Datasheet

www.ti.com
t
RESTART
+
3.3 C
SS
I
SSDIS
(s)
(49)
UVLO Programming
5
UVLO 1.33 V
+
TPS40100
UDG−04139
10 µA
R
1
R
2
UVLO
R
1
+
V
HYST
I
UVLO
W
(50)
R
2
+
V
UVLO
R
1
V
ON
* V
UVLO
* R
1
I
UVLO
W
(51)
TPS40100
SLUS601–MAY 2005
APPLICATION INFORMATION (continued)
where
• t
RESTART
is the initial restart time (s)
• C
SS
is soft start capacitance (F)
• I
SSDIS
is the soft start discharge current – 5 µA
If the output fault is persistent, and an overcurrent is declared on the restart, both of the MOSFETs are turned off
and the soft-start capacitor continues to charge to 3.5 V and then discharge to 200 mV before another restart is
attempted.
The TPS40100 provides the user with programmable UVLO level and programmable hysteresis. The UVLO
detection circuit schematic is described in Figure 16 from a functional perspective.
Figure 16. UVLO Circuit Functional Diagram
To program this circuit, first select the amount of hysteresis (the difference between the startup voltage and the
shutdown voltage) desired:
Then select the turn-on voltage and solve for R
2
.
where
• V
HYST
is the desired level of hysteresis in the programmable UVLO circuit
• I
UVLO
is the undervoltage lockout circuit hysteresis current (10 µA typ)
• V
UVLO
is the UVLO comparator threshold voltage (1.33 V typ)
25