TPS54073PWP datasheet(11/25 Pages) TI1

Part #	TPS54073PWP

Description	2.2 ??4 -V, 14-A SYNCHRONOUS BUCK CONVERTER WITH DISABLED SINKING DURING START-UP

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SWITCHING FREQUENCY

OUTPUT FILTER COMPONENTS

Inductor Selection

R4(kW) +

500 kHz

ƒs(kHz)

100 kW

(1)

INPUT CAPACITORS

0.8

x

F

I

K

V

)

V

(V

V

L

SW

OUT

IND

IN(MAX)

OUT

IN(MAX)

OUT

MIN

´

-

´

=

(4)

I

LMAX v

2

I

LIMIT(MIN) *

I

(MAX)

(5)

DVPVIN +

I

OUT(MAX)

0.25

C

BULK

ƒsw )

I

OUT(MAX)

ESR

MAX

I

CIN +

I

OUT(MAX)

2

(3)

I

L(RMS) +

I2

OUT(MAX) )

1

12

V

OUT

V

in(MAX) *

V

OUT

V

IN(MAX)

L

OUT

Fsw

0.8

2

TPS54073

www.ti.com ............................................................................................................................................................................................ SLVS547 – FEBRUARY 2005

for 16 V, and the ripple current capacity is greater

than 3 A at the operating frequency of 700 kHz. Total

The switching frequency can be set to either one of

ripple current handling is in excess of 10.4 A. It is

two internally programmed frequencies or set to a

important that the maximum ratings for voltage and

externally programmed frequency. With the RT pin

current are not exceeded under any circumstance.

open, setting the SYNC pin at or above 2.5 V selects

550-kHz operation, while grounding or leaving the

SYNC pin open selects 350-kHz operation. For this

design,

the

switching

frequency

is

externally

Two components need to be selected for the output

programmed using the RT pin. By connecting a

filter, L1 and C2. Because the TPS54073 is an

resistor (R4) from RT to AGND, any frequency in the

externally compensated device, a wide range of filter

range of 250 kHz to 700 kHz can be set. Use

component types and values can be supported.

Equation 1 to determine the proper value of RT.

To calculate the minimum value of the output

inductor, use Equation 4

In this example circuit, R4 is calculated to be 71.5 k

Ω

and the switching frequency is set at 700 kHz.

The

TPS54073

requires

an

input

de-coupling

KIND is a coefficient that represents the amount of

capacitor and, depending on the application, a bulk

inductor ripple current relative to the maximum output

input

capacitor.

The

minimum

value

for

the

current. For designs using low ESR output capacitors

de-coupling capacitor, C9, is 10

µF. A high-quality

such as ceramics, use KIND = 0.3. When using higher

ceramic type X5R or X7R is recommended. The

ESR output capacitors, KIND = 0.2 yields better

voltage rating should be greater than the maximum

results. If designing for high output currents, the

input voltage. Additionally, some bulk capacitance

minimum current limit trip point must also be taken

may be needed, especially if the TPS54073 circuit is

into consideration when choosing the output inductor.

not located within approximately 2 inches from the

The minimum current limit trip point for the TPS54073

input voltage source. The value for this capacitor is

is 14.5 A. The maximum inductor ripple current can

not critical but it also should be rated to handle the

be calculated using Equation 5:

maximum input voltage including ripple voltage, and

should filter the output so that input ripple voltage is

acceptable.

This input ripple voltage can be approximated by

For a 14 A maximum output current, the peak-to-peak

Equation 2:

inductor ripple current must be less than 1 A. This

corresponds to a KIND of 0.071 in Equation 4.

FSW is the nominal switching frequency. Use 0.8

times the nominal switching frequency to account for

(2)

internal variations from the set frequency.

Where IOUT(MAX) is the maximum load current. ƒsw is

The minimum inductor value is calculated to be 1.54

the switching frequency, C(BULK) is the bulk capacitor

µH. A 2.2-µH inductor which is slightly larger than the

value and ESRMAX is the maximum series resistance

minimum is selected.

of the bulk capacitor.

For the output filter inductor, it is important that the

The maximum RMS ripple current also needs to be

RMS current and saturation current ratings not be

checked. For worst-case conditions, this can be

exceeded. The RMS inductor current can be found

approximated by Equation 3:

from Equation 6:

In this case, the input ripple voltage would be 329 mV

and the RMS ripple current would be 7 A. The

(6)

maximum voltage across the input capacitors would

be Vin max plus delta Vin/2. The chosen bulk

and the peak inductor current can be found from

capacitor, a Sanyo POSCAP 6TPD330M is rated for

Equation 7

6.3 V and 4.4 A of ripple current; two bypass

capacitors, TDK C3225X7R1C226KT are each rated

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