DP9502AB datasheet(7/10 Pages) DEPUW

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Peng Jijun

13326967551 translated to English by Yevhen Stadnik 380972333363

DP950XB

Non-Isolated, Step-Down Quasi-Resonant LED Power Switch

Functional Description

The DP950XB series is a highly integrated constant

current LED power switch. The chip adopts a

quasi-resonant working mode and does not require an

auxiliary winding to detect demagnetization. The chip

also integrates a 500V power switch and a high-voltage

self-powered circuit. Only a few peripheral devices are

required to achieve excellent constant current

characteristics, and the system cost is extremely low.

□

Power by HVDD

DP950XB integrates a 650V high-voltage power supply

circuit. The gate drive of the power MOSFET is directly

no external VDD capacitor is required.

□

Constant current control

The DP950XB series samples the inductor current cycle

by cycle. When the inductor current reaches the current

comparator threshold voltage (VCS_max=600mV), the

power MOSFET is immediately turned off and the

inductor enters the demagnetization state. When the

inductor current demagnetization is completed, the next

cycle is started. The system works in the inductor current

critical mode, so the output constant current value is

determined by the following formula:

1 Vcs(max)

300mV

□

Degaussing detection

DP950XB uses an internal integrated demagnetization

detection circuit, which does not require an auxiliary

winding and greatly reduces system cost.

□

Maximum and minimum shutdown time

When the power MOSFET is turned off, the DP950XB

is designed with a typical minimum off time limit of

1us to avoid interference. At the same time, the typical

maximum off time inside the chip is designed to be 270us.

□

Output Overvoltage Protection (OVP)

The DP950XB output overvoltage protection can be

adjusted through the resistor (ROVP) between the ROVP

pin and the ground. The chip flows out IROVP=40uA current

at the ROVP pin, which generates a voltage VROVP IROVP

ROVP on the ROVP resistor. At the same time, the chip

samples the CS peak voltage VCS_PK. VROVP and VCS_PK

work together to generate an overvoltage protection

time Tovp in each cycle. When the output is open, the

output voltage will increase and the inductor

demagnetization time Tdem will decrease. When Tdem is

less than Tovp, the system will trigger the output OVP

protection and enter the automatic restart state until the

output is restored. The system will work normally.

CC_OUT

Where:

Rcs - The setup resistor connected between the

CS pin and the GND pin.

□

Current sampling and leading edge blanking

At each moment when the power MOSFET is turned on,

the voltage across the sampling resistor is compared

with the internal overcurrent comparator to control the

output current. However, at the moment when the

MOSFET is turned on, a voltage spike caused by the

parasitic capacitance of the MOSFET and the reverse

recovery current of the freewheeling diode will also be

generated. In order to avoid the wrong shutdown of the

drive signal, the chip is designed with a leading edge

blanking time. During this time (typical value 500ns),

the internal PWM comparator stops working to ensure

that the drive signal is stably turned on.

During the shutdown process or when the input voltage

is very low, the system will encounter the maximum on

time, and VCS_PK and Tovp will decrease proportionally,

which can avoid the false triggering of the output

overvoltage protection. In a non-isolated buck system,

the inductor demagnetization voltage is the output voltage.

Therefore, the demagnetization time Tdem during

overvoltage protection satisfies the following equation:

CS_PK

Where:

dem

ovp

OVP

VCS_PK is the current peak sampling voltage,

which is the overcurrent comparator reference

voltage (600mV) during normal operation.

VOVP is the overvoltage protection voltage value

DP9502AB Datasheet(PDF) 7 Page - Shenzhen Developer Microelectronics Co., Ltd

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