SP6682EU datasheet(2/5 Pages) SIPEX

2 / 5 page

USING THE EVALUATION BOARD

1) Powering Up the SP6682 Circuit

The SP6682 Evaluation Board can

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 Jumpers and posts

There are two jumpers (J1 and J2) and

seven posts on the Evaluation Board. The

output of SP6682 is open as the default. If

the customer has discrete white LEDs, the

5.1 ohm “RFB” resistor needs to be removed

from the board first. Then the discrete white

LEDs should be soldered to the D1-D4

positions and bias resistors should be

soldered to the R6-R9 positions. For

selection of the bias resistors, please refer

to 3).

If the customer has a white LED

module, they can plug the two terminals of

the module to the “LEDA” and “LEDK” posts.

Note that a 5.1ohm bias resistor was put on

the “RFB” position to regulate a 60mA

output current as the default. If the output

current is not 60mA in the customer’s

application, an appropriate bias resistor

should be selected to replace the 5.1ohm

resistor. 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

Total

LED

(1)

Where ILED_Total is the total output current.

Ω

−

LED

(2)

Where ILED_D1-D4 is the operating current of

D1-D4.

4) Selecting of Vmode and Divider Resistor

SP6682 can automatically change from X1.5

mode to X2 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

SP6682 will work in X1.5 mode, when the

input voltage drops to Vth threshold voltage,

it will switch to X2 mode automatically. The

Vth threshold voltage for mode change can

be calculated by (3)

() 5.

out

LED

⋅

(3)

Where VF and m are the forward voltage

and number of the white LEDs, Rout is the

output resistance of the SP6682.

The equation for the voltage divider R1 and

R2 with Vmode=1.25V is:

)

(

⋅

(4)

which can be expressed as R1:

()

⋅

−

(5)

For the typical Sp6682 Evaluation Board,

using

VF =3.6V, m=4, ILED =15mA,

Rout=16ohms, the Vth will be 3.24V. Select

R2=100kohm, then R1=158kohm.

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 2.2uF

ceramic capacitors. Input and output ripple

could be further reduced by using larger low

ESR input and output capacitor.

6) Brightness Control

Dimming control can 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 recommended frequency range

of the PWM signal is from 60Hz to 200Hz. A

repetition rate of at least 60Hz is required to

prevent flicker.

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