TPS54040DGQ  

Manufacturer Part Number  TPS54040DGQ 
Description  IC STEPDOWN SWIFT CONV 10MSOP 
Manufacturer  Texas Instruments 
Series  SWIFT™, EcoMode™ 
Type  StepDown (Buck) 
TPS54040DGQ datasheet 

Specifications of TPS54040DGQ  

Internal Switch(s)  Yes  Synchronous Rectifier  No 
Number Of Outputs  1  Voltage  Output  0.8 ~ 39 V 
Current  Output  500mA  Frequency  Switching  100kHz ~ 2.5MHz 
Voltage  Input  3.5 ~ 42 V  Operating Temperature  40°C ~ 150°C 
Mounting Type  Surface Mount  Package / Case  10MSOP Exposed Pad, 10HMSOP, 10eMSOP 
Mounting Style  SMD/SMT  Duty Cycle (max)  98 % 
Input / Supply Voltage (max)  42 V  Input / Supply Voltage (min)  3.5 V 
Maximum Operating Temperature  + 150 C  Minimum Operating Temperature   40 C 
Output Current  0.5 A  Output Voltage  0.8 V to 39 V 
Supply Current  116 uA  Switching Frequency  2500 KHz 
Dc To Dc Converter Type  Step Down  Pin Count  10 
Input Voltage  42V  Switching Freq  2500KHz 
Package Type  HTSSOP EP  Output Type  Adjustable 
Switching Regulator  Yes  Mounting  Surface Mount 
Input Voltage (min)  3.5V  Operating Temperature Classification  Automotive 
Lead Free Status / RoHS Status  Lead free / RoHS Compliant  Power  Output   
Other names  296242285 
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TPS54040
SLVS918 – MARCH
2009...................................................................................................................................................................................................
Output Inductor Selection (L
O
To calculate the minimum value of the output inductor, use
K
is a coefficient that represents the amount of inductor ripple current relative to the maximum output current.
IND
The inductor ripple current will be filtered by the output capacitor. Therefore, choosing high inductor ripple
currents will impact the selection of the output capacitor since the output capacitor must have a ripple current
rating equal to or greater than the inductor ripple current. In general, the inductor ripple value is at the discretion
of the designer; however, the following guidelines may be used.
For designs using low ESR output capacitors such as ceramics, a value as high as K
When using higher ESR output capacitors, K
part of the PWM control system, the inductor ripple current should always be greater than 30 mA for dependable
operation. In a wide input voltage regulator, it is best to choose an inductor ripple current on the larger side. This
allows the inductor to still have a measurable ripple current with the input voltage at its minimum.
For this design example, use K
IND
design, a nearest standard value was chosen: 47 H. For the output filter inductor, it is important that the RMS
current and saturation current ratings not be exceeded. The RMS and peak inductor current can be found from
Equation 30
and
Equation
31.
For this design, the RMS inductor current is 0.501 A and the peak inductor current is 0.567 A. The chosen
inductor is a MSS1048473ML. It has a saturation current rating of 1.44 A and an RMS current rating of 1.83A.
As the equation set demonstrates, lower ripple currents will reduce the output voltage ripple of the regulator but
will require a larger value of inductance. Selecting higher ripple currents will increase the output voltage ripple of
the regulator but allow for a lower inductance value.
The current flowing through the inductor is the inductor ripple current plus the output current. During power up,
faults or transient load conditions, the inductor current can increase above the calculated peak inductor current
level calculated above. In transient conditions, the inductor current can increase up to the switch current limit of
the device. For this reason, the most conservative approach is to specify an inductor with a saturation current
rating equal to or greater than the switch current limit rather than the peak inductor current.
Vinmax
Vout

Lo min =
´
Io
K
´
IND
(
V
Vin max
´
OUT
I
=
RIPPLE
Vin max
L
´ f
´
O
æ
V
1
( )
2
OUT
=
+
´ ç
I
I
ç
L(rms)
O
12
Vinmax
è
Iripple
ILpeak
Iout
=
+
2
Output Capacitor
There are three primary considerations for selecting the value of the output capacitor. The output capacitor will
determine the modulator pole, the output voltage ripple, and how the regulators responds to a large change in
load current. The output capacitance needs to be selected based on the more stringent of these three criteria.
The desired response to a large change in the load current is the first criteria. The output capacitor needs to
supply the load with current when the regulator can not. This situation would occur if there are desired holdup
times for the regulator where the output capacitor must hold the output voltage above a certain level for a
specified amount of time after the input power is removed. The regulator also will temporarily not be able to
supply sufficient output current if there is a large, fast increase in the current needs of the load such as
transitioning from no load to a full load. The regulator usually needs two or more clock cycles for the control loop
30
Submit Documentation Feedback
)
Equation
= 0.2 yields better results. Since the inductor ripple current is
IND
= 0.3 and the minimum inductor value is calculated to be 42 H. For this
Vout
Vinmax
ƒsw
´
)
 V
OUT
SW
2
(
)
ö
´
Vinmax  V
OUT
÷
÷
´
´
L
f
ø
O
SW
Product Folder Link(s):
TPS54040
28.
= 0.3 may be used.
IND
Copyright © 2009, Texas Instruments Incorporated
www.ti.com
(28)
(29)
(30)
(31)
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