PR4402 datasheet(7/12 Pages) PREMA

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LED Driver PR4401 / PR4402

Application Notes

TYPICAL BATTERY LIFE TIME

Battery

Lifetime

L1 = 22 µH

LED mean

current 12 mA

Battery

L1 = 10 µH

LED mean

current 23 mA

AA (Mignon,

LR 6/AM-3)

55 h

27 h

AAA (Micro,

LR 03/AM-4)

22 h

8 h

Conditions: one white LED connected, measured with

single 1.5 V TDK Alkaline battery.

Battery lifetime depends on battery capacity and

operating conditions. Therefore the times indicated

here can only give a rough indication of achievable

times.

USING DIFFERENT BATTERY TYPES

The input voltage must be 1.9 V at maximum. At

higher voltages the circuit may not trigger and

start up correctly. Therefore operation with one

Alkaline, NiCd, or NiMH cell (AA or AAA type) is

recommended.

Alkaline button cells can also be used for

supply. However, since high peak currents are

drawn from the battery, button cells are

recommended only with inductors of 22 µH or

more, depending on the battery type. A

capacitor at the supply pins of PR4401 may also

improve performance with button cells.

Lithium batteries are not suitable due to their

higher voltage.

CONNECTING SEVERAL LEDs IN PARALLEL

When several LEDs are connected in parallel, it

is necessary to match the forward voltage of

these LEDs, to achieve a uniform brightness.

The total current of all LEDs together

corresponds approximately to the mean output

current for operation with one LED.

Vcc

Gnd

Vout

PR4402

Vbat = 1.2 V

or 1.5 V

L1 = 4.7 µH

Matching

White LEDs

470 nF

Vcc

Gnd

Vout

PR4401/02

Vbat = 1.2 V

or 1.5 V

White

LED

OPERATION OF LEDs WITH SMOOTHED CURRENT

(RECTIFIER)

With a diode (preferably a Schottky diode) and a

smoothing capacitor the voltage at the LED can

be buffered if necessary. The capacitance must

be small enough so that the voltage at the

capacitor will exceed a voltage of 2.5 V in the

first cycle, otherwise the circuit may not start

up.

In most cases, values between 100 nF and

1 µF are appropriate. Due to different load

characteristics, output current and efficiency

are typically higher than without capacitor,

especially in the high-current range.

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