2

USING THE EVALUATION BOARD

1) Powering Up the SP7650EB Circuit

Connect the SP7650 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

It’s best to GND reference scope and digital meters using the Star GND post in the

center of the board. VOUT ripple can best be seen touching probe tip to the pad for C3

and scope GND collar touching Star GND post – avoid a GND lead on the scope which

will increase noise pickup.

3) Using the Evaluation Board with Different Output Voltages

While the SP7650 Evaluation Board has been tested and delivered with the output set

to 3.30V, by simply changing one resistor, R2, the SP7650 can be set to other output

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

output to the feedback pin VFB, which is set to an internal reference voltage of 0.80V.

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

Vout = 0.80V ( R1 / R2 + 1 ) => R2 = R1 / [ ( Vout / 0.80V ) – 1 ]

Where R1 = 68.1K

Ω and for Vout = 0.80V setting, simply remove R2 from the board.

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

output voltage setting by restricting R1 resistance range such that 50K

Ω ≤ R1 ≤ 100KΩ

for overall system loop stability.

Note that since the SP7650 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

SP7650ER provides short circuit protection by sensing Vout at GND.

POWER SUPPLY DATA

The SP7650ER is designed with a very accurate 1.0% reference over line, load and

temperature. Figure 1 data shows a typical SP7650 Evaluation Board Efficiency plot,

with efficiencies to 90% and output currents to 3A. SP7650ER Load Regulation is

shown in Figure 2 of only 0.1% change in output voltage from no load to 3A load.

Figures 3 and 4 illustrate a 1.5A to 3A and 0A to 3A Load Step. Start-up Response 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 SP7650ER is configured for hiccup mode in response to an output dead

short circuit condition and will Softstart until the over-load is removed. Figure 9 and 10

show output voltage ripple less than 40mV at no load to 3A load.

While data on individual power supply boards may vary, the capability of the SP7650ER

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

impressive and desirable for accurate power supply design.