Rev. 5/23/01

SP6122 Evaluation Board Manual

DESCRIPTION

The SP6122 Evaluation Board is designed to help the user evaluate the performance
of the SP6122 for use as a low voltage input, low voltage output PFET Buck DC-DC
Controller. The SP6122 operates from a 5V or 3.3V input supply, and delivers output
voltages as low as 1.5V with an accuracy of 1.5% over line, load and temperature.
Unlike other "Micro-8" parts, the SP6122 has an array of value added features for you to
evaluate including: optional hiccup mode, over-current protection and fault flag output.

The evaluation board is a completely assembled and tested surface mount power
supply board which provides easy access to the SP6122 Input and Outputs so that the
user can quickly measure electrical characteristics and waveforms.

The next two sections describe the SP6122 Board Layout and Using the SP6122
Evaluation Boards. A section on SP6122 Power Supply Data is also included with
graphs on Efficiency, Line and Load Regulation. Then, drawings of the PC Layout and
a schematic are included as a design-in tool for the user of the SP6122. Finally, a
SP6122 Evaluation Board List of Materials table is provided with some manufacturers
part numbers to use as a reference.

BOARD LAYOUT
The SP6122 Evaluation Board has been designed for quick and easy connection to
the Input and Output of the SP6122 Power Supply under test. Position the board with
the silkscreen lettering upright, (also see the drawing on the front page of this manual)
and you will see U1 the SP6122 8-pin

SOIC, in the center left of the board. To the left

of U1 are the output capacitor Cout and the Vout pin. To the right of U1 are Q1 and the
Vin post and the input capacitor Cin. Below Cin and Cout are the two GND posts.

Easy Evaluation for the
SP6122 Low Voltage PFET
Buck Converter

Ideal for 1A to 5A, Small
Footprint, DC-DC Power
Converters

Very Accurate 1.5%
Reference over Line, Load,
Temperature

Small Micro 8 Package

SP6122

Evaluation Board Manual

Rev. 5/23/01

SP6122 Evaluation Board Manual

USING THE EVALUATION BOARD

1) Powering Up the SP6122 Circuit
The SP6122 Evaluation Board can be powered from inputs from a +3V to +7V power
supply. Connect with short leads directly to the "Vin" and "Gnd" posts. Monitor the
Output Voltage and connect the Load between the "Vout" post and the 2

"GND" post.

2) Using the J1 Jumper: Enabling the SP6122 Output and using the Hiccup Mode
As you can see in table 1, the SP6122 output will be Enabled if the J1 Jumper is left
open. If J1 is in the pin 2 to 3 position, the ENABLE pin is brought to GND, which puts
the SP6122 in the Sleep Mode. If the Jumper at J1 is in the pin 1 to 2 position, FFLAG
U1 pin 2 is connected to ENABLE U1 pin 4, and Hiccup Mode is activated. Hiccup
Mode occurs if the output current exceeds the Over-Current-Protection threshold, and
the part will "Soft-start", which happens every 1.2msec for a CEN capacitor value of
4.7nF. This is determined by the following relationship:

I = CEN*dV/dt

which yields dt = CEN*dV/I = 1.2msec

where the value of the CEN capacitor is 4.7nF, dV is the 1V internal threshold for
charging, and I is the Enable pin source current of 4uA.

Table 1. SP6122 Enable/Hiccup Jumper

3) Using External Divider Resistors: Programming the SP6122 Output Voltage
As you can see by the schematic in Figure 1, the SP6122 uses an internal feedback
divider to initially trim the output voltage using Rin1 and Rin2, where Rin2 is
approximately 62.5K. To accommodate the user who wants to externally program the
SP6122 output voltage, the SP6122 Evaluation Board has 2 external divider resistors,
R1 and R2, which can be used to program the output voltage above, but not below the
voltage set by the internal resistor divider. The relationships for the external divider
resistors are derived below:

i1 = Va/Rin2 = 1.25/62.5K = 20uA

Since Rin2 has +/-50% tolerance, ib change is +20uA/-7uA. If the SP6122 is trimmed to
1.5V output, Vb will be fixed at 1.5V in a closed loop. As a result, i2 is not affected by
the variation of the internal resistors, and the +20uA/-7uA current variation will be
passed on to i3.

Vout = Vb+i3*R1,
Therefore,

Vout =

i3*R1=+20uA/-7uA*R1.

That is, the additional variation on the output voltage is caused by the internal voltage
divider. For example, with R1 selected to be 500ohm, the variation on the output
voltage will be +10mV/-3.5mV.

SP6122

J1 Position

Mode

Condition

open

Enabled

Normal

1 to 2

Hiccup

Softstarts if Over-Current

2 to 3

Sleep

Iq = 20uA (max)

Rev. 5/23/01

SP6122 Evaluation Board Manual

SP612 Evaluation Board Divider Resistors: The values of R1 and R2 are selected
to program 1.9V output, with 1.5V trim voltage Vb, and R1 = 500ohm:

i3 = (Vout-Vb)/R1=(1.9-1.5)/500 = 800uA.

The external voltage divider will add only 800uA to the load. Divider Resistor R2 is:

R2 = Vb/(i3-i1)=1.5/(800uA-20uA) = 1.9K

The user of the SP6122 Evaluation Board can use the above equations for i3 and R2 to
modify R2 and change the output voltage to be any voltage from Vb (1.5V) to as high as
the input voltage. And if you want the output voltage to be the preset voltage Vb (1.5V),
just short a wire across R1.

Figure 1. Schematic: Output Voltage Divider Resistors

POWER SUPPLY DATA

The SP6122 is engineered for size and minimum pin count, yet has a very accurate
1.5% reference over line, load and temperature. Figure 2 data shows a typical SP6122
Evaluation Board Efficiency plot, with efficiencies to 88% and output currents to 4A.
Load Regulation plot in Figure 3 shows an essentially flat response of only 3mV change
for up to 4A load. Figure 4 Line Regulation illustrates a 1.90V output that varies only
4mV or 0.2% for an input voltage change from 3.3V to 5.5V. While data on individual
power supply boards may vary, the capability of the SP6122 of achieving high accuracy
over load and line shown here is quite impressive and desirable for accurate power
supply design.

Vout

Rin1

Rin2

62.5K

500

Error
Amplifier

1.25

SP6122

Pin3

1.9K

Rev. 5/23/01

SP6122 Evaluation Board Manual

Figure 2. SP6122 Efficiency with Vin = 3.3V, Vout = 1.93V

Figure 3. SP6122 Load Regulation with Input Voltage = 3.3V

Figure 4. SP6122 Line Regulation with Iload = 2A

SP6122 Efficiency

Iload (A)

Efficiency (%)

SP6122 Load Regulation

1.897

1.898

1.899

1.900

1.901

1.902

Iload (A)

Vout (V)

SP6122 Line Regulation

1.899

1.900

1.901

1.902

1.903

1.904

1.905

Iload (A)

Vout (V)

Rev. 5/23/01

SP6122 Evaluation Board Manual

FIGURE 8: SP6122 EVALUATION BOARD SCHEMATIC

TABLE 2: SP6122EB LIST OF MATERIALS

ORDERING INFORMATION

Part Number

Package Type

SP6122UEB....................................................................................... SP6122 Evaluation Board
SP6122CU..................................................................................................................8-pin

SOIC

Ref.

Qty.

Manuf.

Layout

Component

Vendor

Des.

Part Number

Size

Phone Number

PCB

Sipex

146-6427-00

1"X1.5"

SP6120 Eval PCB

978-667-7800

Sipex

SP6122UEB

uSO-8

5A PFET Buck Ctrl

978-667-7800

Fairchild

FDS6375

SO-8

PFET

310-322-3331

STMicroelectronics

STPS2L25U

SMB

2A Schottky 10A RMS

781-861-2650

Coilcraft

DO3316P-222

12.9x9.4mm

2.2uH Coil 5A 0.012ohm

847-639-6400

CIN

TDK

C4532X5R0J476M

1812

47uF Ceramic SM 6.3V

847-803-6100

COUT

Sanyo

6TPB470M

7343H

470uF 6.3V 0.035ohm

978-922-6573

TDK

C3216X5R1C475K

1206

4.7uF 10V SM X5R

847-803-6100

CEN

Panasonic

ECJ-1VB1H472K

0603

4700pF Ceramic X7R 50V

800-DIGI-KEY

Panasonic

ERJ-8ENF5000V

1206

500 OHM Thick Film Res 1%

800-DIGI-KEY

Panasonic

ERJ-8ENF1911V

1206

1.91K OHM Thick Film Res 1%

800-DIGI-KEY

Panasonic

ERJ-8ENF1001V

1206

1.00K OHM Thick Film Res 1%

800-DIGI-KEY

Ð­Ð»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: SP6122CU

ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: SP6122CU