lm5027mhx National Semiconductor Corporation, lm5027mhx Datasheet - Page 4

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

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Pin
Note: The pin numbers shown are only for the eTSSOP package.
17
18
19
20
Name
SSSR
UVLO
RES
OTP
EP
Description
Restart timer
Soft-start for synchronous rectifier
output.
Over-Temperature Protection
Line under-voltage lockout
Exposed pad, underside of package
Application Information
If cycle-by-cycle current limit is reached during any cycle, a 22 µA
current is sourced into the RES capacitor. If the RES capacitor voltage
charges to 1.0V, a hiccup sequence is initiated. The SS and SSSR
capacitors are discharged and the control outputs are disabled. The
voltage on the RES capacitor is ramped between 4V and 2V eight
times. After the eighth cycle, the SS capacitor is released and the
normal start-up sequence begins.
An external capacitor and an internal 25 µA current source sets the
soft-start and soft-stop ramps for the synchronous rectifier output
(OUTSR).
The OTP comparator can be used for over-temperature shutdown
protection with an external NTC thermistor voltage divider setting the
shutdown temperature. The OTP comparator threshold is 1.25V.
Hysteresis is set by an internal current source that sources 20 µA into
the external resistor divider when the OTP pin voltage is above the
threshold.
An external voltage divider from the power source sets the shutdown
and standby comparator levels. When UVLO reaches the 0.4V
threshold, the VCC and REF regulators are enabled. When UVLO
reaches the 2.0V threshold, the SS pin is released and the device
enters the active mode. Hysteresis is set by an internal current source
that pulls 20 µA from the external resistor divider when the UVLO pin
is below the 2.0V threshold.
No electrical contact to the LM5027 integrated circuit. Connect to
system ground plane for reduced thermal resistance.
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