www.austriamicrosystems.com/Power-Management/AS1390

Revision 1.04

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AS1390A, AS1390B

Datasheet - D e t a i l e d D e s c r i p t i o n

Peak current:

RMS inductor current:

This peak current is flowing through MN1 during phase 1 and through D1 during phase 2 of each cycle. Therefore this peak current is important

for a proper diode D1, MOSFET MN1 and inductor L1 selection.

Note:

The saturation current of the inductor should be about 20 to 30% larger than the peak current

8.1.6

Input Capacitor

The input capacitor has to supply the delta inductor current and it should be selected according to:

8.1.7

Output Capacitor

The output capacitor must be chosen according to the max allowable output ripple at high load.

8.1.8

Current Sense Resistor

Note:

Low inductance and specifically designed current sensing resistors should be used, e.g. Stackpole Electronics CSR/CSRN series of

sensing resistors with less than 0.2nH (typ.).

8.1.9

Compensation Network

For typical use cases a compensation network should be implemented by C10, C11 and R11 for 2D mode and optional by different component

values C12, C13, R13 for 3D mode (see Figure 18 on page 10).

A typical choice for values of the compensation network is C10 = 100pF, C11 = 10nF, R11 = 100K

Ω. Use these values as initial choice and

evaluate the transient response of the system to verify the behavior at output load change. To be able to do a different compensation for 3D

mode, a second pin COMP_3D is available. If no separate compensation for 3D mode is necessary, PINs COMP_2D and COMP_3D can be

connected to one common compensation network.

(EQ 10)

I

pk

I

L

I

L

∆

2

--------

I

OUT

1

D

–

-------------

D

V

IN

×

2

f

S

×

L

×

-----------------------

+

=

+

=

(EQ 11)

I

R MS

I

L

2

1 12

⁄

I

L

∆

×

(

)

2

+

=

(EQ 12)

C

IN

I

L

∆

4

V

IN

∆

×

f

SW

×

------------------------------------

>

(EQ 13)

ESR

V

IN

∆

2

I

L

∆

×

-----------------

<

(EQ 14)

C

OUT

I

OUT

max

–

D

×

V

OUT

∆

f

SW

×

------------------------------------

>

(EQ 15)

ESR

V

OUT

∆

I

OUT

1

D

–

-------------

V

IN

D

×

2

L

×

f

SW

×

---------------------------

+









-----------------------------------------------------

<

(EQ 16)

R

S

max

–

V

SEN SE

I

L

0 5

,

I

L

∆

×

+

-----------------------------------

=

(EQ 17)

P

RS

I

2

L

rms

–

R

S

D

×

×

=