lm5035mhx National Semiconductor Corporation, lm5035mhx Datasheet - Page 21

• Manufacturer Part Number: lm5035mhx
• Description: Pwm Controller With Integrated Half-bridge And Syncfet Drivers
• Manufacturer: National Semiconductor Corporation

Applications Information
The typical operating ranges of undervoltage and overvolt-
age thresholds are calculated from the above equations. For
example, for resistor values R1 = 86.6kΩ, R2 = 2.10kΩ and
R3 = 1.40kΩ the computed thresholds are:
To maintain the threshold’s accuracy, a resistor tolerance of
1% or better is recommended.
The design process starts with the choice of the voltage
difference between the UVLO enabling and disabling thresh-
olds. This will also approximately set the difference between
OVP enabling and disabling regulation:
Next, the combined resistance of R
choosing the threshold for the UVLO disabling threshold:
Then R
threshold:
Outputs disabled due to VIN falling below UVLO threshold
Outputs enabled due to VIN rising above UVLO threshold
Outputs disabled due to VIN rising above OVP threshold
Outputs enabled due to VIN falling below OVP threshold
3
is determined by selecting the OVP disabling
2
and R
FIGURE 13. Remote Standby and Disable Control
3
TABLE 1. UVO/OVP Divider Formulas
(Continued)
is calculated by
21
UVLO turn-off = 32.2V
UVLO turn-on = 34.2V
OVP turn-on = 78.4V
OVP turn-off = 80.5V
Finally, R
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 13.
FAULT PROTECTION
The Over Voltage Protection (OVP) comparator of the
LM5035 can be configured for line or load fault protection or
thermal protection using an external temperature sensor or
thermistor. Figure 11 shows a line over voltage shutdown
application using a voltage divider between the input power
supply, V
Figure 14 demonstrates the use of the OVP pin for latched
output over-voltage fault protection, using a zener and opto-
coupler. When V
the opto-coupler diode and zener, the opto-coupler momen-
tarily turns on Q1 and the LM5035 enters standby mode,
disabling the drivers and enabling the hysteresis current
source on the OVP pin. Once the current source is enabled,
the OVP voltage will remain at 2.3V (23µA x 100kΩ) without
additional drive from the external circuit. If the opto-coupler
transistor emitter were directly connected to the OVP pin,
PWR
3
is subtracted from R
, and AGND to monitor the line voltage.
UVLO
OVP
OUT
R
on
on
2
= OVP
exceeds the conduction threshold of
= R
= UVLO
COMBINED
off
- [23µA x (R1 + R2)]
off
COMBINED
+ (23µA x R
- R
20177536
3
to give R
1
)
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2
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