MAX5072ETJ View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

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

CIN

=

4

∆IL × D

× fSW × ∆VQ

ESR = ∆VESR

∆IL

where

∆IL

=

(VIN − VDS ) ×

L × fSW

D

where VDS is the total voltage drop across the internal

MOSFET plus the voltage drop across the inductor

ESR. ∆IL is the peak-to-peak inductor ripple current as

calculated above. ∆VQ is the portion of input ripple due

to the capacitor discharge and ∆VESR is the contribu-

tion due to ESR of the capacitor.

Output Capacitor Selection

For the boost converter, the output capacitor supplies

the load current when the main switch is ON. The

required output capacitance is high, especially at high-

er duty cycles. Also, the output capacitor ESR needs to

be low enough to minimize the voltage drop due to the

ESR while supporting the load current. Use the follow-

ing equation to calculate the output capacitor for a

specified output ripple tolerance.

ESR = ∆VESR

IO

COUT

=

IO ×

∆VQ

DMAX

× fSW

IO is the load current, ∆VQ is the portion of the ripple

due to the capacitor discharge and ∆VESR is the contri-

bution due to the ESR of the capacitor. DMAX is the

maximum duty cycle at minimum input voltage.

Power Dissipation

The MAX5072 includes a high-frequency, low RDS_ON

switching MOSFET. At +85°C, the RDS_ON of the inter-

nal switch for converter 1 and converter 2 are 290mΩ

and 630mΩ, respectively. The DC loss is a function of

the RMS current in the switch while the switching loss is

a function of switching frequency and input voltage. Use

the following equations to calculate the RMS current,

DC loss, and switching loss of each converter. The

MAX5072 device is available in a thermally enhanced

package and can dissipate up to 2.7W at +70°C ambi-

VOUT

R1

-

gM

R2

VREF +

RF

CF

COMP

CCF

Figure 7. Type II Compensation Network.

VOUT

CCF

RI

R1

CI

R2

RF

CF

-

gM

VREF +

COMP

Figure 8. Type III Compensation Network

ent temperature. The total power dissipation in the pack-

age must be limited so the junction temperature does not

exceed its absolute maximum rating of +150°C at maxi-

mum ambient temperature.

For the buck converter:

IRMS =

(I2DC

+I2PK

+

(IDC

×

IPK

))

×

DMAX

3

where

PDC = I2RMS × RDS(ON)MAX

IDC

= IO

−

∆IL

2

IPK

= IO

+

∆IL

2

See the Electrical Characteristics table for the RDS(ON)MAX

value.

20 ______________________________________________________________________________________

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