LM5035A

50

0.1 PF

VIN

LM5035A

www.ti.com

SNVS537F – JANUARY 2008 – REVISED APRIL 2013

Thermal Protection

Internal Thermal Shutdown circuitry is provided to protect the integrated circuit in the event the maximum rated

junction temperature is exceeded. When activated, typically at 165°C, the controller is forced into a low power

standby state with the output drivers (HO, LO, SR1 and SR2), the bias regulators (VCC and REF) disabled. This

helps to prevent catastrophic failures from accidental device overheating. During thermal shutdown, the soft-start

capacitor is fully discharged and the controller follows a normal start-up sequence after the junction temperature

falls to the operating level (145°C).

Applications Information

The following information is intended to provide guidelines for the power supply designer using the LM5035A.

VIN

The voltage applied to the VIN pin, which may be the same as the system voltage applied to the power

gate charge provided to the output drivers, the switching frequency, and any external loads on the VCC and REF

pins. It is recommended the filter shown in Figure 18 be used to suppress transients which may occur at the

input supply. This is particularly important when VIN is operated close to the maximum operating rating of the

LM5035A.

When power is applied to VIN and the UVLO pin voltage is greater than 0.4V, the VCC regulator is enabled and

supplies current into an external capacitor connected to the VCC pin. When the voltage on the VCC pin reaches

the regulation point of 7.6V, the voltage reference (REF) is enabled. The reference regulation set point is 5V. The

HO, LO, SR1 and SR2 outputs are enabled when the two bias regulators reach their set point and the UVLO pin

potential is greater than 1.25V. In typical applications, an auxiliary transformer winding is connected through a

diode to the VCC pin. This winding must raise the VCC voltage above 8.3V to shut off the internal start-up

regulator.

After the outputs are enabled and the external VCC supply voltage has begun supplying power to the IC, the

current into VIN drops below 1 mA. VIN should remain at a voltage equal to or above the VCC voltage to avoid

reverse current through protection diodes.

Figure 18. Input Transient Protection

FOR APPLICATIONS >100V

For applications where the system input voltage exceeds 100V or the IC power dissipation is of concern, the

LM5035A can be powered from an external start-up regulator as shown in Figure 19. In this configuration, the

VIN and the VCC pins should be connected together, which allows the LM5035A to be operated below 13V. The

voltage at the VCC pin must be greater than 8.3V yet not exceed 15V. An auxiliary winding can be used to

reduce the power dissipation in the external regulator once the power converter is active. The NPN base-emitter

reverse breakdown voltage, which can be as low as 5V for some transistors, should be considered when

selecting the transistor.

Copyright © 2008–2013, Texas Instruments Incorporated

Submit Documentation Feedback

19

Product Folder Links: LM5035A