2
USING THE EVALUATION BOARD
1) Powering Up the SP7648 Circuit
The SP7648 Evaluation Board can be powered from inputs from +2.7V to +4.2V from a Li-Ion
battery. Connect with short leads directly to the “Vbatt” and “Gnd” posts. Monitor the Output,
Vref Voltage and connect the LED between the “Vout” post and the “Vref” post.
2) Using the SW1 switch and the J3 Jumper: Enabling the SP7648 Output and using the
Shutdown Mode
Pressing the ON/OFF button (SW1) will put the SHDN pin to VIN, which enables the SP7648.
Otherwise the 1M R5 pull-down puts 0V to the SHDN pin and puts the SP7648 in the low
quiescent Shutdown Mode. The SP7648 output will be in FLASH mode if the J3 Jumper is in the
top or pin 1 to 2 position. If J3 is in the pin 2 to 3 position, the SP7648 will be in the Torch
mode.
3) Using the Rlim Function
The peak inductor current, I
PEAK
, is programmed externally by the
RLIM resistor connected
between the RLIM pin and GND. The peak inductor current is defined by:
I
PEAK
= 1600/R
LIM
The SP7648 has a range for RLIM of 1.0K to 9.09K ohms. Using the IPEAK equation above
gives an IPEAK range of
I
PEAK
range = 176mA to 1600mA.
The saturation current specified for the inductor needs to be greater then the peak current to
avoid saturating the inductor, which would result in a loss in efficiency and could damage the
inductor. The SP7648 evaluation board uses an Rlim value of 1.0K for an Ipeak = 1600mA to
allow the circuit to deliver 700mA for 3.6V input. Other values could be selected using the
above relationships.
