2

USING THE EVALUATION BOARD

1) Powering Up the SP6683 Circuit

The SP6683 Evaluation Board can be

powered from inputs from a +2.7V to +5.5V

battery or a power supply. Connect with

short leads directly to the “VIN” and “GND”

posts.

2) Using the evaluation board

The Evaluation Board was set up for a 4

15mA LED application even though there

are 6 LED spots on the board. The output of

SP6683 was open as default. If the

customer has discrete white LEDs, then the

discrete white LEDs should be soldered to

the D1-D6 positions and bias resistors

should be soldered to the R4-R9 positions.

Selection of the bias resistors please refers

to 3).

If the customer has white LED

module, they can plug the two terminals of

the module to the “VOUT” and “Vfb” posts,

and use R4 as the bias current to regulate

the total current. The value of the bias

resistor could be calculated by equation (1).

3) Selecting the Bias Resistor

The bias resistor could be estimated by (1)

Ω

=

=

=

5

60

3

.

0

_

mA

V

I

V

R

Total

LED

FB

Total

(1)

Ω

=

=

=

−

−

20

15

3

.

0

6

1

_

9

4

mA

V

I

V

R

D

LED

FB

(2)

D1-D6.

SP6683 can automatically change from X1

mode to X1.5 mode for highest efficiency.

To use this feature, divider resistors should

be chosen according to the specific

application. The guideline for divider resistor

selections is as follows. For high input

voltage, the SP6683 will work in X1 mode,

voltage, it will switch to X1.5 mode

mode change can be calculated by (3)

()

out

LED

F

th

R

I

m

V

V

⋅

⋅

+

+

=

3

.

0

(3)

output resistance of the SP6683.

)

R

R

1

(

V

25

.

1

V

2

1

th

+

⋅

=

(4)

which can be expressed as R1:

(

)

2

th

1

R

1

25

.

1

V

R

⋅

−

=

(5)

For the typical Sp6683 Evaluation Board,

5) Selecting of Capacitors

Ceramic capacitors are used on the

evaluation board due to their inherently low

ESR, which will help produce low peak to

peak output ripple, and reduce high

frequency spikes.

Selection of the flying capacitor is a trade-off

between the output voltage ripple and the

output current capability. Decreasing the

flying capacitor will reduce the output

voltage ripple because less charge will be

delivered to the output capacitor. However,

smaller flying capacitor leads to larger

output resistance, thus decrease the output

current capability and the circuit efficiency.

In the evaluation board, the input, output

and flying capacitors are selected as 1uF

ceramic capacitors. Input and output ripple

could be further reduced by using larger low

ESR input and output capacitor.

6) Brightness Control

Obvious dimming control could be achieved

by applying a PWM control signal to the

ENABLE/PWM pin. The brightness of the

white LEDs is controlled by increasing and

decreasing the duty cycle of The PWM

signal. The recommend frequency range of

the PWM signal is from 60Hz to 700Hz. A

repetition rate of at least 60Hz is required to

prevent flicker.