AN9922B LED Driver IC应用说明书,可用于LED灯照明行业

AN9922B,福建安特LED 驱动器产品(100MA)

15.06.2010 1Revision 1.0

AN9922B,福建安特LED 驱动器产品(100MA)

Functional Block Diagram

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AN9922B,福建安特LED 驱动器产品(100MA)

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AN9922B,福建安特LED 驱动器产品(100MA)

Absolute Maximum Ratings

Parameter

Operating temperature rangePower dissipation (SOT89)Operating voltage on D output with regard to GND (Vd)

-0.5Min-40

Typ25

Max701300550

Units°СmWV

Area = 1570 x 1600 ScribeLine = 100

Area with SL= 1670 x1700

PadSize

Coordinate

DRAIN (100 x 210)(1352,6; 1220,3)CU (100 x 100)(122,1; 277,0)

VSS (100 x 160)(130,6; 677,0)VSS1 (100 x 100)(1446,6; 787,5)Diameter of wafer: 150 mm

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AN9922B,福建安特LED 驱动器产品(100MA)

Inductor choice

In AN9921/22/23 ICs output peak current (Ith) is controlled. Hence output current of the

driver circuit can be calculated as

Io=Ith-(ΔIo/2) , (1)

where ripple current

ΔIo=(Vo Toff)/L1 , (2)

where Vo – voltage drop of on the converter load (strictly depends on the number of LED diodes in string), Toff- specified off time, L1 – inductor value.

In this approach to get output current close to Ith it is necessary to reduce ΔIo and hence

with fixed Vo and Toff to enlarge L1 value. In typical applications inductor value in this case ranges from 60 to 120mH for 20mA current.

In the B modifications (AN9922B) internally implies that ripple current is not small value

and in wafer test condition is controlled not a peak current Ith but an average output current Io. Value of tuned average output current is set to specified Iom, at fixed condition of Vo=Vom and L1=L1m. Tuning of Iom is fulfilled with tuning of Ith and after tuning Ith will be set to some unspecified but constant for given chip value Ithm. Combining (1) and (2) we get

Iom=Ithm-Vom Toff/(2 L1m) . (3)

It should be noted that during tuning influence of variations of Toff time is compensated

through Ithm tuning. So to get nominal output current for given voltage drop Vo on LED string it is necessary to choose inductor value L1 to keep ratio

Vo/L1=Vom/L1m =2(Ithm-Iom)/Toff=1/Ko. (4)

To calculate necessary inductance in this case one should use next expression

L1=Ko Vo (6).

It should be noted, that for “B” modifications Ko factor is equal to 4.5e-4 H/V. In the

“B” series to keep small ripple of LED string current it is necessary to keep shunt capacitor Co large enough (in order of 0.1uF or large).

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AN9922B,福建安特LED 驱动器产品(100MA)

Demo board

Schematic diagram and printed board of 100mA LED driver based on AN9922B is presented

below. L2 value is chosen for LED string with voltage drop about 50V (16LEDS).

15.06.2010

6Revision 1.0