ADP5072 datasheet(18/24 Pages) AD

No de pièce	ADP5072

Description	1 A/0.6 A DC to DC Switching Regulator Independent Positive and Negative Outputs

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ADP5072

Data Sheet

Rev. 0 | Page 18 of 24

For the inductor ripple current in continuous conduction mode

(CCM) operation, the input (VIN) and output (VPOS) voltages

determine the switch duty cycle (DUTY1) by the following

equation:

DIODE1

POS

IN

1

POS

DIODE1

V

VV

DUTY

VV



−+

= 



+



where VDIODE1 is the forward voltage drop of the Schottky diode

(D1).

The dc input current in CCM (IIN) can be determined by the

following equation:

(1

)

OUT1

IN

1

I

DUTY

=

−

Using the duty cycle (DUTY1) and switching frequency (fSW),

determine the on time (tON1) using the following equation:

1

ON1

SW

DUTY

t

f

=

The inductor ripple current (∆IL1) in steady state is calculated by

IN

ON1

L1

Vt

I

L1

×

∆ =

Solve for the inductance value (L1) using the following equation:

IN

ON1

L1

Vt

L1

I

×

=

∆

Assuming an inductor ripple current of 30% of the maximum

dc input current results in

(1

)

0.3

1

IN

ON1

OUT1

V

t

DUTY

L1

I

×

× −

=

×

Ensure that the peak inductor current (the maximum input

current plus half the inductor ripple current) is less than the

rated saturation current of the inductor. Likewise, ensure that

the maximum rated rms current of the inductor is greater than

the maximum dc input current to the regulator.

When the ADP5072 boost regulator is operated in CCM at duty

cycles greater than 50%, slope compensation is required to stabilize

the current mode loop. This slope compensation is built in to

the ADP5072. For stable current mode operation, ensure that

the selected inductance is equal to or greater than the minimum

calculated inductance, LMIN1, for the application parameters in

the following equation:

0.13

0.16

(1

)

MIN1

IN

1

L1 L

V

DUTY



>=

×

−



−



(µH)

Table 10 suggests a series of inductors to use with the ADP5072

boost regulator.

Inductor Selection for the Inverting Regulator

The inductor stores energy during the on time of the power

switch, and transfers that energy to the output through the

output rectifier during the off time. To balance the tradeoffs

between small inductor current ripple and efficiency, inductance

values in the range of 1 µH to 22 µH are recommended. In

general, lower inductance values have higher saturation current

and lower series resistance for a given physical size. However,

lower inductance results in a higher peak current that can lead

to reduced efficiency and greater input and/or output ripple and

noise. A peak-to-peak inductor ripple current close to 30% of

the maximum dc current in the inductor typically yields an

optimal compromise.

For the inductor ripple current in continuous conduction mode

(CCM) operation, the input (VIN) and output (VNEG) voltages

determine the switch duty cycle (DUTY2) by the following

equation:

||

DIODE2

NEG

2

DIODE2

IN

NEG

VV

DUTY

VV

V





+

= 







++





where VDIODE2 is the forward voltage drop of the Schottky diode

(D2).

The dc current in the inductor in CCM (IL2) can be determined

by the following equation:

(1

)

OUT2

L2

2

I

DUTY

=

−

Using the duty cycle (DUTY2) and switching frequency (fSW),

determine the on time (tON2) by the following equation:

2

ON2

SW

DUTY

t

f

=

The inductor ripple current (∆IL2) in steady state is calculated by

IN

ON2

L2

Vt

I

L2

×

∆=

Solve for the inductance value (L2) by the following equation:

IN

ON2

L2

Vt

L2

I

×

=

∆

Assuming an inductor ripple current of 30% of the maximum

dc current in the inductor results in

(1

)

0.3

IN

ON2

2

OUT2

V

t

DUTY

L2

I

×

×−

=

×

Ensure that the peak inductor current (the maximum input current

plus half the inductor ripple current) is less than the rated

saturation current of the inductor. Likewise, ensure that the

maximum rated rms current of the inductor is greater than the

maximum dc input current to the regulator.

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