SP7686 datasheet(13/16 Pages) SIPEX

13 / 16 page

Jul16-07 RevP

SP7686: 500mA LED Driver



2007 Sipex Corporation

- 13 -

Part Reference

Value

Tolerance

Size

Manufacturers

RSENSE

0.22ohms

1% or 5%

0603

Panasonic or Vishay

RSENSE

0.27ohms

1% or 5%

0603

Panasonic or Vishay

RSENSE

0.33ohms

1% or 5%

0603

Panasonic or Vishay

RSENSE

0.39ohms

1% or 5%

0603

Panasonic or Vishay

RSENSE

0.47ohms

1% or 5%

0603

Panasonic or Vishay

RSENSE

0.56ohms

1% or 5%

0603

Panasonic or Vishay

RSENSE

0.68ohms

1% or 5%

0603

Panasonic or Vishay

Table 2. Resistor Selection

Resistor Selection for SP7686

The SP7686 part uses an internal 5 bit DAC to set the

LED current. The DAC input is at the CTRL pin. The

user inputs a pulse train of up to 1MHz to set the LED

current. The DAC sets the feedback voltage point from

60mV to 360mV in 10mV steps. The LED current is

determined by the equation:

ILED = VFB/RSENSE

The curves below show the feedback and LED currents

for the CTRL pin pulse count and standard RSENSE

resistor values.

After the desired count is reached the CTRL input must

remain high to hold the count. If the CTRL pin goes low

for more than 200µs the part will shutdown. See the

timing

diagrams

the

Typical

Performance

Characteristics. The first pulse turns on the SP7686. The

first pulse needs to occur at least 600µsec after VIN is

applied in order to activate after the power on reset

(POR). The second pulse resets the DAC to 0. The

timing between the first and second pulse needs to be

25µsec typical to as long as 75µsec. After the second

pulse the feedback voltage remains at ground. The third

pulse sets the feedback voltage to 60mV. Subsequent

pulses set the feedback voltage in 10mV steps as shown

in the Typical Performance Characteristics.

APPLICATION INFORMATION

(Continued)

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