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
V
OUT
ripple can best be seen touching the probe tip to the pad for C3 and the scope
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
output to the feedback pin V
FB
, which is set to an internal reference voltage of 0.80V.
Standard 1% metal film resistors of surface mount size 0603 are recommended.
V
OUT
= 0.80V (R1 / R2 + 1) => R2 = R1 / [ ( Vout / 0.80V ) – 1 ]
Where R1 = 68.1K
Ω
and for V
OUT
= 0.80V setting, simply remove R2 from the board.
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 50K
Ω
≤
R1
≤
100K
Ω
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
SP7651ER provides short circuit protection by sensing V
OUT
at GND.
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.