12

Rev: C Date: 2/3/04

SP6134H Dual Supply, Synchronous Buck Controller

© Copyright 2004 Sipex Corporation

APPLICATIONS INFORMATION: Continued

The goal of loop compensation is to manipulate

loop frequency response such that its gain crosses

over 0db at a slope of -20db/dec. The first step

of compensation design is to pick the loop

crossover frequency. High crossover frequency

is desirable for fast transient response, but often

jeopardizes the system stability. Crossover fre-

quency should be higher than the ESR zero but

less than 1/5 of the switching frequency. The

ESR zero is contributed by the ESR associated

with the output capacitors and can be deter-

mined by:

1

2

The next step is to calculated the complex con-

jugate poles contributed by the LC output filter,

1

2

π

Frequency

(Hz)

Error Amplify Gain

Bandwidth Product

Condition:

C22 >> CP1, R1 >> RZ3

20 Log (RZ2/R1)

Gain

(dB)

Bode Plot of Type III Error Amplify Compensation.

When the output capacitors are of a Ceramic

Type, the SP6134CU Evaluation Board requires

a Type III compensation circuit to give a phase

boost of 180

° in order to counteract the effects of

an under damped resonance of the output filter

at the double pole frequency.

Table 1. Input and Output Stage Components Selection Charts.

INDUCTORS - SURFACE MOUNT

Inductor Specification

Inductance

Manufacturer/Part No.

Series R

Size

Inductor Type

Manufaturer

(uH)

mΩ

(a)

LxW(mm)

Ht.(mm)

Website

2.7

Easy Magnet SC5018-2R7M

4.30

12.0

12.6x12.6

4.5

Shielded Ferrite Core

inter-technical.com

2.7

TDK RLF 12560T-2R7N110

4.50

12.2

12.5x12.8

6.0

Shielded Ferrite Core

tdk.com

3.3

Coilcraft DO5010P-332HC

8.60

17.0

14.7x15.2

8.0

Unshielded Ferrite Core

coilcraft.com

1.2

Easy Magnet SC5018-1R2M

1.96

20.0

12.6x12.6

4.5

Shielded Ferrite Core

inter-technical.com

1.2

Inter-Technical SC4015-1R2M

4.37

17.0

10.0x10.0

3.8

Shielded Ferrite Core

inter-technical.com

1.5

Coilcraft DO5010P-152HC

4.00

25.0

14.7x15.2

8.0

Unshielded Ferrite Core

coilcraft.com

1.9

TDK RLF 12560T-1R9N120

3.60

13.2

12.5x12.8

6.0

Shielded Ferrite Core

tdk.com

CAPACITORS -SURFACE MOUNT

Capacitance

Manufacturer/Part No.

ESR

Ripple Current

Size

Voltage

Capacitor

Manufaturer

(uF)

Ω (max)

(A)@45°C

LxW(mm) Ht.(mm)

(V)

Type

Website

22

TDK C3225X5R1C226M

0.002

4.00

3.2x2.5

2.0

16.0

X5R Ceramic

tdk.com

47

TDK C3225X5ROJ476M

0.002

4.00

3.2x2.5

2.5

6.3

X5R Ceramic

tdk.com

MOSFET - Surface Mount

MOSFET

Manufacturer/Part No.

RDS (on)

ID Current

Qg

Qg

Voltage

Foot Print

Manufaturer

Ω (max)

(A)

nC(Typ)

nC(Max)

(V)

Website

N-Channel

Fairchild Semi FDS6676S

0.006

14.50

43

60.0

30.0

SO-8

fairchildsemi.com

N-Channel

Fairchild Semi FD7088N3

0.005

21.10

37

48.0

30.0

SO-8

fairchildsemi.com

N-Channel

Vishay Si4336DY

0.004

25.0

32

50.0

30.0

SO-8

vishay.com

Note: Components highlighted in Bold are those used on the SP6134H Evaluation Board.