MAX5072 datasheet(21/30 Pages) MAXIM

21 / 30 page

MAX

RMS

DC PK

+(I

I ))

×η

(

)

−×

∆=

∆

−

∆

RMS

DS(ON)MAX

where VDS is the drop across the internal MOSFET. See

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

O IN

t ) f

××

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.

INMAX SUPPLY

The total power dissipation PT in the device is:

DC1

DC2

SW1

SW2

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 following

equation:

J C

)

−

×θ

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-ambient 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 flex-

ibility 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 compo-

nent size-sensitive applications, use low-ESR tantalum

or ceramic capacitors at the output. 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 frequency

(fC). Type III compensation is necessary when the ESR

zero frequency is higher than fC or when compensating

for a continuous mode boost converter that has a right-

half plane zero.

Use the following procedure 1 to calculate the compensa-

tion network components when fZERO,ESR < fC.

Buck Converter Compensation

Procedure 1 (see Figure 7):

Calculate the fZERO,ESR and LC double pole:

ZERO,ESR

OUT

2 ESR C

π×

Calculate the unity-gain crossover frequency as:

www.maximintegrated.com

Maxim Integrated │ 21

MAX5072

2.2MHz, Dual-Output Buck or Boost

Converter with POR and Power-Fail Output

MAX5072 Datasheet(PDF) 21 Page - Maxim Integrated Products

MAX5072 Datasheet(HTML) 21 Page - Maxim Integrated Products

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Datasheet Download

Link URL