SP6648EU-L Datasheet, PDF (25/34 Pages) Sipex Corporation – Ultra-low Quiescent Current, High Efficiency Boost Regulator

USING THE EVALUATION BOARD
1) Powering Up the SP6648 Circuit
The SP6648 Evaluation Board can be powered from inputs from a +0.95V to +3.3V from 1 or 2
alkaline cells. Connect with short leads directly to the “Vbatt” and “Gnd” posts. Monitor the
Output Voltage and connect the Load between the “Vout” post and the 2^nd “GND” post.
2) Using the J1 Jumper: Enabling the SP6648 Output and using the Shutdown Mode
The SP6648 output will be Enabled if the J1 Jumper is in the top or pin 1 to 2 position. If J1 is
in the pin 2 to 3 position, the Shutdown pin is brought to GND, which puts the SP6648 in the low
quiescent Shutdown 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 = 1400/R_LIM
The SP6648 datasheet specifications for RLIM give a range of 1750 to 4000 ohms. Using the
IPEAK equation above gives an IPEAK range of
I_PEAK range = 350 to 800mA.
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 SP6648 evaluation board uses a Rlim value of 1.87K for an Ipeak = 750mA to
allow the circuit to deliver up to 180mA for 1.3V input and 400mA for 2.6V input. Other values
could be selected using the above relationships.
4) Using the LBON - Low Battery Output Function
The Low Battery Output function, LBON, is programmed externally by the R3 and R4 resistor
divider connected between Vbatt, the LBI input pin and GND. The LBON is an open drain
output, which is active low and is pulled up by a 1M resistor R5 to Vout. When the LBI
comparator falling threshold of 0.625V is reached, the LBON output goes low as determined by
the relationship:
LBON falling = Vbatt*R4/(R3 +R4)
The SP6648 evaluation board R3 & R4 resistors have been set to trip for a falling battery
threshold of about 2.0V. Using this relationship, other low battery threshold values can be set
by the user.