USING THE EVALUATION BOARD
1) Powering Up the SP7656EB Circuit
Connect the Vin supply to the “VIN” and “GND” posts of SP7656 Evaluation Board with
short leads. Connect a Load between the VOUT and GND posts, again using short
leads to minimize parasitic inductance and voltage drop.
2) Measuring Output Load Characteristics
It’s best to GND reference scope and digital meters using a single GND post in the
output of the board. VOUT ripple can best be seen touching probe tip to the pad for C4
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 SP7656 Evaluation Board has been tested and delivered with the output set
to 3.3V, by simply changing one resistor, R2, the SP7656 can be set to other output
voltages. The relationship in the 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 0.60V.
Standard 1% metal film resistors of surface mount size 0603 are recommended.
Equation 1
R1 resistance must remain 200kΩ for overall system loop stability.
Note that since the SP7656 Evaluation Board design was optimized for 12V down
conversion to 3.3V, changes of output voltage and/or input voltage will alter
performance from the data given in the Power Supply Data section.
POWER SUPPLY DATA
The SP7656ER is designed with an accurate 2.0% reference over line, load and
temperature. Figure 1 & 2 data show a typical SP7656 evaluation board efficiency and
regulation plots, with efficiencies up to 87% and output currents up to 4A. The output
voltage ripple of less than 6.6mV at full load and the LX node are shown in Figure 3.
Figures 4 and 5 illustrate a 0.3A to 3A and 1.5A to 3A Load Step. Hiccup due to
overcurrent is shown in Figure 6. Typical startup characteristics into a full load and no
load are shown in Figure 7 and 8. All waveforms were taken under 12V to 3.3V
conversion.
While data on individual power supply boards may vary, the capability of the
SP7656ER of achieving a high accuracy over a range of load conditions shown here is
quite impressive and desirable for accurate power supply design.
