LP3936 datasheet(21/30 Pages) TI1

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WLED VOLTAGE (V)

Set value = FFh

Set value = 80h

Set value = 40h

-40

°C

+85

°C

LP3936

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SNVS259D – NOVEMBER 2003 – REVISED MAY 2013

WLED Current Adjustment

WLED[7:0]

WLED Current (Typical)

Units

0000 0000

0000 0001

0.1

0000 0010

0.2

0000 0011

0.3

•

1111 1101

25.3

1111 1110

25.4

1111 1111

25.5

Figure 26. WLED Output Current vs Voltage

Temperatures

−40°C, +25°C, +85°C

Recommended External Components

OUTPUT CAPACITOR, COUT

The output capacitor COUT directly affects the magnitude of the output ripple voltage. In general, the higher the

value of COUT, the lower the output ripple magnitude. Multilayer ceramic capacitors with low ESR are the best

choice. At the lighter loads, the low ESR ceramics offer a much lower VOUT ripple than the higher ESR tantalums

of the same value. At the higher loads, the ceramics offer a slightly lower VOUT ripple magnitude than the

tantalums of the same value. However, the dv/dt of the VOUT ripple with the ceramics is much lower than the

tantalums under all load conditions. Capacitor voltage rating must be sufficient, 10V is recommended. It should

be noted that with some capacitor types the actual capacitance depends heavily on the capacitor DC voltage

bias.

INPUT CAPACITOR, CIN

The input capacitor CIN directly affects the magnitude of the input ripple voltage and to a lesser degree the VOUT

ripple. A higher value CIN will give a lower VIN ripple. Capacitor voltage rating must be sufficient, 10V is

recommended.

OUTPUT DIODE, DOUT

A Schottky diode should be used for the output diode. To maintain high efficiency the average current rating of

the schottky diode should be larger than the peak inductor current (1A). Schottky diodes with a low forward drop

and fast switching speeds are ideal for increasing efficiency in portable applications. Choose a reverse

breakdown of the schottky diode larger than the output voltage. Do not use ordinary rectifier diodes, since slow

switching speeds and long recovery times cause the efficiency and the load regulation to suffer.

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