WS9931EP datasheet(4/6 Pages) ETC2

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WS9931 Product Description

WINSEMI MICROELECTRONICS

Application Information

The WS9931 is an adaptive linear current regulator to

eliminate LED low frequency ripple current. It adopts adaptive

control method and integrates MOS and current sense resistor

to eliminate ripple current without additional electrical design.

The maximum output current of the WS9931 can be up to

300mA, and the value of

VOVP-VO_MIN should be less than 60V.

Theory of Current Ripple Removing

The WS9931 acquires the sense voltage signal through

sampling the output currents signal of the load, and makes the

signals filter. Then it magnifies the error between sense voltage

signals and filter voltage signals, and outputs the signal of error

compensation to regulate output current signals. The WS9931

drives MOSFET to transfer the LED ripple current to voltage

ripple on MOSFET, and ensures the constant voltage across

LED string and the current flow through LED string, thus

eliminating ripple current.

Start Up

The WS9931 integrates soft-start function and is supplied

by the preceding stage system. When

VVIN rises up over 5V, the

WS9931 starts to work. At first, it has 350ms blanking time

without current filter function to build up stable reference

internally. Then the LED ripple current is decreased by WS9931

gradually.

The typical value of the startup current is 500uA, and

the start-up resistor can be calculated by the equation:

TYP

VIN

MAX

500









Where,

Vo is the load voltage in practical application;

VIN_MAX is the maximum clamp voltage, about 5.2V;

IVIN_TYP is the operating current, about 500uA.

Over Thermal Protection

The WS9931 has temperature regulator control. When

the temperature goes to 120 ℃ , the temperature

compensation is turned on to increase LED current ripple

and reduce the maximum voltage of LEDN. When the

temperature goes to 135 ℃ , over temperature protection

starts, and the MOSFET will be in On-State all the time

without suppresses function.

PCB Layouts

The following advices should be followed in WS9931

PCB layout:

IC Layout ： The IC should be away from heating

devices, such as driver MOSFET, freewheeling diodes,

inductor and so on.

LEDN Pin：To increase the copper area of LEDN pin or

to connect to other NC pins for better thermal dissipation.

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