USING THE EVALUATION BOARD

1) Powering Up the SP6648LED Circuit

The SP6648LED Evaluation Board can be powered from inputs from a +1.8V to +3.2V power

supply or from 2 alkaline cells. Connect with short leads directly to the “VIN” and “GND” posts.

Plug the 1W LumiLED between the “VOUT” and “REF” posts. Unlike other boost regulators, the

part has self-protection feature. It will not be damaged when the output is open as long as there

is a low resistance from FB to GND. As shown in Figures 1 and 2, if the board is powered up

before the LumiLED is plugged in, the circuit will bring the Feedback pin to 0V and the SP6648

has a feature to set the output voltage to be 3.3V. Once the LumiLED is plugged in, the

Feedback pin will go up to 1.25V and begin to regulate. The output voltage will go from 3.3V to

LumiLED. When the LumiLED is open, the Feedback pin voltage will go to 0V and the output

voltage will go to 3.3V which will protect the part (as shown in Fig 2).

Fig 1. Plug in the LumiLED

Fig. 2. Unplug the LumiLED

2) Using the J1 Jumper: Enabling the SP6648 Output and using the Shutdown Mode

The SP6648 output will be enabled if the J1 Jumper is in the top or pin 1 to 2 position. If J1 is in

the pin 2 to 3 position, the Shutdown pin is brought to GND, which puts the SP6648 in the low

quiescent Shutdown Mode.

3) Selecting the Bias Resistor

In the white LEDs application, the SP6648 is generally programmed as a current source. The

bias resistor is used to set the operating current of the white LED as equation

F

REF

b

I

V

R

=

4) Vout Programming

The SP6648 can be programmed as either a voltage source or a current source. To program the

output voltage. To set Vout in the voltage mode, use the equation:

7

out

6

R

1

61

.

0

V

R

•













−

=