Datasheet

OVP
LM5046
1.25V
20 PA
STANDBY
V
PWR
5V
R1
R2
UVLO
LM5046
1.25V
20 PA
SHUTDOWN
V
PWR
R1
R2
STANDBY
0.4V
R
2
=
1.25V x R
1
V
PWR
-1.25V + (20 PA x R1)
V
HYS
20 PA
R
1
=
LM5046
SNVS703G –FEBRUARY 2011–REVISED MARCH 2013 www.ti.com
Two external resistors can be used to program the maximum operational voltage for the power converter as
shown in Figure 27. When the OVP pin voltage rises above the 1.25V threshold, an internal 20µA current source
is enabled to raise the voltage at the OVP pin, thus providing threshold hysteresis. Resistance values for R
1
and
R
2
can be determined from the following equations:
(9)
If the LM5046 is to be disabled when V
PWR-OFF
reaches 80V and enabled when it is decreased to 78V. R
1
should
be 100kΩ, and R
2
should be 1.5 kΩ. The voltage at the OVP pin should not exceed 7V at any time.
Figure 26. Basic UVLO Configuration
Figure 27. Basic OVP Configuration
The UVLO and OVP can also be set together using a 3 resistor divider ladder as shown in Figure 28. R
1
is
calculated as explained in the basic UVLO divider selection. Using the same values, as in the above two
examples, for the UVLO and OVP set points, R
1
and R
3
remain the same at 100kΩ and 1.5kΩ. The R
2
is 2.7kΩ
obtained by subtracting R
3
from 4.2kΩ.
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