Datasheet

OV turn-on =
V
OV
R
3
- I
UVHCS
(R
1
+ R
2
)
+ V
OV
OV turn-off =
R
1
+ R
2
+ R
3
R
3
V
OV
UV turn-off =
R
1
+ R
2
+ R
3
R
2
+ R
3
V
UV
UV turn-on =
R
1
R
2
+ R
3
V
UV
+ V
UV
+ I
UVHCS
R
1
UV
OV
LM5068
V
EE
V
DD
OV HYSTERESIS CS
2.5V
2.5V
UV HYSTERESIS CS
20PA
20PA
+
-
+
-
R
1
R
2
R
3
Vsupply
+
C
F
R
F
LM5068
SNVS254C –JANUARY 2004–REVISED MARCH 2013 www.ti.com
Figure 25. UV/OV Setting
Hysteresis is necessary to prevent a possible “chattering” condition when the controller enables or disables the
external MOSFET. The change in line current interacts with the line impedance. This interaction can cause
several rapid on/off cycles on the MOSFET. A hysteresis window larger than the line impedance voltage drop
prevents this condition.
The impedance seen looking into the resistor divider from the UV and OV pin determines the hysteresis level.
UV/OV ON and OFF thresholds are calculated as follow:
(1)
(2)
(3)
(4)
The independent UV and OV pins provide complete flexibility for the user to select the operational voltage range
of the system. However, due to the UV Abs Max rating, the UV and OV thresholds can't be simultaneously set to
extremes in one resistor string. For the wide ranges of input voltages (i.e. UV threshold to12V and OV threshold
to 90V) it is recommended to use two separate voltage dividers to set the UV and OV thresholds independently.
14 Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM5068