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...................................................................................................................................................................................................
Under Voltage Lock Out Set Point
The Under Voltage Lock Out (UVLO) can be adjusted using an external voltage divider on the EN pin of the
TPS54040. The UVLO has two thresholds, one for power up when the input voltage is rising and one for power
down or brown outs when the input voltage is falling. For the example design, the supply should turn on and start
switching once the input voltage increases above 8.9V (enabled). After the regulator starts switching, it should
continue to do so until the input voltage falls below 7.9V (UVLO stop).
The programmable UVLO and enable voltages are set using a resistor divider between Vin and ground to the EN
pin.
Equation 2
through
Equation 3
application, a 332kΩ between Vin and EN and a 56.2kΩ between EN and ground are required to produce the 8.9
and 7.9 volt start and stop voltages.
Output Voltage and Feedback Resistors Selection
For the example design, 10.0 kΩ was selected for R2. Using
nearest standard 1% resistor is 52.3 kΩ. Due to current leakage of the VSENSE pin, the current flowing through
the feedback network should be greater than 1
requirement makes the maximum value of R2 equal to 800 kΩ. Choosing higher resistor values will decrease
quiescent current and improve efficiency at low output currents but may introduce noise immunity problems.
Compensation
There are several methods used to compensate DC/DC regulators. The method presented here is easy to
calculate and ignores the effects of the slope compensation that is internal to the device. Since the slope
compensation is ignored, the actual cross over frequency will usually be lower than the cross over frequency
used in the calculations. This method assume the crossover frequency is between the modulator pole and the
esr zero and the esr zero is at least 10 times greater the modulator pole. Use SwitcherPro software for a more
accurate design.
To get started, the modulator pole, fpmod, and the esr zero, fz1 must be calculated using
Equation
42. For Cout, use a derated value of 21.2 f. Use equations
a starting point for the crossover frequency, fco, to design the compensation. For the example design, fpmod is
753 Hz and fzmod is 1505 kHz. Equation 43 is the geometric mean of the modulator pole and the esr zero and
Equation 44
is the mean of modulator pole and the switching frequency.
Equation 44
gives 16.2 kHz. Use the lower value of
For this example, fco is 16.2 kHz. Next, the compensation components are calculated. A resistor in series with a
capacitor is used to create a compensating zero. A capacitor in parallel to these two components forms the
compensating pole.
Ioutmax
¦
p mod =
2 ×
p
× Vout × Cout
1
z mod =
¦
2
´ p ´
Resr × Cout
f
f
mod
f
mod
=
´
co
p
z
f
sw
f
f
mod
=
´
co
p
2
To determine the compensation resistor, R4, use
gmps, is 1.9A/V. The output voltage, Vo, reference voltage, VREF, and amplifier transconductance, gmea, are
3.3V, 0.8V and 92 A/V, respectively. R4 is calculated to be 77.1 kΩ, use the nearest standard value of 76.8kΩ.
Use
Equation 46
to set the compensation zero to the modulator pole frequency.
compensating capacitor C5, a 2700 pF is used on the board.
34
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can be used to calculate the resistance values necessary. For the example
Equation
A in order to maintain the output voltage accuracy. This
Equation 43
or
Equation 44
Equation
45. Assume the power stage transconductance,
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1, R1 is calculated as 52.5 kΩ. The
Equation 41
Equation 43
and
Equation
44, to estimate
Equation 43
yields 33.7 kHz and
for an initial crossover frequency.
Equation 46
yields 2754 pF for
Copyright © 2009, Texas Instruments Incorporated
and
(41)
(42)
(43)
(44)
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