Sept12-06

SP7651 Evaluation Manual

©2006 Sipex Corporation

Page 2 of 8

USING THE EVALUATION BOARD

1) Powering Up the SP7651EB Circuit

Connect the SP7651 Evaluation Board with an external +12V power supply. Connect

with short leads and large diameter wire directly to the “VIN” and “GND” posts. Connect

a Load between the VOUT and GND2 posts, again using short leads with large

diameter wire to minimize inductance and voltage drops.

2) Measuring Output Load Characteristics

GND collar touching the GND side of C3 using short wrapped wire around the collar –

avoid a GND lead on the scope which will increase noise pickup.

3) Using the Evaluation Board with Different Output Voltages

While the SP7651 Evaluation Board has been tested and delivered with the output set

to 3.30V, by simply changing one resistor, R2, the SP7651 can be set to other output

voltages. The relationship in the following formula is based on a voltage divider from the

Standard 1% metal film resistors of surface mount size 0603 are recommended.

Furthermore, one could select the value of the R1 & R2 combination to meet the exact

output voltage setting by restricting R1 resistance range such that 50KΩ ≤ R1 ≤ 100KΩ

for overall system loop stability.

Note that since the SP7651 Evaluation Board design was optimized for 12V down

conversion to 3.30V, changes of output voltage and/or input voltage will alter

performance from the data given in the Power Supply Data section. In addition, the

POWER SUPPLY DATA

The SP7651ER is designed with a very accurate 1.0% reference over line, load and

temperature. Figure 1 data shows a typical SP7655 Evaluation Board Efficiency plot,

with efficiencies to 87% (including generation of 5V Vcc) and output currents to 3A.

SP7651ER Load Regulation is shown in Figure 2 to have only 0.5% change in output

voltage from 0.5A load to 3A load. Figures 3 and 4 illustrate a 1.5A to 3A and 0A to 3A

Load Step. Start-up Responses in Figures 5, 6 and 7 show a controlled start-up with

different output load behavior when power is applied where the input current rises

smoothly as the Softstart ramp increases. In Figure 8 the SP7651ER is configured for

hiccup mode in response to an output dead short circuit condition and will Soft-start until

the over-load is removed. Figure 9 and 10 show output voltage ripple less than 25mV at

no load to 3A load.

While data on individual power supply boards may vary, the capability of the SP7651ER

of achieving high accuracy over a range of load conditions shown here is quite

impressive and desirable for accurate power supply design.