SP6138ER1 datasheet(2/9 Pages) SIPEX

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Aug 24-06

SP6138 Evaluation Manual

Page 2 of 9

USING THE EVALUATION BOARD

1) Powering Up the SP6138EB Circuit

Connect the SP6138 Evaluation Board with an external +12V power supply. Connect

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

Load between the “VO” and “GO” posts, again using short leads with large diameter wire

to minimize inductance and voltage drops.

2) Measuring Output Load Characteristics

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

the center of the board. VOUT ripple can best be seen by touching the probe tip to the

pad for COUT and the scope GND collar touching the Star GND post – avoid a GND lead

on the scope which will increase noise pickup.

3) Using the Evaluation Board with Different Output Voltages

The SP6138 Evaluation Board has been tested and delivered with the output set to

3.30V. By simply changing one resistor, R2, the SP6138 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 = 68.1KΩ and for the VOUT = 0.80V setting, simply remove R2 from the

board. Furthermore, one could select the value of 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 SP6138 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.

POWER SUPPLY DATA

The SP6138EB is designed with an accurate 1.5% reference over line, load and

temperature. Figure 1 data shows a typical SP6138ER Evaluation Board efficiency plot,

with efficiencies to 86% and output currents to 3A. SP6138ER Load Regulation in

Figure 2 shows only 0.09% change in output voltage step response from no load to 3A

load. Figures 3 and 4 show the fast transient response of the SP6138. 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 soft-start

ramp increases. In Figure 8 the hiccup mode gets activated in response to an output

dead short circuit condition and will soft-start until the over-load is removed. Figures 9

and 10 show output voltage ripple less than 10mV over the complete load range.

While data on individual power supply boards may vary, the capability of the SP6138ER

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

impressive and desirable for accurate power supply design.

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