Feb21-07 SP7662 Evaluation Manual ©2007 Sipex Corporation
Page 2 of 11
Using the Evaluation Board
1) Powering Up the SP7662EB Circuit
Connect the SP7662 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 GND posts, again using short leads with large diameter wire to minimize
inductance and voltage drops. Provide >=100lfm of airflow if powering the evaluation board
beyond 10 Amps for extended periods.
2) Measuring Output Load Characteristics
VOUT ripple can best be seen by touching the probe tip to the pad for C5 and the scope GND
collar touching the Output 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 SP7662 Evaluation Board has been tested and delivered with the output set to 3.30V,
by simply changing one resistor, R2, the SP7662 can be set to other output voltages. The
relationship in Equation 1 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. Note, due to the common mode voltage
range of the current sense amplifier, output voltages greater than 3.3V are only possible if the
current sense is disabled. To disable current limit, remove R3 and R4. Standard 1% metal film
resistors of surface mount size 0603 are recommended.
−
=
1
.80V
Vout
R1
R2 Equation 1
Where R1 = 10kΩand for VOUT = 0.80V setting, simply remove R2 from the board.
Furthermore, one could select the value of the R1 and R2 combination to meet the exact output
voltage setting by restricting R1 resistance range such that 10KΩ≤R1 ≤100KΩfor overall
system loop stability.
Note that since the SP7662 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 SP7662ER provides short circuit protection by
sensing VOUT at GND. The current limit of the converter is set to about 17A which is
accomplished by sensing the current through the inductor. To adjust the current limit, follow
Equations 2 and 3 to set the current limit accordingly. The current limit should be set to about
50% higher than the maximum output current that is desired. This will prevent the part from
accidentally triggering the current limit during large transient load steps.
Adjusting the Current upward is done by adjusting resistor R9.
60mV)-DCR(max
R4)R3(60mV
R9 ⋅
=
IEquation 2
Where DCR is the Inductor winding resistance
IMAX is the desired output current
