Datasheet

( )
Vin min Vout
Vout
Icirms = Iout
Vin min Vin min
-
´ ´
Iout max 0.25
ΔVin =
Cin sw
´
´ ¦
Cout Vout 0.8
Tss >
Issavg
´ ´
TPS54060
www.ti.com SLVS919A –JANUARY 2009–REVISED JULY 2010
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Table 1. Capacitor Types
VENDOR VALUE (mF) EIA Size VOLTAGE DIALECTRIC COMMENTS
1.0 to 2.2 100 V
1210 GRM32 series
1.0 to 4.7 50 V
Murata
1.0 100 V
1206 GRM31 series
1.0 to 2.2 50 V
1.0 10 1.8 50 V
2220
1.0 to 1.2 100 V
Vishay VJ X7R series
1.0 to 3.9 50 V
2225
1.0 to 1.8 100 V
X7R
1.0 to 2.2 100 V
1812 C series C4532
1.5 to 6.8 50 V
TDK
1.0. to 2.2 100 V
1210 C series C3225
1.0 to 3.3 50 V
1.0 to 4.7 50 V
1210
1.0 100 V
AVX X7R dielectric series
1.0 to 4.7 50 V
1812
1.0 to 2.2 100 V
Slow Start Capacitor
The slow start capacitor determines the minimum amount of time it will take for the output voltage to reach its
nominal programmed value during power up. This is useful if a load requires a controlled voltage slew rate. This
is also used if the output capacitance is large and would require large amounts of current to quickly charge the
capacitor to the output voltage level. The large currents necessary to charge the capacitor may make the
TPS54060 reach the current limit or excessive current draw from the input power supply may cause the input
voltage rail to sag. Limiting the output voltage slew rate solves both of these problems.
The slow start time must be long enough to allow the regulator to charge the output capacitor up to the output
voltage without drawing excessive current. Equation 40 can be used to find the minimum slow start time, tss,
necessary to charge the output capacitor, Cout, from 10% to 90% of the output voltage, Vout, with an average
slow start current of Issavg. In the example, to charge the 47mF output capacitor up to 3.3V while only allowing
the average input current to be 0.125A would require a 1 ms slow start time.
Once the slow start time is known, the slow start capacitor value can be calculated using Equation 6. For the
example circuit, the slow start time is not too critical since the output capacitor value is 47mF which does not
require much current to charge to 3.3V. The example circuit has the slow start time set to an arbitrary value of
3.2ms which requires a 0.01 mF capacitor.
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Bootstrap Capacitor Selection
A 0.1-mF ceramic capacitor must be connected between the BOOT and PH pins for proper operation. It is
recommended to use a ceramic capacitor with X5R or better grade dielectric. The capacitor should have a 10V
or higher voltage rating.
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