LM5030

SNVS215B – MAY 2004 – REVISED MARCH 2005

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DETAILED OPERATING DESCRIPTION

The LM5030 High Voltage PWM controller contains all of the features needed to implement Push-Pull and Bridge

topologies, using current-mode control in a small 10 pin package. Features included are, startup regulator, dual

mode current limit, dual alternating gate drivers, thermal shutdown, softstart and slope compensation. This high

speed IC has total propagation delays <100nS. The Functional Block Diagram of the LM5030 is shown in

Figure 2.

The LM5030 is designed for Current-Mode Control converters which require alternating outputs, such as Push-

Pull and Half/Full Bridge topologies. The features included in the LM5030 enable all of the advantages of

Current-Mode Control, line feed-forward, cycle by cycle current limit and simplified loop compensation. The

oscillator ramp is internally buffered and added to the PWM comparator input to provide slope compensation

necessary for current mode control at higher duty cycles.

High Voltage Start-Up Regulator

The LM5030 contains an internal high voltage startup regulator. The input pin (Vin) can be connected directly to

line voltages as high as 100V. The regulator output is internally current limited to 10mA. Upon power up, the

below 6.1V or if the SS/SHUTDOWN pin is pulled to ground or an over temperature condition occurs. In typical

voltage greater than 8V, effectively shutting off the internal startup regulator and saving power while reducing the

greater than 6.1V during the initial start-up. During a fault mode when the converter self bias winding is inactive,

controller. An external start-up or other bias rail can be used instead of the internal start-up regulator by

Error Amplifier

An internal high gain error amplifier is provided within the LM5030. The amplifier's non-inverting reference is tied

to 1.25V. In non-isolated applications the power converter output is connected to the VFB pin via the voltage

setting resistors and loop compensation is connected between the COMP and VFB pins.

For most isolated applications the error amplifier function is implemented on the secondary side ground. Since

the internal error amplifier is configured as an open drain output it can be disabled by connecting VFB to ground.

The internal 5K pull-up resistor, connected between the 5V reference and COMP, can be used as the pull-up for

an optocoupler or other isolation device.

PWM Comparator

The PWM comparator compares the compensated current ramp signal to the loop error voltage from the internal

error amplifier (COMP pin). This comparator is optimized for speed in order to achieve minimum discernable duty

cycles. The comparator polarity is such that zero Volts on the COMP pin will cause a zero duty cycle.

Current Limit/ Current Sense

The LM5030 contains two levels of over-current protection. If the voltage on the current sense comparator

exceeds 0.5 Volts the present cycle is terminated (cycle by cycle current limit). If the voltage on the current sense

comparator exceeds 0.625 Volts, the controller will terminate the present cycle and discharge the softstart

capacitor. A small RC filter, located near the controller, is recommended for the CS pin. An internal MOSFET

discharges the current sense filter capacitor at the conclusion of every cycle, to improve dynamic performance.

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