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
×=
TLV62130, TLV62130A
www.ti.com
SLVSB74B –FEBRUARY 2012–REVISED JUNE 2013
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 38.
spacing
(11)
Figure 38. Voltage Tracking Relationship
Once the SS/TR pin voltage reaches about 1.2V, the internal voltage is clamped to the internal feedback voltage
and device goes to normal regulation. This works for rising and falling tracking voltages with the same behavior,
as long as the input voltage is inside the recommended operating conditions. For decreasing SS/TR pin voltage,
the device doesn't sink current from the output. So, the resulting decrease of the output voltage may be slower
than the SS/TR pin voltage if the load is light. When driving the SS/TR pin with an external voltage, do not
exceed the voltage rating of the SS/TR pin which is V
IN
+0.3V.
If the input voltage drops into undervoltage lockout or even down to zero, the output voltage will go to zero,
independent of the tracking voltage. Figure 39 shows how to connect devices to get ratiometric and simultaneous
sequencing by using the tracking function.
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