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
TPS54328
SLVSAN2C –NOVEMBER 2010–REVISED NOVEMBER 2012 www.ti.com
Table 1. Recommended Component Values
Output Voltage (V) R1 (kΩ) R2 (kΩ) C4 (pF) L1 (µH) C8 + C9 (µF)
1 6.81 22.1 1.5 22 - 68
1.05 8.25 22.1 1.5 22 - 68
1.2 12.7 22.1 1.5 22 - 68
1.8 30.1 22.1 5 - 22 2.2 22 - 68
2.5 49.9 22.1 5 - 22 2.2 22 - 68
3.3 73.2 22.1 5 - 22 2.2 22 - 68
5 124 22.1 5 - 22 3.3 22 - 68
6.5 165 22.1 5 - 22 3.3 22 - 68
Since the DC gain is dependent on the output voltage, the required inductor value increases 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 5,
Equation 6 and Equation 7. 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 6 and the RMS
current of Equation 7.
(5)
(6)
(7)
For this design example, the calculated peak current is 3.49 A and the calculated RMS current is 3.01 A. The
inductor used is a TDK SPM6530-1R5M100 with a peak current rating of 11.5 A and an RMS current rating of
11 A.
The capacitor value and ESR determines the amount of output voltage ripple. The TPS54328 is intended for use
with ceramic or other low ESR capacitors. Recommended values range from 22µF to 68µF. Use Equation 8 to
determine the required RMS current rating for the output capacitor.
(8)
For this design two TDK C3216X5R0J226M 22µF output capacitors are used. The typical ESR is 2 mΩ each.
The calculated RMS current is .271A and each output capacitor is rated for 4A.
Input Capacitor Selection
The TPS54328 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 from pin 14 to ground is recommended to improve the stability of the over-current limit function. 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.
VREG5 Capacitor Selection
A 1-µF. ceramic capacitor must be connected between the VREG5 to GND pin for proper operation. It is
recommended to use a ceramic capacitor.
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