Datasheet

V V
V
IN(max)
OUT
OUT
= x
IPP
V L x
IN(max)
O SW
-
I
f
lpp
= +
Ipeak
O
2
I
I I
2 2
=
IPP
Lo(RMS) O
1
+
12
I I I
IN
OUT OUT
=
Co(RMS)
IN
O SW
V x (V - V )
12 x V x L x
I
f
TPS54329
www.ti.com SLVSAZ6A –SEPTEMBER 2011–REVISED MARCH 2012
Table 1. Recommended Component Values
Output Voltage (V) R1 (kΩ) R2 (kΩ) C4 (pF)
(1)
L1 (µH) C8 + C9 + C10 (µF)
1 6.81 22.1 1.5 20 - 68
1.05 8.25 22.1 1.5 20 - 68
1.2 12.7 22.1 1.5 20 - 68
1.5 21.5 22.1 1.5 20 - 68
1.8 30.1 22.1 5 - 22 2.2 20 - 68
2.5 49.9 22.1 5 - 22 2.2 20 - 68
3.3 73.2 22.1 5 - 22 2.2 20 - 68
5 124 22.1 5 - 22 3.3 20 - 68
6.5 165 22.1 5 - 22 3.3 20 - 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 650 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 3.49 A and the calculated RMS current is 3.01 A. The
inductor used is a TDK CLF7045T-1R5M with a peak current rating of 7.3 A and an RMS current rating of 4.9 A.
The capacitor value and ESR determines the amount of output voltage ripple. The TPS54329 is intended for use
with ceramic or other low ESR capacitors. Recommended values range from 20 µF to 68 µF. Use Equation 7 to
determine the required RMS current rating for the output capacitor.
(7)
For this design three TDK C3216X5R0J106M 10 µF output capacitors are used. The typical ESR is 2 mΩ each.
The calculated RMS current is 0.284 A and each output capacitor is rated for 4A.
Input Capacitor Selection
The TPS54229 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) is required to provide additional high frequency filtering and insure accurate current limit operation.
This capacitor must be placed as close to the IC pins 2 (VIN) and 4 (GND) as possible. 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.
Copyright © 2011–2012, Texas Instruments Incorporated 13
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