Datasheet

VFB [V]
VSS/TR
[V]
0.2 0.4 0.6 0.8
0.4
1.2
0.8
TRSSFB
VV
/
64.0 ×»
[ ]
F
V
A
tC
SSSS
251
52
.
. m
×=
TPS62130, TPS62130A
TPS62131, TPS62132, TPS62133
SLVSAG7B –NOVEMBER 2011–REVISED JUNE 2013 www.ti.com
Input Capacitor
For most applications, 10µF will be sufficient and is recommended, though a larger value reduces input current
ripple further. The input capacitor buffers the input voltage for transient events and also decouples the converter
from the supply. A low ESR multilayer ceramic capacitor is recommended for best filtering and should be placed
between PVIN and PGND as close as possible to those pins. Even though AVIN and PVIN must be supplied
from the same input source, it's required to place a capacitance of 0.1uF from AVIN to AGND, to avoid potential
noise coupling. An RC, low-pass filter from PVIN to AVIN may be used but is not required.
Soft Start Capacitor
A capacitance connected between SS/TR pin and AGND allows a user programmable start-up slope of the
output voltage. A constant current source supports 2.5µA to charge the external capacitance. The capacitor
required for a given soft-start ramp time for the output voltage is given by:
(10)
where
C
SS
is the capacitance (F) required at the SS/TR pin and
t
SS
is the desired soft-start ramp time (s).
spacing
NOTE
DC Bias effect: High capacitance ceramic capacitors have a DC Bias effect, which will
have a strong influence on the final effective capacitance. Therefore the right capacitor
value has to be chosen carefully. Package size and voltage rating in combination with
dielectric material are responsible for differences between the rated capacitor value and
the effective capacitance.
spacing
Tracking Function
If a tracking function is desired, the SS/TR pin can be used for this purpose by connecting it to an external
tracking voltage. The output voltage tracks that voltage. If the tracking voltage is between 50mV and 1.2V, the
FB pin will track the SS/TR pin voltage as described in Equation 11 and shown in Figure 39.
spacing
(11)
Figure 39. Voltage Tracking Relationship
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