MAX8529 データシートの表示（PDF） - Maxim Integrated

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MAX8529

1.5MHz Dual 180° Out-of-Phase PWM Step-Down Controller with POR

Maxim Integrated 

1.5MHz Dual 180° Out-of-Phase

PWM Step-Down Controller with POR

fP1 = 0

fP2 =

1

2π × R2 ×

C3

fP3

=

2π

×

R1

1

×

(C1

(C1

×

+

C2)

C2)

fLC =

1

2π LO × CO

fZ1 =

1

2π × R1 × C1

fZ2

=

2π

×

(R2

1

+

R3)

×

C3

fZESR =

1

2π × RESR × CO

Unity-gain crossover frequency:

f0 =

R1 ×

C3 ×

VVIN,MAX

VOSC

×

2π ×

1

LO

×

CO

where:

VIN,MAX = Maximum input voltage

VOSC = Oscillator ramp voltage = 1V

LO = Output inductance

CO = Output capacitance

The goal is to place the two zeros below crossover and

the two poles above crossover so that crossover

occurs with a single-pole slope. The compensation pro-

cedure is as follows:

1) Select the crossover frequency such that:

f0 <

fZESR

and f0 <

1

5

× fS

fS = switching frequency

2) Select R1 such that:

R1 > 2

gm

3) Place the first zero before the double pole:

C1 ≥

1

2π × (0.75) ×

fLC

×

R1

4) Place the third pole at 1/2 the switching frequency:

C2

≤

1

2π × (0.5) ×

fS

×

R1

C2 < 10pF can be omitted.

5) C3 ≤ 2π × f0 × LO × CO × VOSC

R1

VIN

6) Place the second pole afer the ESR zero:

R2 ≤

1

2π × fZESR × C3

If R2 < 1 (= 550Ω), increase R1 and go back

gm

to step 2.

7) Place the second zero at the double pole frequency:

R3 ≥

1

- R2

2π × fLC × C3

8) See the Setting the Output Voltage section for

selecting R4.

Setting the Output Voltage

For 1V or greater output voltages, set the MAX8529 out-

put voltage by connecting a voltage-divider from the

output to FB_ to GND (Figure 7). Calculate R4 (OUT_ to

FB_ resistor) with the following equation:

R4 = R3 [ VSET ]

VOUT − VSET

where VSET = 1V (see the Electrical Characteristics)

and VOUT can range from VSET to 18V.

For output voltages below 1V, set the MAX8529 output

voltage by connecting a voltage-divider from the output

to FB_ to REF (Figure 7). Calculate R4 (FB_ to REF

resistor) with the following equation:

R4 = R3 [ VREF − VSET ]

VSET − VOUT

where VSET = 1V, VREF = 2V (see the Electrical

Characteristics), and VOUT can range from 0 to VSET.

OUT_

REF

R3

R4

FB_

FB_

MAX8529

R4

MAX8529

R3

OUT_

VOUT_ > 1V

VOUT_ < 1V

Figure 7. Adjustable Output Voltage

______________________________________________________________________________________ 15

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