Large -scale power operation

""On the film"" 700V V (br) DSS power MOS

65 kHz internal oscillator

2.5V ± 2%internal benchmark [123 123 ]

Standby mode, light load

over -current and atresia

overvoltage protection

Non -dissipated built -in startup circuits

Has behind heat shutdown

Power disconnection protection (SMD packaging is limited)

The main application

Wall-mounted power supply up to 15 W

AC-DC adapter

] Auxiliary power supply:

-CRT and LCD display (blue angel)

-TV PC/server

-Fax, television, laser printer

-Household Electric/Lighting

line card, DC-DC converter

Instructions

L6590 is a single-chip switching voltage with BCD offline technology. The voltage range is widely 15W output power. The internal power switch is a horizontal power MOSFET with a typical RDS (ON) V (BR) DSS with a minimum voltage of 700V.

Electric characteristics (tj u003d -25 to 125 ° C, VCC u003d 10V; unless otherwise regulations)

]

Electric characteristics (continued)

(1) The parameters of mutual follow -up

(2) The parameter is guaranteed by the design guarantee , Non -testing in production

(3) design guarantee parameters, the function of testing in production

123]

Application information

In the following chapters, the most important internal functions of functional blocks and devices will be will describe.

The launch circuit

When the circuit is powered on for the first time, and the voltage on the large capacitor is high enough, the internal high -voltage current generator has sufficient bias, which can start running, and through the transformer at a time Winding and drain. Most currents are charged by bypass capacitors connected between pins VCC (3) and ground to increase their voltage linearly. When the VCC voltage reaches the start threshold (14.5During the typical values u200bu200bof V), after all the internal logic is reset, when the chip is started, the internal power MOSFET can be switched, and the internal high -voltage generator disconnects the connection. IC is powered by the energy stored in VCC capacitors until the self -supply circuit (usually the auxiliary winding of the transformer) generates a sufficiently high voltage to maintain it. When the integrated circuit is running, the power supply voltage generated by the self -power supply winding can be between 16 volts (overvoltage protection limit, see the relevant chapters) and 7 V, and the underwriting lock threshold. The following value device is closed (the internal activation is activated). These two thresholds tracking. The voltage on the VCC pin is limited to the safety value by the clamp circuit. Its 17V threshold tracking overvoltage protection threshold.

Power MOSFET and Gallery Drive

The power switch is implemented with horizontal N -channel MOSFET. ON) is 13 . It has a SenseFet structure that allows almost non -destructive current (only for protection). When running at the discontinuous conductive mode of the low power supply, the drain voltage is likely to be lower than the ground. The internal structure around the switch can prevent any risk of injecting the IC substrate. The grid drive of the power MOSFET is designed to minimize the co -mode EMI in the turnover and closure. Under the UVLO conditions, the internal drop -down circuit keeps the gate at a lower level to ensure that the power MOS FET will not be accidentally opened.

oscillator and PWM control

PWM adjustment is achieved by implementing voltage mode control. As shown in Figure 33, this block includes an oscillator, PWM comparator, PWM memory and error amplifier. The oscillator works at a frequency of 65 kHz internal fixation, with accuracy of ± 10%. The maximum load cycle is limited to 70%of the typical value. PWM locks (reset) are set up by the clock pulse of the oscillator, and the PWM communication distributor or overcurrent comparator reset. Error amplifier (E/A) is an operational amplifier with MOS input and AB output stage. The amplifier is to compensate the closed loop stability under the unit gain, with a small signal DC gain of 70 dB (typical) and the width of the gain bandwidth above 1 MHz. In the case of over -current, the output of the error amplifier is saturated, and the power of power MOSFET is stopped by the OCP comparator instead of the PWM comparator. Under zero load conditions, the error amplifier is close to its low saturation, and the output of the gate drive is also very short as possible, which is limited by internal delay. However, they are too long to maintain long -term energy balance. Therefore, sometimes need to skip some cycles to make the operation asynchronous. This is automatically completed by the control loop.

Spare function

The spare function is optimized for anti -exciting topology, which can automatically detect the light load of the converter and reduce the oscillatorfrequency. When the output load is accumulated and exceeds the defined threshold. This function allows minimizing power loss related to the switching frequency. The main part of the switching frequency is the main part of the loss of light load, and the advantages of higher switching frequency under heavy load are not given up. The spare function is achieved by monitoring the peak current in the power switch. If the load is very low, the threshold is not reached (80 mA typical values), and the oscillator frequency will be set to 22 kHz (typical values). When the load requires a larger power, and the current peak of the current exceeds the second threshold (190 mAh typical value), the oscillator frequency is reset to 65 kHz. This 110 mAh's stagnation can prevent the frequency change of accidents from making the peak current close to any threshold. The signal from the detection circuit is filtered by digital to avoid large or noise due to the load.

Power off protection (only L6590D)

Power off protection protection is basically a non -locking device shutdown function. It is usually used to detect power supply voltage (power off). This situation may cause the main power supply to be overheated, because it exceeds the average square current.

Another problem is that during the transformer, if the input voltage is slowly attenuated (for example, the large -capacity input capacitor) will cause Zero -order channel. The closure of the inverter can be used by L6590D to complete the voltage on the input capacitor through an internal comparator. The internal reference 2.5V of the comparison device and the voltage applied by the non -inverted input terminal available outside it is lower than the reference value, the PWM is disabled. When the voltage at the pin of the needle is higher than 2.5 volts, the PWM operation is reopened. Brownout comparator is equipped with a current stagnation ring, not a more common voltage lag: As long as the voltage that is applied at the non -inverse input end exceeds 2.5V, the internal 50 μA current generator will turn on if the voltage is lower than 2.5V. This method provides extra degrees of freedom: you can set the resistance of the outer parts by appropriately selecting the external parts, and set the open threshold and turnover threshold, which is an impossible voltage lag.

Overvoltage protection

Integrated circuit integrates an overvoltage protection (OVP), which is a load that protects the converter and the voltage feedback circuit failure. This failure can cause the output voltage to be damaged by the load and the converter itself without being handled properly. If such an incident occurs, the voltage generated by the auxiliary winding of the integrated circuit will fly up the output voltage. The internal comparator continues to monitor the VCC voltage and stops IC. If the voltage exceeds 16.5 V, the state is locked and maintained until the VCC voltage drops to the UVLO threshold. The converter will then intermittent work.

Over current protection

This device uses pulse flow restrictions for overcurrent protection (OCP) to preventExcessive internal MOSFET: Its current is monitored at the turnover time. If it exceeds a certain value, the conduction is terminated immediately. MOSFET will open again in the subsequent switching cycle. As mentioned earlier, the internal power MOSFET has a SenseFet structure: the source of some units is connected together and separated from other power supply to achieve a 1: 100 dwerry. The ""sensing"" part is connected to a ground -reference sensor with a low heating coefficient. This OCP comparator sensor is dropped through the voltage of the sensing resistance. If the voltage drops exceeds the threshold, the PWM locks are reset to close the MOSFET. In this way, the over -current threshold is set to about 0.65 A

(typical value).

When opening, due to the discharge of parasitic capacitors and the operation of the continuous transmission mode, the reverse recovery of the secondary diode will generate a larger current peak, which may accidentally trigger the OCP comparator Essence In order to increase the antidity, the output of the OCP comparator is shielded by a short time (about 120 nan seconds) after the MOSFET is connected, and any interference in the gap will be suppressed (the guide edge is faint).

heat shutdown

Avoid the equipment that is too hot to shut down due to excessive power or insufficient heat dissipation. The thermoser monitoring power near MOSFET and the knot temperature near MOSFET. When the temperature exceeds 150 ° C (minimum value), alarm signal is set to stop the operation of the device. This is a non -locking function. When the temperature drops about 40 ° C, the power MOSFET is reopened.