LM5033

SNVS181B – APRIL 2004 – REVISED APRIL 2013

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In the event of a current fault, (see Current Sense section) the softstart capacitor will be discharged by an

internal pull-down device. The falling voltage at pin 10 will pull down the COMP pin, thereby ensuring a minimum

output duty cycle when the outputs are re-enabled. The softstart capacitor will then begin to ramp up, allowing

the COMP voltage to increase. As the COMP voltage increases, the output duty cycle increases from zero to the

value required for regulation. However, if the fault condition is still present the above sequence repeats until the

fault is removed.

and the softstart capacitor is discharged. The falling voltage at pin 10 will pull down the COMP pin, thereby

upper threshold (typically 9.5V), the outputs are enabled, and the softstart capacitor will begin to ramp up,

allowing the COMP pin voltage to increase. The output duty cycle will then increase from zero to the value

required for regulation.

In the event of a fault which results in an excessively high die temperature, an internal Thermal Shutdown circuit

is provided to protect the IC. When activated (at 165°C) the IC is forced into a low power reset state, disabling

Using an externally controlled switch, the outputs (Pins 5 & 6) can be disabled at any time by pulling pin 10

below 0.5V. This will pull down the COMP pin to near ground, causing the output duty cycle to go to zero. Upon

releasing pin 10, the softstart capacitor will ramp up, allowing the COMP pin voltage to increase. The output duty

cycle then increases from zero to the value required for regulation.

OUT1, OUT2 (Pins 5, 6)

The LM5033 provides two alternating outputs, OUT1 and OUT2, each capable of sourcing and sinking 1.5A

peak. Each will toggle at one-half the internal oscillator frequency. The voltage output levels are nominally

The outputs can drive power MOSFETs directly in a push-pull application, or they can drive a high voltage gate

driver (e.g., LM5100) in a bridge application.

The outputs are disabled when any of the following conditions occur:

1. An overcurrent condition is detected at pin 8,

3. An over-temperature condition is detected, or

4. The voltage at Pin 10 is below 0.5V

Thermal Protection

The system design should limit the LM5033 junction temperature to not exceed 125°C during normal operation.

However, in the event of a fault which results in a higher die temperature, an internal Thermal Shutdown circuit is

provided to protect the IC. When thermal shutdown is activated, typically at 165°C, the IC is forced into a low

failures from accidental device overheating. When the die temperature has reduced (typical hysteresis = 15°C)

Application Information

The following information is intended to provide guidelines for implementing the LM5033. However, final selection

of all external components is dependent on the configuration and operating characteristics of the complete power

conversion system.

The voltage applied at pin 1, normally the same as that applied to the main transformer’s primary, can be in the

Vin is close to the absolute maximum rating of the LM5033, it is recommended the circuit of Figure 13 be used to

filter transients which may occur at the input supply.

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