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| TPS40100_16 Datasheet, PDF (23/40 Pages) Texas Instruments – MIDRANGE INPUT SYNCHRONOUS BUCK CONTROLLER WITH ADVANCED SEQUENCING AND OUTPUT MARGINING | |||
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www.ti.com
APPLICATION INFORMATION (continued)
COMP
1
FB
2
SS
10
CSS
20 µA
350 mV
+
+
690 mV
COMP
Error Amplifier
5 µA
CHARGE
From UVLO circuits,
Fault controller
UDGâ04138
Figure 14. Error Amplifier and Soft-Start Functional Diagram
TPS40100
SLUS601 â MAY 2005
4.8 V
3.5 V
UVLO
(Internal Logic State)
1.04 V
0.35 V
SS
Tss
Tss Delay
VOUT
PDG
Figure 15. Relationship Between UVLO (Internal Logic State), SS, VOUT and PGD at Startup
Interaction Between Soft-Start and Tracking Startup
Since the TPS40100 provides two means of controlling the startup (closed loop soft-start and tracking) care must
be taken to ensure that the two methods do not interfere with each other. The two methods should not be
allowed to try and control the output at the same time. If tracking is to be used, the reference input to the tracking
amplifier (TRKIN) should be held low until soft-start completes, or the voltage at the SS pin is at least above 1.04
V. This ensures that the soft-start circuit is not trying to control the startup at the same time as tracking circuit. If
it is desired to have soft-start control the startup, then there are two options:
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