Datasheet

www.ti.com
1
10
2
COMP
FB
SS
+
+
+
690 mV
350 mV
COMP
CHARGE
From UVLO circuits,
Fault controller
Error Amplifier
5 µA
20 µA
C
SS
UDG−04138
Tss
Tss Delay
1.04 V
0.35 V
UVLO
SS
VOUT
PDG
3.5 V
4.8 V
(Internal Logic State)
Interaction Between Soft-Start and Tracking Startup
TPS40100
SLUS601–MAY 2005
APPLICATION INFORMATION (continued)
Figure 14. Error Amplifier and Soft-Start Functional Diagram
Figure 15. Relationship Between UVLO (Internal Logic State), SS, VOUT and PGD at 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:
23