4

Rev.1.1

6 -

■Application notes

1) Setting peak current with external resistor Rs

ELM915BA uses open loop peak current mode driver with internal power switch; peak current is determined

by the value of Rs which is connected between CS and GND.

Ipk = 0.25/Rs (A)

2) Setting constant off time period Toff

RT is used to set the fixed off time of internal NMOS switch . The fixed off time is determined by the value of

the resistor which is connected to RT and GND. The connection between Rt and ToffIt is shown as following

chart. When RT is set to be 100kΩ, Toff becomes 700ns.

0.1

1

10

10

100

1000

Toff-Rt characteristic

Toff (�S)

3) Dimming function

ELM915BA provides two types of dimming function: linear dimming and PWM one. Linear dimming activates

when DC voltage added to LD/PWM is within the range from 0.25V to 2.5V; the luminance would be 0% under

0.25V, and 100% under 2.5V. For PWM dimming function, ELM915BA is able to adjust the luminance by

digital signal when voltage of LD/PWM is under 0.25V.

0

5

T

LD/PWM(V)

PWM

0

0.5

1

1.5

2

2.5

3

0

20

40

60

80

100

120

LD/PWM-Luminance

LD/PWM (V)