As a member of the SWIFT™ family of dc/dc regulators, the TPS54073 low-input voltage high-output current synchronous buck PWM converter integrates all required active components

TPS54073

Manufacturer Part NumberTPS54073
DescriptionAs a member of the SWIFT™ family of dc/dc regulators, the TPS54073 low-input voltage high-output current synchronous buck PWM converter integrates all required active components
ManufacturerTexas Instruments
TPS54073 datasheet
 


Specifications of TPS54073

Iout(max)(a)14Vin(min)(v)2.2
Vin(max)(v)4Vout(min)(v)0.9
Vout(max)(v)2.5Iq(typ)(ma)13
Switching Frequency(max)(khz)700Switch Current Limit(typ)(a)14.5
TopologyBuckOperating Temperature Range(c)-40 to 85
Pin/package28HTSSOPDuty Cycle(max)(%)90
Regulated Outputs(#)1  
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............................................................................................................................................................................................
SWITCHING FREQUENCY
The switching frequency can be set to either one of
two internally programmed frequencies or set to a
externally programmed frequency. With the RT pin
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
programmed using the RT pin. By connecting a
resistor (R4) from RT to AGND, any frequency in the
range of 250 kHz to 700 kHz can be set. Use
Equation 1
to determine the proper value of RT.
R4(kW) + 500 kHz
100 kW
s(kHz)
In this example circuit, R4 is calculated to be 71.5 kΩ
and the switching frequency is set at 700 kHz.
INPUT CAPACITORS
The
TPS54073
requires
an
capacitor and, depending on the application, a bulk
input
capacitor.
The
minimum
de-coupling capacitor, C9, is 10
ceramic type X5R or X7R is recommended. The
voltage rating should be greater than the maximum
input voltage. Additionally, some bulk capacitance
may be needed, especially if the TPS54073 circuit is
not located within approximately 2 inches from the
input voltage source. The value for this capacitor is
not critical but it also should be rated to handle the
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
Equation
2:
I
0.25
OUT(MAX)
DV
) I
+
PVIN
OUT(MAX)
C
sw
BULK
Where I
is the maximum load current. ƒ
OUT(MAX)
the switching frequency, C
is the bulk capacitor
(BULK)
value and ESR
is the maximum series resistance
MAX
of the bulk capacitor.
The maximum RMS ripple current also needs to be
checked. For worst-case conditions, this can be
approximated by
Equation
3:
I
OUT(MAX)
I
+
CIN
2
In this case, the input ripple voltage would be 329 mV
and the RMS ripple current would be 7 A. The
maximum voltage across the input capacitors would
be Vin max plus delta Vin/2. The chosen bulk
capacitor, a Sanyo POSCAP 6TPD330M is rated for
6.3 V and 4.4 A of ripple current; two bypass
capacitors, TDK C3225X7R1C226KT are each rated
Copyright © 2005, Texas Instruments Incorporated
for 16 V, and the ripple current capacity is greater
than 3 A at the operating frequency of 700 kHz. Total
ripple current handling is in excess of 10.4 A. It is
important that the maximum ratings for voltage and
current are not exceeded under any circumstance.
OUTPUT FILTER COMPONENTS
is
externally
Two components need to be selected for the output
filter, L1 and C2. Because the TPS54073 is an
externally compensated device, a wide range of filter
component types and values can be supported.
Inductor Selection
(1)
To calculate the minimum value of the output
inductor, use
L
=
MIN
V
input
de-coupling
K
is a coefficient that represents the amount of
IND
inductor ripple current relative to the maximum output
value
for
the
current. For designs using low ESR output capacitors
F. A high-quality
such as ceramics, use K
ESR output capacitors, K
results. If designing for high output currents, the
minimum current limit trip point must also be taken
into consideration when choosing the output inductor.
The minimum current limit trip point for the TPS54073
is 14.5 A. The maximum inductor ripple current can
be calculated using
I
v 2
LMAX
For a 14 A maximum output current, the peak-to-peak
inductor ripple current must be less than 1 A. This
corresponds to a K
ESR
MAX
F
is the nominal switching frequency. Use 0.8
SW
times the nominal switching frequency to account for
(2)
internal variations from the set frequency.
is
sw
The minimum inductor value is calculated to be 1.54
H. A 2.2- H inductor which is slightly larger than the
minimum is selected.
For the output filter inductor, it is important that the
RMS current and saturation current ratings not be
exceeded. The RMS inductor current can be found
from
Equation
(3)
I
+
L(RMS)
and the peak inductor current can be found from
Equation 7
Product Folder Link(s):
TPS54073
TPS54073
SLVS547 – FEBRUARY 2005
Equation 4
V
(V
V
)
´
-
OUT
IN(MAX)
OUT
K
I
F
x
0.8
´
´
´
IN(MAX)
IND
OUT
SW
= 0.3. When using higher
IND
= 0.2 yields better
IND
Equation
5:
I
* I
LIMIT(MIN)
(MAX)
of 0.071 in
Equation
4.
IND
6:
* V
V
in(MAX)
) 1
I
2
V
OUT(MAX)
OUT
12
V
L
IN(MAX)
OUT
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(4)
(5)
2
OUT
F sw
0.8
(6)
11