Datasheet

2
(max)
(max)(max)
L
OUTL
I
II
D
+=
÷
÷
ø
ö
ç
ç
è
æ
-= 1
21
REF
OUT
V
V
RR
TPS62175, TPS62177
SLVSB35B –OCTOBER 2012–REVISED JANUARY 2014 www.ti.com
APPLICATION INFORMATION
Programming The Output Voltage
While the output voltage of the TPS62175 is adjustable, the TPS62177 is programmed to a fixed output voltage
of 3.3V. For the fixed output voltage version, the FB pin is pulled low internally by a 400kΩ resistor. It is
recommended to connect the FB pin to AGND to improve thermal resistance. The adjustable version can be
programmed for output voltages from 1V to 6V by using a resistive divider. The voltage at the FB pin is regulated
to 800mV. The value of the output voltage is set by the selection of the resistive divider from Equation 5. It is
recommended to choose resistor values which allow a current of at least 5uA. Lower resistor values are
recommended to increase noise immunity. For applications requiring lowest current consumption, the use of the
fixed output voltage version is recommended.
spacing
(5)
spacing
As a safety feature, the device clamps the output voltage at the VOS pin to typically 7.4V, if the FB pin gets
opened.
External Component Selection
The external components have to fulfill the needs of the application, but also the stability criteria of the device's
control loop. The TPS62175/7 is optimized to work within a wide range of external components. The LC output
filter's inductance and capacitance have to be considered together, creating a double pole that is responsible for
the corner frequency of the converter. Table 1 shows the recommended output filter components.
Table 1. Recommended LC Output Filter Combinations
(1)
10µF 22µF 47µF 100µF 200µF 400µF
6.8µH
10µH √
(2)
√ √ √
22µH √ √
33µH
(1) The values in the table are nominal values. Variations of typically ±20% due to tolerance, saturation and DC bias are assumed.
(2) This LC combination is the standard value and recommended for most applications. For output voltages of ≤2V, an output capacitance
of at least 2x22uF is recommended.
Output Filter And Loop Stability
The TPS62175/7 devices are internally compensated and are stable with LC output filter combinations
recommended in Table 1. Further information on other values and loop stability can be found in SLVA543.
Inductor Selection
The inductor selection is determined by several effects like inductor ripple current, output ripple voltage, PWM-to-
Power Save Mode transition point and efficiency. In addition, the inductor selected has to be rated for appropriate
saturation current and DC resistance (DCR). Equation 6 and Equation 7 calculate the maximum inductor current
under static load conditions.
spacing
(6)
spacingspacing
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