGRAMMING THE OUTPUT VOLTAGE
Within the TPS6126x 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 the VOUT, FB and GND pins.
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 4.0 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 the FB and GND pins, R
2
, is typically 500 mV. Based on these 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 also recommended to keep the total value for the resistor divider, R1 + R2, in the range of 1 MΩ. From that,
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)
Figure 19. Typical Application Circuit for Adjustable Output Voltage Option
PROGRAMMING THE OUTPUT CURRENT
The devices of the TPS6126x family also support average output current regulation. An external resistor is used
to program the average output current. The resistor must be connected between the RI and GND pins. When the
average output current is regulated properly, the typical value of the voltage at the RI pin is 400 mV. The
maximum recommended value for the regulated average output current is 100 mA. The value of the resistor R3
should be between 2 kΩ and 20 kΩ. It can be calculated, depending on the needed average output current
(I
OUT
), using Equation 2:
(2)
Accurate regulation of the average output current only is possible if the inductor current is continuous. Please
check the INDUCTOR SELECTION section to calculate the required parameters for selecting an appropriate
inductor.
INDUCTOR SELECTION
To properly configure the TPS6126x devices, an inductor must be connected between the VIN pin and the L pin.
To estimate the minimum inductance value for accurate average output current regulation, Equation 3 is used.
(3)
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