lm5045sqx National Semiconductor Corporation, lm5045sqx Datasheet - Page 23

• Manufacturer Part Number: lm5045sqx
• Description: Full-bridge Pwm Controller With Integrated Mosfet Drivers
• Manufacturer: National Semiconductor Corporation

The UVLO and OVP can also be set together using a 3 re-
sistor divider ladder as shown in Figure 15. R
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
and 1.5kΩ. The R
4.2kΩ.
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 16.
Figure 17 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
2
is 2.7kΩ obtained by subtracting R
1
and R
3
remain the same at 100kΩ
FIGURE 16. Remote Standby and Disable Control
FIGURE 17. Remote Thermal Protection
1
is calculated
3
from
23
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
the desired trip point (for VREF = 5V). In a temperature band
from 20ºC below to 20ºC above the OVP threshold, the volt-
age divider is nearly linear with 25mV per ºC sensitivity.
R
parator input by R
selected for R
x 20µA = 506mV. The NTC temperature must therefore fall
by 506mV / 25mV per ºC = 20ºC before the LM5045 switches
from standby mode to the normal mode.
1
2
to one-third of this resistance (665Ω) establishes 130ºC as
provides temperature hysteresis by raising the OVP com-
2
, then the OVP pin voltage will increase by 22k
2
x 20µA. For example, if a 22kΩ resistor is
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