Datasheet

pFR
f
zero
252
1
1
××
=
p
CL
f
LC
×
=
p2
1
TPS62140
PVIN
AVIN
EN
SS/TR
DEF
FSW
SW
VOS
PG
FB
AGND
PGND
TPS62140
PVIN
AVIN
EN
SS/TR
DEF
FSW
SW
VOS
PG
FB
AGND
PGND
R1
R2
VOUT1
VOUT2
TPS62140, TPS62140A
TPS62141, TPS62142, TPS62143
www.ti.com SLVSAJ0B –NOVEMBER 2011–REVISED JUNE 2013
Figure 40. 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.
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:
(12)
Proven nominal values for inductance and ceramic capacitance are given in Table 1 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.
The TPS6214X devices, both fixed and adjustable versions, include an internal 25 pF feed-forward capacitor,
connected between the VOS and FB pins. This capacitor impacts the frequency behavior and sets a pole and
zero in the control loop with the resistors of the feedback divider, per equations Equation 13 and Equation 14:
spacing
(13)
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Product Folder Links: TPS62140 TPS62140A TPS62141 TPS62142 TPS62143