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LM5030 Datasheet(PDF) 7 Page - National Semiconductor (TI) |
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LM5030 Datasheet(HTML) 7 Page - National Semiconductor (TI) |
7 / 11 page Typical Performance Characteristics Unless otherwise specified: T J = 25˚C. (Continued) Feedback Amplifier Gainphase 20058115 Detailed Operating Description The LM5030 High Voltage PWM controller contains all of the features needed to implement Push-Pull and Bridge topolo- gies, 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, soft- start and slope compensation. This high speed IC has total propagation delays <100nS. The Functional Block Diagram of the LM5030 is shown in Figure 1. The LM5030 is designed for Current-Mode Control convert- ers 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 Con- trol, line feed-forward, cycle by cycle current limit and sim- plified 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 regu- lator. 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 con- nected 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 control- ler 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 VCC voltage greater than 8V, effectively shutting off the internal startup regulator and saving power while reducing the con- troller 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 out- put 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 inter- nal 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 ex- ceeds 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 dy- namic performance. The LM5030 CS and PWM comparators are very fast, and as such will respond to short duration noise pulses. Layout considerations are critical for the current sense filter and sense resistor. The capacitor associated with the CS filter must be placed very close to the device and connected directly to the pins of the IC (CS and RTN). Also if a current sense transformer is used, both leads of the transformer secondary should be routed to the sense resistor, which should also be located close to the IC. If a current sense resistor located in the drive transistor sources is used, for current sense, a low inductance resistor should be chosen. www.national.com 7 |
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