SP7615 Evaluation Board Manual

Aug 24,2006

2

Figure 2. SP7615 Evaluation board with four LED

with matched currents

Capacitor C1 is a decoupling capacitor. Resistor R2 is used to turn device on at power on. The SP7615 has internal

pull down resistor at EN input and will be in the Sleep Mode if EN pin isn’t connected to Vin voltage. If EN pin isn’t

used for modulation, it may be connected to Vin voltage directly.

USING THE EVALUATION BOARD

1) Powering Up the SP7615 Circuit

The SP7615 Evaluation Board can be powered from a 4.5V power supply or from 3 alkaline cells. Connect 4.5V

source pin with short lead directly to the “Vin” and -4.5V /GND pin to the “GND” posts.

2) Selecting the Bias Resistor

LED current can be adjusted up to 125mA per string with an external resistor R1. The R1 value may be determined

3) Dimming

The device has an enable function that is designed for TTL level inputs. This input will also track the VCC pin so

levels up to VCC are acceptable. The enable pin can also be used to control the LED brightness with a pulse width

modulated control signal. Duty Cycle or PWM control of the LED current maintains constant LED color while

brightness is changing. The SP7615 responds in less than 10µs to PWM signals applied to this pin. To change LED

brightness apply 70Hz – 1kHz PWM rectangle pulse TTL level to EN post in respect to GND. Logic one turns the

device on and logic zero turns it off.

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

2.5

3

3.5

4

4.5

5

5.5

Vin Voltage, V

Vdiode_f

Vcat

Iin x100mA

Idiode x100mA

Iquies x100mA

Graph 1. LED Forward Voltage (Vdiode_f), LED cathode voltage (Vcat), Evaluation Board Input Current (Iin), sum

of LED Currents (Idiode), and Quiescent Current (Iquies) vs. Input Voltage at R1 = 10k