2

USING THE EVALUATION BOARD

1) Powering Up the SP6644/6645 Circuit

The SP6644/6645 Evaluation Board can be powered from inputs from a +0.8V to +3.3V from 1

or 2 alkaline cells or a power supply. Connect with short leads directly to the “Vbatt” and “Gnd”

“GND” post.

2) Using the J1 Jumper: Enabling the SP6644/6645 Output and using the Shutdown Mode

The SP6644/6645 output will be Enabled if the J1 Jumper is in the left 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

SP6644/6645 in the low quiescent Shutdown Mode.

3) Using the LDO Output

The SP6644/6645 output connects to an LDO, the SP6201 ultra low drop-out CMOS regulator

which has a 3.0V output at up to 150mA. To evaluate the SP6201 performance with the

SP6644/6645 input, connect the load across the +3V post and GND and measure both the

SP6644/6645 output and SP6201 output with an oscilloscope configured for AC millivolts. As

you can see from figure 8 the output ripple voltage is reduced from 60mV to less than 3mV by

the LDO.

4) Using the Rlim Function

between the RLIM pin and GND. The peak inductor current is defined by:

The SP6644/45 datasheet specifications for RLIM give a range of 2.5 to 9.3K ohms. Using the

IPEAK equation above gives an IPEAK range of

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 SP6644/6645 evaluation board uses a Rlim value of 2.5K to allow the circuit to

deliver up to 80mA for 1.3V input and 150mA for 2.6V input. Other values could be selected

using the above relationships.

POWER SUPPLY DATA

The SP6644/6645’s high efficiency is illustrated in figures 1 & 2 which has 90 to 93% efficiency

for 2 fully charged alkaline cells. Figure 1 with Rlim of 2.5K can deliver more output current than

figure 2 with an Rlim of 5K because it has greater peak current, at a price of reduced efficiency.

Line/Load curves in figures 3 & 4 show only 10 to 15mV change in output voltage at rated loads

of 80mA for 1-cell and 150mA for 2-cell. The no-load battery current the SP6644/6645

application circuit consumes for different Rlim’s of 2.5K & 5K is illustrated in figure 5. In figure 6

the maximum load current the SP6644/6645 can deliver for different Rlim’s of 2.5K & 5K is

illustrated. Load transient response to a 15mA to 150mA output load step is shown in figure 7.

Finally, in figure 8, SP6644 output ripple of 60mV is improved with the addition of the SP6201

LDO achieving an output ripple of only 3mV.