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TPS54040Q1
TPS54040Q1  

Manufacturer Part Number  TPS54040Q1 
Description  The TPS54040 device is a 42V 0 
Manufacturer  Texas Instruments 
TPS54040Q1 datasheet 

Specifications of TPS54040Q1  

Iout(max)(a)  0.5  Vin(min)(v)  3.5 
Vin(max)(v)  42  Vout(min)(v)  0.8 
Vout(max)(v)  39  Iq(typ)(ma)  0.116 
Switching Frequency(max)(khz)  2500  Switch Current Limit(typ)(a)  0.6 
Topology  Buck,Inverting BuckBoost  Operating Temperature Range(c)  40 to 125 
Pin/package  10MSOPPowerPAD, 10SON  Duty Cycle(max)(%)  95 
Regulated Outputs(#)  1 
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Design Guide — StepByStep Design Procedure
This example details the design of a high frequency switching regulator design using ceramic output capacitors.
A few parameters must be known in order to start the design process. These parameters are typically determined
at the system level. For this example, we will start with the following known parameters:
Output Voltage
Transient Response 0 to 1.5A load step
Maximum Output Current
Input Voltage
Output Voltage Ripple
Start Input Voltage (rising VIN)
Stop Input Voltage (falling VIN)
Selecting the Switching Frequency
The first step is to decide on a switching frequency for the regulator. Typically, the user will want to choose the
highest switching frequency possible since this will produce the smallest solution size. The high switching
frequency allows for lower valued inductors and smaller output capacitors compared to a power supply that
switches at a lower frequency. The switching frequency that can be selected is limited by the minimum ontime of
the internal power switch, the input voltage and the output voltage and the frequency shift limitation.
Equation 12
and
Equation 13
must be used to find the maximum switching frequency for the regulator, choose
the lower value of the two equations. Switching frequencies higher than these values will result in pulse skipping
or the lack of overcurrent protection during a short circuit.
The typical minimum on time, t
onmin
and the maximum input voltage is 42 V, which allows for a maximum switch frequency up to 1012 kHz when
including the inductor resistance, on resistance and diode voltage in
runaway is not a concern during short circuits in your design use
determine the maximum switching frequency. With a maximum input voltage of 42 V, assuming a diode voltage
of 0.5 V, inductor resistance of 130mΩ, switch resistance of 400mΩ, a current limit value of 0.94 A and a short
circuit output voltage of 0.1V. The maximum switching frequency is approximately 1055 kHz.
Choosing the lower of the two values and adding some margin a switching frequency of 700kHz is used. To
determine the timing resistance for a given switching frequency, use
The switching frequency is set by resistor R
Figure 50. High Frequency, 3.3V Output Power Supply Design with Adjusted UVLO.
Copyright © 2010–2011, Texas Instruments Incorporated
APPLICATION INFORMATION
5.0 V
ΔVout = 4%
0.5 A
34 V nom. 12V to 42 V
1% of Vout
8.9 V
7.9 V
, is 130 ns for the TPS54040. For this example, the output voltage is 5.0 V
Equation 13
Equation 11
shown in
Figure
50.
3
TPS54040Q1
SLVSA26C – JANUARY 2010 – REVISED AUGUST 2011
Equation
12. To ensure overcurrent
or the solid curve in
Figure 41
or the curve in
Figure
39.
to
29
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