SC4524DEVB View Datasheet(PDF) - Semtech Corporation

Part Name

Description

MFG CO.

SC4524DEVB

18V 2A Step-Down Switching Regulator

Semtech Corporation 

SC4524D

Applications Information (Cont.)

integrator pole (-90deg) and the dominant pole (-90deg).

The high frequency pole nulls the ESR zero and attenuates

high frequency noise.

60

where gm=0.3mA/V is the EA gain of the SC4524D.

Example: Determine the voltage compensator for an

800kHz, 12V to 3.3V/2A converter with 22uF ceramic

output capacitor.

30

Fz1

Fp1

0

Fp

COMPENSATOR GAIN

CONVERTER

Fc

GAIN

LOOP GAIN

-30

Fz Fsw/2

Choose a loop gain crossover frequency of 80kHz, and

place voltage compensator zero and pole at FZ1=16kHz

(20% of FC), and FP1=600kHz. From Equation (9), the

required compensator gain at FC is

AC



20

˜

log¨¨©§

18.5

˜

1

5.5

˜103

˜

2ʌ

1

˜ 80 ˜103 ˜

22 ˜106

˜

1.0

3.3

¸¸¹·

11.4dB

Then the compensator parameters are

-60

1K

10K

100K

1M

10M

AC

=

−F2R0EQ⋅UloENgCYG(HCz1A)R S

⋅1

2πFCC O

⋅ VFB

VO



11.4

R7

10 20

0.3 ˜103

12.4k

Figure 8. Bode plots for voltage loop design

TthheerSeCfo45re2,4tDhecapnrobcAeeCsdu=umr−em2oa0frit⋅zhleoedgvao2sl:8ta⋅g6e.11lo⋅o1p0

−d3e⋅si2gπn ⋅

f8o0r

⋅

1

1

03

C5

⋅ 22 ⋅10 −6

C8

1

⋅ 213ʌ..03˜16 ˜=10135˜.192d.4B˜103

1

2 ʌ˜ 600 ˜103 ˜12.4 ˜103

0.8nF

21pF

(f(1r12ue0))qn%PSuceltioariloeetnndctdht.cet2oh0cme%oponpeovnfeesrnttahRCelteoro75ogrs==pwgaia0c2intir.cπn,o2hi1,.s⋅8eAi01sn.oC⋅61cg.125voI0.9⋅n0efn1rrt−et0yf3rqrop31eu=liq⋅cet22uaon22lecfane..y13pec.kpdyA⋅ 1,lbtiFc0aFCac,3Ctk,ibo=fteinrn0taswdn.w4est5ifehtenhnerF

Select R7=12.4k, C5=1nF, and C8=22pF for the design.

Compensator parameters for various typical applications

are listed in Table 5. A MathCAD program is also available

ctheerarmeqicuoiruedtpcuotmcappCean8csi=atot2orsrπ,g⋅t6ahie0n0EaS⋅t1RF0Cz1e3cra⋅on2i2bs.en1ee⋅sg1tli0emc3tae=ted1da2bnpydF

upon request for detailed calculation of the compensator

parameters.

(2(340))%UPsloaefAAc tteCChh==eethcc−−eroo 22mcs00ospom⋅⋅ellvoonpeVVggse rocanf=trG2soea8C(rq1t1Aop⋅uR6+r eoS.nlsz11e⋅ce,/2⋅yrFG1ωo,πPPF0,p1FW 1,C)FC−.M(t31CZo(11,O⋅+c2ba+⋅snπeVsV/tcF⋅RwOωeB8ElenS0tQReh⋅Cn1+eO01sE)(103S29%R)/⋅ 2ωza2en2nr)⋅od1,

0

−6

Thermal Considerations

For the power transistor inside the SC4524D, the

cc⋅oir13nc..ud03iutPcl=otTiOso1Tsn5APL.lB9=oSTdsP, sBcCaPn+C,PbthSeWee+sswtiPmiBtScaThte+indPgaQlsofsosllPoSwW,s:and bootstrap

C O 

FZ.

(5)

Then,

the

paramGPeWtMer≈s

15.9

R

GofCAth⋅ ReS

c,ompensaωtiop n≈

nRe1CtOw,ork

can

beRCc75al==cu02l.aπ2t1⋅e801d⋅612b0R⋅0y17−03=31=1⋅g022m22A2C0..

3k

1⋅

1

0

3

= 0.45nF

ωZ

=1,

PRC E=SRDC⋅OVCESAT

⋅ IO

PSW

=

1

2

⋅

tS

⋅ VIN

⋅IO

⋅ FSW

PQ = VIN ⋅ 2mA

(10)

C8

=

2

π⋅

60

C

0

5 = 12

⋅10 3

1

π⋅ 2FZ21.

R

1

7⋅ 1

0

3

= 12pF

PBST

=D⋅

VBST

⋅

IO

40

C8

=

1

2 πFP1

R7

Vo

Vc

=

(1

+

s

GPWM (1 +

/ ωp )(1 + s

sRESR CO)

/ ωn Q + s 2

/

ωn2 )

wherePVDBST=is(1th−eDB)S⋅TVsDu⋅pIpO ly voltage and tS is the equivalent

PIND = (1.1 ~ 1.3) ⋅ I2O ⋅ R DC

14

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