Datasheet

LM5030
SNVS215C –APRIL 2003–REVISED MARCH 2013 www.ti.com
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
regulator is enabled and sources current into an external capacitor connected to the V
CC
pin. The recommended
capacitance range for the V
CC
regulator is 0.1µF to 50µF. When the voltage on the V
CC
pin reaches the
regulation point of 7.7V, the controller outputs are enabled. The outputs will remain enabled unless, V
CC
falls
below 6.1V or if the SS/SHUTDOWN pin is pulled to ground or an over temperature condition occurs. In typical
applications, an auxiliary transformer winding is diode connected to the V
CC
pin. This winding raises the V
CC
voltage greater than 8V, effectively shutting off the internal startup regulator and saving power while reducing the
controller dissipation. The external V
CC
capacitor must be sized such that the self-bias will maintain a V
CC
voltage
greater than 6.1V during the initial start-up. During a fault mode when the converter self bias winding is inactive,
external current draw on the V
CC
line should be limited as to not exceed the maximum power dissipation of the
controller. An external start-up or other bias rail can be used instead of the internal start-up regulator by
connecting the V
CC
and the Vin pins and feeding the external bias voltage (8 - 15V) to that node.
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.
8 Submit Documentation Feedback Copyright © 2003–2013, Texas Instruments Incorporated
Product Folder Links: LM5030