IC STEP-DOWN SWIFT CONV 10-MSOP

TPS54040DGQ

Manufacturer Part NumberTPS54040DGQ
DescriptionIC STEP-DOWN SWIFT CONV 10-MSOP
ManufacturerTexas Instruments
SeriesSWIFT™, Eco-Mode™
TypeStep-Down (Buck)
TPS54040DGQ datasheet
 


Specifications of TPS54040DGQ

Internal Switch(s)YesSynchronous RectifierNo
Number Of Outputs1Voltage - Output0.8 ~ 39 V
Current - Output500mAFrequency - Switching100kHz ~ 2.5MHz
Voltage - Input3.5 ~ 42 VOperating Temperature-40°C ~ 150°C
Mounting TypeSurface MountPackage / Case10-MSOP Exposed Pad, 10-HMSOP, 10-eMSOP
Mounting StyleSMD/SMTDuty Cycle (max)98 %
Input / Supply Voltage (max)42 VInput / Supply Voltage (min)3.5 V
Maximum Operating Temperature+ 150 CMinimum Operating Temperature- 40 C
Output Current0.5 AOutput Voltage0.8 V to 39 V
Supply Current116 uASwitching Frequency2500 KHz
Dc To Dc Converter TypeStep DownPin Count10
Input Voltage42VSwitching Freq2500KHz
Package TypeHTSSOP EPOutput TypeAdjustable
Switching RegulatorYesMountingSurface Mount
Input Voltage (min)3.5VOperating Temperature ClassificationAutomotive
Lead Free Status / RoHS StatusLead free / RoHS CompliantPower - Output-
Other names296-24228-5  
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TPS54040
SLVS918 – MARCH
2009...................................................................................................................................................................................................
V
ORIPPLE
R
<
ESR
I
RIPPLE
Vout
´
(Vin max
Icorms =
12
Vin max
´
´
Catch Diode
The TPS54040 requires an external catch diode between the PH pin and GND. The selected diode must have a
reverse voltage rating equal to or greater than Vinmax. The peak current rating of the diode must be greater than
the maximum inductor current. The diode should also have a low forward voltage. Schottky diodes are typically a
good choice for the catch diode due to their low forward voltage. The lower the forward voltage of the diode, the
higher the efficiency of the regulator.
Typically, the higher the voltage and current ratings the diode has, the higher the forward voltage will be. Since
the design example has an input voltage up to 42V, a diode with a minimum of 42V reverse voltage will be
selected.
For the example design, the B160A Schottky diode is selected for its lower forward voltage and it comes in a
larger package size which has good thermal characteristics over small devices. The typical forward voltage of the
B160A is 0.50 volts.
The diode must also be selected with an appropriate power rating. The diode conducts the output current during
the off-time of the internal power switch. The off-time of the internal switch is a function of the maximum input
voltage, the output voltage, and the switching frequency. The output current during the off-time is multiplied by
the forward voltage of the diode which equals the conduction losses of the diode. At higher switch frequencies,
the ac losses of the diode need to be taken into account. The ac losses of the diode are due to the charging and
discharging of the junction capacitance and reverse recovery.
dissipation, conduction losses plus ac losses, of the diode.
The B160A has a junction capacitance of 110pF. Using
Watts. This power dissipation, depending on mounting techniques, should produce a 5.9°C temperature rise in
the diode when the input voltage is 42V and the load current is 0.5A.
If the power supply spends a significant amount of time at light load currents or in sleep mode consider using a
diode which has a low leakage current and slightly higher forward voltage drop.
(Vin max
-
Vout)
´
Iout
Pd =
Vin max
Input Capacitor
The TPS54040 requires a high quality ceramic, type X5R or X7R, input decoupling capacitor of at least 3 F of
effective capacitance and in some applications a bulk capacitance. The effective capacitance includes any dc
bias effects. The voltage rating of the input capacitor must be greater than the maximum input voltage. The
capacitor must also have a ripple current rating greater than the maximum input current ripple of the TPS54040.
The input ripple current can be calculated using
The value of a ceramic capacitor varies significantly over temperature and the amount of dc bias applied to the
capacitor. The capacitance variations due to temperature can be minimized by selecting a dielectric material that
is stable over temperature. X5R and X7R ceramic dielectrics are usually selected for power regulator capacitors
because they have a high capacitance to volume ratio and are fairly stable over temperature. The output
capacitor must also be selected with the dc bias taken into account. The capacitance value of a capacitor
decreases as the dc bias across a capacitor increases.
For this example design, a ceramic capacitor with at least a 60V voltage rating is required to support the
maximum input voltage. Common standard ceramic capacitor voltage ratings include 4V, 6.3V, 10V, 16V, 25V,
50V or 100V so a 100V capacitor should be selected. For this example, two 2.2 F, 100V capacitors in parallel
have been selected.
Table 1
shows a selection of high voltage capacitors. The input capacitance value
determines the input ripple voltage of the regulator. The input voltage ripple can be calculated using
Using the design example values, Ioutmax = 0.5 A, Cin = 4.4 F, ƒsw = 500 kHz, yields an input voltage ripple of
40.6 mV and a rms input ripple current of 0.247A.
32
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-
Vout)
Lo
sw
´ ¦
Equation 37
Equation
(
Cj
´
ƒsw
´
Vin + Vƒd
´
Vƒd
+
2
Equation
38.
Product Folder Link(s):
TPS54040
is used to calculate the total power
37, the selected diode will dissipate 0.290
2
)
Equation
Copyright © 2009, Texas Instruments Incorporated
www.ti.com
(35)
(36)
(37)
39.