PT4556 non-isolated step-down LED constant current driver chip

Overview

PT4556 is a high precision non-isolated step-down LED constant current driver chip. The chip works in quasi-resonant mode and is suitable for non-isolated step-down LED constant current power supply with a full range of input voltage from 85Vac to 265Vac.

PT4556 has built-in 500V power MOS, high-voltage power supply circuit and sampling circuit, without starting resistor and VDD capacitor, the system only needs few peripheral components, which greatly saves system cost and volume.

The PT4556 adopts a high-reliability constant current control method to achieve excellent linear regulation, load regulation and temperature characteristics. The output current mass production deviation is within +/-5%.

PT4556 provides complete protection functions: including LED short-circuit protection and over-temperature drop current protection.

PT4556 is packaged in SOP-7 and other packages

Features

? Built-in 500V power tube, high stability

? No startup resistor and VDD capacitor required

? Inductor current quasi-resonant mode (QR) to reduce switching losses

? Efficiency up to 93%_? +/-3% current accuracy

? Excellent line regulation, load regulation and temperature characteristics

? LED short circuit protection

? Over temperature drop current protection

? Packages such as SOP-7

application

? LED candle light, bulb light

? LED downlights, fluorescent lamps

? Other LED lighting

Function description

PT4556 is a constant current driver chip dedicated to LED lighting, which is used in non-isolated step-down LED driver power. The chip has a built-in 500V power MOS, which can achieve excellent constant current characteristics with only a few external components. And no auxiliary winding power supply and detection is required, and the system cost is extremely low.

Startup and VDD Capacitors

After the system is powered on, the bus voltage supplies power to the internal VDD module through the HV pin. When the chip is working normally, the required VDD current is extremely low, so no auxiliary winding is required to supply power. Therefore, no external capacitor is required for VDD, which reduces peripheral components and costs.

Constant current control, output current setting

The chip detects the peak current of the inductor cycle by cycle. The CS terminal is connected to the input terminal of the internal peak current comparator and compared with the internal 387mV threshold voltage. When the CS voltage reaches the internal detection threshold, the power tube is turned off. Inductor peak current

Multiple protection functions

The PT4556 has built-in various protection functions, including LED short-circuit protection. When the LED is short-circuited, the system works at a low frequency of 2-4KHz, and the CS turn-off threshold is reduced by about half, so the power consumption is very low. Once an abnormal situation occurs, the fast detection circuit inside the chip will trigger the protection logic, and the system will immediately stop the switching operation, thereby ensuring the safe operation of the system.

Overheat protection function

PT4556 has overheat protection function. When the chip temperature exceeds 150℃, the chip will gradually reduce the output current to control the output power and temperature rise. The system will continuously detect the chip temperature. When the chip temperature drops below 140℃, the system will resume normal operation.