SP7616EB datasheet(2/4 Pages) SIPEX

2 / 4 page

USING THE EVALUATION BOARD

1) Vin requirements and PWM pin

The user of the SP7616 will need to supply Vin and an PWM signal that is active high. The

PWM pin signal is a logic level signal and should range between 0 an 5V. The threshold is 2.4V

for a logic high.

2) Setting the LED current

The LED current is set through the Iset resistor. The SP7616 provides an internal reference

voltage that is set to 1V at the ISETPin (Pin3). RSET is then determined by using equation 1.

R2 = VISET*IMULT/ILED (kΩ),

(1)

Where

VISET is the internal reference (1V)

IMULT Current Multiplication Ratio

ILED is the desired Led current.

In example 1: For a 20mA LED current, the current set resistor should be

R2=1V*920/20mA (kΩ),

R2=46K

3) LED dimming

PWM dimming

The LED dimming control is done through the PWM pin. The acceptable frequency range of this

signal is 100Hz to 5 kHz. The acceptable duty cycle range of the signal is 10% to 90% at 1KHZ.

When the PWM pin is driven low, only the LED current sources are disabled while the rest of the

chip is still enabled. .

Analog dimming control

Besides digital PWM control, the LED current can be controlled continuously (from high to low

LED current) by raising the voltage at the bottom of RSET from 0V to 1V maximum. RSET value

may be determined from equation 1. Equation 2 shows the effect of using a VMOD in the circuit

on the Led current

ILED = (1V – VMOD)*IMULT/RSET mA

(2)

Where

typical ISET pin voltage

IMULT Current Multiplication Ratio

ILED is the desired Led current.

VMOD is the adjustment voltage

VMOD is an adjustment voltage applied to the bottom side of R2, 920 is a typical current

multiplication ratio IMULT, and ILED is a required LED current in mA/channel. Figure 2 shows the

location of the external VMOD source.

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