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MAX5072ETJ

2.2MHz, Dual-Output Buck or Boost Converter with POR and Power-Fail Output

Maxim Integrated 

2.2MHz, Dual-Output Buck or Boost

Converter with POR and Power-Fail Output

PSW = VINMAX × IO × (tR + tF) × fSW

4

For the boost converter:

IRMS =

(I2DC

+I2PK

+

(IDC

×

IPK

))

×

DMAX

3

IIN

=

VO × IO

VIN × η

∆IL

=

(VIN − VDS )

L × fSW

×

D

IDC

=

IIN

−

∆IL

2

IPK

= IIN

+

∆IL

2

PDC = I2RMS × RDS(ON)MAX

where VDS is the drop across the internal MOSFET. See

the Electrical Characteristics for the RDS(ON)MAX value.

PSW

=

VO

× IIN

×

(tR

4

+

tF)

×

fSW

where tR and tF are rise and fall times of the internal

MOSFET. The tR and tF are typically 20ns, and can be

measured in the actual application.

The supply current in the MAX5072 is dependent on

the switching frequency. See the Typical Operating

Characteristics to find the supply current of the

MAX5072 at a given operating frequency. The power

dissipation (PS) in the device due to supply current (IS)

is calculated using following equation.

PS = VINMAX × ISUPPLY

The total power dissipation PT in the device is:

PT = PDC1 + PDC2 + PSW1 + PSW2 + PS

where PDC1 and PDC2 are DC losses in converter 1 and

converter 2, respectively. PSW1 and PSW2 are switching

losses in converter 1 and converter 2, respectively.

Calculate the temperature rise of the die using the fol-

lowing equation:

TJ = TC + (PT x θJ-C)

where θJ-C is the junction-to-case thermal impedance

of the package equal to +2°C/W. Solder the exposed

pad of the package to a large copper area to minimize

the case-to-ambient thermal impedance. Measure the

temperature of the copper area near the device at a

worst-case condition of power dissipation and use

+2°C/W as θJ-C thermal impedance. The case-to-ambi-

ent thermal impedance (θC-A) is dependent on how

well the heat is transferred from the PC board to the

ambient. Use large copper area to keep the PC board

temperature low. The θC-A is usually in the +20°C/W to

+40°C/W range.

Compensation

The MAX5072 provides an internal transconductance

amplifier with its inverting input and its output available

to the user for external frequency compensation. The

flexibility of external compensation for each converter

offers wide selection of output filtering components,

especially the output capacitor. For cost-sensitive

applications, use high-ESR aluminum electrolytic

capacitors; for component size-sensitive applications,

use low-ESR tantalum or ceramic capacitors at the out-

put. The high switching frequency of MAX5072 allows

use of ceramic capacitors at the output.

Choose all the passive power components that meet

the output ripple, component size, and component cost

requirements. Choose the small-signal components for

the error amplifier to achieve the desired closed-loop

bandwidth and phase margin. Use a simple pole-zero

pair (Type II) compensation if the output capacitor ESR

zero frequency is below the unity-gain crossover fre-

quency (fC). Type III compensation is necessary when

the ESR zero frequency is higher than fC or when com-

pensating for a continuous mode boost converter that

has a right-half plane zero.

Use the following procedure 1 to calculate the compen-

sation network components when fZERO,ESR < fC.

Buck Converter Compensation

Procedure 1 (see Figure 7):

Calculate the fZERO,ESR and LC double pole:

______________________________________________________________________________________ 21

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