TPS62140_15 Datasheet, PDF (16/40 Pages) Texas Instruments – TPS6214x 3-V to 17-V 2-A Step-Down Converter in 3 × 3 QFN Package

TPS62140, TPS62140A
TPS62141, TPS62142, TPS62143
SLVSAJ0C – NOVEMBER 2011 – REVISED AUGUST 2015
www.ti.com
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 goes to zero,
independent of the tracking voltage. Figure 9 shows how to connect devices to get ratiometric and simultaneous
sequencing by using the tracking function.
spacing
PVIN
SW
AVIN
VOS
EN
PG
TPS62140
SS/TR
FB
DEF
AGND
FSW
PGND
VOUT1
PVIN
SW
AVIN
VOS
R1
EN
PG
TPS62140
SS/TR
FB
R2
DEF
AGND
FSW
PGND
VOUT2
Figure 9. Sequence for Ratiometric and Simultaneous Startup
The resistive divider of R1 and R2 can be used to change the ramp rate of VOUT2 faster, slower, or the same as
VOUT1.
A sequential start-up is achieved by connecting the PG pin of VOUT1 to the EN pin of VOUT2. A ratiometric
start-up sequence happens if both supplies are sharing the same soft-start capacitor. Equation 10 calculates the
soft-start time, though the SS/TR current must be doubled. Details about these and other tracking and
sequencing circuits are found in SLVA470.
Note: If the voltage at the FB pin is below its typical value of 0.8 V, the output voltage accuracy may have a
wider tolerance than specified.
9.2.2.4 Output Filter and Loop Stability
The devices of the TPS6214x family are internally compensated to be stable with L-C filter combinations
corresponding to a corner frequency to be calculated with Equation 12:
spacing
f _LC
=
2p
1
L×C
(12)
Proven nominal values for inductance and ceramic capacitance are given in Table 2 and are recommended for
use. Different values may work, but care must be taken on the loop stability, which is affected. More information
including a detailed L-C stability matrix can be found in SLVA463.
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