Datasheet

IN
OUT OUT
=
Co(RMS)
IN
O SW
V x (V - V )
12 x V x L x
I
f
2 2
=
IPP
Lo(RMS) O
1
+
12
I I I
lpp
= +
Ipeak
O
2
I
I I
V V
V
IN(max)
OUT
OUT
= x
IPP
V L x
IN(max)
O SW
-
I
f
TPS54227
www.ti.com SLVSAU2B –MAY 2011–REVISED JUNE 2013
Table 1. Recommended Component Values
Output Voltage (V) R1 (kΩ) R2 (kΩ) C4 (pF)
(1)
L1 (µH) C8 + C9 (µF)
1 6.81 22.1 1.5 - 2.2 22 - 68
1.05 8.25 22.1 1.5 - 2.2 22 - 68
1.2 12.7 22.1 2.2 22 - 68
1.5 21.5 22.1 2.2 22 - 68
1.8 30.1 22.1 5 - 22 3.3 22 - 68
2.5 49.9 22.1 5 - 22 3.3 22 - 68
3.3 73.2 22.1 5 - 22 3.3 22 - 68
5 124 22.1 5 - 22 4.7 22 - 68
6.5 165 22.1 5 - 22 4.7 22 - 68
(1) Optional
Since the DC gain is dependent on the output voltage, the required inductor value will increase as the output
voltage increases. For higher output voltages at or above 1.8 V, additional phase boost can be achieved by
adding a feed forward capacitor (C4) in parallel with R1
The inductor peak-to-peak ripple current, peak current and RMS current are calculated using Equation 4,
Equation 5 and Equation 6. The inductor saturation current rating must be greater than the calculated peak
current and the RMS or heating current rating must be greater than the calculated RMS current. Use 700 kHz for
f
SW
.
Use 700 kHz for f
SW
. Make sure the chosen inductor is rated for the peak current of Equation 5 and the RMS
current of Equation 6.
(4)
(5)
(6)
For this design example, the calculated peak current is 2.311 A and the calculated RMS current is 2.008 A. The
inductor used is a TDK CLF7045T-2R2M with a peak current rating of 5.5 A and an RMS current rating of 4.3 A.
The capacitor value and ESR determines the amount of output voltage ripple. The TPS54227 is intended for use
with ceramic or other low ESR capacitors. Recommended values range from 22uF to 68uF. Use Equation 7 to
determine the required RMS current rating for the output capacitor.
(7)
For this design two TDK C3216X5R0J226M 22uF output capacitors are used. The typical ESR is 2 mΩ each.
The calculated RMS current is 0.18 A and each output capacitor is rated for 4A.
Input Capacitor Selection
The TPS54227 requires an input decoupling capacitor and a bulk capacitor is needed depending on the
application. A ceramic capacitor over 10 μF is recommended for the decoupling capacitor. An additional 0.1 µF
capacitor (C3) from pin 8 to ground is optional to provide additional high frequency filtering. The capacitor voltage
rating needs to be greater than the maximum input voltage.
Bootstrap Capacitor Selection
A 0.1 µF. ceramic capacitor must be connected between the VBST to SW pin for proper operation. It is
recommended to use a ceramic capacitor.
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