TPS53015_15 Datasheet, PDF (15/22 Pages) Texas Instruments – Single Synchronous Step-down Controller for Low Voltage Power Rails

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TPS53015
SLVSBF0B – JULY 2012 – REVISED AUGUST 2012
C_OUT
=
ΔI_LOAD2
2×V_OUT ×ΔV_OS
×L
OUT
(8)
C_OUT =
ΔI_LOAD2
2×K×ΔV_US
×L _OUT
(9)
Where:
( ) K=
V_IN -V_OUT
×
T_ON
T_ON -T_OFF(MIN)
(10)
• ΔV_OS = The allowable amount of overshoot voltage in load transition
• ΔV_US = The allowable amount of undershoot voltage in load transition
• T_OFF(MIN) = Minimum off time
Select the capacitance value greater than the largest value calculated from Equation 7, Equation 8 and
Equation 9. The minimum recommended output capacitance is 44 μF.
INPUT CAPACITOR
The TPS53015 requires an input decoupling capacitor and a bulk capacitor is needed depending on the
application. A minimum 10-μF high-quality ceramic capacitor is recommended for the input capacitor. The
capacitor voltage rating needs to be greater than the maximum input voltage.
BOOTSTRAP CAPACITOR
The TPS53015 requires a bootstrap capacitor from SW to VBST to provide the floating supply for the high-side
drivers. A minimum 0.1-μF high-quality ceramic capacitor is recommended. The capacitor voltage rating should
be greater than 10 V.
VREG5 CAPACITOR
The TPS53015 requires that the VREG5 regulator is bypassed. A minimum 4.7-μF high-quality ceramic capacitor
must be connected between the VREG5 and PGND for proper operation. The capacitor voltage rating should be
greater than 10 V.
CHOOSE OUTPUT VOLTAGE RESISTORS
The output voltage is set with a resistor divider from output voltage node to the VFB pin. It is recommended to
use 1% tolerance or better resistors. Select R2 between 10 kΩ and 100 kΩ and use Equation 11 to calculate R1.
R1
=
æ
ç
V_OUT
ö
-1_÷ ×R2
è ^VVFB ø
(11)
spacer
LAYOUT SUGGESTIONS
• Keep the input switching current loop as small as possible.
• Place the input capacitor close to the top switching FET. The output current loop should also be kept as small
as possible.
• Keep the SW node as physically small and short as possible as to minimize parasitic capacitance and
inductance and to minimize radiated emissions. Kelvin connections should be brought from the output to the
feedback pin (VFB) of the device.
• Keep analog and non-switching components away from switching components.
• Make a single point connection from the signal ground to power ground.
• Do not allow switching current to flow under the device.
Copyright © 2012, Texas Instruments Incorporated
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