lm5027mhx National Semiconductor Corporation, lm5027mhx Datasheet - Page 16

• Manufacturer Part Number: lm5027mhx
• Description: Voltage Mode Active Clamp Controller
• Manufacturer: National Semiconductor Corporation

www.national.com
External Over-Temperature
Protection
An external set-point voltage divider between the REF, OTP,
and AGND pins, as shown in
plement over-temperature protection shutdown. Typically a
NTC thermistor is installed as the lower device of the voltage
divider. The divider must be designed such that the voltage
at the OTP pin will be greater than 1.25V when there is not
an over-temperature condition, and the OTP pin must drop
below 1.25V during an over-temperature event. OTP hystere-
sis is accomplished with an internal 20 µA current source that
is switched on or off into the impedance of the external set-
point divider. When the OTP pin voltage exceeds 1.25V
threshold, the current source is activated to quickly raise the
voltage at the OTP pin. When the OTP pin voltage falls below
the 1.25V threshold, the current source is turned off causing
the voltage at the OTP pin to quickly fall. When OTP falls be-
low 1.25V the LM5027 will go through a soft-stop turn-off
sequence.
Figure
FIGURE 6. Soft-Start Synchronous Rectifier Timing
7, is one method to im-
16
Fault/Events Summary Table
Table 1
that control the LM5027 drive outputs. For example the first
event is with UVLO being pulled below 0.4V, a possible re-
mote shutdown condition. When this occurs the SS, and
SSSR capacitors are discharged, and the three drive outputs
will stop switching (outputs low). The last fault is if the OTP
pin is pulled low <1.25V, this would occur if an OTP protection
circuit is used, see
goes into a soft-stop shutdown.
is a Truth Table which describes the faults and events
FIGURE 7. External OTP Protection
Figure
7. In an OTP event, the LM5027
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