9

Oct10-07 RevJ

SP6652 1A, High Efficiency, Current Mode PWM Buck Regulator

© 2007 Sipex Corporation

APPLICATIONS INFORMATION

Manufacturers/ Website

Part Number

Inductance/ Isat

Rating

Inductor

Length/Width/Thickness

DCR Max

ohms

Coilcraft/ www.coilcraft

MSS5131-332MX

3.3uH/1.6A

5.1x5.1x3.1mm

0.032

Coilcraft/ www.coilcraft

MSS5131-332MX

4.7uH/1.4A

5.1x5.1x3.1mm

0.045

Sumida/ www.sumida.com

CDRH3D28-3R3

3.3uH/2.0A

4.0x4.0x3.0mm

0.058

Sumida/ www.sumida.com

CDRH3D28-4R7

4.7uH/1.65A

4.0x4.0x3.0mm

0.071

Wurth Elektronik/ www.we-online.de

WE-TPC #744042003

3.3uH/1.8A

4.8/4.8/1.8mm

0.065

Wurth Elektronik/ www.we-online.de

WE-TPC #744042004

4.7uH/1.65A

4.8/4.8/1.8mm

0.082

Table 2. Inductor Selection

The range of typical inductor values and sizes are shown here in Table 2.

The output voltage can be set using the

formula:

Compensation Component Selection

For simplicity in compensation with ce-

ramic output capacitors, the SP6652 uses

current mode PWM control, so all that is

at the COMP pin to compensate the error

amplifier. To see the actual SP6652 re-

sponse with frequency, in figure 3 we have

taken a bode plot of gain and frequency re-

sponse of the SP6652 circuit with 3.3Vout.

Looking first at the SP6652 Modulator Gain

at low frequency you see a constant gain

of about 26dB and the first pole or -3dB

point at about 4 kHz, where the slope of

the gain curve becomes about -20dB/de-

cade. At high frequency on the SP6652

Modulator Gain curve one can see the

modulator curve slope increase down-

ward for a high frequency pole at about

150KHz, which is widely separated in

frequency from the low frequency 4kHz

pole, so that the SP6652 can be compen-

sated by a zero at the low frequency pole

where the gain slope is only -20dB/decade.

The gain for the error amplifier is the cross-

Figure 3. SP6652 Gain and Frequency

Response 3.3V output voltage

Manufacturers/ Website

Part Number

Capacitance/

Voltage

Capacitor

Size/Type/Thickness

ESR at

100KHz

TDK/www.tdk.com

C1005X5R0J105M

1uF/6.3V

0402/X5R/0.5mm

0.03

TDK/www.tdk.com

C1608X5R0J475K

4.7uF/6.3V

0603/X5R/0.9mm

0.02

TDK/www.tdk.com

C2012X5R0J106M

10uF/6.3V

0805/X5R/1.35mm

0.02

Murata/www.murata.com

GRM155R60J105KE19B

1uF/6.3V

0402/X5R/0.55mm

0.03

Murata/www.murata.com

GRM188R60J475KE19

4.7uF/6.3V

0603/X5R/0.9mm

0.02

Murata/www.murata.com

GRM21BR60J106KE19L

10uF/6.3V

0805/X5R/1.35mm

0.02

Table 1. Capacitor Selection

Note: Component highlighted in bold is used on the SP6652EB Evaluation Board.

Note: Component highlighted in bold is used on the SP6652EB Evaluation Board.

SP6652 Bode Plot

.

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

100

1000

10000

100000

1000000

Log

Frequency

-180

-150

-120

-90

-60

-30

0

30

60

90

120

150

180

SP6652 Loop Gain

SP6652 Modulator Gain

SP6652 Loop Phase

SP6652 Modulator Phase

pole1 -3dB

at 4kHz

At 0dB Loop Gain

Fo = 80kHz

Loop Phase = 50deg

3.3Vout

Rz = 4K

Ω

Cc = 10nF

-20dB/dec

(Hz)