Datasheet

UVLO
LM5046
1.25V
20 PA
SHUTDOWN
V
PWR
R1
STANDBY
0.4V
STANDBY SHUTDOWN
R2
1.25V
20 PA
0.4V
SHUTDOWN
OVP
1.25V
STANDBY
V
PWR
5V
R1
R2
R3
LM5046
STANDBY
UVLO
20 PA
LM5046
www.ti.com SNVS703G –FEBRUARY 2011–REVISED MARCH 2013
Figure 28. UVLO/OVP Divider
Remote configuration of the controller’s operational modes can be accomplished with open drain device(s)
connected to the UVLO pin as shown in Figure 29.
Figure 30 shows an application of the OVP comparator for Remote Thermal Protection using a thermistor (or
multiple thermistors) which may be located near the main heat sources of the power converter. The negative
temperature coefficient (NTC) thermistor is nearly logarithmic, and in this example a 100kΩ thermistor with the β
material constant of 4500 Kelvin changes to approximately 2kΩ at 130ºC. Setting R
1
to one-third of this
resistance (665Ω) establishes 130ºC as the desired trip point (for VREF = 5V). In a temperature band from 20ºC
below to 20ºC above the OVP threshold, the voltage divider is nearly linear with 25mV per ºC sensitivity.
R
2
provides temperature hysteresis by raising the OVP comparator input by R
2
x 20µA. For example, if a 22kΩ
resistor is selected for R
2
, then the OVP pin voltage will increase by 22k x 20µA = 506mV. The NTC temperature
must therefore fall by 506mV / 25mV per ºC = 20ºC before the LM5046 switches from standby mode to the
normal mode.
Figure 29. Remote Standby and Disable Control
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